A Strategy for GC/MS Quantification of Polar Compounds via their Silylated Surrogates: Silylation and Quantification of Biological Amino Acids

Substitution of polar functionalized compounds with silylated (e.g., trimethylsilylated) surrogates prior to GC/ MS analysis is a widely used analytical strategy. Calibration is a most demanding step of this strategy. In fact, a calibration function is usually acquired by converting known amounts of the pure analyte to its silylated surrogate using the same conditions employed for processing unknown samples. The cumbersome need of acquiring a new calibration function prevents, to a large extend, the possibility of modifying silylation and instrumental settings on a sample by sample basis as would be appropriate in a number of cases. The modified standard additions calibration method, suggested in this paper, overcomes this difficulty by integrating in a single analytical procedure calibration and sample analysis. Furthermore, the suggested procedure compensates for matrix effects which may be a serious source of inaccuracy and is a tool that can be used during method development in order to find the most suitable silylation conditions for a given analyte. The implementation and benefits of the modified standard additions calibration method are explored in this paper on the basis of a symbolic but enlightening experiment dealing with the very representative GC/MS quantification of biological amino acids via their trimethylsilylated derivatives.