chem 2001 exam 2
retention time
is the characteristic time it takes for a particular molecule to pass through the system under set conditions.
Chromaography
is the collective term for a family of laboratory techniques for the separation of mixtures. involves passing a mixture which contains the analyte through a stationary phase, which separates it from other molecules in the mixture and allows it to be isolated
emissions testing (stack sampling/monitoring)
is the experimental process for evaluating the characteristics of industrial waste gas stream emissions into the atmosphere. Materials emitted to the air from these sources can be solid, liquid, or gas; organic or inorganic
ph
is the measure of the hydrogen ion [H+ ] concentration of an aqueous solution. The scale of this measurement typically ranges from 0 to 14.
stationary phase
is the substance which is fixed in place for the chromatography procedure and is the phase to which solvents and the analyte travels through or binds to. Examples include the silica layer in thin layer chromatography.
extraction
is the transfer of a solute between two immiscible liquids, or from one phase to another most common case is of aqueous solutions with an immiscible organic solvent
chromatogram
is the visual output of the chromatograph
fractional distillation
is used for separating a mixture of substances with narrow differences in boiling points, and is the most important step in petroleum refining.
Gas Chromatography
is used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition.
preparative chromatography
is used to nondestructively purify sufficient quantities of a substance for further use, rather than analysis.
the tcd detector
is useful because it detects all molecules, not just hydrocarbons, so it is commonly used for fixed gas analysis (O2, N2, CO, CO2, H2S, NO, NO2, etc.) where the target analytes do not respond well on other more sensitive detectors. it is able to detect concentrations from 100% down to about 100 ppm, but detection limits of 300 ppm are more realistic
gas chromatography
is widely used in analytical chemistry; though the high temperatures make it unsuitable for high molecular weight biopolymers, encountered in biochemistry, it is well suited for use in petrochemical, environmental monitoring, and industrial chemical fields. It is also used extensively in chemistry research.
~2.5
k' is optimum from _______. Adjusting this for some analytes makes it outside this range for other analytes.
absorbance
linearly proportional to concentration except at very high concentrations (~>0.1M)
SE-30
liquid stationary phase that Retains hydrocarbons best, polar analytes not substantially retained.
carbowax 20M
liquid stationary phase that is composed . of poly(ethylene glycol) HO(-CH2CH2-O-)nH retains alcohols, polar RCOOH
OV-17
liquid stationary phase that retains more polar . compounds(aromatics) .
dry milling
makes up production of 80% of corn ethanol in united states done by the entire corn kernel is ground into flour, or "mash," which is then slurried by adding water. Enzymes are added to the mash to hydrolyze the starch into simple sugars. Ammonia is added to control the pH and as a nutrient for the yeast, which is added later. The mixture is processed at high-temperatures to reduce the bacteria levels. The mash is transferred and cooled in fermenters. Yeast are added, which ferment the sugars into ethanol and carbon dioxide. The entire process takes 40 to 50 hours, during which time the mash is kept cool and agitated to promote yeast activity. The ethanol is purified through a combination of distillation and dehydration to create fuel ethanol.The mash is then transferred to distillation columns, where the ethanol is removed. • The ethanol is dehydrated to about 200 proof using a molecular sieve system. • A denaturant such as gasoline is added to render the product undrinkable. • The product is then ready to ship to gasoline retailers or terminals. The remaining stillage is processed into a highly nutritious livestock feed known as distiller's dried grains and solubles (DDGS). • The carbon dioxide released from the process is used to carbonate beverages and to make dry ice.
single beam spectrophotometer
measures the absolute light intensity
double beam spectrophotometer
measures the ratio of light intensity on two different light paths
HPLC-Detection
most common is is UV/VIS absorbance - can detect many analytes • UV/VIS absorbance detectors can collect spectra for chromatographic peaks (diode array detectors) • Mass Spectrometry is also a common detection method for HPLC - particularly for biology • Refractive Index is used for detection - especially for preparative work (very general, not very sensitive) • Electrochemistry (Amperometry = current measurement) is used for detection • Fluorescence is used for detection • NMR is being used for HPLC Detection (poor sensitivity, high cost, structural information)
q^n=q= (v1/[v1+kv2])^n
n extraction steps equation
photoionization
occurs when a molecule absorbs a photon (light energy) of sufficient energy, creating a positive ion and an electron: R + hn = R^+ + e^-
tcd
one of these resistors is placed in contact with mobile phases leaving the column and another in a reference stream containing only pure mobile phase as a current is passed through the circuit. the wire in the resistors are heated. for those in contact with the mobile phase and reference sttream, some of the heat is removed ttempchanges leads to resistance changes of resistors most compound separated in GC have thermal conducivity of 1-4*10^-5
response factor = standard concentration / peak area unknown concentration = peak height x response factor
peak area method formula
response factor = standard concentration / peak height unknown concentration = peak height x response factor
peak height method formula
wavelength selection devices
prisms monochromators grating-monochromators
• One major factor is the type of photosensors that are available for different spectral regions, but infrared measurement is also challenging because virtually everything emits IR light as thermal radiation, especially at wavelengths beyond about 5 μm.
problem with IR spec
detector
produces an electrical signal when struck by photons
thin layer chromatography
r, it involves a stationary phase of a thin layer of adsorbent like silica gel, alumina, or cellulose on a flat, inert substrate. Compared to paper, it has the advantage of faster runs, better separations, and the choice between different adsorbents. Different compounds in the sample mixture travel different distances according to how strongly they interact with the adsorbent. This allows the calculation of an Rf value and can be compared to standard compounds to aid in the identification of an unknown substance.
split injection
routine for introducing small sample volume into open tubular column
isocratic elution
s accomplished with a single solvent, or a constant solvent mixture.
gas chromatography
s based on a partition equilibrium of analyte between a solid stationary phase and a mobile gas. The stationary phase is adhered to the inside of a smalldiameter glass tube (a capillary column) or a solid matrix inside a larger metal tube (a packed column). is widely used in analytical chemistry; though the high temperatures used in ___ make it unsuitable for high molecular weight biopolymers, encountered in biochemistry, it is well suited for use in petrochemical, environmental monitoring, and industrial chemical fields. It is also used extensively in chemistry research.
analyte
s the substance which is to be purified or isolated during chromatography
monochromators
separate wavelengths of light; they consist of both entrance & exit slits, mirrors, and diffraction grating or refraction lens/prisms, and filters.
distillation
separates a mixture of two or more substances into its components when heat is applied. The separation is based on differences in the boiling points of the components.
chiral chemistry
separation of chiral compounds is important for pharmaceuticals
boiling points
separations using distillation are based on differences in ...
Flame Photometric Detector (FPD)
similar to fid except that the detector body is completely light tight and a second flow of hydrogen purges the optical path between the photomultiplier tube (PMT) and the hydrogen-rich flame. A bandpass filter at 393 nm for sulfur or 525 nm for phosphorus mounts in front of the PMT so only the emissions from sulfur or phosphorus are detected while other wavelengths are rejected. While not 100% selective, the .... is 100,000 times more sensitive for S-P compounds than for hydrocarbons. Sulfur compounds such as H2S or SO2 can be detected down to about 200 ppb and phosphorus to 10 ppb. The phosphorus response is linear, but the sulfur response is exponential (twice the sulfur yields four times the peak area).
problem with reproducibility of measurements due to variations in power source and detector & that one must measure the background/reference or blank first followed by the sample
single beam spec problems
Types of interactions that have been used for LC separations
surface adsorption solvent partitioning ion exchange relative size of solutes hydrophilicity/hydrophobicity
true
t/f Separations are needed for both qualitative and quantitative analysis of mixtures
t
t/f Separations are needed for both qualitative and quantitative analysis of mixtures.
true
t/f Separations are needed for both qualitative and quantitative analysis of mixtures.
t
t/f separations can be used to remove impurities
true
t/f separations can be used to remove impurities
chromatograph
takes a chemical mixture carried by liquid or gas and separates it into its component parts as a result of differential distributions of the solutes as they flow around or over the stationary phase
thermal conductivity detectors
a universal detector measures the ability of a substance to transport heat from a hot region to a cold region
august beer
(July 31, 1825 - November 18, 1863), German mathematician, chemist, physicist. Beer was born in Trier, where he studied mathematics and natural sciences. He worked for Julius Plücker in Bonn afterwards, where he made Ph.D. in 1848 and professor in 1850. In 1854, he published his book "Einleitung in die höhere Optik". His findings, together with those of Johann Heinrich Lambert, make up the Beer-Lambert law.
reversed phase . hplc
*Almost the same as in thin layer chromatography. *The column is filled with modified tiny silica particles to make it nonpolar. *Used for polar compounds
The almost simultaneous measurement of the blank/reference signals allows for minimization of problems associated with power fluctuations to the detector and source. (achieved using a chopper or rotating half mirror)
advantages of double beam spec
joseph priestly
ENGLISH PHILOSOPHER, CHEMIST, THEOLOGIAN, AND POLITICAL THEORIST HE BELIEVED THAT THE SCIENTIFIC PROCESS DEPENDED MORE ON THE ACCUMULATION OF "NEW FACTS" WHICH ANYONE COULD FIND, RATHER THAN THEORETICAL INSIGHTS FROM A FEW MEN OF GENIUS HE STUDIED DIFFERENT KINDS OF "AIRS" WITH EXPERIMENTS BASED ON GASES This lead him to discover ten kinds of new gases: Oxygen • Nitrous Oxide Nitrogen • Hydrogen Chloride Carbon Monoxide • Nitric Oxide Ammonia • Sulfur Dioxide Nitrogen Dioxide • Silicon Tetrafluoride He based his work on phlogiston theory, which was that every combustible substance was composed of fire George Cuvier praised his work, but lamented his refusal to abandon this theory, calling Priestly "the father of modern chemistry, who never acknowledged his daughter" Fun Fact: He accidentally invented carbonated water after infusing water with carbon dioxide by suspending a bowl of water above a beer vat at a brewery
thalidomide
First marketed in West Germany under the trade name "Cantergan". It claimed to alleviate morning sickness in pregnant women. • Shortly after it was sold, between 5,000 to 7,000 babies were born with phocomelia (malformation of limbs) and only 40% survived. • While there was no findings of individual guilt, the foundation responsible had to pay a one time sum + monthly payments to those affected. • The chief of the company apologized for this incident for the first time in 2012, over 50 years after it occurred.
AAS
The process consumes the photon and puts the atom or molecule in an excited state ● Few interference ● Element by element, single element analysis ● Prepare points for calibration for each element ● Long time for standards preparation ● The lamp provides the source of photons (flame) ● Flame uses to ionize the sample ● Consumes a lot of glare ware ● One report for each element
dilution factor
-factor used to multiply the initial concentration of reagent to find the diluted concentration
A. 7,512 theoretical plates
. A solute with a retention time of 325 seconds has a base width of 15 seconds. The column is 11,500 cm long. The column has how many theoretical plates?
q= v1/[v1+kv2]
1 step extraction
q^2=q= [v1/[v1+kv2]]^2
2 step extraction equation
visible region
400-700nm used extensively in colorimetry Ink manufacturers, environmental laboratories, chemical manufacturers, hospitals, medical laboratories and many more, use data provided through colorimetry If the compound is more concentrated more light is absorbed by the sample.
gravity flow
A simple laboratory column runs by _________. The flow rate of such a column can be increased by extending the fresh eluent filled column above the top of the stationary phase or decreased by the tap controls. Better flow rates can be achieved by using a pump or by using compressed gas (e.g. air, nitrogen, or argon) to push the solvent through the column (flash column chromatography).
tlc plate
A small spot of solution containing the sample is applied to a plate, about one centimeter from the base. The plate is then dipped in to a suitable solvent, such as ethanol or water, and placed in a sealed container. The solvent moves up the plate by capillary action and meets the sample mixture, which is dissolved and is carried up the plate by the solvent. Different compounds in the sample mixture travel at different rates due to differences in solubility in the solvent, and due to differences in their attraction to the stationary phase.
retention factor, k',
A term called the _______ is often used to describe the migration rate of an analyte on a column. You may also find it called the capacity factor.
PBBS
ADDED TO PLASTICS IN VARIETY OF CONSUMER PRODUCTS SUCH AS: • COMPUTER MONITORS • TV SCREENS • TEXTILES • FOAMS • NO NATURAL SOURCES • NO LONGER MADE IN THE UNITED STATES
normal phase hplc
Almost the same as in thin layer chromatography. *The column is filled with tiny silica particles. *Used for Non-polar compounds.
Chromatography
An analyte and solvent mixture is pumped through the chromatographic column • Different components of analyte are separated throughout the column based on the binding affinity of the analyte to the stationary phase. • Different bands are created along the column, corresponding to different substances within the analyte. • A detector measures the amount of time it took for a analyte band to pass through the column, as well as the concentration of the analyte within the band.
2.6 %
An organic chemist is planning to extract 1.00 grams of an organic compound dissolved in 200.0 mL of water into a diethyl ether solvent. The distribution coefficient (K) for this system is 9.5 favoring the ether solvent. If the chemist washes the aqueous solution three times with 50.0 mL of diethyl ether, what percent of the original organic compound remains in the aqueous solvent?
gas chromatography
Analytes must be volatile! • Column temperature is controlled (oven) • Flow rate of the mobile phase must be constant
crystallization
Another term to describe precipitation separations is...
spectrophotometry
Any technique that uses light to measure chemical concentrations.
petroleum distillation
As a substance in the vapor reaches a height where the temperature of the column is equal to that substance's boiling point, it will condense to form a liquid. • The substance with the lowest boiling point will condense at the highest point in the column; substances with higher boiling points will condense lower in the column. The trays collect the various liquid fractions. • The collected liquid fractions may pass to condensers, which cool them further, and then go to storage tanks, or the liquids may be transferred to other processes for chemical processing.
A=eBc
Beer's Law
2. 2.5 ug/L
Calculate the concentration of ethylbenzene if a 10 ug/L standard read 20,000 counts, and the unknown peak area was 5,000 counts
solubility
Chemistry separations using precipitation are based on differences in ....
SE-30 OV-17 Carbowax 20M
Common Liquid (polymer) Stationary Phases
light sources for uv spec
Deuterium Lamp electrical discharge yields fluorescence photons
Beer-Lambert
The linearity of the _______ law is limited by chemical and instrumental factors
DDT (Dichlorodiphenyltrichloroethane)
a synthetic organic compound used as an insecticide. Like other chlorinated aromatic hydrocarbons, DDT tends to persist in the environment and become concentrated in animals at the head of the food chain. Its use is now banned in many countries.
higher
GC Samples are often dissolved in a volatile solvent and injected with a syringe - the injector port is held at a temperature ______ than the column Autosamplers are common for GC and other separation techniques!
Polybrominated biphenyls (PBBs)
HAS BEEN DETECTED IN AIR, SEDIMENTS, SURFACE WATER AND MARINE ANIMALS • HYDROPHILIC • BINDS TO SOIL OR SEDIMENT PARTICLES • ENTERS THE ENVIRONMENT THROUGH THE MANUFACTURING USDH declared them carinogens also caused Weight loss • Skin disorders • Nervous system effects • Endocrine system effects
triple quad
HIGH PERFORMANCE GAS CHROMATOGRAPHY TANDEM MASS SPECTROMETRY OF • "HPGC TANDEM MASS SPEC"
monochromator
Historically, spectrophotometers used a _______ to analyze the spectrum, but there are also spectrophotometers that use arrays of photosensors.
a. 16(12.83)^2/0.307^2=2.8x10^4 plates b. h=158(2.80*10^4)=5.64 um
How many theoretical plates produce a chromatography peak eluting at 12.83 min with a width at the base of 18.4 s? (Hint: use minutes as units) (b) If the length of the column is 15.8 cm, find the plate height. n=16tr^2/w^2 n=l/h
flash column chromatography (flash)
In 1978, W. C. Still introduced a modified version of column chromatography called _________ The technique is very similar to the traditional column chromatography, except for that the solvent is driven through the column by applying positive pressure. This allowed most separations to be performed in less than 20 minutes, with improved separations compared to the old method. Modern flash chromatography systems are sold as pre-packed plastic cartridges, and the solvent is pumped through the cartridge.
polarity electrical charge molecular size
In general, three primary characteristics of chemicals can be used for HPLC separations. They are:
Polychlorinated biphenyls (PCBs)
Industrial products or chemicals Can breakdown/degrade the environment (depending on chemical makeup) Persistent organic pollutant Banned from the U.S. in 1979 because of their impact on human and environmental health Broken down by sunlight or microorganisms Leads to bioaccumulation and biomagnification (also affect humans)
ultraviolet-visible spectrophotometry
Involves the spectroscopy of photons. In this region of energy, molecules undergo electronic transitions. The method is used in a quantitative way to determine concentrations of an absorbing species in solution, using the Beer-Lambert law.
raman spectroscopy
Light scattering technique based on the Raman effect: provides info about chemical structure, phase and polymorphy, and crystallinity and molecular interactions
thermal conductivity detector
Measures the ability of a substance to transport heat - difference between analyte (in peak) and the carrier gas!
fractional distillation
The mixture of two or more substances (liquids) with different boiling points I heated to a high temperature. Heating is usually done with high pressure steam to temperatures of about 1112 degrees Fahrenheit / 600 degrees Celsius. • As the mixture boils, vapors are formed; most substances from crude oil go into the vapor phase. • The vapor is introduced to the bottom of a long column that is filled with trays or plates. The trays have many holes or bubble caps (like a loosened cap on a soda bottle) in them to allow the vapor to pass through. • As the vapor rises in the column, trays at various heights are used to collect liquids that form within the column. There is a temperature difference across the column (hot at the bottom, cool at the top). As the vapor rises through the trays in the column, it cools to form a liquid.
packed stationary
Originally GC used ______ columns exclusively ~2-4 mm internal diameter tube packed with particles containing the _______ phase (1-5 m long)
sir alan walsh
Originator and developer of the atomic absorption method, which revolutionized quantitative analysis
grating-monochromators
Polychromatic light is collimated (focused) into a beam of parallel rays by a concave mirror (monochromatic-one wavelength; polychromaticmany wavelengths). Rays strike the reflection grating and different wavelengths are diffracted (separated) at different angles. Diffracted light is focused by a second concave mirror so that only one wavelength passes through the exit slit at a time
spectrum
Rainbow-like series of colors, in the order violet, blue, green, yellow, orange, and red, produced by splitting a composite light, such as white light, into its component colors.
hpcl injectors
Reproducible injection is critical for quantitative analysis • most often uses a fixed-volume loop • Injection volumes range from nL to mL • Automated injection and fraction collection (eluted) is common (robotics)
1 half mirrored chopper 2. source/monochromator 3. kinetic measurements
Rotation of the ______1_____ allows light to pass to the reference cuvette when the mirror is in the path of the light beam, and light travels to the sample cuvette when the mirrored region is not in the path of the light beam from the _____2______. This rapid switching of signal measurement between the sample and reference enables rapid and reliable measurements to be achieved. Such instruments also make use of a scanning monochromator and a result, very fast spectroscopic events (_____3_____) can be monitored at a variety of wavelengths.
mikhail tswett
Russian botanist • Born March 21, 1872 | Died June 26, 1919 • Invented chromatography in 1900 during his research on plant pigments • He produced separation of plant pigments through liquidabsorption chromatography to separate chlorophylls and carotenoids • His work was ignored for several years due to the fact that there were failed recreation attempts and it was written only in Russian
Flame Ionization Detector (FID)
Sensitive detection of hydrocarbons Most-widely used GC detector As the effluent (carrier gas and any organic compounds) comes out of the column they are ignited in a flame made of hydrogen and air. The compounds produce ions as they burn. These ions conduct electricity. Changes in current within the flame are measured and sent to the computer to be observed as peaks on the chromatogram. is a good general detector for organic compounds, and is able to detect at the nanogram (ppb) level
boiling points
Separations using distillation are based on differences in ...
ir spectrophotometers
Spectrophotometers designed for the main infrared region are quite different because of the technical requirements of measurement in that region.
splitless injection
Technique used in capillary gas chromatography for trace analysis and quantitative analysis. The entire sample in a low-boiling solvent is directed to the column, where the sample is concentrated by solvent trapping (condensing the solvent below its boiling point) or cold trapping (condensing solutes far below their boiling range). The column is then warmed to initiate separation.
retention
The ______ of a compound often differs considerably between experiments and laboratories due to variations of the eluent, the stationary phase, temperature, and the setup. It is therefore important to compare the retention of the test compound to that of one or more standard compounds under absolutely identical condition
beer's law
The absorbance of a sample can be related to the concentration of the absorbing species through ______
ICP
The process creates the photon and takes the atom or molecule in an excited state back to the ground state ● Many interference ● All elements in the sample can be analyzed for the same time, multi element analysis ● Prepare points for calibration for all required elements ● Short time for standards preparation ● The sample itself is the source of emission ● A plasma is used to ionize the sample ● Consumes less glare ware ● One report for all results
Photo ionization detector
The provides a response to a wide range of organic and some inorganic compounds at part per billion (ppb) levels. consists of an ultraviolet lamp and an ion chamber. The detector measures the concentration of gases present in a sample using the method of photoionization. has a linear range of better than seven decades (>107), is nondestructive, and can be used in series with other detectors.
atomic absorption spectroscopy
The sample being tested is vaporized and then the elements of interest get atomized at a high temperature. The concentration is calculated based off the absorption of light at a certain wavelength by the elements being analyzed. Normally,
gas chromatography
The stationary phase of ______ is adhered to the inside of a small diameter glass tube (a capillary column) or a solid matrix inside a larger metal tube (a packed column)
Van Deemter equation
The variance per unit length of the column is taken as the ratio of the column length to the column efficiency in theoretical plates. ______ is a hyperbolic function that predicts that there is an optimum velocity at which there will be the minimum variance per unit column length and, thence, a maximum efficiency.______ equation was the result of the first application of the rate theory to the chromatography elution process.
purge and trap sampling
The volatile compounds are retained in an adsorbent trap, which allows the purge gas to pass through to vent. The volatiles are desorbed by heating the trap: the VOCs are injected into the GC by backflushing the trap using the GC carrier gas.
TCD
The_______ consists of four tungsten-rhenium filaments in a Wheatstone bridge configuration. Electric current flows through the four filaments causing them to heat up. Carrier gas (typically helium which has very high thermal conductivity) flows across the filaments removing heat at a constant rate.
chromatography elution
There is a problem which arises in all types of ___________, when samples of widely differing retention properties are present in the same sample. If the ________ conditions are correct for the early eluting compounds, the late ones will remain in the column too long.
open tubular capillaries stationary
Today most GC columns are ________ ~0.1-0.5 mm internal diameter with the _______ phase attached to the inner walls of the capillary (15-100 m long)
t
True or False - Separations can be used to remove impurities?
light sources for visible spect
Tungsten Lamp (~ tungsten filament light)
Gas Chromatography
Typical uses of ______ include testing the purity of a particular substance, or separating the different components of a mixture. • Can be organic and inorganic, but MUST be volatile
split injections
Used in capillary gas chromatography to inject a small fraction of sample onto the column while the rest of the sample is discarded.
on-column injection
Used in gas chromatography to place a thermally unstable sample directly on the column without excessive heating in an injection port. Solute is condensed at the start of the column by low temperature, and then the temperature is raised to initiate chromatography.
. The transfer of a solute between two immiscible liquids, or from one phase to another.
What is an extraction?
The transfer of a solute between two immiscible liquids, or from one phase to another.
What is an extraction?
flame ionization detector (FID)
Which GC detector works well for hydrocarbon analysis?
A.Thermal Conductivity Detector TCD
Which detector is universal for detecting any analyte?
A.Electron Capture Detector (ECD) or ELCD
Which of the following GC detectors works great with low levels of chlorinated compounds?
4. GC
Which of the following has a gas as the mobile phase? 1.HPLC 2.TLC 3.LC 4.GC 5.None of the above.
1. HPLC 2. LC 3. TLC
Which of the following has a liquid for the mobile phase? 1. HPLC 2. LC 3. TLC 4. GC 5. 1,2,3
Separations are often essential for analysis of mixtures. 2. Synthesis often requires a purification step based on separations. 3. Often it is necessary to isolate pure compounds
Why are separations important in chemistry?
good source for both uv and vis regions of uv/vis spec
Xenon Lamp (Quartz Halogen Lamp)
TCD
a ___ measures the change in voltage it is universal because it responds to all analytes however it is not sensitive enough for capillary columns < 0.53 mm diameter. It has very wide linear range, up to 100% for many compounds.
photometer
a device which measures light intensity
flow rate
a faster ____ of the eluent minimizes the time required to run a column and thereby minimizes diffusion, resulting in a better separation
essential parts of spectrometer
a light source • a wavelength selection device such as a monochromator or filter • a sample chamber • a light detector • a readout device, usually includes a computer, which is used for storage and analysis of the spectra.
spectrophotometer
a photometer that can measure intensity as a function of the color, or more specifically, the wavelength of light; an instrument that measures the absorbance.
Size exclusion chromatography (SEC) is also known as gel permeation chromatography or gel filtration chromatography
and separates particles on the basis of size. Smaller molecules enter a porous media and take longer to exit the column, whereas larger particles leave the column earlier. It is generally a low resolution chromatography and thus it is often reserved for the final, "polishing" step of a purification. It is also useful for determining the tertiary structure and quaternary structure of purified proteins, especially since it can be carried out under native solution condition
radiation
any object that is heated emits _____
colorimetry
any technique that uses color to measure chemical concentrations
separations
are based on the solubility differences of various components
lamps
are broad-band, polychromatic light sources. Typically they are inexpensive and stable.
slits
are constructed by machining a sharp edge onto two metal pieces. These lie in a plane and the spacing between them, the slit width, can be adjusted. The smaller the slit width, the better the spectral resolution
electrons
are ejected from the cathode proportional to the radiant power (photons) striking its surface.
hplc pumps
are expensive, high-performance devices producing high pressure and very stable flow • Flow rates are typically 1 mL/min to several mL/min (capillary LC - preparative LC) • It is important and difficult to produce flow at these pressures that is not pulsed and to maintain constant flow rates
tlc plates
are made by mixing the adsorbent, such as silica gel, with a small amount of inert binder like calcium sulfate (gypsum) and water. This mixture is spread as a thick slurry on an inert carrier sheet, usually glass, thick aluminum foil, or plastic, and the resultant plate is dried and activated by heating in an oven. The thickness of the adsorbent layer is typically around 0.1-0.25 mm for analytical purposes and around 1-2 mm for preparative TLC.
sorbent tubes
are the most widely used collection media for sampling hazardous gases and vapors in air, mostly as it relates to Industrial hygiene. They were developed by the US National Institute for Occupational Safety and Health (NIOSH) for air quality testing of workers.
sorbent tubes
are typically made of glass and contain various types of solid adsorbent material (sorbents). Commonly used sorbents include activated charcoal, silica gel, and organic porous polymers. are attached to air sampling pumps for sample collection. A pump with a calibrated flow rate in ml/min is normally placed on a worker's belt and it draws a known volume of air through the sorbent tube. Alternatively, pumps and sorbent tubes are placed in areas for fixed-point sampling.`
filters
are used to pass on only desired wavelengths of light. A filter could be colored glass. Most likely they are also based on constructive or destructive interference of light waves.
diode arrays
assemblies of individual photo diodes in a linear array.
tlc
bc of simplicity it is often used for monitoring chemical reactions and for the qualitative analysis of reaction products.
ratio measurements are easier . and generally more stable
benefits of double beam spec
larger dynamic range very inexpensive more rugged
benefits of single beam spectrophotometer
on column injections
best for thermally unstable solutes and high boiling solvents; best for quantitative analysis
splitless injections
best for trace levels of high boiling solutes in low boiling solvents
PMTs
can be destroyed/damaged by intense light sources like daylight orr stray light
• deviations in absorptivity coefficients at high concentrations (> 0.01 M) due to electrostatic interactions between molecules in close proximity • scattering of light due to particulates in the sample • fluorescence or phosphorescence of the sample • changes in refractive index at high analyte concentration • shifts in chemical equilibria as a function of concentration • non-monochromatic radiation, deviations can be minimized by using a relatively flat part of the absorption spectrum such as the maximum of an absorption band stray light
causes of linearity in beer lambert
gradient elution
changes the ratio of solvent A to solvent B to create a gradient of mixed solvents.
chloroform dichloromethane carbon tetrachloride
common organic solvents for extractions more dense than water
benzene diethyl ether hexan e
common organic solvents less dense than water
cathode
consists of a photo-emissive surface.
Photo Ionization Detector (PID)
consists of a special UV lamp mounted on a thermostatted low volume flow-through cell. The temperature is adjustable from ambient to 250ºC. is the detector of choice for aromatics and unsaturated hydrocarbons. The 10.6 electron volt UV lamp emits energy at a wavelength of 120 nanometers, which is sufficient to ionize most aromatics (benzene, toluene, xylene, etc.) and many other molecules (H2S, hexane, ethanol) whose ionization potential is below 10.6 ev. Methanol and water, for instance, have ionization potentials greater than 10.6 ev and do not respond on the ...... Detection limits for aromatics are in the low picogram range (ppb) and because the .... is non-destructive, it is often run in series with another detector (FID/ELCD) for multiple chromatograms from a single injection. Use of a ..... is mandated in several EPA methods because of its sensitivity and selectivity.
- requires a large amount of land that is used entirely for growing corn than cannot be consumed by humans or animals - refineries no longer having to blend biofuel into their gasoline so corn no longer needs to be used
controversy of corn ethanol
mobile phase
is the analyte and solvent mixture which travels through the stationary phase
e (molar absorptivity)
is the characteristic of a substance that tells how much light is absorbed at a particular wavelength.
ELCD
converts eluting compounds with the target heteroatom (halogens, S or N) to an ionizable gas (HX) using reductive conditions at temperatures from 800 to 1,100 °C in a catalytic micro reactor. The gaseous reaction products continue to the detector cell where they quickly dissolve in a flowing deionized solvent stream, increasing its electrolytic conductivity. A conductivity detector amplifies the change in conductivity, producing a signal proportional to the mass of target species. The solvent stream then flows through a deionizing resin bed and filter as it is continuously recycled.
column bleed
describes when the stationary phase detaches from the column is caused by decomposition and evaporation of the stationary phase of a column (occurs for both GC and LC). also oxidation of the stationary phase
electron capture detector
detector is extremely sensitive, probably one of the most sensitive GC detectors available (minimum detectable concentration ca. 10-13 g/ml) and is widely used in analysis of pesticides.
not rugged often expensive
disadvantages of double beam spec
types of separations
distillation crystallization (precipitation) centrifugation (gravity) electrophoresis extraction (liquid-liquid, liquid-solid, membrane filters) chromatography
~107
each electron in PMT causes ______ additional electrons to be produced
q= v1/[v1+kv2]
equation for a solute partitions between two immiscible liquids
IR spectrophotometry
for the _____ there are spectrophotometers that use a Fourier transform technique to acquire the spectral information in a technique called Fourier Transform InfraRed Spectrophotometry (FTIR).
column conditioning
g is a process that is used with new columns, or older columns that have not been used recently to remove contaminants. Carrier gas is introduced through a GC column at elevated temperature to flush out residual contaminants to provide a steady baseline. LC columns are conditioned by flushing solvent solutions until a steady baseline is achieved.
van deemter
h=a+B/u+Cu
photomultiplier tube (PMT)
has cathodes, anodes, and dynodes which produce a cascade effect on the electron emission production
general elution problem
here is a problem which arises in all types of chromatography, when samples of widely differing retention properties are present in the same sample. If the elution conditions are correct for the early eluting compounds, the late ones will remain in the column too long.
PMTs
high sensitivity, good s/n ratio, excellent dynamic range
ethanol
highly flammable, can cause coughing or headaches is a generally recognized as safe substance meaning it can be used in food products
PMTs
highly sensitive to visible and UV excitations at extremely low power conditions
the wavelengths they work with the measurement techniques they use how they acquire spectrum sources of intensity variation they are designed to measure
how are spectrophotometers classified?
multiple extractions changing pH metal chelants, salts
how can you enhance extractions
He used a liquid-adsorption column containing calcium carbonate to separate plant pigments. The method was described on December 30, 1901 at the XI Congress of Naturalists and Doctors (XI съезд естествоиспытателей и врачей) in St. Petersburg. The first printed description was in 1903, in the Proceedings of the Warsaw Society of Naturalists, section of biology.
how did semyonovich invent chromatography
Both the ECD and ELCD detectors are useful for halogenated analytes. The ECD detects fluorine while the ELCD does not. Both detectors detect chlorine and bromine. The ELCD is much more selective than the ECD, which detects electro-negative molecules like oxygen as well as halogens. PCBs for example can be detected by the ELCD even in the presence of massive co-eluting hydrocarbons. On the other hand the ELCD is less sensitive than the ECD, so larger amounts must be extracted and injected on-column.
how to decide between ecd and elcd?
interrupted development systems like TLC
in _____ the retention is measured as the retention factor (Rf) the run length of the compound divided by thee run length of the eluent front
in continuous development systeems like HPLC or GC
in _______________, where compounds are eluted with the eluent, the retention is usually measured as the retention time Rt or tR, the time between injection and detection.
Van Deemter equation
in chromatography relates the variance per unit length of a separation column to the linear mobile phase velocity by considering physical, kinetic, and thermodynamic properties of a separation.
lower thermal conductivity increase
in tcd When a sample molecule with __________ exits the column and flows across the two sample filaments, the temperature of the filaments _______ unbalancing the Wheatstone bridge and generating a peak as the sample molecules transit through the detector.
R1/R2=r3/r4
in tcds when the current is applied, the voltage between pints + and - in the circuit will be zero as long as the following relationship is true :
column chromatography
includes a number of techniques which use a vertical glass column filled with some form of solid support, with the sample to be separated placed on top of this support. The sample is dissolved in a small quantity of solvent (the eluent) and applied to the top of the column. The eluent flows down through the column filled with the adsorbent The rest of the column is filled with a solvent which, under the influence of gravity, moves the sample through the column. Similar to other types of chromatography, differences in rates of movement through the solid packing material leads to different exit times from the bottom of the column for the individual components of the original sample mixture.
c.v raman
indian physicist won noble prize for physics in 1930 known for ground breaking work in field of light scattering
arnold o beckham
invented ph meter Developed the DU Spectrophotometer ● Developed the Beckman IR-1 Spectrophotometer ● Created the IR-4 which could use either a single or double beam of infrared light ● Created the Micro-Ammeter - Manhattan Project ● Key in identifying the sources of Air Pollution in California ● Awarded the National Medal of Technology in 1988
paper chromatography
involves placing a small spot of sample solution onto a strip of chromatography paper. The paper is placed into a jar containing a shallow layer of solvent and sealed. As the solvent rises through the paper it meets the sample mixture which starts to travel up the paper with the solvent. Different compounds in the sample mixture travel different distances according to how strongly they interact with the paper. This allows the calculation of an Rf value and can be compared to standard compounds to aid in the identification of an unknown substance. After development, the spots corresponding to different compounds may be located by their color, by ultraviolet light, ninhydrin or by treatment with iodine vapors. The final chromatogram can be compared with other known mixture chromatograms to identify sample mixes using the Rf value. As in most other forms of chromatography, paper chromatography uses Rf values to help identify compounds. The Rf values are calculated by dividing the distance the pigment travels up the paper by the distance the solvent travels.
Chloroprene
is a colorless volatile liquid, almost exclusively used as a monomer for the production of the polymer polychloroprene, which is a type of synthetic rubber. Polychloroprene is better known as Neoprene, the trade name given by DuPont. s designated with a category 2 health hazard (temporary incapacitation or residual injury), a category 3 fire hazard (ignition under the presence of moderate heat), and a category 1 reactivity (unstable at high temperatures and pressures) release is predominately as an air pollutant, but other feasible fates and transport of chloroprene in the environment are discussed below. • Due to its volatility and extreme reactivity, the threat of chloroprene exists predominantly as an air pollutant and is not expected to bioaccumulate or persist in the environment according to the U.S EPA Toxicological Review
the electrolytic conductivity detector (ELCD)
is a destructive, mass-sensitive selective detector. • Its main use is for regulated methods designed for selective detection of halogen-containing compounds. • consists of three principal components: the reactor assembly, the cell-solvent assembly, and the detector controller. • Although the principal mode of operation of the....is the halogen mode (X), sulfur (S) and nitrogen (N) modes are also possible. • Each detection mode requires a specific reactor, resin cartridge, and solvent. • The ..... can be used as a stand-alone detector or in tandem following a photoionization detector (PID) or other nondestructive detectors.
retention
is a measure of the speed at which a substance moves in a chromatographic system
retention
is a measure of the speed at which a substance moves in a chromatographic system. In continuous development systems like HPLC or GC, where the compounds are eluted with the eluent, the _____ is usually measured as Rt or tR, the time between injection and detection. In interrupted development systems like TLC it is measured as Rf , the run length of the compound divided by the run length of the eluent front
Glyphosate
is a non-selective, weak acid herbicide which is applied to leaves of broadleaf plants and grasses in us was first registered for use and is one of the most widely used herbicides It targets the shikimic acid pathway, which is a 7 step metabolic pathway used by plants and microorganisms to biosynthesize folates and aromatic amino acids (phenylalanine, tyrosine, and tryptophan) by inhibiting 5-enolpyruvylshikimate-3- phosphate synthase (EPSP). ● It persists in the soil for about 6 months and then is broken down by bacteria ● Although concerning, studies of pesticide residues by the United Nations and World Health Organization (WHO) determined that glyphosate is not likely to be carcinogenic. ● Ex: Roundup Weed killer
Size Exclusion Chromatography
is an HPLC technique where the different sizes of the compounds are used to create the separation. There is no chemical attraction involved. The stationary phase particles have openings, called pores, which are of a controlled size.
wheatstone bridge
is an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, one leg of which includes the unknown component
High Performance Liquid Chromatography (HPLC)
is an improved form of column chromatography * The solvent is forced by a pump through a column under high pressures of up to 400 atm. the pressure makes itmuch faster than column chromatography Use of much smaller particles for the column packing material. • Much better separation of the components in the mixture
mass spec
is an instrument designed to separate gas phase ions according to their m/z (mass to charge ratio) value measures exact mass of compound
teratogen
is any agent or product that can disturb the development of an embryo or fetus.
mobile phase (eluent)
is either a pure solvent or a mixture of different solvents. It is chosen so that the retention factor value of the compound of interest is roughly around 0.75 in order to minimize the time and the amount of ______ to run the chromatography. The _____ has also been chosen so that the different compounds can be separated effectively. The ____ is optimized in small scale pretests, often using thin layer chromatography (TLC) with the same stationary phase.
Cu
is equal to the equilibration point. In a column, there is an interaction between the mobile and stationary phases, _____ accounts for this.
b/u
is equal to the longitudinal diffusion of the particles of the compound
A (eddy-diffusion)
is equal to the multiple paths taken by the chemical compound, in open tubular capillaries, this term will be zero as there are no multiple paths. The multiple paths occur in packed columns where several routes through the column packing, which results in band spreading
corn ethanol
is ethanol produced from corn biomass and is the main source of ethanol fuel in the United States. is produced by fermentation and distillation. It is debatable whether the production and use of corn ethanol results in lower greenhouse gas emissions than gasoline. Approximately 40% of the U.S. corn croplands are used for ethanol production.
plate theory
the ____ of chromatography was developed by Archer John Porter Martin and Richard Laurence Millington Synge. it describes the chromatography system, the mobile and stationary phases, as being in equilibrium. The partition coefficient K is based on this equilibrium,
headspace analysis
the analysis of characteristic volatile compounds associated with liquids or solids without direct sampling of the matrix. • Typical samples can include water, effluents, soil, food, and beverages. • The purpose of the analysis can be to evaluate and identify individual components or to relate chromatographic profiles to odor or aroma characteristics. • Most manufacturers provide automatic equipment for many of these applications, and include air analyzers, water analyzers, automatic headspace analyzers, thermal desorbers, and purge and trap analyzers.
helium
the carrier gas most commonly used with a TCD. It has the 2nd highest thermal conductivity after H2, so any analyte mixed with it lowers the conductivity of the gas stream. As the eluate emerges from the end of the GC column, the conductivity of the gas stream decreases, the filament gets hotter, and its electrical resistance increases, and the voltage across the filament changes.
flame ionized detector
the eluate is burned in a mixture of hydrogen and air. In the flame, carbon atoms produce CH radicals, which produce CHO+ ions and electrons. CH + O à CHO+ + e- Only about 1 in 105 carbon atoms produces an ion. The collector (positive electrode) attracts the electrons; changes in the detector response are converted to a voltage, amplified, filtered to remove noise, and then converted to a digital signal. The detector responds only to hydrocarbons, and is insensitive to gas atoms and non-hydrocarbon molecules such as H2, He, N2, O2, CO, CO2, H20, NH3, H2S, and NO. 100-fold better detection than TCD, 107 linear response range.
spectrum
the graph of absorbance versus wavelength
uv and visible
the most common spectrophotometers are used in ____ & _____ regions of the spectrum. some of these instruments also operate into the near-infrared region as well
solid silica gel then alumina
the stationary phase or adsorbent in column chromatography is a ______. the most common one is ___
chromatogram
the visual output of the chromatograph. Different peaks or patterns on the chromatogram correspond to different components of the separated mixture
quartz halogen lamp
ultraviolet and visible lamp
deuterium arc lamp
ultraviolet lamp
phototube
used frequently as a detector in UVVis spectrometers.
prism
used in order instruments to select wavelength . quarts or salt crystals
Analytical chromatography
used to determine the identity and concentration of molecules in a mixture
atomic emission spectroscopy
uses quantitative measurement of the optical emission from excited atoms to determine analyte concentration uses ICP - a type of mass spectrometry that uses an inductively coupled plasmas to ionize the sample.
tungsten lamp
visible and near infrared lamp
Pierre Bouguer
was a French mathematician and astronomer. He is also known as "the father of naval architecture". His father, Jean Bouguer, one of the best hydrographers of his time, was regius professor of hydrography at Croisic in lower Brittany, and author of a treatise on navigation. In 1713 Pierre was appointed to succeed his father as professor of hydrography. In 1727 he gained the prize given by the French Academy of Sciences for his paper On the best manner of forming and distributing the masts of ships ; and two other prizes, one for his dissertation On the best method of observing the altitude of stars at sea, the other for his paper On the best method of observing the variation of the compass at sea. These were published in the Prix de l'Academie des Sciences. In 1729 he published Essai d'optique sur la gradation de la lumière, the object of which is to define the quantity of light lost by passing through a given extent of the atmosphere, and became the first known discoverer of what is now more commonly known as the Beer-Lambert law. He found the light of the sun to be 300 times more intense than that of the moon, and thus made some of the earliest measurements in photometry. In 1730 he was made professor of hydrography at Havre, and succeeded Pierre Louis Maupertuis as associate geometer of the Academy of Sciences. He also invented a heliometer, afterwards perfected by Joseph von Fraunhofer. He was afterwards promoted in the Academy to the place of Maupertuis, and went to reside in Paris. In 1735 Bouguer sailed with Charles Marie de La Condamine for Peru, in order to measure a degree of the meridian near the equator. Ten years were spent in this operation, a full account of which was published by Bouguer in 1749, Figure de la terre determine. In 1746 he published the first treatise of naval architecture,Traite du navire, which among other achievements first explained the use of the metacenter as a measure of ships' stability. His later writings were nearly all upon the theory of navigation and naval architecture. A crater on Mars was named in his honor. His name is also recalled as the meteorological term Bouguer's halo (also known as Ulloa's halo, after Antonio de Ulloa, a Spanish member of his Peru expedition) which an observer may see infrequently in fog when sun breaks through (for example, on a mountain) and looks down-sun -- effectively a "fog-bow" (as opposed to a "rain-bow"). An infrequently observed meteorological phenomenon; a faint white, circular arc or complete ring of light that has a radius of 39 degrees and is centered on the antisolar point. When observed, it is usually in the form of a separate outer ring aro
Separations are often essential for analysis of mixtures. 2. Synthesis often requires a purification step based on separations. 3. Often it is necessary to isolate pure compounds.
what are separations important in chemistry
the water protects the bill from the alcohol and it is vaporized from the heat causing a large flame around the bill
what happens when you dip a dollar bill into a . mixture of water and alcohol then light it on fire?
The R form was therapeutically active while the S form was ineffective and caused birth defects
what is the importance of thalidomide and sterochemistry?
k'=tr-tm/tm
what is the retention factor
denaturant which makes it bitter
what keeps people from drinking ethanol?
PLANT OWNED BY VELSICOL CHEMICAL ACCIDENTLY SHIPPED A TOXIC RETARDANT CHEMICAL TO LIVESTOCK FEED PLANT. • AS A RESULT, IT CONTAMINATED BEEF, CHICKEN, PORK, EGGS AND MILK. • EMORY UNIVERSITY STUDIED PEOPLE AROUND THE AREA AND FOUND: • HIGH LEVELS OF THYROID DISEASE • FEW MORE BREAST CANCER CASES • PBBS WAS TRANSFERRED TO CHILDREN IN THE WOMB.
what occured during the michigan toxic food contamination in 1973?
raman effect
when incident light excites molecules in a tissue, the molecules will reflect light in a different wavelength
WHEN YOU ARE TRYING TO ANALYZE VOLATILE GAS MIXTURES • IT IS VERY COMMON, IN TERMS OF QUALITY CONTROL, FOR RESEARCH AND INDUSTRIAL LABORATORIES, AS WELL AS FOR IDENTIFYING AND QUANTIFYING COMPOUNDS IN A GAS MIXTURE. • BECAUSE IT ALLOWS FOR THE ANALYSIS, SEPARATION AND QUANTIFICATION OF GAS MIXTURES, IT IS VERY USEFUL FOR ENVIRONMENTAL AND FORENSIC LABS AS WELL, BECAUSE IT CAN DETECT VERY SMALL QUANTITIES ALLOWING FOR CLEANER AIR CONTROL
when would you use gas chromatography?
WE USE HPLC WHEN WE WANT TO SEPARATE A MIXTURE OF COMPOUNDS (ANALYTES) • SEPARATING THESE MIXTURES ALLOWS US TO IDENTIFY, QUANTIFY AND PURIFY THE INDIVIDUAL COMPONENTS OF THE MIXTURE • HPLC IS USED FOR WATER PURIFICATION, DETECTING IMPURITIES IN PHARMACEUTICALS, AND OTHER QUANTITATIVE AND QUALITATIVE ANALYSIS
when would you use high performance liquid chromatography
russian botanist mikhail semyonovich tsvet
who invented chromatography in 1901?