Single injection quantification of cocaine using multiple isotopically labeled internal standards

The standard addition method and its validation in forensic toxicology

Purpose

In the quantitative forensic toxicological analyses using instruments, major methods to be employed are conventional matrix-matched calibration method (MMCM). However, nowadays, the needs for using the standard addition methods (SAM) are increasing. In spite of this situation, there are no reports of the guidelines for the validations of SAM. In this review, the principle, how to perform it, advantages, disadvantages, reported application data, and the details of validation procedures for the SAM are described.

Methods

Various databases such as SciFinder, Google and Google Scholar were utilized to collect relevant reports referring to the SAM. The long experiences of our research group on the SAM were also included in this review.

Results

Although the experimental procedures for the SAM are much more laborious than those of the MMCM, the SAM is essential to quantify target xenobiotic(s) in special matrices such as human solid tissues or biles, which remarkably interfere with the usual quantitative analyses. The validation methods for the SAM have been also proposed for the cases in the absence of the blank matrices.

Conclusions

To our knowledge, this is the first presentation of detailed SAM procedure and its validation, which will facilitate the use of the SAM in forensic toxicology. Especially for its validation, new simple methods have been proposed.

Compensate for or Minimize Matrix Effects? Strategies for Overcoming Matrix Effects in Liquid Chromatography-Mass Spectrometry Technique: A Tutorial Review

In recent decades, mass spectrometry techniques, particularly when combined with separation methods such as high-performance liquid chromatography, have become increasingly important in pharmaceutical, bio-analytical, environmental, and food science applications because they afford high selectivity and sensitivity. However, mass spectrometry has limitations due to the matrix effects (ME), which can be particularly marked in complex mixes, when the analyte co-elutes together with other molecules, altering analysis results quantitatively. This may be detrimental during method validation, negatively affecting reproducibility, linearity, selectivity, accuracy, and sensitivity. Starting from literature and own experience, this review intends to provide a simple guideline for selecting the best operative conditions to overcome matrix effects in LC-MS techniques, to obtain the best result in the shortest time. The proposed methodology can be of benefit in different sectors, such as pharmaceutical, bio-analytical, environmental, and food sciences. Depending on the required sensitivity, analysts may minimize or compensate for ME. When sensitivity is crucial, analysis must try to minimize ME by adjusting MS parameters, chromatographic conditions, or optimizing clean-up. On the contrary, to compensate for ME analysts should have recourse to calibration approaches depending on the availability of blank matrix. When blank matrices are available, calibration can occur through isotope labeled internal standards and matrix matched calibration standards; conversely, when blank matrices are not available, calibration can be performed through isotope labeled internal standards, background subtraction, or surrogate matrices. In any case, an adjusting of MS parameters, chromatographic conditions, or a clean-up are necessary.