lec04.measure - MEASUREMENT SOURCES OF ERRORS Instrument...

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MEASUREMENT
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Method errors unknown side reactions, precipitation of reactants, impurities in reagents, etc. Operator errors math errors, sloppy measurement, etc. 2 +2 5 Instrument errors non calibrated scales or glassware, etc. SOURCES OF ERRORS
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Constant Proportional Measurement of other compounds along with analyte Incorrect slope of standard curve Interference from the matrix Incorrect assumption of linearity Incorrect blank correction Sensitivity change in instruments over time Contamination Adsorption of analyte by sample containers Instrumental problems TYPES OF ERRORS CONSTANT - Do not change with analyte concentration PROPORTIONAL - Varies with analyte concentration
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Relative frequency of the error cause encountered in chemical analysis obtained as the percentage of respondents TYPICAL ERRORS
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Accuracy and Precision Comparisons Accuracy Good Poor Precision Good Poor
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BLANKS Used to: Correct for background effects Take into account interferences from the matrix or reagents . Blanks are as identical to the MATRIX as possible (but must not contain the analytes )
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EXTERNAL STANDARDS Calibration Curve
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This document was uploaded on 07/31/2011.

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lec04.measure - MEASUREMENT SOURCES OF ERRORS Instrument...

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