DECREASING THE CHROMATOGRAPHIC QUANTITATION UNCERTAINTY USING THE EXTERNAL STANDARD AND STANDARD ADDITION METHODS WITH ADDITIONAL STANDARDS
There are three methods from the known methods of the quantitative chromatographic analysis (external standard, absolute calibration, and standard addition) that are most “sensitive” to the reproducibility of the sample injection. Non-controlled constituents losses of the injected samples lead to the increase of both random and systematic errors of the results. The modifications of external standard and standard addition methods with the use of additional standards were characterized. It is important to note that there are no restrictions on the chemical origin of such standards, so far as they are required for calculation of the relative peak areas only. All calculations were conducted not with absolute, but with relative peak areas. Relative standard deviations of the relative peak areas were 6-38 times less than those of absolute peak areas, which was established in the result of special experiments. This allowed quantitation with the appropriate precision even at the low reproducibility of the injection. The use of histograms for the peak areas was recommended for revealing the losses of samples during injection. However, their application required at least 20 parallel experiments. The equations for calculations, including those for evaluations of values of possible errors, were presented for modified methods of external standard and standard addition supported with additional standards.