A suggested protocol for value assignment using isotope-dilution-LC-MS/MS in reference measurement procedures – Exemplary application for ciprofloxacin in serum

•A novel protocol for the application of isotope-dilution-LC-MS/MS in reference measurement procedures is described.•An spreadsheet file is used as an essential tool for result generation, data review and validation of series and results.•A method for the quantification of ciprofloxacin in human serum was investigated as an example. Reference measurement procedures for assigning values to calibration materials play a crucial role in the concept of metrological traceability in laboratory medicine. ISO standard 15,193 specifies the requirements for such measurement procedures, albeit in a very general terms. A standard structure of analysis series for value assignment by LC-MS/MS was developed and tested,this structure was complemented by a spreadsheet file for result calculation, metadata evaluation, and finally validation and confirmation of individual analysis runs and individual results, and measurement uncertainty evaluation. This framework was applied to a procedure for the quantification of ciprofloxacin in serum as an example. The approach of a detailed description of the analytical procedures of isotope dilution LC-MS/MS reference measurement methods together with a highly standardized spreadsheet-based method for data processing was found to be practical and efficient. The described measurement procedure for the quantification of ciprofloxacin in serum was found to be fit for purpose. A standardized, detailed procedure for the application of isotope dilution LC-MS/MS in reference measurement procedures can complement the ISO 15193 standard with respect to this particular analytical technique, which is now widely used in the context of metrological traceability in laboratory medicine.