Final Exam
bulk sample
(also called a gross sample) is taken from the lot for analysis or for archiving (storing for future reference). must be representative of the lot.
flame ionization detector
(eluate is burned in a mixture of H2 and the air) a destructive mass-sensitive detector whose response is proportional to mass of carbon entering per unit time. 100-fold lower detection limit than thermal conductivity, 10^7 linear response range
safety data sheets
-are provided with each chemical sold in the united states -list hazards and precautions for the chemical -provide first aid procedures and instructions for handling spills
standard uncertainty for x decreases with:
-smaller standard deviation in measurements - greater slope of calibration - more replicate measurements of unknown - more calibration points -sample data range closer to center -wide calibration range
critical functions of the lab notebook
-state what you did -state what you observed to be understandable to a stranger
3 types of experimental error
-systematic -random -gross (blunders)
sample preparation
.transforming a sample into a state that is suitable for analysis by dissolving the sample, removing or masking species that interfere with the analysis.
steps in a chemical analysis
1. formulate the question. 2. form analytical procedure. 3. Sampling 4. Sample preparation 5. Analyze 6. Report and interpret 7. Draw conclusions
solutes are ____ and ____ in programmed temperatures
1. strongly retained (trapped) at the column head for most of the time on the column 2. weakly retained when eluted due to higher temperatures and thus appear as sharper peaks
thermal conductivity detector
10^5 linear response range. H2 and He give lowest detection limit. sensitivity increases with increasing filament current decreasing flow rate, lower detector block temperature. nondestructive
molarity
A common measure of solute concentration, referring to the number of moles of solute per liter of solution.
concentration
A measurement of how much (mol) solute exists within a certain volume (L) of solvent
surfactant
A molecule with a hydrophilic end and a hydrophobic end that accumulates a the interface between 2 phases
common ion effect
A salt is less soluble if one of its ions is already present in the solution
What is a segregated heterogeneous material?
A segregated heterogeneous material contains large regions of obviously different compositions.
Grubbs test
A statistical test in which one only point of data may be discarded because it is far away from other other points.
Microwave digestion
A teflon lined bomb is heated in a microwave oven is a convenient means of dissolving difficult samples. metal would absorb microwaves. bomb should be cooled prior to opening to prevent loss of volatile products
Beer Lambert Law
Absorbance increases as concentration increases. The molar absorptivity value is chromophore and wavelength specific. The absorption spectrum is a graph showing how absorbance changes with wavelength.
The chemist has identified some analytical procedures to test for cadmium and mercury in soil samples. What is the next step? Please choose the correct answer from the following choices, and then select the submit answer button. Answer choices
After identifying an appropriate analytical procedure, the next step in a chemical analysis is sampling. Having a representative sample is important to obtain meaningful data.
How are the chromatographic methods divided?
By there mechanism of interaction of solute with the stationary phase
what is the most common supercritical fluid solvent?
Carbon dioxide because it is inexpensive, and eliminates the need for costly disposal.
What are the most accurate grade of burets
Class A burets
T-test
Compares mean values of a continuous variable between 2 categories/groups.
capillary electrophoresis
DNA fragments can be separated and identified by (gas chromatography, capillary electrophoresis).
wet ashing
Destruction of organic matter in a sample by a liquid reagent prior to analysis of an inorganic component.
normal error curve
Gaussian curve with unit area
selected ion monitoring
Graph of detector response versus time when a mass spectrometer monitors just a few selected
van Deemter equation:
H = A + B/u + Cu
retention gap
In gas chromatography, a 3- to 10-m length of empty, silanized capillary ahead of the chromatography column. The retention gap improves the peak shape of solutes that elute close to solvent when large volumes of solvent are injected or when the solvent has polarity from that of the stationary phase.
What is the advantage of using solid-phase extraction for sample preparation in the analysis of caffeine in chocolate over the traditional method?
In the traditional sample preparation process, fat and other nonpolar substances were extracted from the chocolate using an organic solvent. The caffeine was then extracted from the sample using hot water. Finally, fine particles that could ruin the expensive chromatography column were removed with repeated centrifugation and filtration. Solid-phase extraction is able to replace these steps, reducing the sample preparation time. In solid-phase extraction, caffeine and other nonpolar substances are retained on the silica column. Polar, water-soluble substances are washed from the column using water. The caffeine is then washed from the column using methanol, leaving the fats and other nonpolar substances on the column.
weighing by difference
Is a method used to accurately weigh the amount of material transferred. The mass of a container before (with dry material) and after transferring the material is taken and the difference between these values is the mass of material transferred. necessary for hygroscopic reagents
measuring pipet
Is graduated and can be used to measure various volumes of liquid accurately
Molarity vs. Molality (Temperature change)
Molarity changes as temperature changes because it is a unit of moles per volume. However, molality is a unit of moles per mass which remains unchanged
ppb
Parts Per Billion. A Unit Used To Express The Concentration In A Solution.
ppm
Parts per million - measuring system for the amount of substance present.
What types of columns are used with gas-solid chromatography?
Porous layer open tubular columns
preconcentration
Process of concentrating trace components of a mixture prior to their analysis.
The chemist collects a representative sample of the very fine, uniform stamp sands near the town. What is the chemist's next step?
Remove or mask any interfering substances.
ashless filter paper
Specially treated paper that leaves a negligible residue after ignition of a precipitate. It is used for gravimetric analysis.
solvent trapping
Splitless gas chromatography injection technique in which solvent is condensed about 15 degrees celsius below its boiling point at the start of the column. - leads to sharp chromatographic peaks entire solute dissolve in a narrow band in the condensed solvent.
analyte
Substance being analyzed
experimental error
The difference between the true value of a measurement and the measured value
The real rule
The first digit of the absolute uncertainty is the last significant digit in the answer.
Denby and Scott used an organic solvent to extract fats from the crude sample before extracting the caffeine and theobromine from the chocolate sample in hot water. In the solid-phase extraction, the crude sample is extracted with hot water first. Then the fats are extracted from this aqueous extract using an organic solvent.
The method used by Denby and Scott used petroleum ether, an organic solvent, to remove fats from the crude sample before using hot water to extract the caffeine and theobromine. In the solid-phase extraction, caffeine and theobromine are first extracted using hot water. The aqueous sample is then applied to a silica column and the fats remain adhered to the disposable column throughout the procedure.
formal concentration
The molarity of a substance if it did not change its chemical form on being dissolved. It represents the total number of moles of substance dissolved in a liter of solution, regardless of any reactions that take place when the solute is dissolved. Also called analytical concentration or formality.
light as a wave
The product of the frequency and wavelength of a wave of light is the speed of light. Frequency is the number of oscillations that a wave makes each second. The speed of light in a vacuum is 2.998 × 108 m/s. Light travels slower through matter than through a vacuum.
storing samples
The sample composition may change with time after collection because of chemical changes, reaction with air, or interaction of the sample with its container. Glass is a notorious ion exchanger that alters the concentrations of trace ions and proteins in solution. Plastic containers must be washed before use. Polyethylene containers can contribute a measurable flux of analyte even after being soaked in acid for several months.
Why is it more difficult to provide an accurate analysis of the caffeine content of a chocolate bar containing macadamia nuts than a pure chocolate bar?
The sampling strategy is more complex for the heterogeneous material than for the homogeneous material.
Example of sample preparation
The students are frustrated when their sample is cloudy after repeated extractions, centrifugations, and filtrations.
mean
The sum of measured values divided by the number of measurements. aka the average or the center of the distribution
Another pair of students repeated the analysis of caffeine in chocolate bars performed by Denby and Scott to verify their results. However, they were in a hurry and after extracting the fat, they performed only one aqueous wash and transfer of the fat-free chocolate residue. Predict how their results will compare to those of Denby and Scott.
Their data will likely show a lower caffeine content because they did not completely transfer all of the fat-free chocolate residue. These students likely did not make a quantitative transfer of the fat-free chocolate residue because they performed only one rinse and transfer, so the amount of caffeine in their final sample is likely less than if they would have repeated these steps multiple times to ensure the complete transfer of the residue.
The temperature program for a separation starts at a temperature of 50 degrees Celsius and ramps the temperature up to 270 degrees Celsius at a rate of 10 degrees celsius/min.
Weakly retained solutes will separate and elute early in the separation. Strongly retained solutes will remain at the head of the column when the temperature is low. At 10 degrees Celsius /min, a total of 22 min are needed to reach 270 degrees Celsius. The vapor pressure of strongly retained solutes will increase as the temperature increases.
aqua regia solution
a 3:1 (vol/vol) mixture of HCl and NHO3 used to dissolved Au and Pt (these strong oxidizing agents can dissolve difficult substances)
dessicator
a closed chamber containing a drying agent
outlier
a datum far from other points
open tubular column
a hollow capillary tube with inner walls that are coated with stationary phase material
Gas Chromatography
a method of separating chemicals to establish their quantities mobile phase: gas stationary phase: usually a nonvolatile liquid like polymer but sometimes a solid analyte: gas or volatile liquid
buret
a precisely manufactured glass tube with graduations enabling you to measure the volume of liquid delivered through the stopcock (the valve) at the bottom. (0 mL marker is at the top) interpolate the reading to 0.01 mL
derivatization
a procedure in which analyte is chemically modified to make it easier to detect or separate.
Temperature programming
a procedure used in gas chromatography in which the temperature of the column is raised during the separation to increase analyte vapor pressure and decrease retention times of late-eluting components.
absorption
a process in which one substance is taken inside another (example: water absorbs into the sponge)
tris
a pure compound that measures concentrations of acids as a primary standard
excess reagent
a reagent present in a quantity that is more than sufficient to react with a limiting reagent; any reactant that remains after the limiting reagent is used up in a chemical reaction
High pressure asher
a resistive heating element inside a chamber for digestion at temperatures up to 270 under a pressure of 140 barr.
ambient temperature
a sample reaches this particular temperature when it is equal to the temperature of the surroundings
green chemistry
a set of principles intended to change our behavior to help sustain a habitable planet
Student's t
a statistical tool used most frequently to express confidence intervals and to compare results from different experiments
method of least squares
a statistical way to find the best-fitting line through a set of data points. y=mx+b
a low pka means
a strong acid
electrolyte
a substance that dissociates into ions in solution. (strong or weak)
coprecipitation
a substance whose solubility is not exceeded precipitates along with another substance whose solubility is exceeded
primary standard
a weighed amount of pure reagent in a known volume of solution. pure enough to be weighed and used directly. (greater than 99.9%) should not decompose under ordinary storage stable when dried by heat or vacuum Examples: CaCO3, AgNO3, Ni(metal)
relative uncertainty
absolute uncertainty/magnitude of measurement . can be reduced by increasing volume delivered by the buret.
cloud point extraction
accomplishes a liquid-liquid extraction plus preconcentration of analyte by use of a surfactant that forms spherical micelles (Box 26-1) into which analyte is extracted
What is the purpose of a guard column?
accumulate nonvolatile substances that would otherwise contaminate the chromatography column and degrade its performance
The first 3- to 10-m length of a capillary column serves as a guard column and retention gap. Guard columns
accumulate nonvolatile substances to prevent column contamination.
standard mass
affected by buoyancy, ways less in air than in a vacuum
cold trapping
an alternative means of condensing solutes in a narrow band at the beginning of the column by using an initial column temperature at least 100°C lower than the boiling point of the solutes of interest
steel needles
an avoidable source of metal contaminatio n
metal chelating agent
an ion or molecule that binds with a metal to allow transfer into another phase
linear range
analyte concentration range over which response is proportional to concentration
gas-solid adsorption chromatography
analyte is adsorbed directly on solid particles of stationary phase
extraction
analyte is dissolved in a solvent that does not necessarily dissolve the entire sample and does not decompose the analyte
species
any chemical of interest
limiting reagent
any reactant that is used up first in a chemical reaction; it determines the amount of product that can be formed in the reaction
eratic readings
balance door open, object hot or cold, static charge on object
symptoms of excessive column bleeding
base line high or rising at lower temperatures than normal increasing broadening and tailing with successive injections changing retention times in successive injections
on column injection
best injection method for quantitative work and thermally sensitive compounds. injected directly into the column liner without going through a hot injector. limited to clean samples containing little to no nonvolatile components
gross error
blunders. aka. extreme instances of random or systematic error due to departures from procedure unrecoverable errors
transfer pipet
calibrated to deliver one fixed volume
static charge
can be dissipated by patting balance and object with antistatic brush
Random sample
collected by taking portions from an appropriate number of segments chosen at random
Derived units
combinations of SI base units examples: Force (N), heat (J) , and Pascal (Pa)
quantitative transfer
complete transfer
reliability
consistency of measurement
standard solutions
contain known concentrations of analyte
When extracting a sample with a liquid, the liquid is __________ from the sample.
decanted
raising column temperature
decreases retention time and sharpens peaks
micropipets
deliver volumes from 0 to 1,000 microliters. require repeated calibration and maintenance.
agate mortar
designed for grinding small particles into fine powder
anhydrous
destitute of (without) water
random heterogeneous material
differences in composition occur randomly and on a fine scale
linear velocity
distance per unit time traveled by solvent
composite sample
draws from each region, and the number of samples from each region is proportional to the area of the region
Silanization
end capping. used by column manufacturers to reduce tailing by blocking the silanol groups with nonpolar (SiOH) groups
matrix
everything in the unknown other than the analyte . may cause systematic error thus it is crucial to know what is in the sample
liquid - liquid extraction
extract nonvolatile analyte, typically from an aqueous solution into an organic solvent. The vapors condense into the extraction vessel. Passing through the liquid, analyte is extracted and passes to the solvent reservoir where it is increasingly concentrated as extractions continue
packed column
filled with particles of stationary phase
eluent
fluid entering the column
eluate
fluid exiting the column
adjusted retention time
for a retained solute is the additional time required to travel the length of the column, beyond that required by solvent
retention time
for each component is the time that elapses between injection of the mixture onto the column and the arrival of that component at the detector
Under what condition is on column injection used?
for samples that decompose above their boiling point
headspace
gas phase above a solid or liquid in a sealed container
carrier gas
gaseous mobile phase in GC
reverse pipetting
good for methanol and hexane. a technique for micropipettes
accuracy
how close a measurement is to the true value
ion pair extraction
hydrophobic cations and anions bring ions of opposite charge from aqueous phase into an immiscible organic solvent.
reading drifts up
hygroscopic material absorbing moisture from the air
aqua regia
if a non-oxidizing agent is insufficient, these oxidizing acids are used to dissolve inorganic materials
causes of excessive column bleed
include excessive column temperature, oxygen from leaking septum or fitting, oxygen contamination from carrier gas, injection of chemicals that react with the stationary phase.
increasing inlet pressure
increases the flow of the mobile phase and decreases retention time.
antilogarithm
inverse of the logarithm
retention volume
is the volume of mobile phase required to elute a particular solute from the column
what is the main source of uncertainty for most elements ?
isotopic variations in different measurements
segregated heterogeneous material
large regions have obviously different compositions
plate height
length of column required for one equilibration of solute between the mobile and stationary phases.
metal chelation extraction
ligand + metal to allow transfer into the organic phase
reading drifts down
liquid evaporating
mother liquor
liquid from which a substance precipitates or crystallizes
filtrate
liquid that passes through the filter
below the optimum linear velocity
longitudinal diffusion broadening becomes dominant
temperature limits of gas chromatography
lower limit: it is the temperature at which the stationary phase no longer behaves like a liquid
open tubular column
made of fused silica with an exterior coating of polyimide (a plastic capable of withstanding ) for support and protection from atmospheric moisture. offer higher resolution, shorter analysis time, and greater sensitivity than packed columns, but they have less sample capacity.
absolute uncertainty
margin of uncertainty associated with a measurement (with units)
Which is measured more precisely? Mass or volume?
mass
true mass
mass measured in a vacuum (buoyancy)
sampling constant
mass of sample that will produce a relative sample standard deviation of 1%.
tare
mass of the empty vessel
above the optimum linear velocity
mass transfer broadening becomes dominant
Linearity error
maximum error of a balance that can occur as a result of non-linear balance response
linear response
means that peak area is proportional to analyte concentration. For very narrow peaks, peak height is often substituted for peak area.
standard deviation
measure of reproducibility
standard deviation of the mean
measures uncertainty of the mean. equals the standard deviation divided by the square root of the sample size. also called standard uncertainty
fusion
melting. substances may be dissolved in hot, molten inorganix flux. carried out in a Pt-Au crucible. large amount of impurities may be introduced due to the large amount of solid reagent.
SI base units
meter, kilogram, second, kelvin, mole, ampere, candela
Chemical analysis
middle portion of a process that begins with a question and ends with a conclusion.
solute vs. solvent
minor species vs. major species
Strong electrolyte
mostly dissociated into ions in solution
laboratory sample
must have the same composition as the bulk sample and the individual aliquots are then used for analysis.
degrees of freedom
n-1.
to improve resolution:
narrower column longer column different stationary phase
dry ashing
no liquid used - halogens in coal -metals in plant material
pyrolysis
nonvolatile samples are heated to temperatures that cause thermal decomposition. The resulting gas is transferred to the gas chromatography.
weak electrolyte
partially dissociated into ions in solution
standard test sieves
particles can be sorted by passing them through a series of mesh sieves. particle diameter range varies with each sieve
grinding
performed in a mortar and pestle
chromatogram
plot of detector response versus retention time
aliquots
portions
decant
pour off gently
Under what condition is split injection used?
preferred for samples where the analytes of interest constitute >0.1% of the sample.
Under what condition is splitless injection used ?
preferred for trace analysis of analytes that are less than parts-per-million in the sample.
blank solutions
prepared with the same reagents and solvents as standard solutions and unknowns but there is no desired analyte added. Are there impurities or interfering species in the solution?
elution
process of passing a liquid or a gas through a chromatography column
QuEChERS
quick, easy, cheap, effective, rugged and safe sample preparation procedure used in analytical chemistry. First the analyte is extracted, followed by sample cleanup to remove matrix components before chromatography.
indeterminate error
random error. arises from uncontrolled variables in measurement. equal chance of being positive and negative. Always present, cannot be eliminated. Might be reduced with better technique. Ex: subjective reading of a scale, electrical noise in an instrument.
retention index
relates the retention time of a solute to the retention times of linear alkanes and provides a scale of relative retention that remains constant for all columns with the same stationary phase
Clausius-Clapeyron equation
relates the vapor pressure of a substance at different temperatures to its heat of vaporization
Gaussian distribution
represents a set of experimental data that is normally distributed. Repeated experiments approaches this sort of distribution. Known as "normal distribution" characterized by the average and the standard deviation
splitless injection
required for very dilute samples. also requires solvent trapping or cold trapping. Temperature programming is also necessary.
universal detector
responds to all analytes but not to carrier gas
selective detector
responds to limited classes of analytes
septum
rubber disk in which a sample is injected through for gas chromatography
the field consists of several different regions, areas that are covered with grass, areas that are covered with brush and small shrubs, and several small areas with trees growing on them. What term best describes the field, and what type of sample should the laboratory construct?
segregated heterogeneous material and composite sample
size exclusion chromatography
separated by size and sometimes molecular weight
Chromatography
separates analytes and measures the quantity of each compound. (based on polarity) analytes are able to absorb uv radiation from lamp.
calibration curve
shows the response of a chemical analysis to known quantities (standard solutions) of analyte. less certainty in y
readability
smallest increment of mass that can be indicated
What is the equation for calculating the overall variance?
so^2=sa^2 + ss^2
SPE
solid phase extraction. removes sugars, fats, and fine particles all on one small column.
affinity chromatography
solute binds to a molecule specific for the solute
partition chromatography
solute equilibrates between mobile phase and film of liquid attached to stationary phase
ion exchange chromatography
solute ions of the opposite charge are attracted to the stationary phase
interference
species other than the analyte decreases or increases the response of the analytical method. making it appear that there is more or less analyte present
shatterbox laboratory mill
spins a puck and ring inside a grinding container pulverizing up to 100 g of material.
Cold trapping and solvent trapping are used with ________ injection to give _________ peaks.
splitless;sharper
Calibration curve
standard curve, measures detector response for known concentration of each analyte. Peak height versus concentration
relative standard deviation
standard deviation expressed as a percentage of the mean value. aka coefficient of variation
Trouton's Rule
states that the heat of vaporization is proportional to the atmospheric-pressure boiling temperature near 88 j/mol * K
gas liquid partition chromatography
stationary phase is a nonvolatile liquid bonded to the inside of the column or to a fine solid support
determinants
summarize arithmetic operations. Used in the least square method to express the final solution for slope and intercept
slurry
suspension of a solid into a liquid
aerosol
suspension of fine liquid droplets or solid particles in the gas phase
determinate error
systematic error. arises from a flaw in equipment or experimental design. can be discovered and corrected
Selected Reaction Monitoring (SRM)
technique in which a precursor ion selected by one mass separator passes through a collision cell in which the precursor breaks into several fragment ions. A second separator then selects one of these ions for detection
gravimetric analysis
the MASS of product from a reaction is measured to determine how much unknown was present
slope
the change in y over the change in x. equals 'm' in the equation of the line
molality
the concentration of a solution expressed in moles of solute per kilogram of solvent
dynamic range
the concentration range over which there is a measurable response to analyte, even if the response is not linear
mantissa
the decimal part of a log
vertical deviation
the difference between the y value of a data point and the y value of the least squares curve for the same x value.
desiccant
the drying agent . example : 98% wt sulfuric acid
parallax
the error that occurs when your eye is not at the same height as the liquid
precision
the exactness of a measurement
Chromatogram
the graph of detector response versus time confirm identity of individual peaks by: spectral characteristics, spike with verified caffeine solution to see if one peak grows)
ignition
the heating to high temperature of some gravimetric precipitates to convert them into a known, constant composition that can be weighed. Usually over a burner or in a furnace
characteristic
the integer of a log
supernatant
the liquid above the packed solid
extraction
the physical transfer of a solute from one phase to another
adsorption
the process in which a substance sticks to a surface
calibration
the process of measuring the actual quantity that corresponds to an indicated quantity on the scale of an instrument.
serial dilution
the process of successive solutions to reach a desired concentration of reagent
analysis may be meaningless if
the sample was collected improperly, measures to ensure reliability were not performed, or the results weren't communicated clearly
sample preparation
the series of steps required to transform a sample so that it is suitable for analysis. (dissolving the sample, extracting analyte from matrix, concentrating dilute analyte, chemical conversion, mask interfering species)
The larger the transfer pipet ..
the smaller the relative uncertainty
variance
the square of the standard deviation
null hypothesis
the statement that two sets of data are drawn from populations with the same properties such as standard deviation ( F test) or mean ( T test)
Formula mass
the sum of the average atomic masses of all atoms represented in its formula or the molecular mass of a strong electrolyte
variance of an analysis
the sum of the sampling variance and the analytical variance
masking
the transformation of an interfering species into a form that is not detected
standard deviation
the width of the distribution . How closely are the data gathered about the mean?
Fcalc>Ftest
there is a significant difference between the population standard deviations of the two populations.
What is the purpose of a serial dilution?
to transfer accurately small amounts of material that are too little to weigh accurately.
lot
total material from which samples are taken
True or false? Many small extractions are more effective than a few large extractions
true
True or false? in Gas chromatography solutes equilibrate between the stationary and vapor phases.
true
split injection
used for relatively concentrated samples. Only 0.2-2.0% of the sample is delivered to the column and the remaining flows to waste, Injection of the entire sample could overload the column. (use packed liner)
confidence interval
used to compare mean values measured by different methods. compared measured result to a "known" calue
acid washing
used to replace H+ to surfaces with low cation concentrations
supercritical fluid extraction
uses a supercritical fluid as the extraction solvent.
Ball mill
uses steel or ceramic balls rotated inside a drum to crush sample into a fine powder
As the temperature of the GC column increases, the ______ of the analyte increases, the retention time _____, and the peak shape _____ .
vapor pressure; decreases; sharpens
gas chromatograph
volatile liquid or gaseous sample is injected through a septum (a rubber disk) into a heated port, in which it rapidly evaporates.
volume percent
volume of solute/volume of solution
flow rate , F
volume of solvent per unit time traveling through column
a strong acid has
weak conjugate base and a low pKa.
spiking
when an authentic compound is added to the unknown. The most reliable way to compare retention times
y-intercept
where a line crosses the y-axis, x=0, b in the equation of the line
general elution problem
which is the inability of a single isothermal column temperature to provide adequate separation within reasonable time for samples containing compounds with very different boiling points.
abscissa
x-axis of a coordinate graph
ordinate
y-axis of a coordinate graph
