Calibration

Question 1

What is quality assurance

Answer 1

Methods used to make sure the process is working and it up to a proper standard

Question 2

What are the stages of data analysis when doing quality assurance

Answer 2

First you have raw data (your own measurements)

Then treated data (worked up data by finding concentrations and making a graph, might cut out some raw data)

Results (the final values and interpretations)

Question 3

What are the steps to making a quality assurance prootocol

Answer 3

Set objectives (what are the goals, why are we analyzing, what do we need to know about the samples

Build specifications (what tests do you do, what min and max values do we want)

Make an assessment (stats, do the values agree with the specifications)

Question 4

What do you include when trying tobuild specifications

Answer 4

You set a target value, min acceptable value, max acceptable value (tells the accuracy)

Max acceptable variance (tells the inconsistency in data)

Question 5

What is a false postive

False negative

Answer 5

Test give “yes” value when actual sample should be no

Test give “no” value when actual sample should be yes

Question 6

What is a blank sample

Answer 6

Sample with no analyte

Used to measure background signals/response

Question 7

What is a reagent blank

Answer 7

A sample with all of the additional reagents (buffers, solvents) but still no analyte

Hasn’t been subjected to all preparation steps

Question 8

What is a method blank

Answer 8

A reagent blank that’s also run through all of the processing steps (filtration, boiling, etc.)

Has everything except for analyte

Question 9

What is a field blank

Answer 9

A method blank that is taken out into an environment that is similar to the analysis samples environment

Question 10

What is a sample matrix

Answer 10

The rest of the sample (everything other than the analyte)

Can be simple like DI water or complex like ocean water

We need to account for the affects of the matrix components in blanks and the analysis solutions

Question 11

What is a spike

Answer 11

1. Identification: add more of the analyte to a sample and look for a change in response
2. Spike recovery: adding known amount of analyte and seeing if the change in the signal is proportionate. If not, instrument might be faulty or the matrix could be in the way of the analysis

Question 12

How do you makes sure you’re method of analysis is good?

Answer 12

Build a standard operating procedure and share it with other analysts

Question 13

What is the error of selectivity

Give example

Answer 13

If the method of analysis responds to things other than the analyte

Ex. Measuring ph: ph electrodes respond to high [Na]

If low na then it’s fine

Question 14

How do instruments respond to increasing analyte concentration

Answer 14

Linear response.

Question 15

In terms of r^2 what is a good fit and what is a bad fit

Answer 15

1 is good
0 is bad

Question 16

What do we want to see in residual plots

Answer 16

Scattered and random distributions of residuals

No patterns

Question 17

What are methods to use to know if the value we measured is “true” and not just reproducible and wrong

Answer 17

Test the sample against a standard reference material (that been pre analyzed by trusted labs like NIST)

Test it against analysis done by another (trusted) lab (by sending it to that lab)

Test it against another trusted method (use an old method, spike recovery)

Test it with internal standards, standard addition, and spike recovery (to see if matrix or sample prep affect your method)

Question 18

What are the two thing included precision and what do they mean

Answer 18

Reproducibility: repeating your own data, similar trial to trial or day to day

Repeatability: the similarity of results between different analysts or labs (other people repeating your values)

Question 19

What is range

Answer 19

The concentration interval where the linearity, accuracy, and precision are all acceptable

Question 20

What is included in range

Answer 20

Dynamic range

Working range

Limit of linearity

Question 21

What is the dynamic range

Answer 21

The concentration range where there’s a measurable response to the analyte, even if the response isn’t linear

Question 22

What is the working range

Answer 22

Concentration range where it includes the limitations of the sample prep or lab capability (not just the limitations of instrument response or the theoretical limits)

Where these condition can give a proper response

Question 23

What is the limit of linearity (LOL)

Answer 23

The upper bound when instrument response stops being linear

Linear range is the range where the calibration curve is linear

Starts to plateau

Question 24

What is the definition of sensitivity

Answer 24

It’s describes the lower limit

How small of a concentration or amount of analyte that we can reliably measure

If the concentration of analyte changes how much change it there in the signal

Question 25

What is included in sensitivity

Answer 25

Limit of detection Limit of quantification Reporting limit

Question 26

What is limit of detection

Answer 26

The lowest amount of analyte we can reliably DETECT that is significantly diff from the blank (give an actual detectable value) The concentration of anaylte that gives a signal that is 3 times the sd of the blank (3sd)

Question 27

How do you calculate concentration limit What about signal limit

Answer 27

3s/m B+3s M is slope of the calibration curve B is y int of the curve/mean blank value S is the standard error of the actual signals from the samples in the experiment (not the blanks)

Question 28

What is the limit of quantitiation

Answer 28

Lowest amount of analyte we can reliably quantify (know the concentration of) LOQ, the formulas is 10(sd) =B+10sy

Question 29

What is the reporting limit

Answer 29

The lowest concentration we can get, below this, the concentration is reported as zero

Question 30

What is an example of reporting limit

Answer 30

The reporting limit on fats is 0.5 but in canola oil it’s below this so it’s reported as zero

Question 31

What is robustness in experiments

Answer 31

The ability of the method (experiment) to withstand small variations in conditions and still give acceptable results Does the experiment run the same if the temperature changes?

Question 32

If you find the limit of quantification using B+10sy, what does you do to convert the units

Answer 32

This equation gives units of whatever y axis is in, if we want to convert to x value units. Divide the answer by the slope (m)

Question 33

What are calibration curves

Answer 33

Taking the instrument signal and finding the amount of analyte in the sample Ideally linear (signal increases as concentration increases) They have a large range and good sensitivity The y intercept is mostly but NOT ALWAYS zero

Question 34

How are calibration curves made

Answer 34

Measure the signal from A increasing series of standards that have known concentrations, also measure the blank (no analyte) and measure the analyte with unknown concentrations . These standards of known concentrations are called external standards

Question 35

What are the best practices for calibration curves

Answer 35

Check the plot and residual plot for outliers Use =LINEST() in excel (it gives the error and it’s easier to exclude outliers) Choose standards with a concentration range that the unknown concentration falls within Measure the standards in random order (not low to high or high to low) this makes the slope bigger than is actually is

Question 36

What is the recommended minimum to making a calibration curve

Answer 36

Measure 5 diff standard solutions and 5 replicates of each

Question 37

When finding concentration of unknown from calibration curve how do you first make the graph?

Answer 37

Subtract each values absorbance from the blanks then make the graph

Question 38

To find the error for the calibration curve calculation what do you do?

Answer 38

Use LINEST and delta X equation to find error

Question 39

What is an internal standard

Answer 39

A known amount of a compound that isn’t the analyte that’s added to the sample. Ex. Using F (standard) instead of cl (analyte) in the sample The same amount of it is added to each standard (anaylte in known concentration) and unknown flask

Question 40

Why does an internal standard help

Answer 40

Is help smooth out the variance between each trial of the experiment Corrects for random errors caused by run to run variation

Question 41

What is on the x and y axis of calibration curves with internal standards

Answer 41

X= [analyte]/[internal standard] or just analyte Y= analyte area/internal standard area

Question 42

What is standard addition

Answer 42

When a constant amount of the unknown sample is added to the standards (unknown is in every sample) Then add increasing amounts of standards to each flask (0,5,10,15,etc.) This means that 0ml of standard DOES NOT mean 0 signal since it still has analyte

Question 43

Why do we do standard addition

Answer 43

The the matrix of the sample is complex (can’t replicate it in the standards) is makes it easier to just put the unknown in the sample. Higher Analyte concentration overall might just help as well

Question 44

What is special about calibration curves for standard addition

Answer 44

The y intercept does not equal zero Added volume of standard (ml) is the x axis The x intercept gives the equivalent amount of standard signal to unknown signal

Question 45

What is selectivity

Answer 45

The extent at which a analytical method can distinguish analyte from other species in the sample (avoiding interference)

Question 46

How do you find concentration of something given the signal and blank mean

Answer 46

The samples signal-the blank mean= the slope x concentration Solve for concentration

Question 47

If something falls so thin the control limits but not the specification limits is it still acceptable?

Answer 47

No it must fall within specification limits