Laboratory Sample Preparation

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Questions and Answers

What is the primary purpose of coning and quartering in laboratory sample preparation?

To reduce the size of a granular or powdered sample (correct)
To evaluate a reagent blank
To separate a free-flowing sample into equal parts
To mechanically reduce the particle size of a sample

What is the result of milling or grinding a sample?

Homogenization of a heterogeneous population
Separation of a sample into equal parts
Reduced particle size (correct)
Increased particle size

What is the primary objective of collecting grab samples in a heterogeneous target population?

To collect a representative sample of the entire population
To establish its properties over time and/or space (correct)
To identify the properties of a specific location
To characterize the properties of the sampling device

What is the difference between a homogeneous and heterogeneous population?

A homogeneous population is one that has uniform characteristics, while a heterogeneous population is one that has non-uniform characteristics (D) Signup and view all the answers

What is a sample unit in the context of analytical chemistry?

A single portion removed from a bulk lot (D) Signup and view all the answers

What is the purpose of riffling in laboratory sample preparation?

To separate a free-flowing sample into equal parts (D) Signup and view all the answers

What is the relationship between particle size and homogeneity among test portions?

Smaller particle sizes result in more homogeneity among test portions (B) Signup and view all the answers

What is the main advantage of using composite samples in analytical chemistry?

Combination of multiple samples into a single sample (C) Signup and view all the answers

What is the term used to describe a portion of material selected in some manner to represent a larger body of material?

Sample (B) Signup and view all the answers

Can sampling errors be corrected by evaluating a reagent blank?

No, sampling errors cannot be corrected by evaluating a reagent blank (D) Signup and view all the answers

What is the outcome of sampling a heterogeneous population?

A heterogeneous sample is obtained (D) Signup and view all the answers

What type of sampling is used to collect a sample in its original, unaltered state?

In-situ sampling (D) Signup and view all the answers

Why is it important to consider the distinction between homogeneous and heterogeneous populations when developing a sampling plan?

To ensure that the sample is representative of the population (C) Signup and view all the answers

What is the main limitation of using composite samples in analytical chemistry?

Loss of individual sample information (C) Signup and view all the answers

What is the primary purpose of sampling in analytical chemistry?

To obtain an estimate of the quantity or concentration of a constituent or property (B) Signup and view all the answers

What is the term used to describe the process of collecting a portion of material at a specific time and/or location?

Grab sampling (B) Signup and view all the answers

What is the primary goal of sampling in chemical analysis?

To obtain a representative portion of the sample (B) Signup and view all the answers

What is the term for the component of interest in a sample?

Analyte (A) Signup and view all the answers

What is the process of selecting a portion of the sample for analysis called?

Sampling (B) Signup and view all the answers

What is the term for the process of separating the analyte from the matrix?

Separation (C) Signup and view all the answers

What is a potential source of error in sampling?

Sampling error (D) Signup and view all the answers

What is the primary purpose of sample preparation?

To convert the sample into a form suitable for analysis (D) Signup and view all the answers

What is the term for the process of reducing the sample size for easier handling?

Sample reduction (B) Signup and view all the answers

What is the term for the process of selecting a sampling strategy?

Sampling plan (C) Signup and view all the answers

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Study Notes

Laboratory Sampling

Coning and quartering: reducing sample size by forming a conical heap, dividing into quarters, and combining two opposite quarters.
Riffling: separating a free-flowing sample into equal parts using a mechanical device.
Milling/grinding: mechanical reduction of particle size by attrition, impact, or cutting.

Sampling Strategies

Homogeneous population: uniform composition throughout.
Heterogeneous population: varying composition throughout.
Sampling plan: necessary to determine homogeneity or heterogeneity.

Types of Samples

Grab sample: a portion of the target population collected at a specific time and/or location.
Composite sample: a combination of grab samples analyzed together.
In-situ sample: a sample analyzed in its natural environment.

Sampling Considerations

Sample unit: a single portion removed from a bulk lot, usually taken with a sampling device.
Sampling errors: independent of analytical method errors and cannot be corrected by evaluating a reagent blank.

Chemical Analysis

Definition: providing chemical or physical information about a sample.
Analyte: the component of interest in the sample.
Matrix: the remainder of the sample excluding the analyte.
Analysis outcomes: identity, concentration, or properties of an analyte.

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