Matrix effects significance

Quantitative depth profiling using polyatomic MCs+ and MCs2+ ions instead of atomic ions M= ions is well established in surface analysis using SIMS. The MCs+ technique, which reduces matrix effects significantly, was proposed by Gao in 1988.100 The formation of MCs+ has been explained by the recombination of sputtered neutral atoms (M) with... 

Another problem is that the Nernst equation is a function of activities, not concentrations. As a result, cell potentials may show significant matrix effects. This problem is compounded when the analyte participates in additional equilibria. For example, the standard-state potential for the Fe "/Fe " redox couple is +0.767 V in 1 M 1TC104, H-0.70 V in 1 M ITCl, and -H0.53 in 10 M ITCl. The shift toward more negative potentials with an increasing concentration of ITCl is due to chloride s ability to form stronger complexes with Fe " than with Fe ". This problem can be minimized by replacing the standard-state potential with a matrix-dependent formal potential. Most tables of standard-state potentials also include a list of selected formal potentials (see Appendix 3D). 

The usage of the ratio of chai acteristic lines as analytical parameter in the process of formation of the calibration curve provides a significant decrease of the residual error. In Realization of this method simultaneously with the decrease of the matrix effects causes some decrease or even full compensation of the fonu and condition of the measured surface. 

Under Cs bombardment the matrix effect can be significantly reduced by using the MCs" ion signals for quantification of species M. The detection limit is increased, i.e. the detection power deteriorates, by two or more orders of magnitude, but sometimes even standard-free quantification has been reported [3.51]. MCs" ions have high masses this is a disadvantage because many mass interferences occur in this mass range. 

Active matrix contributes significantly to the overall performance of the FCC catalyst. The zeolite pores are not suitable for cracking of large hydrocarbon molecules generally having an end point > d00 [-(482°C) they are too small to allow diffusion of the large molecules to the cracking sites. An effective matrix must have a porous structure to allow diffusion of hydrocarbons into and out of the catalyst. 

The analytical response generated by an immunoassay is caused by the interaction of the analyte with the antibody. Although immunoassays have greater specificity than many other analytical procedures, they are also subject to significant interference problems. Interference is defined as any alteration in the assay signal different from the signal produced by the assay under standard conditions. Specific (cross-reactivity) and nonspecific (matrix) interferences may be major sources of immunoassay error and should be controlled to the greatest extent possible. Because of their different impacts on analyses, different approaches to minimize matrix effects and antibody cross-reactivity will be discussed separately. 

A sulfathiazole immunoassay was utilized to determine residues present in raw milk. The LOD was found to be 12 pg kg (based on 80% Bo) however, comparison of the calibration curve from an aqueous solution with a raw milk calibration curve indicated a significant matrix effect. 

Note that the interfacing of LC techniques with MS puts significant constraints on the solvents that can be used i.e., they must be volatile, with a low salt concentration, for MS compatibility. Narrow-bore columns, which use much smaller amounts of salt and organic modifier, appear to have potential for facilitating IEC-MS applications.40 Despite the excellent sensitivity of MS detection for most elements, however, there are cases where matrix effects can interfere. In this situation, combination of IEC with atomic emission spectrometry (AES) or atomic absorption spectrometry (AAS) may be preferable, and can also provide better precision.21 32 4142 Other types of... 

The coefficients a,- are estimated from the results of experiments carried out according to a design matrix such as Table 5.9 which shows a 23 plan matrix. The significance of the several factors are tested by comparing the coefficients with the experimental error, to be exact, by testing whether the confidence intervals Aai include 0 or not. The experimental error can be estimated by repeated measurements of each experiment or - as it is done frequently in a more effective way - by replications at the centre of the plan (so-called zero replications ), see Fig. 5.2. 

Multifactorial experiments are used in analytical chemistry for diverse applications, e.g., checking up significant influences before optimization procedures, recognizing matrix effects, and testing the robustness of analytical procedures (Wegscheider [1996]). 

Polymer Matrix Effects. In order to approximate the environment experienced by the arylcarbamate moieties in coatings based on aromatic diisocyanates, we chose to study the photochemistry of alkyl N-arylcarbamates in polymethacrylate (PMMA) and polypropyl-methacrylate (PPMA) films. First, however, 2a and 3a were irradiated in ethyl propionate (a model solvent for PMMA and PPMA) to determine the effect of the solvent polarity (dielectric) on the photolysis of the carbamates. Upon excitation at 280 nm, where the solvent absorbance was negligible, is 0.006 for 2a and 0j) is 0.005 for 3a. These values are significantly smaller... 

Vandecasteele et al. [745] studied signal suppression in ICP-MS of beryllium, aluminium, zinc, rubidium, indium, and lead in multielement solutions, and in the presence of increasing amounts of sodium chloride (up to 9 g/1). The suppression effects were the same for all of the analyte elements under consideration, and it was therefore possible to use one particular element, 115indium, as an internal standard to correct for the suppressive matrix effect, which significantly improved experimental precision. To study the causes of matrix effect, 0.154 M solutions of ammonium chloride, sodium chloride, and caesium chloride were compared. Ammonium chloride exhibited the least suppressive effect, and caesium chloride the most. The results had implications for trace element determinations in seawater (35 g sodium chloride per litre). 

Matrix effect — To demonstrate that the assay performance was independent from the sample matrix, QC samples were prepared using two different lots of matrix. The QC samples were evaluated using the same calibration curve. With regard to analytical recovery, no significant difference was observed for the QCs prepared in two lots of plasma. 

As a general rule, APCI is less likely to demonstrate matrix effects and ESI is more likely to be affected by matrix effects. Sample clean-up is another important factor—protein precipitation is more likely to result in matrix effects than is solid phase extraction. Matrix effects may be caused by sample constituents that are not parts of the biological matrix. Mei et al.126 129 showed that certain brands of sample tube containers can produce matrix effects. They also demonstrated that Li-heparin, a common anticoagulant for plasma samples, can produce significant matrix effects... 

In certain circumstances the matrix, defined as everything except the analyte, contributes significantly to the absorbance of a sample and is also highly variable. One method that can be used to improve results is the method of standard additions. The basic idea is to add standard to the analyte so that the standard is subjected to the same matrix effects as the analyte. This method assumes that the system obeys the Beer-Lambert Law. 

Matrix effects can influence significantly the extraction efficiency and signal intensity. For heavily contaminated samples such as sewage sludge, this problem is particularly relevant, and therefore the use of internal standards is essential in these applications. Internal standards applied in the extraction procedures for non-ionic surfactants include perinaphtenone [8], 4-fluoro-4,-hydroxyl-benzophenone [5] and 4-bro-mophenyl acetic acid [9]. More appropriate are internal standards from the same compound class butylphenol [10], heptylphenol [11],... 

Matrix effects are typically divided into spectral (isobaric) and non-spectral types. The spectral or isobaric effects include 1) elemental isobaric interferences such as Cr at " Fe, 2) molecular interferences such as Ca O at Fe and Ar N at Fe, 3) double charge interferences such as Ca at Mg. Non-spectral matrix effects are largely associated with changes in the sensitivity of an analyte due to the presence of other elements (Olivares and Houk 1986). Changes in sensitivity correspond to a change in instrumental mass bias, and therefore non-spectral matrix effects can have a significant impact on the accuracy of isotope measurements. 

Luminescence is often much more sensitive to molecular dynamics than other optical techniques where temperature, viscosity, pH and solvent effects can have a significant influence on the emission response. Analyte degradation for light sensitive fluors and photobleaching for static measurements also influence the emission signal. Because of the wide variety of potential matrix effects, a thorough investigation should be conducted or the sample matrix well understood in terms of its potential impact on emission response. A complete discussion on the fate of the excited states and other measurement risk considerations can be found elsewhere. ... 

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