Module 5

Question 1

5 steps to designing a sampling plan

Answer 1

1. Where writhing target population should sample be collected
   2.what type of sample should be collected
2. what’s the minimum amount of sample needed for analysis
3. How many samples should be analyzed
4. How can overall variance be memorized

Question 2

When do sampling errors occur

Answer 2

When sample composition is not identical to the population it’s drawn from

Question 3

What is a homogenous sample

Answer 3

Analyte of interest evenly distributed
Samples can be taken without regard to sampling errors
Determinate sampling errors are insignifigant

Question 4

What is a heterogeneous sample

Answer 4

Analyte of interest unevenly distributed in matrix
Analyte scan vary in time or space
Determinate errors can be significant

Question 5

4 types of sampling

Answer 5

1. Random
2. Judgemental
3. Systematic
4. Convenience

Question 6

Random sampling

Answer 6

Samples collected at random
Makes no judgement about the population
Require more times and expense because a greater number of samples are needed to be representative

Question 7

Judgemental sampling

Answer 7

Collected from population using information about analyte distribution within population
Selective
More biased than random

Question 8

Systematic sampling

Answer 8

Falls between random and judgemental
Samples collected from target population at regular intervals in time and space

Question 9

Convenience sampling

Answer 9

Samples collected from population because they are easily obtained
Cost, experience and accessibility are the primary factors

Question 10

3 methods to obtain samples

Answer 10

Grab sampling
Composite sampling
In situ sampling

Question 11

Grab sampling

Answer 11

Single sample grabbed from target population at a given time and space
Represents a snapshot of target population
Good to use if population is homogenous

Question 12

Composite sample

Answer 12

A series of grab samples combined to form one sample
Analyzing a single sample saves time and cost

Question 13

In situ sample

Answer 13

Taken within population without physically removing the sample
Analytical sensor placed directly in population
Allows for continuous monitoring without removing samples

Question 14

How to minimize variance

Answer 14

Collecting s’more samples of proper size

Question 15

3 steps of sampling

Answer 15

1. Physicality removing samples from target population
2. Preserving the sample
3. Preparing the sample for analysis

Question 16

Why do samples need to be preserved

Answer 16

Samples can undergo chemical and physical changes if not properly preserved and would result in it not being representative of the population

Question 17

What is an interfering component

Answer 17

Any chemical that contributes to the measured signal of the analyte

Question 18

What is selectivity

Answer 18

If the method responds primarily to the analyte of interest and is little affected by other substances

Question 19

How is a methods sensitivity determined

Answer 19

The relative difference in its sensitivity toward the analyte of interest

Question 20

What’s the goal of analytical separation

Answer 20

To remove the analyte or interfere the from the sample matrix

Question 21

What must be present to bring about a separation

Answer 21

Significant difference in either the chemical or physical properties

Question 22

What are separations based on size done by

Answer 22

A porous medium through only target analyte or interference can pass

Question 23

What is size exclusion chromatography

Answer 23

A physical method of separation that distributes components into two phases, a mobile and stationary phase where one can be extracted from

Question 24

What is a size exclusion chromatography column packed of

Answer 24

A column packed with a stationary phase of small porous particles of cross linked dextrin or polyacrylamide

Question 25

What is the stationary phase in SEC controlled by

Answer 25

The degree of cross
Greater cross linking= smaller pore size

Question 26

How does SEC work

Answer 26

Sample added to head of column and pass with gravity or pump
Chemicals with a molecular size too large to go through pores flow through column unrestricted
Chemicals small i enough to fit in pores of stationary phase will do so and take longer to pass through the length of the column

Question 27

What is done to separate when there is a difference in mass or density

Answer 27

Separation through centrifugation
Partials experience a greater centrifugal force have faster sedimentation rated and pulled to bottom of centrifuge tube

Question 28

How is masking done

Answer 28

Transforming the interference into a form that’s not detected
Done by binding interference to a masking agent

Question 29

Why is masking not a separation technique

Answer 29

Because target analyte and interferent are never physically separated from each other

Question 30

What is a separation based on partitioning betwwwn two phases

Answer 30

Selective partitioning of the target analyte or interferent between two immiscible phases

Question 31

What is extraction

Answer 31

When a solute is transferred from one phase to a new one
The sample is extracted one or more times with portions of the second phase

Question 32

Liquid solid extraction or solid phase extractions

Answer 32

Liquid sample passed through a column containing solid particulates that serve as adsorbent material

Question 33

How is choice of solid adsorbent

Answer 33

Based on properties of target analyte and the matrix it’s in