1. The Role of an Analytical Chemist

In our defining the “Role of the Analytical Chemist”, what are the 5 primary steps that an analytical chemist must consider and perform? (5.1)

1) Sampling

2) Sample Preparation

3) Chemical Analysis

4) Calibration/Validation

5) Reporting/Statistical Analysis

What is the purpose of sample preparation and what are some of the considerations that one must make when selecting a sample preparation protocol? (5.6)

Sample preparation is performed to reduce the complexity of a sample prior to chemical analysis. A primary goal can be to remove or reduce chemical species that could interfere with a particular chemical analysis. Sample preparation can be as simple as sample dilution, or it can be a multi-step process involving extraction(s) and chemical transformation(s) (e.g. derivatization). It may also be desirable to concentrate analytes of interest prior to analysis, depending on the sensitivity of the instrumental method.

Some considerations:

• Sample phase (s,l,g)

• Complexity of sample; physiological nature of interferents

• Physiological nature of analyte (volatility, polarity, etc.)

• Compatibility of sample and analytes with particular chemical analysis method

• Limitations or susceptibility to interference of a given chemical analysis method (e.g. sensitivity)

• Desire for throughput; how many samples to be processed? Cost, time, constraints

What is the purpose of method validation? List the 5 parameters that are commonly assessed as part of a method validation procedure. (6.4)

The purpose of method validation is to prove that the method is fit for the appropriate task. To determine its reliability and limits for operation.

Parameters (all):

• Accuracy

• Precision

• LOD/LOQ

• Robustness

• Selectivity/Specificity

• Sample stability

• Calibration Model

• Recovery

What is the purpose of sampling and the considerations that need to be assessed?

The purpose of sampling is to ultimately make a conclusion about a population, broader population of samples = broader conclusions. Homogenous samples are easier to prepare for replications. Heterogenous might have to take into account random sampling (every member of a population has an equal chance of being included) or composite (increments, are combined into a single, larger sample for analysis).

Some considerations:

• Making sure you have enough for replications (multiple samples for multiple times)

• Sample form, homogeneity, and phase

• Is it representative for the population (i.e. pond water from one specific area may differ from others)

What is the purpose of chemical analysis and the considerations that need to be assessed?

The purpose of chemical analysis is to determine what instrument is best for analyzing the sample, this can include spectroscopy (mass, absorption), chromatography (gas, liquid), and combinations thereof.

Some considerations:

• Qualitative vs Quantitative (this is important bc instrumentation/approach can differ)

• Analyte type: size, volatility, phase, etc.

What is the purpose of calibrating an analytical instrument? (2.1)

Calibration is performed for quantitative analysis. It is important because we want to relate our instrumental response (e.g. peak area) to an amount of analyte present. Different analytes exhibit different responses on different instruments, especially when present at different concentrations and in the presence of different matrix components.

What is the purpose of interpretation/reporting and what considerations and acknowledgements must you make?

The purpose is to draw reliable conclusions from analytical data and communicate them clearly.

Some considerations:

• Audience (Expert vs Public)

• Acknowledge limitations in data and ask appropriate questions when given a sample to analyze

• Statistical analysis (what are some statistical results, statistical difference?)