Exam 4: QC and other photometric methods

Question 1

Quality Control

Answer 1

Includes regular operational activities that ensure high quality test results
What we do each day to ensure valid results

Question 2

Quality Assurance

Answer 2

Monitoring/evaluation of QC to identify and correct problems

Question 3

Statistical QC

Answer 3

Quantitative/qualitative controls

Question 4

Non-statistical QC

Answer 4

Maintenance procedures, monitoring, checks

Question 5

Random error

Answer 5

Bad precision, good accuracy

Question 6

Systematic error

Answer 6

Good precision, bad accuracy

Question 7

Gross error

Answer 7

Bad precision, bad accuracy

Question 8

Which type of error is represented by bad precision, good accuracy?

Answer 8

Random error

Question 9

Which type of error is represented by good precision, bad accuracy?

Answer 9

Systematic error

Question 10

Coefficient of variation (%CV)

Answer 10

Another description of spread; the SD expressed as a percentage
Independent of units, allows for the comparison of different data sets

Question 11

A lower CV indicates:

Answer 11

better precision

Question 12

Analytical run

Answer 12

A set interval that we can expect performance (accuracy and precision) to remain stable

Question 13

Basic troubleshooting approach to a potential system issue

Answer 13

FIRED - Figure out what is going on (repeat), Isolate the cause, Resolve the issue, Evaluate the resolution, Document all steps and outcomes

Question 14

Stages of the quality hierarchy from top to bottom

Answer 14

TQM - total quality management
QM - quality management
QS - quality system
QA - quality assurance (assessment)
QC - quality control

Question 15

Examples of non-statistical quality control

Answer 15

Production/monitoring of high quality water for use in analytical procedures
Regular calibration of lab equipment
Ensuring the stability of the electrical power supply
Regular monitoring of temps
Performance and documentation of maintenance and troubleshooting
Monitoring the prep and storage of reagents and standards
Performance of linearity checks

Question 16

Wavelength isolated to measure sodium in flame emission photometry

Answer 16

589nm

Question 17

Wavelength isolated to measure potassium in flame emission photometry

Answer 17

766nm

Question 18

Wavelength isolated to measure lithium in flame emission photometry

Answer 18

670nm

Question 19

Four sources of error in light scattering measurements

Answer 19

Variations in particle size
Matrix effects
Dust particles in the reagents and dirt on the cuvets
Fluorescence

Question 20

Stokes shift

Answer 20

The difference between the maximum wavelength absorbed and the maximum wavelength emitted
A measure of the energy lost

Question 21

In fluorometry, what does the primary monochromator do?

Answer 21

Isolates the excitation wavelength

Question 22

In fluorometry, what does the secondary monochromator do?

Answer 22

Isolates the emission wavelength

Question 23

Six limitations of fluorescence measurements

Answer 23

Inner filter effect
Quenching
Light scattering
Solvent effects
Sample matrix effects
Temperature

Question 24

Interferences in flame emission photometry

Answer 24

Spectral - other emitting substances, self-absorption, mutual excitation
Ionization - too high of flame temp
Physical - large sample droplets will reduce flame temp

Question 25

How do we account for self-absorption in flame emission photometry?

Answer 25

Initial dilution of all samples

Question 26

How do we account for mutual excitation in flame emission photometry?

Answer 26

Using both Na and K in standards, also internal standard acts as a radiation buffer

Question 27

How do we control ionization in flame emission photometry?

Answer 27

By keeping the flame temperature low

Question 28

How do we control the size of sample droplets in flame emission photometry?

Answer 28

By using a wetting agent to control the surface tension, creating smaller sample droplets

Question 29

Difference between turbidimetry and nephelometry

Answer 29

Turbidimetry measures the decrease in incident light due to scatter (inverse relationship to concentration). Nephelometry measures the amount of light that is scattered (direct relationship to concentration).

Question 30

Clinical uses of turbidimetry

Answer 30

Coagulation analyzers, antibiotic sensitivities

Question 31

Clinical uses of nephelometry

Answer 31

Hematology cell counters, immune complexes

Question 32

Interferences in turbidimetry and nephelometry

Answer 32

Lipemia, particulates, fibrin clots, dirty cuvettes, fluorescence NOT colour interferences (eg hemolysis)

Question 33

Principle of fluorometry

Answer 33

Atoms excited by a short wavelength (high energy) of light will emit a longer wavelength (lower energy) Typically uses UV light to excite, and measures in the visible spectrum

Question 34

Clinical uses of fluorometry

Answer 34

Immunoassays, hematology cell counters/flow cytometry, micro

Question 35

Interferences in fluorometry

Answer 35

``` Inner filter effect Self-absorption Light scatter Solvent effects Sample matrix effects Temperature ```

Question 36

How to we control for inner filter effect and self-absorption in fluorometry?

Answer 36

By diluting samples

Question 37

How do we control for light scatter in fluorometry?

Answer 37

By careful selection of wavelengths measured

Question 38

Minimum number of times we run a control to get a control range

Answer 38

20

Question 39

Principle of flame emission photometry

Answer 39

Excited atoms are generated by heat, and light energy liberated during the fall to the ground state is measured