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R9 Laboratory SOP 835
CHROMATOGRAPHIC INTEGRATION PROCEDURES
Summary
The procedures and principles described in this standard operating procedure (SOP) apply to all generation of data in the EPA Region 9 Laboratory. Analytical systems of various types are employed throughout the laboratory to quantitate and qualify numerous environmental contaminants and constituents. Gas chromatography using many detectors - including mass spectrometers - and ion chromatography are two such analytical systems. Most of these systems employ computerized data acquisition and reduction techniques to aid the analyst in generating accurate data in a timely fashion. While these data systems are capable of reducing far more data than an analyst with pen and ruler could complete, they are not fool-proof. All computerized data reduction must be reviewed carefully by the analyst to determine the accuracy and appropriateness of the quantitation and qualification performed by the data system and any errors must be corrected using either the computerized tools available in the software or manually. The purpose of this SOP is to define appropriate data reduction - particularly appropriate integration - and provide procedures for completing and documenting corrections to analytical results.
The emphasis of this SOP is on chromatographic data reduction but the principles apply to all analytical procedures which employ an instrument response measurement which can be manipulated by the analyst. Such manipulation may include adjusting the instrument baseline or zero point either during or after the analytical event, manipulating the integration area through adjusting peak width or baseline, or any other manual adjustment which has the effect of altering the analytical result.
The EPA Region 9 laboratory utilizes software developed by instrument manufacturers or third party suppliers to reduce data from an analog signal to a concentration present in the sample. Most of the software used for chromatography is capable of quantitating using either peak area or peak height and employs mathematical algorithms related to the slope of the response to detect the beginning and end of peaks. Depending upon the sophistication of the software package the analyst has flexibility within the parameters of the software to designate internal standards for either quantitation, qualification or both; establish peak thresholds (at an appropriate level above instrument noise); and similar data reduction guidelines.
Efforts should be made during method development to include the best instrument parameters that allow for automatic integration by the data system in most cases. However, regardless of the sophistication of the software, instances occur when the automated software does not integrate a peak correctly. The failure of the software to appropriately integrate a peak is usually obvious from visual inspection of the chromatogram (at an appropriate scale). Various errors occur which include, but are not limited to, peak splitting, adding area due to a coeluting interferant, failure to detect a peak, excessive peak tailing due to failure of the instrument response to return to baseline or a rise in the baseline, and failure to separate peaks. The software packages invariably provide a procedure where by the analyst can review the individual data file and provide peak specific instructions on integration to correct these problems. This procedure is referred to as "manual integration" and relies solely upon the experience of the analyst to determine proper integration for each peak.
All data must be integrated consistently in standards, samples and QC samples. Integration parameters - both automated and manual - must adhere to valid scientific chromatographic principles. Manual integration is employed to correct an improper integration performed by the data system and must always include documentation clearly stating the reason the manual integration was performed, who completed the work, and the initials of the supervisor approving the manual integration. Under no circumstances should manual integration be performed solely for the purpose of meeting quality control criteria. In other words, peak shaving, peak enhancing, or manipulations of the baseline to achieve these ends must never occur as this results in an improper integration rather than correcting a data system error.