Food Analysis
According to FDA regulations for nutrition labeling, how many samples should be drawn to form composite samples, and how many subsamples are needed?
12 composite samples and 6 subsamples
How many significant figures would you report for the sum (16.175) of 7.45 and 8.725?
16.18 Addition & Subtraction: smallest decimal point Multiplication & Division: lowest significant figure
When is it hard to perform probability sampling?
???
What can you claim "calorie free"?
A food product can be "calorie free" if it is less than five calories
Define chromatography?
A method for separating components in order to detect, identify, and quantify
What is a composite sample?
A single sample made up of individual samples that were combined together
What is the difference between systematic error and random error?
A systematic error is when the results consistently deviate from the true value (pipette calibrated incorrectly) Random error can fluctuate and sometimes are unavoidable (differences between balances)
What is the difference between atomic absorption spectroscopy (AAS) and atomic emission spectroscopy (AES)?
AAS measures the absorption of light whereas AES measures the emission of light by atoms
Name the different forms of radiation/matter interactions?
Absorption, light scattering, diffraction, fluorescence, refraction, interference, emission
What is the difference between accuracy and precision?
Accuracy is how close a result is to the true value and it is assessed by percent relative error Precision is how close the results are to each other (how reproducible a result is) and it is assessed by coefficient of variation to correct for the size of the mean
Name examples of adsorption chromatography?
Adsorption chromatography has a liquid mobile phase and a solid stationary phase Ion-exchange chromatography, affinity chromatography, hydrophobic interaction chromatography
UV-Vis HPLC detector: Photodiode array detector
All the light from a deuterium lamp (provides light in the UV range) is spread out into a spectrum that falls across an array of photodiodes Can see the absorption of the compound at different wavelengths NO monochromator used PDA scans a range of wavelengths and continually generates spectral information Wavelength, absorbance, and time can all be plotted Helpful for detecting co-elution
Is nutrition labeling required for all food?
Almost all food Exceptions include: supplements, individually packaged food within a larger container, produce
How does temperature impact resolution?
An increase in temperature can help improve resolution because the mobile phase will be less viscous which enhances fast movement and reaches equilibrium faster Do not want to increase the temperature too much because the column could become damaged and too fast of movement of the mobile phase could result in no separation
Name spectroscopy/spectrometry analytical techniques?
Atomic absorption spectroscopy, emission spectroscopy, infrared spectroscopy
Source of excitation in AAS and ICP-AES?
Atomization is the source that would break the molecular bonds to release the atom and make the atom in the gaseous phase Excitation is the source that would bring an atom from the ground state to the excited state AAS: light emitted from the cathode lamp - cathode is made up of metallic form of the element of interest - light is emitted in the spectra specific to the atom ICP-AES: plasma is both the source of atomization and excitation
What are the different species of matter that can be analyzed using spectroscopy?
Atoms and molecules
What is the difference between attribute and variable sampling?
Attribute sampling is when the constituents are not normally distributed in a sample (Clostridium botulinum) Variable sampling is when the constituents are normally distributed in a sample (fat, ash, moisture, carbohydrates)
What are the advantages of a narrow diameter column?
Better resolution and better separation due to the packing of the stationary phase and how much stationary phase you have
What are advantages of HPLC over low pressure LC?
Better resolution because there is better packing of the column so there is not a lot of space between particles in the stationary phase so the compounds being analyzed are not going in multiple directions and being delayed on the column - sharper and purer peaks HPLC has better reproducibility Low pressure LC does not have sharp peaks - mostly wide peaks
What is the partition coefficient?
Concentration of the solute in the mobile phase over the concentration of the solute in the stationary phase It is a constant when equilibrium is reached
How do we get the minerals in solution?
Dissolve the minerals in acid and dilute the acid so the minerals become part of the solution
Monochromatic light
Electromagnetic radiation composed of waves having a single frequency and wavelength (have equivalent energy)
What is the difference between electronic and vibrational energy and to what spectral region each corresponds to?
Electronic energy is associated with the energy delivered by UV and visible light and valance electrons in an atom or molecular move from ground state to excited state due to picking up energy from a photon Vibrational energy has to do with the vibrations of the bonds within a molecule which occurs when a molecule absorbs light in the IR region - bending and stretching of the bond
What are some sample preparation considerations?
Enzyme elimination or control Avoid lipid oxidation Limit microbial growth or contamination Avoid sample alteration
Hollow cathode lamp
Excitation source for flame AAS Hollow lamp filled with argon or neon Anode made up of tungsten Cathode is made up of the metallic form of the element of interest Emits radiation of exactly the right energy (right wavelengths) to excite the element of interest
What agencies regulate nutrition labeling?
Food and Drug Administration (FDA) for almost all food except meat, poultry, and eggs are inspected by Food Safety and Inspection Service of the USDA (FSIS)
List three types of chromatography.
Gas chromatography, liquid chromatography, and supercritical fluid chromatography
What is gradient elution in HPLC?
Gradient elution is changing the concentration of the mobile phase (solvent) over time and this is done to reduce the analysis time
What is guard column and its function?
Guard column is just before the column in the flow direction and it protects the column from any impurities that would bind strongly to the stationary phase and not leave the column during the analysis time and blocking the functional groups in the stationary phase and reducing the capacity and efficiency of the column
What is the order of elution in hydrophobic chromatography? Ion-exchange? Size-exclusion?
Hydrophobic chromatography: least hydrophobic Ion-exchange: least ionized (carries the least amount of charge) Size-exclusion: largest
Brightness or radiant intensity
I = EA/t energy that is applied across an area per unit time
What are some applications for spectroscopy/spectrometry?
Identification, quantification, structural elucidation, compositional analysis, quality assurance and forensics, and qualitative detection
What is the difference absorption and fluorescence?
In absorption, the molecule or atom is absorbing the same amount of energy that hit it so the photons of light that hit that molecule or atom it is absorbing that same amount - every molecule and atom has different allowable amounts of energy to be absorbed so that is why every molecule and atom absorbs at a different wavelength and has a unique spectrum Fluorescence is when a molecule or atom goes from being in the excited state to the ground state and it emits a photon of light (photons that are emitted are at a longer wavelength and smaller energy than the photon that was absorbed) - molecules or atoms go back to the ground state by either giving the energy as heat (dissipation of heat) or some will fluoresce
Why absorbed light is not equal incident beam minus transmitted light?
In addition to light being absorbed, light is also scattered, fluoresced, and diffracted so that is why absorbed light does not equal the incident beam minus the transmitted light
What is the importance of a monochromator in terms of Beer's law?
In order to obey Beer's law, there needs to be a singular wavelength because the absorptivity differs at each wavelength
How does flow rate impact resolution?
Increasing the flow rate will result in reaching equilibrium faster, faster movement, and rate of diffusion which is longitudinal diffusion will be lower Too fast of a flow rate will result in poor resolution and peaks will come together Decreasing the flow rate will increase the retention time
Flame AAS vs Electrothermal AAS
Instead of using a flame for the source of excitation, electrothermal AAS uses a graphite tube Electrothermal AAS: can accommodate smaller samples, lower threshold (can detect at lower concentrations), lower sample throughput, more difficult to operate, lower precision, matrix interference
What is the difference between isocratic and gradient elution?
Isocratic elution is when the concentration of the mobile phase does not change for the entire run Gradient elution is when the concentration of the mobile phase changes throughout the run
How does a monochromator function?
It bounces light and then that light is diffracted into multiple wavelengths and then the band width is controlled allowing for a singlular wavelength to reach the sample
UV-Vis HPLC detector: Variable-wavelength detector
Light source: deuterium (provides light in the UV range) and tungsten (provides light in the visible range) lamps The light from the deuterium and tungsten lamps diffracts into individual wavelengths and then there is a slit where only lambda max (wavelength at which there is maximum absorption) can pass through the slit and then lambda max will pass through the sample - when the light at lambda max hits the sample some light will be absorbed and some of the light will be transmitted and the transmitted light will get detected by the detector and converted into absorption example of a monochromator - monochromator transmits either a single or narrow bandwidth of wavelengths onto a sample
What is the first step in developing a separation between solutes of interest in your sample?
Look up literature and find a method - if there is not any literature and methods then ask yourself what do you know about the compound?
In what case CV is a better measure of precision than SD?
Measurements that differ in their size so their means will differ so CV will correct for the differences in the size of the means in order to evaluate the precision of the method
What is the form of mobile phase in GC and what is the form of the stationary phase?
Mobile phase is a gas and stationary phase is a liquid bound to a solid support
What is the form of mobile phase in partition chromatography and what is the form of the stationary phase?
Mobile phase is a liquid and stationary phase is liquid
What is the form of mobile phase in adsorption chromatography and what is the form of the stationary phase?
Mobile phase is a liquid and stationary phase is solid
What is supercritical fluid chromatography?
Mobile phase is commonly liquid CO2 that can be combined with methanol Low viscosity and high diffusivity result in better resolution and higher efficiency Used for separation of non-polar molecules and non-volatile compounds that are not thermally stable Equipment used is similar to HPLC, but detectors are used similar to those used in GC
Is reverse-phase paper chromatography what type of compound travels the most with the mobile phase?
Most polar compound
Is the label in compliance when an added nutrient level is 80% of what is listed on the label?
NO must be equal to or greater than 100% of the amount of the added nutrient claimed on the label in order to be in compliance
What is reverse-phase chromatography?
Non-polar stationary phase and a polar mobile phase
In size-exclusion chromatography, interactions between solute and stationary phase are mostly.... a) hydrophobic b) electrostatic c) hydrogen bonding d) covalent bonding
None
According to the FDA and FSIS nutrition labeling regulation, the following is true... a) nutrition labeling is required only if a food contained an added nutrient b) nutrition labeling is required only if a nutrition claim is made c) showing percent daily value for protein is mandatory d) methods of analysis are to be determined by the manufacturer e) stating % daily value for vitamin A and vitamin B12 is mandatory
None are true
What does increasing the strength of the mobile phase mean?
Normal phase: increase the polarity of the non-polar mobile phase by adding water Reverse-phase: decrease the polarity of the polar mobile phase by adding an organic solvent Gives the mobile phase more power to remove the compounds from the stationary phase
What type of analytical methods are required to obtain that values listed on the nutrition label?
Official method of analysis: method that had been validated to be accurate and precise by an official organization
How many solvents and pumps can one use in HPLC?
One pump: Multiple solvents (1-4) can be pre-mixed under low pressure and then they are pumped in one pump OR Two pumps: Two solvents are pumped in two separate pumps under pressure and then the mixing comes after the pump OR Four pumps: Four solvents are pumped in four separate pumps under pressure and then the mixing comes after the pump The maximum number of pumps used in HPLC is four because it gets really complicated
What is a sampling plan?
Plane to determine how many samples, how each sample will be selected from lot, and how the samples will be prepared, transported, and stored Encompasses everything before the sample is tested.
ICP (inductively coupled plasma) AES
Plasma is the source of excitation and atomization Detector: grating system diffracts the light into multiple wavelengths and each wavelength can go into a photomultiplier tube and get detected Detectors: Sequential (a single PMT) photomultiplier tube detector - used for detecting elements sequentially and rapidly Simultaneous (multiple PMT) photomultiplier tube - used for detecting elements simultaneously Eschelle spectrometer - measure elements simultaneously, can detect a larger number of elements than PMT, combine two light dispersing elements in series: prism and then grating
Monochromators
Product monochromatic light by diffraction using a diffracting grating OR by optical dispersion in a prism
What is the difference between diffraction and refraction of light?
Refraction is the change in direction of the light and is used in the refractive index Diffraction of light is when a beam of light gets diffracted into multiple wavelengths and can be used when generating a monochromatic light for measuring absorption for quantification
What is peak resolution?
Resoluting (separating) two compounds from each other to obtain separate peaks
How do you increase the strength of the mobile phase in reverse-phase chromatography, hydrophobic chromatography, ion-exchange, and affinity chromatography?
Reverse-phase chromatography: add non-polar solvent (organic solvent) in the mobile phase Normal phase chromatography: add polar solvent (water) in the mobile phase Hydrophobic chromatography: decrease salt concentration in the mobile phase Ion-exchange chromatography: reduce the pH or increase the salt concentration in the mobile phase Affinity chromatography: increase ligand concentration in the mobile phase
What is the difference between threshold and sensitivity?
Sensitivity of the instrument is the smallest change in concentration the assay can detect Threshold is the limit of detection - how low can you go? It is the lowest concentration that would be able to be determined from a method
What some applications of chromatography?
Separation of proteins, amino acids, fatty acids, flavors, vitamins, carbohydrates in order to detect, identify, and quantify
How does wavelength impact the frequency and energy?
Shorter wavelength = more energy = higher frequency (more occurrences per unit time) Longer wavelength = less energy = lower frequency (less occurrences per unit time)
What molecular interactions between solute and stationary phase are involved in size exclusion? Ion-exchange? Hydrophobic chromatography? Affinity chromatography?
Size exclusion - none Ion-exchange - electrostatic Hydrophobic chromatography - hydrophobic Affinity chromatography - hydrophobic, electrostatic, hydrogen bonding, van der waals NO covalent bonding
What is the difference between stationary phase and mobile phase, what is the function of each?
Stationary phase interacts with the different components in a mixture so these components can be separated based on their like or dislike of the stationary phase Mobile phase is to move the components in the mixture through the column
How does TLC differ from paper chromatography?
TLC has small and consistent particle size, has better resolution and separation, and better reproducibility (more consistent results) than paper chromatography
What is the difference between retention volume and retention time?
The retention volume is the associated volume of the mobile phase that it took for the compound to reach the detector and it is calculated based on the flow rate The retention time is the amount of time it takes for the compound to reach the detector from the time of injection
What is a solvent front peak?
The solvent front is the peak produced from the moment of injection until the the detector recognizes the presence of the solvent Also called void volume
What is the difference between cation and anion exchange chromatography?
The stationary phase in cation exchange is negatively charged The stationary phase in anion exchange is positively charged
What is the relationship of peak width to resolution?
The wider the peak, the poorer the resolution because it is taking longer on the column to equilibrate and so it is diffusing down the column The longer the peak, the better the resolution
What does TLC stand for?
Thin layer chromatography
How does packing and thickness of the stationary phase impact resolution?
Thinner the stationary phase, the better the resolution Capillary column has very thin layers in the stationary phase so equilibrium is reached very fast but don't have capacity (can not load a lot of sample but you get nice, sharp peaks)
Type of energy absorbed in AAS and ICP-AES?
Three answer choices: electronic energy, vibrational energy, or rotational energy AAS & AES: electronic energy - valance electrons (electrons in the outer shells) are what get excited so these electrons get hit by photons of light and absorb at a particular wavelength
Give an example of a blunder type of error?
Titrating with 0.1 N NaOH instead of 0.1 N HCl
What are spectral regions most relevant to food analysis?
UV, visible, and infrared
What is a Q-test?
Used for identification and rejection of outliers Reject if calculated Q value is greater than Q of rejection Q = X2 - X1 / W X2 = = the next closest value to X1 X1 = the questionable value W = the total spread of all values, obtained by subtracting the lowest value from the highest value
What is the difference between photodiode array detector (PDA) and variable wavelength detector?
Variable wavelength detector allows the selection of the operating wavelength and offers best sensitivity for any absorptive component by selecting an appropriate wavelength PDA scans a range of wavelengths every few milliseconds and continually generates spectral information PDA lets us know if there is co-elusion and poor separation occurring
What are new changes on the nutritional label?
Vitamin A and C removed Vitamin D and potassium required Calories and serving size are in bigger and bolded font Added sugars required No calories from fat removed
Why is a sampling plan important?
Want to obtain samples that are an accurate representative of the whole lot so need a sampling plan in place If there is a mistake, then the consumer could be in danger or the vendor could lose a lot of money
In both absorption and fluorescence spectroscopy... a) UV-Vis radiation is used b) the transmitted beam is the signal measured c) a grating monochromator is needed
a) UV-Vis radiation is used
Following spectroscopy as means of analysis, detection can be based on... a) absorption of a photon b) emission of a photon c) dissipation of heat
a) absorption of a photon b) emission of a photon
Food analysis includes... a) chemical analysis and characterization of food components b) physical analysis of food c) microbiological analysis d) sensory analysis
a) chemical analysis and characterization of food components b) physical analysis of food c) microbiological analysis d) sensory analysis
The following is true about a buffer.... a) consists of mixture of weak acids and their conjugate base b) has a neutral pH c) stabilizes a certain pH
a) consists of mixture of weak acids and their conjugate base c) stabilizes a certain pH
The following is/are associated with a light wave... a) electric field b) magnetic field c) photons
a) electric field b) magnetic field c) photons
The following intermolecular interactions are responsible for adsorption chromatography... a) electrostatic forces b) hydrogen bonds c) hydrophobic interactions
a) electrostatic forces b) hydrogen bonds c) hydrophobic interactions
Indiscriminant error associated with absorbance transmittance measurement... a) has to be small relative to variation from sample preparation, sampling, reagent handling, analyst, etc b) can be tested with repeated measurement of a single homogeneous sample c) can be reduced by the use of intermediate concentrations
a) has to be small relative to variation from sample preparation, sampling, reagent handling, analyst, etc b) can be tested with repeated measurement of a single homogeneous sample c) can be reduced by the use of intermediate concentrations
In hydrophobic interaction chromatography, interactions between solute and stationary phase are mostly... a) hydrophobic b) electrostatic c) hydrogen bonding d) covalent bonding
a) hydrophobic
In affinity chromatography, interactions between solute and stationary phase are mostly... a) hydrophobic b) electrostatic c) hydrogen bonding d) van der waals
a) hydrophobic b) electrostatic c) hydrogen bonding d) van der waals
The advantages of using smaller diameter columns include... a) increased resolution b) increased peak height which causes enhanced detection sensitivity c) reduced equilibrium time
a) increased resolution b) increased peak height which causes enhanced detection sensitivity c) reduced equilibrium time
When monitoring food safety by measurement of mycotoxins... a) many randomly selected samples are required b) a single sampling plan is required c) sampling error is many times greater than the analytical error
a) many randomly selected samples are required c) sampling error is many times greater than the analytical error
Method A is more precise in measuring glucose content than method B, if... a) method A has a lower standard deviation than method B b) method A has a higher standard deviation than method B c) the mean obtained using method A is closer to the true value
a) method A has a lower standard deviation than method B
Absorptivity is a proportionality constant dependent on.... a) molecular properties of species b) wavelength c) chemical environment
a) molecular properties of species b) wavelength c) chemical environment
The following are potential problems associated with sampling that may result in reduced reliability... a) non-statistically viable convenience b) poor storage conditions c) mislabeling of samples
a) non-statistically viable convenience b) poor storage conditions c) mislabeling of samples
In reverse-phase chromatography... a) polar compounds elute first b) non-polar compounds elute first c) the mobile phase is polar liquid
a) polar compounds elute first c) the mobile phase is polar liquid
To extract and analyze fat content in a food product high in carbohydrate and protein, the sample preparation should include... a) pre-drying b) acid hydrolysis c) solvent extraction
a) pre-drying b) acid hydrolysis c) solvent extraction
A health claim related to coronary heart disease may involve the analysis of the following... a) saturated fat b) phytochemicals c) free fatty acids
a) saturated fat b) phytochemicals
In reverse-phase paper chromatography... a) the most polar travels the most b) the least polar travels the most c) Rf value of the polar compound will be higher than the less polar one
a) the most polar travels the most c) Rf value of the polar compound will be higher than the less polar one
Food composition analysis is carried out... a) to meet consumer's demand b) to meet government requirement c) to determine nutritional benefits d) for quality control
a) to meet consumer's demand b) to meet government requirement c) to determine nutritional benefits d) for quality control
Type of analysis to be carried out is determined based on... a) type of the product b) health claims c) purpose
a) type of the product b) health claims c) purpose
The following is true... a) molar extinction coefficient is constant for all analytes b) a highly concentrated sample may result in deviation from beer's law c) incident beam minus exiting beam is equal to the liquid absorbed by the analyte
b) a highly concentrated sample may result in deviation from beer's law
In ion-exchange chromatography, interactions between solute and stationary phase are mostly... a) hydrophobic b) electrostatic c) hydrogen bonding d) covalent bonding
b) electrostatic
For sample preparation, prior to analysis, the following is true... a) for all types of analysis particle size should be reduced to 20-mesh size b) enzyme activity should be eliminated or controlled c) lipid oxidation should be prevented
b) enzyme activity should be eliminated or controlled c) lipid oxidation should be prevented
To determine food quality and acceptance it is essential to... a) monitor the composition and characteristics of the whole lot of a food product or raw ingredient b) evaluate a sample/samples of a lot and then decide to accept or reject a particular lot c) determine sample size and selection protocol based on factors such as nature of the product and the purpose of inspection
b) evaluate a sample/samples of a lot and then decide to accept or reject a particular lot c) determine sample size and selection protocol based on factors such as nature of the product and the purpose of inspection
% daily value for protein is found on the label of... a) food products with reduced-calorie b) food with health claims related to protein content c) food products for athletes d) food products for children (< 4 years)
b) food with health claims related to protein content c) food products for athletes d) food products for children (< 4 years)
The following implies sensitivity... a) detection of only one constituent b) has a very low threshold c) detection of minor change in constituent
c) detection of minor change in constituent
Flame AES
measures the energy emitted going from the excited state to the ground state flame is the source of atomization and excitation so it is useful for elements with relatively low excitation energy for example, sodium and potassium absorb energy at a longer wavelength so they get excited at a lower energy so flame is sufficient for both atomization and excitation - no need for a lamp
Photon flux
number of photons flowing across a unit area perpendicular to the beam per unit time
Why do we analyze food from an industry perspective?
product quality product development (consumers demand) evaluate new processes (cost & profit) solve problems (food forensics) compete government regulations
Why do we analyze food from a consumer's perspective?
quality safety nutrition and health
Interferences in atomic spectroscopy
spectral: lambda max for iron and zinc are very similar so need to select a wavelength where zinc absorbs and iron doesn't incomplete atomization: molecule does not fully atomize (flame too cold) so the molecule will scatter light away from the detector which results in an overestimation fail to add lanthanum chloride for lanthanum chloride when analyzing calcium which results in an underestimation ionization: flame too hot and produces ions - atoms and ions absorb light at different wavelengths so will get lower absorption so will get an underestimation dry ashing: loss of volatile elements which leads to underestimation
What is Beer's law?
the linear relationship between absorption and concentration taking into account the absorptivity of each unique molecule as well as the light path A = abc A = absorbance a = absorptivity b = path length c = concentration
Flame AAS detection
using a monochromator which has a grating system that diffracts light into multiple wavelengths and a slit allows only lambda max or a narrow bandwidth of wavelengths to pass through and go into the photomultiplier tube detector
