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Lecture 5

CHMB16Fall2012 Lecture 5 Notes.docx

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Kagan Kerman

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? False Results o False positive: false result is higher/greater than actual value o False negative: false result is lower than actual value Sensitivity/Selectivity 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 molecules) o Method or equipment must need to be changed if it does not allow for detection of the target analyte at a specific amount Blanks 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 Spike Recovery o also called fortification recovery o refers to the addition of known concentration of analyte to the solution o o whether the percentage of recovery is acceptable or not depends on what is listed as acceptable in your specifications Calibration 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 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 Linearity - shows how linear your range o square of the correlation coefficient is used to measureally is (the closer to 1, the more linear relationship) - 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 contains some sample alreadconcentration with a clean solution contains someof the analyte buffer which does concentration solution not contain of the analyte which does your analyte not contain your analyte 9" o 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 Standard Addition: 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
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