Sampling and Data Handling

Question 1

what is the process involved in ensuring a method is fit for purpose

Answer 1

documentation and quality assessment

Question 2

what is the goal of quality assurance

Answer 2

to minimize errors and deliver high quality results

Question 3

true or false - documentation is not always needed

Answer 3

false - it is critical

Question 4

what does SOP stand for and what does it involve

Answer 4

Standard operating procedure - step by step description of procedure written in detail
- includes sample, prep, standards, calibration, storage and reports

Question 5

define quality assessment

Answer 5

proving method is fit for purpose

Question 6

what are the four requirements for quality assessment

Answer 6

accuracy, specificity, linearity, and limit of detection/concentration

Question 7

what are the measures of precision that can be used; explain each one if needed

Answer 7

repeatability
reproducibility
instrument precision
intra assay precision - multiple aliquots of same material, one person in one day
intermediate precision - same sample, different people, different equipment on different days, same lab
interlaboratory precision - same sample, different people, different labs

Question 8

define quality control

Answer 8

measures used to ensure the validated method is working properly

Question 9

what are the tests we can do to ensure quality control

Answer 9

performance test sample and proficiency test sample
blank - make sure there is no analyte
spike - test if the analyte response is the same in the presence of a matrix

Question 10

define matrix

Answer 10

components of sample other than the analyte (sample itself)

Question 11

1 std dev from the mean = ___ %

Answer 11

68% of all measurements

Question 12

2 std dev from the mean = ___ %

Answer 12

95% of all measurements

Question 13

what is another name for Gaussian distribution

Answer 13

normal distribution

Question 14

why is it good to take replicate measurements (5 reasons)

Answer 14

1. improves estimate of mean
2. does not change std dev
3. decreases the uncertainty
4. greater confidence in true value
5. easier to spot gross errors

Question 15

true or false - if t calc is lower than the t table, we cannot assume the difference is from random variation

Answer 15

false - we can , only if t calc is greater than t table we cannot

Question 16

what is the most common calibration method

Answer 16

external standard

Question 17

what are the steps in the analytical process

Answer 17

1. formulating a question
2. selecting a procedure
3. sampling
4. sample preparation
5. analysis
6. calculation and evaluation of results
7. conclusions

Question 18

what are the three things we should make sure of in formulating a question

Answer 18

accuracy, specificity and sensitivity

Question 19

what is the largest source of uncertainty

Answer 19

sampling

Question 20

what are the differences between heterogeneous and homogeneous sampling

Answer 20

Homogeneous - same composition everywhere
Heterogeneous - non uniform composition made of up A,B and C

Question 21

briefly explain each type of sampling (there are 4)

Answer 21

judgemental - cheap and easy for screening purposes

random - each unit of sample has the same probability of being picked (homogeneous sample)

systematic - for large sample areas where a grid is put overtop the population and random grid samples picked

stratified random - population divided into sections based on homogeneous trait ; random sampling from each section

Question 22

true or false - to decrease sampling error, we need to decrease sample size

Answer 22

false - we need to increase the sample size