CHMB16Fall2012 Lecture 5: Quality Assurance and Calibrating Methods (Chapter 5)
Use Objectives 3"
o Specifications must consider:
o Sampling requirements
o What accuracy and precision are needed?
o What is an acceptable rate of false results?
o What selectivity is necessary?
o How sensitive must the experiment be?
o Will a blank be done? What type?
o What is an acceptable recovery of fortification?
o Is a calibration check necessary?
o Do QC samples need to be run?
o False positive: false result is higher/greater than actual value
o False negative: false result is lower than actual value
o Sensitivity methods and instruents need to be optimized in a certain way to detect a certain value
o The instruments need to be sensitive enough to be able to determine a certain value some instruments are more
sensitive than others
o Selectivity technique and instrument picked must allow for the deterction of the target molecule ONLY (no other
o Method or equipment must need to be changed if it does not allow for detection of the target analyte at a specific
o Method blank: performing the same steps with a solution that does not contain the analyte will give you a background
signal should not give you a result, but if it does it is due to interference from other materials
o The result from the method blank is subtracted from the result of the actual experiment
o Reagent blank: perform only some of the steps in the methodology with a solutions that does not contain the analyte
should not give you a result, but if it does then once again it is due to interference
1 o Field balnk: measure blank samples (without analyte) in the lab as well as at site of collection to see if results match
basically to detect environmental effect on the results
o blind sample sample that you do not know the contents of traditional method used to understand if your
detection procedure works properly or not - it validates the method of detection (can the target analyte be detected
with accuracy/is it reliable as repeatable?)
o placebo: contains every substance but the target analyte can tell this way if results are really due to the analyte or
another substance found in the mixture
o also called fortification recovery
o refers to the addition of known concentration of analyte to the solution
o whether the percentage of recovery is acceptable or not depends on what is listed as acceptable in your specifications
o Dynamic Range: concentration range over which there is an analytical response
o Linear Range: concentration range over which there is a linear analytical response
o the instrument/technique will not allow you to make measurements past concentration C2 you must work within
the linear range and expand it as much as you can as an analyst
- shows how linear your range
o square of the correlation coefficient is used to measureally is (the closer to 1, the more
- shows how linear your range
really is (the closer to 1, the morean 0.990
linear relationship)hing lower than two 9's is not
o - has to be higher than 0.990
o show how linear range is the closer the value is to 1, the more linear the relationship
o acceptable for Dr.Kegan >0.99, anything lower than two 9s is not acceptable
o after blank subtraction, the y-intercept with good linearity should be 0
start to work
sample already with a clean
start to work buffer
sample alreadconcentration with a clean solution
contains someof the analyte buffer which does
concentration solution not contain
of the analyte which does your analyte
o in the standard addition method, the sample already contains some concentration of the analyte, which is why the y-
intercept is not at 0 9"
o for the calibration curve, the y intercept is at 0 because a clean buffer was used which does not contain analyte
o why? because eliminated matrix effects
o matrix: everything in the unknown except the analyte
o matrix effect: a change in what is being measured caused by something in the sa