Acceptability criteria for linear dependence in validating UV-spectrophotometric methods of quantitative determination in forensic and toxicological analysis

Abstract

Introduction. This article is the result of authors’ research in the field of development of the approaches to validation of quantitative determination methods for purposes of forensic and toxicological analysis and devoted to the problem of acceptability criteria formation for validation parameter «linearity/calibration model».

The aim of research. The purpose of this paper is to analyse the present approaches to acceptability estimation of the calibration model chosen for method description according to the requirements of the international guidances, to form the own approaches to acceptability estimation of the linear dependence when carrying out the validation of UV-spectrophotometric methods of quantitative determination for forensic and toxicological analysis.  

Materials and methods. UV-spectrophotometric method of doxylamine quantitative determination in blood.

Results. The approaches to acceptability estimation of calibration models when carrying out the validation of bioanalytical methods is stated in international papers, namely «Guidance for Industry: Bioanalytical method validation» (U.S. FDA, 2001), «Standard Practices for Method Validation in Forensic Toxicology» (SWGTOX, 2012), «Guidance for the Validation of Analytical Methodology and Calibration of Equipment used for Testing of Illicit Drugs in Seized Materials and Biological Specimens» (UNODC, 2009) and «Guideline on validation of bioanalytical methods» (ЕМА, 2011) have been analysed.

It has been suggested to be guided by domestic developments in the field of validation of analysis methods for medicines and, particularly, by the approaches to validation methods in the variant of the calibration curve method for forming the acceptability criteria of the obtained linear dependences when carrying out the validation of UV-spectrophotometric methods of quantitative determination for forensic and toxicological analysis. The choice of the method of calibration curve is dictated by the primary orientation of all studied international guidances on the work exactly by this method.

The next criteria and the order of acceptability estimation of linearity for UV-spectrophotometric methods of quantitative determination analyses in biological fluids used in forensic and toxicological analysis have been offered:

• acceptability estimation of linear dependence parameters is carried out in two stages – for the lines obtained using model solutions (without matrix) and calibration samples respectively;
• two approaches has been suggested for parameters estimation of linear dependence obtained using model solutions; they are based on: 1) assumption of equality of the uncertainty related to the procedure of sample preparation of calibration standards, and the uncertainty of the calibration curve plotted by model solutions; 2) assumption of insignificance of the uncertainty of the calibration curve plotted by model solutions; for both approaches the acceptability criteria have been offered for residual standard deviation  and correlation coefficient ;
• for estimation of parameters of linear dependence obtained using calibration samples it has been suggested to proceed from assumption of equality of the calibration uncertainty and the uncertainty of measuring the absorbance and sample preparation of the sample to be analysed; within this approach the acceptability criteria have been offered for residual standard deviation RSD₀ and correlation coefficient R_с; the parameters of within-run (within-day) and between-run (between-day) linearity should satisfy these criteria.

Conclusion. The criteria and order of acceptability estimation of linearity for UV-spectrophotometric methods of quantitative determination analyses in biological fluids used in forensic and toxicological analysis have been formed. Offered approaches have been tested by example of UV-spectrophotometric method of doxylamine quantitative determination in blood.