Matrix effects interferences

ICP-OES is a destructive technique that provides only elemental composition. However, ICP-OES is relatively insensitive to sample matrix interference effects. Interference effects in ICP-OES are generally less severe than in GFAA, FAA, or ICPMS. Matrix effects are less severe when using the combination of laser ablation and ICP-OES than when a laser microprobe is used for both ablation and excitation. 

Determinations by both techniques can be subject to chemical and/or physical interference effects caused by the sample matrix. However, after fractionation of the sample the species are usually in a less complex matrix, a buffer or electrolyte solution. Consequently, matrix interferences effects are minimised. On the other hand, the species may be diluted in the process and this could be detrimental for the determination of species present at very low concentrations. At the present state of the art GFAAS can be used for the determination of analytes at the 1 pgl level. However, at this level contamination in the reagents and equipment limit the number of species that can be detected with confidence. 

Matrix spikes enable the data user to evaluate the extent of matrix interference effects on the recovery of target analytes and to draw conclusions on the accuracy of environmental sample data. Soils of certain lithological composition have a tendency to retain chemicals, a property that is often demonstrated by MS/MSD recovery data. Such information may be particularly important for the projects where sample concentrations are compared to action levels. Low recoveries from certain soil types may render results inconclusive and warrant a different sampling or analysis approach. That is why matrix spikes provide meaningful data only if performed on the project samples. 

Du L, White RL (2008) Reducing glycerophosphocholine lipid matrix interference effects in biological fluid assays by using high-turbulence liquid chromatography. Rapid Commun Mass Spectrom 22 3362-3370... 

Ross, B.S., and Hieftje, G.M. (1991) Alteration of the ion-optic lens configuration to eliminate mass-dependent matrix interference effects in inductively coupled plasma-mass spectrometry Spectrochim. Acta 46B, 1263-1273. 

AAS is split into two types according to the method by which the sample is atomized. In flame atomic absorption spectrometry (FAAS) the sample is aspirated into a flame which is placed in the path ofthe light. In electrothermal atomic absorption (EAAS) the sample is placed in a graphite tube and heated in a brief pulse by passing an electric current through the tube. Generally, EAAS is more sensitive, giving better detection limits, but suffers from more matrix interference effects than FAAS. 

Spike about every tenth sample with a concentration of analyte similar to that found in the natural sample. This step checks for matrix interference effects and determines recovery. 

One of the most important advantage of NAA is that it is nearly free of any matrix interference effects because the atoms of matrix are composed of H, C, O, N, P, and Si that do not form any radioactive isotopes. This makes the method highly sensitive for measuring trace elements. Thus the vast majority of samples are completely transparent to both the probe (the neutron) and the analytical signal (the y-ray). 

Although it is an elegant approach to the common problem of matrix interference effects, the method of standard additions has a number of disadvantages. The principal one is that each test sample requires its own calibration graph, in contrast to conventional calibration experiments, where one graph can provide concentration values for many test samples. The standard-additions method may also use larger quantities of sample than other methods. In statistical terms it is an extrapolation method, and in principle less precise than interpolation techniques. In practice, the loss of precision is not very serious. 

Chu, Haffner, and Letcher [137] developed an LC—ESI—MS/MS method for the determination of TBBPA and lesser brominated analogs in sediments and wastewater—sludge samples. Sample recovery and matrix interference effects were largely compensated by the use of an isotopically labeled internal standard. Saint-Louis and Pelletier [138] studied ion-suppression effects for the same types of matrices and foimd that ion suppression was more severe for sewage sludge samples than for marine sediment extracts. 

Where components of a sample other than the analyte(s) (the matrix) interfere with the instrument response for the analyte, the use of a calibration curve based on standards of pure analyte may lead to erroneous results. Such matrix interference effects can be largely if not entirely avoided by preparing calibration standards where known amounts of pure analyte are added to a series of equal sized portions of the sample, a procedure known as spiking. In addition, one portion of sample is not spiked with analyte. (Note if spiking sample solutions with analyte changes the volume significantly, volume corrections must be applied.)... 

The previously described space charge effect phenomenon offers an explanation for many of the observed sample matrix interference effects in ICP-MS.The masses of both the analyte element and the matrix are important. The transport of analyte species is suppressed more by heavy matrix ions than light ones, and heavy analyte ions are suppressed less severely than light analyte ions. 

Alternatively, matrix-matching procedures can be used, which involve approximating the matrix of the sample by the addition of a similar quantity of the major component elements in the solids to the calibration standard solutions. This approach can potentially reduce the magnitude of interelement matrix interference effects. The technique can be problematic in that it may be difficult to add a sufficient quantity of salts of the major components to approximate the solid matrix composition. 

ICP-AES has already exerted a major impact on analytical spectroscopy, as more multi-element determinations are presently done by this technique than by any other. ICP-MS could exert a similar impact in the near future, particularly for applications requiring detectability as the main figure of merit. There are some weaknesses and room for improvement in both ICP techniques, however. The main problems in ICP-AES for rare earths are spectral interferences and detection limits that are not quite good enough for many applications. In ICP-MS, suppression of oxide ions, improvements in precision, and alleviation of matrix interference effects are desirable. Nevertheless, both techniques represent substantial improvements upon what was available previously for multi-element determinations, and both are likely to be used for some time to come. 

---