Analytical Chem istry - DePauw University

56 Analytical Chemistry 2.0StartFigure 3.7 Schematic diagram showing a portion of the EPA’sprotocol for determining trace metals in water using graphitefurnace atomic absorption spectrometry.Initial CalibrationThe abbreviations are ICV: initial calibration verification;ICB: initial calibration blank; CCV: continuing calibrationverification; CCB: continuing calibration blank.ICV, ICBOK?NoIdentify andcorrect problemYesCCV, CCBOK?NoYesRun 10 SamplesCCV, CCBOK?NoDiscard results forlast set of samplesYesYesMoreSamples?Noconcentration. If the result is outside this limit the analysis is stopped, andthe problem identified and corrected before continuing.After a successful analysis of the ICV and ICB samples, the lab reverifiesthe calibration by analyzing a continuing calibration verification (CCV)sample and a continuing calibration blank (CCB). Results for the CCV alsomust be within ±10% of its expected concentration. Again, if the lab’s resultfor the CCV is outside the established limits, the analysis is stopped, theproblem identified and corrected, and the system recalibrated as describedabove. Additional CCV and the CCB samples are analyzed before the firstsample and after the last sample, and between every set of ten samples. Ifthe result for any CCV or CCB sample is unacceptable, the results for thelast set of samples are discarded, the system is recalibrated, and the samplesreanalyzed. By following this protocol, every result is bound by successfulchecks on the calibration. Although not shown in Figure 3.7, the protocolalso contains instructions for analyzing duplicate or split samples, and forusing of spike tests to verify accuracy.End