Food Analysis: Test #1 Q&A

Serial dilutions, chromatography, spectroscopy, and mass spec

How do we determine the data reliability to the true value and to each other of individual measurements?

Accuracy and precision

What is how close the measurement is to the true value?

Accuracy

Do we typically know the true value?

No

What is the measurement of reproducibility of results and shows how close individually measured values are to each other?

Precision

Is precision or accuracy easier to measure?

Precision

Are precision and accuracy generally dependent on each other?

No

What are errors that are fixable and avoidable?

Blunders

What are errors due to inherent limits of measurements/technique?

Random error

What type of errors are inconsistent and random?

Random error

What are errors that are consistent and repeatable inaccuracy in measurement?

Systematic error

What type of error causes data to deviate from the true value in one direction?

Systematic error

What is the quantitative difference between experimentally determined value and true value?

Absolute error

What tells us the amount of error?

Absolute error

What is the equation for absolute error?

Absolute error = measured value - true value

What is the relative difference between experimentally determined and true value?

Relative error

What tells us how big or small the error is?

Relative error

What is the formula for relative error?

Relative error = |measured value - true value| / true value * 100

How is accuracy measured?

Absolute and relative error

How can precision be estimated?

Measuring variation in data

What is the “spread” of the data?

Variation

What is used to quantify and estimate the variation?

Standard deviation, coefficient of variance, and confidence interval

What is heterogeneous and undissolved?

Mixture

What is homogeneous and dissolved?

Solution

What is the dissolving agent?

Solvent

What is the thing that dissolves?

Solute

What is the universal solvent?

Water

What is the amount of solute relative to the total amount of the solution?

Concentration

What is molarity (M)?

Moles / liters of solution

What is %w/w (weight to weight)?

% weight of solute to 100g solution

What is % w/v (weight to volume)?

% weight of solute to 100 mL solution

What is % v/v (volume to volume)?

% volume of solute to 100 mL solution

What is a ppm?

1g/1,000,000g = 1 ug/g

What is a ppb?

1g/1,000,000,000 = 1 ng/g

What is the process of decreasing solvent concentration in a solution?

Dilution

What is useful with limited solute volume and helpful when multiple steps or dilute solutions are needed?

Serial dilution

What formula do we use to calculate dilutions?

C1V1=C2V2

What is the formula to calculate the dilution factor?

DF = Cinitial/Cfinal

What fold dilution is the largest dilution at any one time?

100-fold

What is Avogadro’s number?

6.022*10^23

Is salt the same thing as sodium?

No

Who created chromatography?

Mikhail Tsvet

What was Tsvet’s experiment?

The tall, open glass column was filled with sand-like particles. Ground plant extract poured into the column and colored bands developed as extract traveled down the column. This led to the separation of chlorophylls and carotenoids from plant tissues

What is a method to separate components of a mixture?

Chromatography

How does chromatography create separation?

Changing speed of each analyte through competition between mobile and stationary phases

Why is chromatography used?

Separation, identification, and quantification

What is a separation technique based on partitioning analytes in a mixture between mobile and stationary phase?

Chromatography

What is the term used for the extraction of different components of a mixture?

Partition

What is the mixture of analytes?

Sample

Do analytes interact with both mobile and stationary phases and move in two directions?

Yes

What are the two directions that analytes move in?

Direction of the mobile phase flow and between the two phases

What are properties of analytes do we partition analytes by?

MW/size, molecular shape, polarity, and stereochemistry

What is the support for the stationary phase in paper chromatography?

Paper (cellulose)

What is the stationary phase in paper chromatography?

Water (usually)

What is the mobile phase in paper chromatography?

Solvent immiscible in water

What is the procedure for paper chromatography?

(1) Sample applied as small spot (2) Suspend paper in closed container (3) Solvent travels up paper to separate analytes

What was designed to replace paper chromatography?

Thin layer chromatography (TLC)

What are the advantages of TLC over paper chromatography?

Faster, better resolution, more reproducible

What state is the mobile phase in TLC?

Liquid

What state is the stationary phase in TLC?

Solid (silica gel, dichotomous earth, alumina, cellulose) that is bound to inert support

What detects the chromatographic peaks?

Detector that measures some property of analytes

What is the detector output for chromatography?

Signal v. Time

What are the two types of chromatographic separation?

Adsorption and partition

Do most chromatographic methods use a single or multiple separation principles at the same time?

Multiple

What is the oldest form of chromatography?

Adsorption chromatography

What are the states of adsorption chromatography?

Liquid-solid (analytes stick (ie. absorb) to solid stationary phase due to IMFs)

What is the mobile phase of adsorption chromatography?

Liquid (polarity differs from stationary phase)

What is the stationary phase of adsorption chromatography?

Solid (adsorbent with high surface area)

What is the elution strategy of adsorption chromatography?

Change polarity of mobile phase (increase or decrease)

What type of separation chromatography is affinity chromatography?

Adsorption chromatography

What is the stationary phase in affinity chromatography?

Ligand immobilized on silica/alumina support (specific shape/conformation to reversibly bind specific proteins)

What is the mobile phase of affinity chromatography?

Aqueous solvent

What type of ligand characteristic only binds one thing?

Specific

What type of ligand characteristic binds a class of related compounds?

General

What is the elution strategy of affinity chromatography?

Reverse ligand-analyte binding

What type of chromatography do we use for protein separation?

Affinity chromatography or HIC

What type of elution strategy in affinity chromatography changes pH, ionic strength, or temperature?

Nonspecific

What type of elution strategy in affinity chromatography adds excess ligand to the eluent?

Bio-specific

What is a type of adsorption chromatography uses reversible interactions between hydrophobic protein surface and hydrophobic ligands in stationary phase?

HIC (hydrophobic interaction chromatography)

What is the stationary phase in HIC?

Hydrophobic ligands bound to a hydrophilic support

What is the mobile phase in HIC?

Aqueous salt buffer

Why does HIC work?

In pure water, hydrophobic protein surfaces are surrounded by water and cannot interact. Salt disrupts water layer.

What type of adsorption chromatography is specific to proteins binding to specific analytes?

HIC

Does HIC elute the analyte by increasing or decreasing salt concentration?

Decreasing

Is the salt concentration in HIC high or low when the analyte-ligand binding occurs?

High

What is separation in HIC based on?

Analyte surface hydrophobicity

Does the protein with the lowest surface hydrophobicity in HIC elute first or last?

First

Does the protein with the highest surface hydrophobicity in HIC elute first or last?

Last

What type of chromatography has analytes partition between mobile and stationary phases based on polarity?

Partition chromatography

What is the mobile phase of partition chromatography?

Liquid or gas

What is the stationary phase of partition chromatography?

Solid coated with a thin layer of liquid

What are two types of partition chromatography?

Gas-liquid or liquid-liquid chromatography

Does partition chromatography have miscible or immiscible phases?

Immiscible

What is partitioning controlled by?

Polarity and/or buffer pH of stationary and mobile

What is gas chromatography used to separate?

Volatile analytes

What is the mobile phase of GC?

Gas

What is the stationary phase of GC?

Solid support coated with liquid

What controls elution in GC?

Temperature

Do the lowest or highest BP analytes elute first?

Lowest

What type of chromatography is used to separate very polar analytes?

Normal phase liquid chromatography (NPLC)

What is the mobile phase in NPLC?

Water-immiscible, non-polar organic solvent (ex., hexane)