Calibration Methods

Question 1

Put these in order: calibration standard (high concentration), sample (low concentration), instrument blank, sample (high concentration), solvent/reagent blank, solvent/reagent blank, calibration standard (low concentration)

Answer 1

1. instrument blank
2. solvent/reagent blank
3. calibration standard (low concentration)
4. calibration standard (high concentration)
5. solvent/reagent blank
6. sample (low concentration)
7. sample (high concentration)

Question 2

What is on the y-axis of an external calibration graph?

Answer 2

Instrument Response or Avg. Instrument Response with n = # of measurements taken (units)

Question 3

What is on the x-axis of an external calibration graph?

Answer 3

analyte concentration (units)

Question 4

Should an external calibration graph go through (0,0)?

Answer 4

ideally, but does not always

Question 5

matrix effects

Answer 5

something in the matrix that changes the instrument response to the analyte

Question 6

if the slope of the line is less steep, the matrix effect is:

Answer 6

inhibiting the instrument response

Question 7

Should an external calibration graph have error bars?

Answer 7

Yes

Question 8

When would you use single solution of standard addition?

Answer 8

when you are sample-limited

Question 9

Steps of single solution of standard additions

Answer 9

1. add an initial sample volume with an unknown analyte concentration
2. measure instrument response
3. add small volume of known concentration of the standard
4. measure instrument response
5. repeat 2-4

Question 10

how is the standard and analyte of single solutions of standard addition related?

Answer 10

s and x are the same compound

Question 11

formula for single solutions of standard additions, and what goes on x- and y-axis

Answer 11

write down

Question 12

does the matrix effect change the sensitivity of the method?

Answer 12

Yes

Question 13

Standard Addition with Multiple Solutions Steps

Answer 13

1. Gather several of the same size volumetric flasks
2. Place a known volume of a sample with unknown concentration of analyte in each flask
3. Add a known volume of a standard solution of the analyte (Vs) to each flask solution increasing each flask
4. Dilute each flask to the mark and mix. so Vf is the same for each flask. Thus, [X]f is also the same in each flask, but [S]f varies in each flask.
5. Measure the instrument response of each solution.

Question 14

how does using single solutions of standard addition overcome matrix effects?

Answer 14

In this method, most of the volume is from the sample so the matrix for the standard is now the same as for the sample. Thus, any effect the matrix has on the analyte in the sample will also be applied to the analyte from the standard that has been added.

Question 15

What are the constants of the std. additions with multiple solutions?

Answer 15

initial analyte concentration, final analyte concentration, and instrument response of the analyte

Question 16

What are the variables of the std. additions with multiple solutions?

Answer 16

final standard concentration and instrument response of the analyte plus standard

Question 17

Draw graphs of single solution and multiple solutions standard additions

Question 18

What could you do to account for instrument variation when running an unknown concentration?

Answer 18

use an internal standard to monitor the variation present while also analyzing the analyte

Question 19

Internal Standard

Answer 19

known amount of a compound, that is not the analyte, is added to the solution with the unknown concentration of analyte

Question 20

difference between internal and external calibration standards?

Answer 20

in external calibration, x and s are the same compound; in internal calibration, x and IS are different

Question 21

F

Answer 21

instrument response factor, may not respond with the same sensitivity to both x and IS

Question 22

should an internal standard graph go through (0,0)?

Answer 22

yes

Question 23

what does F represent on the graph?

Answer 23

m, slope

Question 24

good IS qualities

Answer 24

1. structurally and chemically similar to analyte
2. instrument response to IS should be close to instrument response to x to get close to F = 1
   2.1 similar instrument sensitivity
3. distinguishable signals
4. IS needs to be chemically unreactive / stable

Question 25

another symbol for instrument response?

Answer 25

I (intensity) or A (area)

Question 26

which method is used when there is significant matrix effects?

Answer 26

standard addition methods

Question 27

which method is used when instrument precision varies or quantity of a sample varies?

Answer 27

internal standard