How to use TargetLynx XS to correct for endogenous or ubiquitous concentrations in standards - WKB224070

OBJECTIVE or GOAL

Correct for C0 in matrix-matched calibration curves using TargetLynx XS.

Almost all bioanalytical or food and environmental LC-MS/MS methods involve spiking authentic matrices to evaluate method precision, matrix effects, accuracy, and linearity [1]. In bioanalytical methods, the matrices used for spiking experiments often contain endogenous levels of the compounds to be quantified. Similarly, in food and environmental analysis, matrices often contain ubiquitous compounds such as persistent organic pollutants (POP). In this article, endogenous or ubiquitous concentrations present in matrices used for spiking experiments will be called Concentration 0 (C0).

In order to overcome matrix effects in LC-MS/MS, calibration curves are often prepared by spiking an authentic matrix with known levels of standards; this is called matrix-matched calibration. Failure to correct for the endogenous or ubiquitous concentration (C0) will introduce a bias.

The objective of this article is to provide guidance on how to correct for C0 in matrix-matched calibration curves using TargetLynx XS. To demonstrate the procedure, a matrix-matched calibration was prepared by spiking a plasma sample at four different levels. Plasma containing an endogenous amount of testosterone is also analyzed without spiking (C0). When ignoring the endogenous amount present in the matrix, the calibration curve shows a high y-intercept, and this leads to a bias.

ENVIRONMENT

• TargetLynx XS

PROCEDURE

To correct for the endogenous concentration present in the matrix, follow these steps:

1. Determination of C0 in the matrix using standard addition experiment
   Because the unspiked matrix (C0) as well as four spike levels were analyzed, it is possible to determine C0 using standard addition calculation. TargetLynx XS offers the possibility to perform this calculation automatically. Refer to the article "How to perform a standard addition calculation in TargetLynx" for details.
2. Correction of the testosterone concentration in the standards
   Now that C0 is known, it is possible to correct the concentrations of the standards. To do so, the testosterone standard concentrations specified in the sample list must be corrected as follows: standard concentration in sample list = spike concentration + C0
3. Process the samples
   When corrected, the calibration curve produces a y-intercept close to zero. The unspiked matrix C0 can also be added as a calibration point.

ADDITIONAL INFORMATION

Reference: 

[1] Desharnais, Lajoie, Laquerre, Savard, Mireault, and Skinner (2019). A Tool for Automatic Correction of Endogenous Concentrations: Application to BHB Analysis by LC-MS-MS and GC-MS. Journal of Analytical Toxicology. 43. 10.1093/jat/bkz024.