This document specifies the critical points to consider while developing an in house mass spectrometry based method for quantitative analysis of multi group organic substances in the scope of physical chemical analysis of water. ISO/TS 13530 provides guidance on the initial characterization of the measurement performances. This document supplements ISO/TS 13530 by providing details on the following points: selection of the characterization-test matrix; internal standards and internal standard recoveries; analyte recovery; checking that performance levels do not degrade over time. Chromatographic separation and identification of analytes are described in ISO/DIS 21253-1. The estimation of measurement uncertainties is integral to the characterization of any quantitative method of analysis, but the process is not described here, as ISO 11352 applies. Similarly, the calibration protocols are not described here but set out in the ISO 8466- series of standards. This document is not intended as a substitute for the currently applicable analytical standards dedicated to organic compounds but as a resource bringing additional characterization elements.