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)
- instrument blank
- solvent/reagent blank
- calibration standard (low concentration)
- calibration standard (high concentration)
- solvent/reagent blank
- sample (low concentration)
- sample (high concentration)
What is on the y-axis of an external calibration graph?
Instrument Response or Avg. Instrument Response with n = # of measurements taken (units)
What is on the x-axis of an external calibration graph?
analyte concentration (units)
Should an external calibration graph go through (0,0)?
ideally, but does not always
matrix effects
something in the matrix that changes the instrument response to the analyte
if the slope of the line is less steep, the matrix effect is:
inhibiting the instrument response
Should an external calibration graph have error bars?
Yes
When would you use single solution of standard addition?
when you are sample-limited
Steps of single solution of standard additions
- add an initial sample volume with an unknown analyte concentration
- measure instrument response
- add small volume of known concentration of the standard
- measure instrument response
- repeat 2-4
how is the standard and analyte of single solutions of standard addition related?
s and x are the same compound
formula for single solutions of standard additions, and what goes on x- and y-axis
write down
does the matrix effect change the sensitivity of the method?
Yes
Standard Addition with Multiple Solutions Steps
- Gather several of the same size volumetric flasks
- Place a known volume of a sample with unknown concentration of analyte in each flask
- Add a known volume of a standard solution of the analyte (Vs) to each flask solution increasing each flask
- 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.
- Measure the instrument response of each solution.
how does using single solutions of standard addition overcome matrix effects?
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.
What are the constants of the std. additions with multiple solutions?
initial analyte concentration, final analyte concentration, and instrument response of the analyte
What are the variables of the std. additions with multiple solutions?
final standard concentration and instrument response of the analyte plus standard
Draw graphs of single solution and multiple solutions standard additions
What could you do to account for instrument variation when running an unknown concentration?
use an internal standard to monitor the variation present while also analyzing the analyte
Internal Standard
known amount of a compound, that is not the analyte, is added to the solution with the unknown concentration of analyte
difference between internal and external calibration standards?
in external calibration, x and s are the same compound; in internal calibration, x and IS are different
F
instrument response factor, may not respond with the same sensitivity to both x and IS
should an internal standard graph go through (0,0)?
yes
what does F represent on the graph?
m, slope
good IS qualities
- structurally and chemically similar to analyte
- instrument response to IS should be close to instrument response to x to get close to F = 1
2.1 similar instrument sensitivity - distinguishable signals
- IS needs to be chemically unreactive / stable
