Surrogate matrix: opportunities & challenges for tissue sample analysis Review Box 1. Evaluation of recovery and matrix effects.
%RE(withoutsamplesubtraction) R(Exp 2) R(Exp1)
=
post extraction spiked preextractionspiked
- - %RE(with sample subtraction) = R(Exp2)Rnotspiked (Exp3)
R(Exp1)R post extraction spiked
preextractionspikednot spiked (Exp3) -
- - Equation 2
%PE(by response) R(Exp4) R(Exp1)R
= preextraction spiked - neat solution - %PE(by conc.) =
[measured] preextraction spiked (Exp1) [measured]notspiked (Exp3) [spiked]
- -
%ME(by response) R(Exp4 R(Exp2)R
=
ME% > 100: enhancement ME% = 100: no matrix effects ME% < 100: suppression
Exp: Experiment; R: Response, such as peak area; RE: Recovery; PE: Process efficiency; ME: Matrix effect; Conc: Concentration; [Spiked]: Spiked concentration; [Measured]pre-extraction spiked [Measured]no spiked: Measured concentration for the sample.
: Measured concentration for pre-extraction spiked sample;
mance, including interference, recovery, matrix effects and stability, in both surrogate and tissue. Based on the successful evaluation results, surrogate matrix can be used to overcome inherent limitations of analysis with respect to matrix availability and complexity and endogenous analyte.
Future perspective HRMS The interference and matrix effect differences between surrogate matrix and tissue are some of the challenges for surrogate matrix approach. HRMS, which has bet- ter mass accuracy and mass resolution, may help to alle- viate those challenges [55]. Meyer et al. reviewed papers on the use of HRMS for drug quantitation and found that in general HRMS offers comparable sensitivity with quadrupole mass spectrometer and is a suitable technology for quantitation [56]. HRMS has been used successfully for surrogate tissue analysis [4,15,31–32]. We believe the adaptation of HRMS for surrogate tissue analysis will be wide-spread in the future.
Surrogate analyte An ideal surrogate matrix has the same matrix prop- erty as the authentic matrix for bioanalysis purposes.
future science group
This tends to be very difficult to accomplish. There- fore, surrogate matrix approaches always have the risk of obtaining inaccurate results due to matrix dissimi- larity. One way to overcome the issue of matrix dif- ference is the surrogate analyte approach, in which a compound similar to the analyte (a surrogate analyte) is used to construct a calibration curve in the authen- tic matrix [57]. By using authentic matrix, the surro- gate analyte approach eliminates the issue of matrix difference. However, the approach is not applicable if there is a shortage of authentic matrix. A stable-labeled analyte that is not present in the authentic matrix is often chosen to be the surrogate analyte. For the anal- ysis of analyte that has an endogenous level, the sur- rogate analyte approach makes achieving low LLOQ possible. Considerations for using surrogate analyte were discussed by Jones et al. and MacNeill et al. [1,58]. Although both articles
focused the discussions on
plasma analysis, the key points and approaches pre- sented by the authors are generally applicable tissue analysis also. Tissue analysis using a surrogate ana- lyte has been demonstrated by Kinoshita et al., who presented the quantitation of d -serine in mouse brain using [2,3,3–2
H]D-serine as surrogate analyte [59]. They also compared the measured d -serine levels
www.future-science.com 2429 post extraction spiked - neat solution - notspiked (Exp3) ) notspiked (Exp3) # 100 Equation 3 # 100 Equation 4 # 100 Equation 5 - # 100 Equation 1 # 100
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