Two different stock standards should be prepared, and dilutions of them made. A series of standards are prepared covering the range from detection limit to the highest sample. At least five different concentrations should be made so that there are enough data points to plot a curve. Gas chromatograph conditions. Peak areas are measured by an integrator or other suitable means.
Any compound having the general retention time of the analyte is an interference.
Possible interferences should be listed on the sample data sheet. GC parameters should be adjusted if necessary so these interferences will pose no problems. Retention time data on a single column is not considered proof of chemical identity. A curve with area counts versus concentration is calculated from the calibration standards. The area counts for the samples are plotted with the calibration curve to obtain the concentration of phenothiazine in solution.