Matrix effects susceptibility

The fact that APCl and electrospray are soft ionization techniques is often advantageous because the molecular ion alone, in conjunction with HPLC separation, often provides adequate selectivity and sensitivity to allow an analytical method to be developed. Again, method development is important, particularly when more than one analyte is to be determined, when the effect of experimental parameters, such as pH, flow rate, etc., is not likely to be the same for each. Electrospray, in particular, is susceptible to matrix effects and the method of standard additions is often required to provide adequate accuracy and precision. 

HPLC/MS and HPLC/MS/MS analyses are susceptible to matrix effects, either signal enhancement or suppression, and are often encountered when the cleanup process is not sufficient. To assess whether matrix effects influence the recovery of analytes, a post-extraction fortified sample (fortified extract of control sample that is purified and prepared in the same manner as with the other samples) should be included in each analytical set. The response of the post-extraction fortified sample is assessed against that of standards and samples. Matrix effects can be reduced or corrected for by dilution of samples, additional cleanup, or using calibration standards in the sample matrix for quantitation. 

Also known as specific susceptibility. mas sa.sep-ta bil-ad-e mass-to-charge ratio analychem In analysis by mass spectroscopy, the measurement of the sample mass as a ratio to its ionic charge. mas to charj. ra sho ) matrix analy chem The analyte as considered in terms of its being an assemblage of constituents, each with its own properties. ma-triks matrix effects analy chem 1. The enhancement or suppression of minor element spectral lines from metallic oxides during emission spectroscopy by the matrix element (such as graphite) used to hold the sample. 2. The combined effect exerted by the various constituents of the matrix on the measurements of the analysis. ma triks i.feks )... 

However, some obstacles still have to be removed before HPLC-MS is fully accepted as a routine technique in the forensic labs. First of all the cost of equipment is still high, despite the reduction trend in the last years, as compared to GC-MS. Second, some problems have to be tackled, i.e., the susceptibility of ion sources (and particularly ESI) to matrix effects on analyte s ionization efficiency (suppression or enhancement) and the scarce reproducibility of MS fragmentation. The third obstacle is actually the other side of the coin of versatility the wide choice of technical alternatives makes HPLC-MS still far from being a highly standardized, one-button technique as GC-MS. 

In ICP-OES, it has been observed that analyte lines with high excitation potentials are much more susceptible to suffer matrix effects than those with low excitation potentials. The effect seems to be related to the ionisation of the matrix element in the plasma, but in fact it is a rather complicated and far from fully characterised effect [8,9]. Therefore, calibration strategies must be carefully designed to avoid problems of varying sensitivity resulting from matrix effects. A possible approach may be to combine experimental designs and multivariate calibration, in much the same way as in the case study presented in the multivariate calibration chapters. 

Although PPE is the most efficient and inexpensive extraction technique, it is also the most nonspecific extraction procedure which is known to be susceptible to matrix effect for LC-MS/MS assay. In contrast, LLE provides a much cleaner extract. LLE, also known as solvent extraction and partitioning, separates analytes based on their relative solubility in two different immiscible solvents, usually water and an organic solvent. The most commonly used solvents for LLE are ethyl acetate (EtOAc), methyl ferf-butyl-ether (MtBE), methylene chloride (CH2C12), and hexane or the combination of the above solvents. In order to manipulate the polarity of the analytes, often a volatile acid or base such as FA or NH4OH respectively at 5-10 %... 

It is acknowledged that ESI is more susceptible to matrix effects compared with APCI or APPI, and that ionization in the negative mode is more selective than the positive mode [55],... 

A number of reports in the literature indicate that matrix effect is dependent on ionization type, sample preparation, and bio-fluid type [104,108,114, 116-119]. In 2003, Dams et al. [119] demonstrated that the APCI was less susceptible to matrix effect, thereby allowing for simplification of sample preparation prior to LC/MS/MS analysis without jeopardizing the quality of quantitative data, as shown in Table 7-8. More recently, Souverain et al. [117] investigated the matrix effect in bio-analysis of illicit drugs with both LC/ESI-MS/MS and LC/APCI-MS/MS. Four procedures—liquid-liquid extraction (LLE), SPE, protein precipitation (PP) with acetonitrile (ACN), and protein precipitation with perchloric acid (PA)— were tested to evaluate... 

If the sample is a bulk solid sample and is an electrical conductor, it is possible to use it as the cathode of a kind of spectral lamp whose functioning principle is identical to that described for a hollow cathode lamp (cf. Section 13.5.1 and Figure 14.5). The atoms sputtered and removed from the surface of the sample are excited by the plasma. This GD-OES technique provides a rapid and accurate surface analysis, less susceptible to matrix effects and sample homogeneity. It has the advantage of yielding spectra with low background levels whose emission lines are narrow since atomization takes place at lower temperatures than that of the previous techniques. 

When the analytical procedure is susceptible to matrix effects, the standard addition method, SAM, can be applied to improve accuracy. SAM involves several additions of known amounts of the analyte (AAdd — Fig. 8.25) to the sample and measurement of the analytical signal (M — Fig. 8.25) after every addition. A specific "analytical curve" (M vs AAdd) is obtained for each assayed sample and the analytical result (C) is obtained by extrapolation. 

In addition, there is no doubt that CMEs are more suspectible to matrix effects than conventional electrodes. This is quite understandable since the electrode surface is now, not only responsible for the electron transfer process, but also for the chemistry (e.g. complexa-tion, ion-exchange, or a catalytic reaction). Obviously an ion-exchange process will be very dependent on the pH and the ionic strength of the sample, as will complexation or precipitation processes. Even more subtle, perhaps, is the susceptibility of modified electrodes to morphology changes in different matrices. Changes in surface area or porosity will influence analytical performance, and we have found that such changes do occur with chemically... 

ICP-AES is normally preferred for trace analysis because of its generally better detection limits, freedom from chemical matrix effects, and multi-element capability. When available, it is used instead of AAS. Like AAS, hydride and mercury vapor attachments can be used to enhance the detection limits of the elements listed above. As an alternative to normal sample preparation or microwave procedures, laser ablation is creeping in as an alternative approach. The same pressed discs used for XRE are ablated by an IR or UV laser in a chamber that replaces the spray chamber used normally. The sample preparation takes minutes rather than days or hours, eliminates reagents (even pure reagents are less pure than ceramic powders), and is less susceptible to external contamination. 

Because of its high nutritional value and the beneficial effects that some of its compounds exert, the price of VOO is relatively higher if we compare it with other edible oils. This fact could explain why so many adulterations have been found for VOO this matrix is susceptible to adulteration with cheaper olive oil categories (olive oil pomace, refined olive oil) and/or other edible oils. Com, cottonseed, canola, palm, peanut, soybean, and sunflower oils have been detected in adnlterated VOOs. 

Over the last few years, due to improvements in the packing material of the chromatographic columns, the use of UHPLC technique has improved the reported HPLC methodologies in terms of peak efficiency, peak resolution, speed, sensitivity, and solvent consumption. However, this technique must operate at high backpressures [41-43]. Another advantage of the UHPLC technique is that, given this high peak resolution, when it is combined with MS as the detector system, it is less susceptible to matrix effects (MEs), one of the main problems when the MS is used to quantify minor components in food samples. This is because an efficient UHPLC separation may contribute to a reduction in ion suppression, when this is only produced by the coelution of two different compounds [44]. 

While these results do suggest that APPI-MS more closely approaches a universal detector, it should be pointed out that in this test APPI used a dopant (toluene) that was not used in the corresponding APCI tests so that this particular comparison is not straightforward. Also, simple detection is a much easier criterion to satisfy than acceptable accuracy and precision in quantitation. At present the characteristics of APPI with respect to important figures of merit such as repeatability, precision, susceptibility to matrix effects etc. remain unclear. 

The generalized matrix effect can take account of ionization suppression ME < 100) or enhancement ME > 100). If the extraction and clean-up procedures were 100 % efficient then C and B would be equal regardless of any matrix effect since both are susceptible to exactly the same effects clearly if RE is significantly > 100, something is wrong with the experiment. The process efficiency PE measures the net effect of extraction efficiency plus matrix effect on the final response of analyte extracted from the matrix. 

Well-known advantages of GC(-MS) over LC(-MS) are an unbeaten chromatographic resolution, which may be of importance for structural isomer separation, for example, for PFOS isomers [34], and less susceptibility to matrix effects. However, only a small fraction of PFC can be directly analyzed by GC methods, owing to the polar or even ionic structure of most of the PFC and their metabolites. Typical PFC that can be directly analyzed by GC are FTOH, fluorotelomer olefins, and other fluorotelomer-based compounds and metabolites [16]. However, the typical PFC such as PFCA and perfiuorosulfonic acids (PFSA) are non-volatile and therefore not suited for GC analysis. This can be circumvented by derivatiza-tion, for example, to the butyl [34] or i-propyl esters [35] of sulfonates or preparation of the anilides [36] or methyl esters [37] from PFCA. 

Electrothermal atomic absorption spectrometry (ETAAS) has also been used for the determination of trace elements in biological samples because of its speed, minimum need for sample preparation, possibility of automation, and good sensitivity. However, ETAAS measurements are susceptible to matrix effects and therefore require standards similar to the samples. In addition. 

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