Matrix suppression/enhancement

Matrix Effect, Matrix Suppression/Enhancement, and Recovery... 

MATRIX EFFECT, MATRIX SUPPRESSION/ENHANCEMENT, AND RECOVERY... 

Matrix effect and matrix suppression/enhancement are terms in bioanalysis that are often used interchangeably. However, the matrix effect is a more specific terminology in bioanalysis and is primarily used to describe whether an assay s performance can be reproduced for individual subject samples, regardless of the difference in matrices. If the response ratio of an analyte to its ISTD can be kept consistent under the same concentration level in different matrices, then no adverse matrix effect can be claimed for the bioanalytical assay. On the other hand, matrix suppression/enhancement is more explicit to evaluate whether an analyte signal is affected by coeluted matrix components even though they are not directly measured by mass spectrometry. The suppression/ enhancement can be ascribed to an analyte s ionization efficiency, which is impacted, either negatively or positively, by the underlying matrix components. 

An assay can have a minimal matrix effect even if substantial matrix suppres-sion/enhancement is observed, provided that labeled ISTDs are employed. An isotopically labeled ISTD can compensate for the ionization variability for the analyte of interest. In comparison, matrix suppression/enhancement can affect assay sensitivity and linearity. 

For high-throughput analysis, it is important to increase the specihcity of each bioanalytical method. The enhancement of chromatographic resolution presents various limitations. Better selectivity can be obtained with TOF mass analyzers that routinely provide more than 5000 resolution (full width at half-mass or FWHM). The enhanced selectivity of a TOF MS is very attractive for problems such as matrix suppression and metabolite interference. In one report of quantitative analysis using SRM, TOF appeared less sensitive than triple quadrupole methods but exhibited comparable dynamic range with acceptable precision and accuracy.102... 

Due to the complexity of the food samples, it is possible that the presence of some compounds in the matrix interferes with analyte determination even when working in LC-MS/MS, certain compounds present in the sample can affect the initial ionization of the analyte through what is often called ion suppression/ enhancement or matrix effects. 

Matrix effect (enhancement or suppression). The effect of a biological matrix on the instrument response of the analyte [20]. 

As shown in Fig. 1.7, the method for evaluating ion suppression/enhancement encountered during a bioanalytical assay involves injection of a processed blank matrix sample on the column with continuous postcolumn infusion of a mixture of an analyte and an internal standard into the LC stream. The analyte and the internal standard are monitored (MRM or SRM scan) throughout the entire LC ran time while the matrix components are eluting from the column. Data from a matrix effect experiment obtained using the postcolumn addition method are given in Fig. 1.8. 

Longerich, H.P. (1989) The effect of nitric acid, acetic acid and ethanol on inductively coupled plasma-mass spectrometric ion signals as a function of nebulizer gas flow, with implications on matrix suppression and enhancements. J. Anal. Atomic Spectroscopy 4, 665-677. 

As discussed in Ch. 6.6.3, some mobile-phase additives are also known to suppress or enhance analyte response. It appears useful to discriminate between effects due to the mobile-phase composition and effects due to the actual analyte matrix. Some additives were found to reduce the matrix suppression [119]. 

All LC-MS techniques tend to be subject to matrix effects, especially suppression, although enhancement effects may also be observed. A procedure has been suggested to systematically investigate matrix effects when developing and validating methods using LC-MS or LC-MS/MS for detection. First, run pure standards to determine the analyte response in the absence of matrices. Next, either prepare standards in a matrix extract or infuse standards in the presence of matrix extract into the mass spectrometer and determine whether the response differs from that observed for pure standards. Differences in response may be attributed to matrix suppression (or enhancement) effects. Finally, fortify blank tissue with standards, perform the extraction and clean-up steps of the method, and then determine the detector response. The difference between the response observed for fortification into matrix extract and fortification into matrix prior to extraction and clean-up is attributed to method recovery. The evaluation of matrix effects is discussed in detail in Chapter 6. 

Matrix Effects. Signal Suppression and Enhancement. Major effects on the LOD can be found due to the unavoidable presence of the sample matrix. These effects can take the form of suppression, enhancement, or masking of the analyte signal. Suppression and enhancement will be discussed here and masking In the next section. Without taking these effects Into account, major errors can be made in Che conclusions drawn from Che evidence. 

Dissolution Inhibitors. One q>proach towards effectively modifying the dissolution behavior of P(NB/MA/AA) and P(NB/MA/AA/TBA) based resists is to use the matrix resin in conjunction with a dissolution inhibitor. Design criteria for an effective 193 nm DI include low absorbance at 193 nm, solubility in spin casting solvents, loading capacity in resin matrix, contrast enhancement of resin matrix and dark erosion suppression. One candidate for such applications is the cholate based esters. 

The availability of a true control (blank) matrix, particularly of multiple lots and/or sources, varies widely and this represents a major consideration in method development, validation and sample analysis. This concern is even greater when there is a possibility of significant matrix effects (suppression/enhancement of ionization efficiency), in which case relative matrix effects (Sections 5.3.6a and 9.6) must be tested for by comparing nominally similar control matrices from different lots and/or suppliers. 

Limits of Detection (LODs) The LCDs are substance and matrix dependent as a result of matrix suppression or enhancement, as can be seen in... 

Modification of the mobile-phase composition and gradient can sometimes be useful in shifting matrix components away from an analyte of interest to reduce ion suppression—enhancement. However, as the number of analytes increases, this option becomes less effective and a modification of the extraction procedure may be in order. 

IDMS is largely unaffected by matrix suppression or enhancement effects, as only isotope ratios have to be measured and both isotopes will be affected in the same way. 

Standard addition experiments can be used to check for matrix effects such as ion enhancement or suppression. 

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