Ch 5 Quality Assurance and Calibration Methods

Question 1

Quality assurance

Answer 1

what we do to get the right answer for our purpose

Question 2

Raw data

Answer 2

individual measurements, such as peak areas from a chromatogram or volumes from a buret

Question 3

Treated data

Answer 3

concentrations or amounts found by applying a calibration procedure to the raw data

Question 4

Results

Answer 4

quantities reported after statistical analysis of treated data

such as mean, standard deviation, and confidence internal

Question 5

Use objective

Answer 5

states purpose for which results will be used

prevent misuse of data and results

Question 6

Specifications might include (9)

Answer 6

• sampling requirements
• accuracy and precision
• rate of false results
• selectivity
• sensitivity
• acceptable blank values
• recovery of fortification
• calibration checks
• quality control samples

Question 7

Sensitivity

Answer 7

the capability of responding reliably and measurably to changes in analyte concentration
p.s. a method must have a detection limit lower than the concentrations to be measured

= slope of the calibration curve

= (change in signal)/(change in analyte concentration)

Question 8

Specifications

Answer 8

stating how good the numbers need to be and what precautions are required in the analytical procedure

Question 9

Quality assurance begins with sampling

Answer 9

• choose representative samples

- analyte must be reserved after the sample is collected

Question 10

Why samples of trace metal analysis are usually collected in plastic or Teflon containers, instead of glass?

Answer 10

Metal ions found on glass surfaces leach out into the sample over time

Question 11

Why samples for organic analysis are usually collected in glass containers - not plastic?

Answer 11

Organic plasticizers leached from plastic containers -> contaminate the sample

p.s samples are often stored in the dark in a refrigerator to minimize the degradation of organic analytes.

Question 12

False-positive

Answer 12

says that the concentration exceeds the legal limit when, in fact, the concentration is below the limit

Question 13

False-negative

Answer 13

says the concentration is below the limit when it is actually above the limit

Question 14

Selectivity (aka specificity)

Answer 14

ability to distinguish analyte from other species in the sample (avoiding interference)

Question 15

Specification could include

Answer 15

required accuracy and precision, reagent purity, tolerances for apparatus, the use of standard reference materials, and acceptable values for blanks

Question 16

Standard reference materials

Answer 16

contain certified levels of analyte in realistic materials that you might be analyzing, such as blood or coal or metal alloys

Question 17

method blank

Answer 17

a sample containing all components except analyte, and it is taken through all steps of the analytical procedure

p.s. subtract the response of the blank from eh response of a real sample prior to calculating the quantity of analyte in the sample

Question 18

reagent blank

Answer 18

similar to method blank, but it has not been subjected to all sample preparation procedures

Question 19

field blank

Answer 19

similar to a method blank, but it has been exposed to the site of sampling

Question 20

matrix

Answer 20

everything else in the sample other than analyte

Question 21

spike (aka fortification)

Answer 21

a known quantity of analyte added to a sample to test whether the response to the spike is the same as that expected from a calibration curve

p.s. analyze same as unknown