Review Ho & Gao
obtained by surrogate analyte approach with those val- ues obtained by quantitating authentic analyte using standard addition. The results generated by the two methods were comparable, within 7.3%. Jones et al. commented that between the surrogate matrix and surrogate analyte approaches, there is no evidence to show that one approach is better than the other [1]. We believe that surrogate analyte approach is a good alternative to the surrogate matrix approach when the analyte is detected by mass spectrometry and there are at least two stable-labeled analytes available (one for surrogate analyte and one for IS).
Recommendations for future authors We make two suggestions for future authors. First: include ‘surrogate’ and/or ‘surrogate matrix’ in the abstract and keyword in their pertinent future writings to facilitate the scientific exchange. We find research- ing the topic of surrogate matrix for tissue analysis is difficult and time consuming. One reason is that most authors do not use the terms ‘surrogate’ and/or ‘surrogate matrix’ anywhere in their writing. Rather, they use a statement such as calibration standards are prepared in solvent X or matrix Y to indicate that a surrogate matrix is used. Another reason is ‘tissue’
Executive summary
Surrogate matrix: opportunities & challenges • Surrogate matrix tissue analysis quantifies tissue samples against a calibration curve in a surrogate matrix that depicts the behavior of the tissue and is free of analyte.
• Surrogate matrix approach offers new opportunities for tissue analysis. It allows tissue quantitation even there is lack of blank authentic tissue. It makes it possible to reach better LLOQ for endogenous analyte. It also improves the sample analysis efficiency in many situations.
• The challenges for surrogate matrix approach are: – There are potential risks of data inaccuracy; – The method establishment takes longer time and cost more; – There may be lack of authentic tissue for method establishment.
Surrogate matrix for tissue analysis • The ideal surrogate matrix should be suitable, available and affordable. • The validity of surrogate matrix can be established by one of the four methods: – Comparing the slopes of calibration curves; – Valuating the accuracy of QC samples; – Determining analyte recovery; – Evaluating matrix effect.
• All four methods involve the assessments in both surrogate matrix and authentic tissue. Method qualification • Surrogate matrix tissue method is often qualified based on fit-for-purpose principle using the tiered approach.
Sample analysis • If possible, it is recommended to include QC samples in both surrogate matrix and matching tissue in each batch during the tissue sample analysis to monitor the method performance.
Conclusion • Surrogate matrix approach is a valuable choice for tissue analysis. However, due to the challenges it faces, it should not be the first choice of method for tissue analysis. If possible, tissue should be analyzed using standards prepared in matching tissue.
is a generic term. The authors often use more spe- cific terms such as ‘brain’ and ‘liver’ to describe their analysis. Due to these two reasons, it is likely we have overlooked many researchers’ work in this area even though we have attempted to provide a comprehensive review on the subject. Second: include the calibration matrix information in the writing. During the prepara- tion of this manuscript, we encountered some papers which possibly used surrogate matrix but we cannot be certain due to the lack of calibration matrix informa- tion [60–62]. We believe the details of analytical meth- odology including calibration matrix are critical infor- mation for understanding data and should be included in the writing.
Financial & competing interests disclosure The authors have no relevant affiliations or financial in- volvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employ- ment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this
manuscript.
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Bioanalysis (2015) 7(18)
future science group
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