Analytical Chemistry

Question 1

Analyte

Answer 1

A substance whose chemical constituents are being identified and measured

Question 2

Representative sample

Answer 2

A sample, resulting from a sampling plan, that can be expected to adequately reflect the properties of interest in the parent population. Or a sample of which has an identical composition to the bulk material, batch, or lot, from which it has been taken

Question 3

Test sample

Answer 3

A much smaller, but still representative, subsample with an often finer particle size, from which the test portions are selected for specific analyte determinations

Question 4

Validation

Answer 4

The process of determining the performance characteristics of a method to establish whether the analytical results obtained will be fit for their intended purpose

Question 5

Matrix

Answer 5

The components of a sample other than the analyte of interest

Question 6

Calibration

Answer 6

The measurement of standard solutions or materials in order to construct a calibration curve

Question 7

Confidence limit

Answer 7

Values greater than or less than the average, between which the results are statistically expected to fall a given percentage of the time

Question 8

Accuracy

Answer 8

The closeness of a test result to an accepted reference value

Question 9

Precision

Answer 9

The reproducibility of a series to replicate measurements obtained under comparable analytical conditions

Question 10

Interference

Answer 10

A substance, other than the assayed material, that can be measured by the chosen analytical method or that can prevent the assayed material from being measured

Question 11

Errors

Answer 11

The difference between the measured value and the true/known value

Question 12

Detection limit

Answer 12

The lowest concentration of the analyte that can be reliably detected

Question 13

Limit of quantification

Answer 13

The lowest analyte concentration that can be quantitatively detected with a stated accuracy and precision

Question 14

Sensitivity

Answer 14

The change in signal per unit change in the amount of analyte

Question 15

Standards

Answer 15

Materials containing a precisely known concentration of a substance for use in quantitative analysis

Question 16

Separation

Answer 16

A method which converts a mixture or solution of chemical substances into two or more distinct product mixtures

Question 17

Qualitative

Answer 17

Determines the presence or absence of a particular compound/element

Question 18

Quantitative

Answer 18

Determines the amount of a particular compound/element

Question 19

What are the six steps to a solution?

Answer 19

1. Defining the problem
2. Sampling
3. Sample preparation
4. Measurements
5. Evaluation
6. Analytical information

Question 20

Trace analysis

Answer 20

refers to a measurement of a compound that is of very low concentration, leading to difficulties in the analysis

Question 21

When defining the problem, what are the 9 most important questions to ask?

Answer 21

1. Where was the sample obtained?
2. Why do you want this tested? Is contamination expected?
3. What is the analyte?
4. Is it a representative sample?
5. Is this a qualitative or quantitative analysis?
6. What is the physical state of the sample?
7. What is the sample matrix?
8. What is the accuracy and precision of the data?
9. Is the measurement bulk or trace analysis?

Question 22

What are the 4 main risks associated with sample analysis?

Answer 22

• The sample may be contaminated
• Sample container may be contaminated
• Risks associated with sample collection
• Risks with analytical procedure

Question 23

Sample integrity

Answer 23

Sample properties must be stable after sampling and during storage

Question 24

Random sampling

Answer 24

Samples collected at random locations to produce a representation of the entire sample

Question 25

Selective sampling

Answer 25

At least two samples, one of a selected area and one from away from the first to determine background levels (control sample)

Question 26

What is the best material for storing evidence, especially with trace analysis? Why not others?

Answer 26

The best material is polyethylene or teflon containers which have been pre-treated which acid to remove metal ions
Not metal ions in solution as can absorb onto the surface of the container, or leach from the to solution
Not glass bottles as metal ions absorb onto surface Si-OH sites
Not plastics as may contain softeners, such as cadmium

Question 27

What are four things which maintain sample integrity?

Answer 27

• Special sample bags must be used at fire scenes to avoid sample degradation and loss of sample components
• Biological samples should be frozen and stored in the dark
• Tamper-proof seals on containers to ensure sample integrity and prevent contamination
• Transport of samples to the lab or between labs must be secure