Interference reduction

Pressure sensors that give temperature-corrected, linear, analog voltage output are available from Motorola and other manufacturers. In such sensors, the on-chip electronics correct any temperature effects and nonlinearities in the output of the piezoresistors. The on-chip electronics replace a shoebox-size collection of printed circuit boards. The price of this kind of smart sensor is considerably less than 100. The integration of a large amount of circuitry on the chip allows functions like amplification, offset correction, self-testing, autocalibration, interference reduction, and compensation of cross-sensitivities (6). 

Higher specificity and selectivity can be obtained by reacting -lactams with suitable reagents to form derivatives with improved ultraviolet chromophores. Thus, precolumn derivatization of penicillins with triazole-mercuric chloride and ultraviolet detection at 325 nm (71, 90, 112, 114, 115, 121, 122), 340 nm (123), or 345 nm (116) has become the method of choice for more selective detection and matrix interferences reduction. An alternative precolumn reaction using iodoacetamide as derivatizing reagent has been described in ceftiofur analysis (124), while imidazole-mercuric chloride has also been suggested for on-line postcolumn derivatization of penicillin G (69). 

Although this technology is effective in resolving a wide range of polyatomic interferences, the increased cost associated with this type of instrumentation (more than twice the price of a quadrupole instrument) limits its use in most routine laboratories, hence alternative methods of interference reduction have been sought for. The use of chemical extraction and chromatography (in order to separate the analyte from the matrix prior to analysis) or the operation of the ICP-MS under so-called cool plasma conditions, allows the elimination of... 

Ross et al. [6] analysed samples of soil leachates from laboratory columns and of soil pore water from field porous cup lysimeters for aluminium by atomic absorption spectrometry under two sets of instrumental conditions. Method 1 employed uncoated graphite tubes and wall atomisation method 2 employed a graphite furnace with a pyrolytically coated platform and tubes. Aluminium standards were prepared and calibration curves used for the colorimetric quantification of aluminium. Method 1 gave results which compared favourably with method 2 in terms of both sensitivity and interference reduction for samples containing 1-15 uM aluminium. 

Coincidence techniques have also been used for Compton interference reduction in the use of large volume Ge(Li) detectors together with plastic scintillator anticoincidence shields 70), In some cases it might be desirable to use the coincidence electronics to gate the multichannel analyzer to accept only non-coincident pulses. In 14 MeV neutron activation procedures the annihilation radiation resulting from the decay of 13N produced indirectly from the carbon in the plastic irradiation unit may be discriminated against by gating the analyzer to accept only non-coincident events. 

A. Krushevska, M. Kotrebai, A. Lasztity, R. M. Barnes, D. Amarasiriwardena, Application of tertiary amines for arsenic and selenium signal enhancement and polyatomic interference reduction in ICP-MS analysis of biological samples, Fresenius J. Anal. Chem., 355 (1996), 793D800. 

G. P. Jackson, F. I. King, D. C. Duckworth, Efficient polyatomic interference reduction in plasma source mass spectrometry via collision induced dissociation, J. Anal. Atom. Spectrom., 18 (2003), 1026-1032. 

The mercury-TMK complex is not formed in the presence of iodide. Many complexing agents (chloride, bromide, sulphate, acetate, citrate, tartrate, and EDTA) do not interfere. Some of these substances may be used to mask hydrolysable metals. Of the cations, only Pd(II), Pt(II), and Au(III) interfere. Reductants and oxidants should be absent. 

Introduction of a collision/reaction cell (CRC) into the ICP/MS is a recent technique for interference reduction (Koppenaal et al., 2004). Interfering ions are eliminated by their gas phase reaction in a gas-filled cell inserted between the... 

Most manufacturers of ICP/MS instruments now offer a model that incorporates a collision cell. Interference reduction by sample purification, use of a collision cell (also called chemical resolution), and mass separation—are said to be orthogonal, i.e., gains in each method are independent and multiplicative with gains in the others. The ultimate instrument in this regard—a collision cell equipped, high resolution, magnetic sector MS—has not yet been built, but would enable the nearest approach yet to detection without interference of any isotope at ultra-trace levels. 

Colored salts like copper, chromium, cobalt, and nickel will reduce the sensitivity of the test, and all heavy metals are expected to interfere. No elements are stated to give a false positive reaction, but a number of ions can interfere. Reductants, like tin(II), can reduce Fe to Fe and will (ultimately) give a false negative result. Ions capable of forming strong complexes with the ions of the test are another cause of interference. Fluoride, acetate, oxalate, and tartrate are examples. 

Metting van Rijn, A. C., Peper, A., and Grimbergen, C. A. (1990). High-quality recording of bioelectric events—Part 1 Interference reduction, theory and practice. Medical Biological Engineering Computing, 28(5), 389-97. 

Properties affected Attraction of (especially) lightweight plastics (films, fibres, etc.) to each other and to other materials improved operation of high-speed machinery (e.g. for packaging) shielding equipment against electromagnetic interference reduction/elimination of spark hazard in handling electronics, chemcials. medical equipment. 

Detection capability Precision/signal stability Accuracy Dynamic range Interference reduction Sample throughput Transient signal capability... 

As mentioned in Chapter 14, there are two major types of interferences that have to be compensated for spectral and matrix (space charge and physical). Although most instruments approach the principles of interference reduction in a similar way, the practical aspect of compensating for them will be different, depending on the differences in hardware components and instrument design. Let us look at interference reduction in greater detail and compare the different approaches used. 

KED process has allowed the analytes to be efficiently separated from their respective polyatomic interfering ions. The additional benefit of using helium is that it is inert and even if it is not being used in an interference reduction mode, it can have a beneficial effect on the other elements in a multielement run by increasing sensitivity via the process of collisional focusing. This makes the use of helium and KED very useful for both quantitative and semiquantitative multielement analysis using one set of tuning conditions. 

For more advanced, research-oriented applications, this technology offers other modes of interference reduction, including ... 

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