Interference problem

A general problem in trace, species and isotope analysis is possible isobaric interferences. In all mass spectrometric techniques, the ability to determine several isotopes is limited due to the occurrence of isobaric interferences of atomic ions of analyte with isobaric atomic ions (e.g., Zr and Mo ) or polyatomic ions (e.g., and at the same nominal mass. Due to the slight mass 

Reducing oxide based isobaric interferences in the ICP mass spectrum via gas flow modulation was proposed by Wetzel and Hieftje. After a careful manipulation of the central chaimel gas flow to impact distinguishable frequency specific behaviour of analyte and oxide ion species and application of a Fourier transform (FT) correction method, contributions from an analyte and oxide species superimposed at a given mass can be mathematically umavelled with a degree of success. Through application of this correction method, a greater than ten-fold error at m/z 156 caused by tlie interference of Ce 0 on Gd has been effectively eliminated.  

To avoid interferences of isobaric atomic ions of different elements and polyatomic ions at the same nominal mass, off line separation of matrix elements or analyte separation can be applied and/or enrichment and hyphenated techniques such as HPLC- or CE-ICP-MS. Analytical procedures have been developed in the author s laboratory for the determination of spallation nuclides in an irradiated tantalum target using HPLC and CE coupled on line to ICP-MS after dissolution and separation of the tantalum matrix. The mass spectra of rare earth elements (REEs) 

The determination of trace impurities in boron nitride of the highest purity for the production of GaAs single crystals is hampered by the formation of disturbing polyatomic and cluster ions. 

Ion-molecular reactions are used to resolve isobaric interferences, as discussed, in ICP-MS with a collision/reaction cell or by utilizing ion traps. The mass spectra of Sr, Y and Zr (Fig. 6.10a) without O2 admitted into the collision cell and (Fig. 6.10b) with 10 Pa Oj are different. By introducing oxygen, selective formation of YO and ZrO, but not SrO, is observed. This behaviour of different oxide formation is relevant for an interference free determination of Sr. Ultrahigh mass resolving power ICP mass spectrometry (at m/Am 260 000) selectively removes unwanted ions prior to transfer to the FTICR analyzer cell by gas-phase chemical reactions, e.g., for separation of Ca from Ar+ obtained with a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer equipped with a 3 tesla superconducting magnet.  

Re02+ and Re03+ ions were detected. In particular, the Re03+ and Re03H+ ions appearing 

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Not surprisingly, methods whose signals depend on chemical reactivity are often less selective and, therefore, more susceptible to interferences. Problems with selectivity become even greater when the analyte is present at a very low concentration. ... 

Impressed Current Ground Beds and Interference Problems... 

The trends begun with the general introduction of FTIR technology will undoubtedly continue. It is safe to say that the quality of the data being produced far exceeds our ability to analyze it. In fact, for many current applications, the principle limitations are not with the equipment, but rather with the quality of the samples. Thus, the shift from qualitative to quantitative work will proceed, reaching high levels of sophistication to address the optical and matrix interference problems discussed above. 

The use of canopy hoods or remote capture of fume is usually considered only after the rejection of source or local hood capture concepts. The common reasons for rejecting source or local hood capture are usually operating interference problems or layout constraints. In almost all cases, a canopy hood system represents an expensive fume collection approach from both capital and opetating cost considerations. Remote capture depends on buoyant ait curtents to carry the contaminated gas to a canopy hood. The rising fume on its way to the hood is often subjected to cross-drafts within the ptocess buildings or deflected away from the hood by objects such as cranes. For many of these canopy systems, the capture efficiency of fume may be as low as 30-50%. 

Other important alternate electrochemical methods under study for pCO rely on measuring current associated with the direct reduction of CO. The electrochemistry of COj in both aqueous and non-aqueous media has been documented for some time 27-29) interferences from more easily reduced species such as O2 as well as many commonly used inhalation anesthetics have made the direct amperometric approach difficult to implement. One recently described attempt to circumvent some of these interference problems employs a two cathode configuration in which one electrode is used to scrub the sample of O by exhaustive reduction prior to COj amperometry at the second electrode. The response time and sensitivity of the approach may prove to be adequate for blood ps applications, but the issue of interfering anesthetics must be addressed more thorou ly in order to make the technique a truly viable alternative to the presently used indirect potentiometric electrode. 

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. 

An alternative is the standard additions method. In this method, a certain volume of the sample solution itself is present in the same proportion in all standard solutions. It is equivalent to adding standard amounts of analyte to the sample solution, hence the term standard additions. This solves the interference problem because the sample matrix is always present at the same component concentrations as in the sample—the matrix is matched. In addition, the sample solution components need not be identified. 

Because of the interference problems with both colorimetric and amperometric analyzers, they are being replaced by instruments based on other principles. (Colorimetric analyzers are no longer commercially available.) One such recently improved technique developed for the specific detection and measurement of ozone is the detection of the... 

A7a. Anonymous, Interference problem with the T4-column and PBI tests. In Handbook of Specialized Diagnostic Laboratory Tests, 8th Ed. BioSci. Lab., 1970. 

First Control Run. A large number (7 to 15) of sets of standards and blanks are run and the results tabulated, as in the trial runs. These data are then plotted (responses vs. concentration for all data points, on one graph) and the means, standard deviations, RSDs, the slope, y-intercept, and correlation coefficient are determined. The smaller the value of the y-intercept, the better (the less chance for a contamination or interference problem). The closer the slope is to 1, the better (the more sensitive). At higher concentrations, the standard deviation should get larger, and the RSDs should get smaller (while approaching some limit). If the RSDs are between 30% and 100%, a close approach to the detection limit is indicated. 

The severity of these problems is quite sensitive to the nature of the particular organic, as expected, and likely to the particular sampling configuration and conditions as well. For example, Calogirou et al. (1997) showed that saturated oxygenated terpenes adsorbed on Tenax were not affected by the presence of 100 ppb 03 whereas as much as 80-90% of the most reactive, unsaturated compounds reacted. Indeed, no a-terpinene was observed when ozone was present. On the other hand, Koppmann et al. (1995) report no significant interference problems with 03 for the C2-C4 hydrocarbons which were sampled using a heated stainless steel inlet line, which destroys as much as half of the initial ozone, and then cryotrapped. 

Q. What interference problems may be encountered with microwave plasmas ... 

Short reviews appeared on the various MS techniques for quantitation of stable isotopes and long-lived radioisotopes and the application of Mg stable isotopes as tracers in biology and medicine. The radioactive isotope Mg is not usually available and has a short half-life (21.3 h), hence its hmited usefulness as a tracer. The sensitivities and interference problems encountered in activation analysis for Al, Mg, Mo, P, Si and Zr were discussed. Much higher sensitivities were found for cyclotron-produced than for reactor-produced fast neutrons or 14 MeV neutrons. ... 

Analytically, epoxy groups are determined by the reaction with hydrogen halide and back titration with a standard base. Other functional groups present may cause interference problems and result in poor end points. Pyridinium chloride-pyridine is a recommended reagent for the analysis of bisphenol-diglycidyl ether resins [22,23],... 

DCP in air samples and, therefore, should seldom cause a problem (11, 12). The other potential interferent, 1,2-dichloro-ethane, is an impurity in reagent-grade 1,2-DCP but typically represents less than 1% (w/w) of the reagent (13). Thus, this compound should not ordinarily pose an interference problem. 

An interference check standard is a standard solution used to verify an accurate analyte response in the presence of possible interferences from other analytes present in the samples. For methods that have known interference problems arising from the matrix or that are inherent in the method, such as ICP-AES (spectral interference lines) and ICP-MS (isotope combinations with similar masses to analyte), these solutions are used in the batch. The interference check standard must be matrix matched to acid content of the samples. Acceptance criteria are set—for example, the magnitude of uncorrected background and spectral interference must not be greater than a stated value. 

The figures of merit of quadrupole-based ICP-MS, such as the precision of isotope ratio measurements and the detection limits, can be improved significantly, especially for elements which are difficult to determine due to the appearance of isobaric interferences (e.g., by the trace, ultratrace and/or isotope ratio measurements of Ca, Fe, S, As, I or Se).16-22 The occurrence of interference problem can be minimized by the insertion of a collision/reaction cell in ICP-MS as the result of defined collision induced reactions using selected collision/reaction gases or gas mixtures (such as H2, He, NH3, 02, CH4 and others). For each analytical problem, which is different, e.g., for U or... 

In addition to these collision/reaction cell instruments, since 2002 Thermo Fisher Scientific has been selling the XSeries ICP-MS with a hexapole collision cell (developed from ThermoElemental PQExel ICP-MS) as a bench top instrument on the analytical market. A special ion extraction system in Thermo s XSeries", ion optics together with a hexapole collision cell to minimize the interference problem in ICP-MS, provides the lowest background signals for ICP-QMS (< 0.5 cps). 

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