Power detection

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. 

Conventional ICP-AES has similar detection limits to FA AS (although inferior to those of ICP-MS) and is much faster when many elements are determined in the same sample. The detection limits of modem, fast ICP-AES are equal to those of conventional, slow GFAAS. Table 8.31 compares the detection power of various atomic emission spectrometries. The greater... 

Higher detection power (substantial dilution in solubilisation procedures)... 

Hybrid systems which have been used to determine metals in solids include ETV-ICP, spark-MIP, spark-flame, arc-flame, laser-flame, laser-ETA and laser-DCP. ETV-ICP-MS is a solid sampling process which is automated, multi-element with high detection power, and amongst the best currently achieved. 

Although following similar nuclear reaction schemes, nuclear analytical methods (NAMs) comprise bulk analysing capability (neutron and photon activation analysis, NAA and PAA, respectively), as well as detection power in near-surface regions of solids (ion-beam analysis, IB A). NAMs aiming at the determination of elements are based on the interaction of nuclear particles with atomic nuclei. They are nuclide specific in most cases. As the electronic shell of the atom does not participate in the principal physical process, the chemical bonding status of the element is of no relevance. The general scheme of a nuclear interaction is ... 

It has been shown (Danzer and Wagner [1993] Danzer and Venth [1994] Venth et al. [1996]) that the reliability of quantitative analyses can be increased when several signals are used for calibration and evaluation. From theoretical considerations it is expected that a multivariate evaluation increases both the sensitivity and the precision and, therefore, the detection power, too. 

The term detection capability (detection power) represents a generic term of the performance of analytical methods at the lower limit of applicability. Mostly it is used descriptively (detection capability of a method is high , good or sufficient ) or for giving order of magnitudes (detection capability is in the ppm-range or ppb-range ). 

This analytical method, based on TXRF, enables a large number of trace elements to be determined simultaneously. The range is suitable for different areas of the sea. The motivation to use TXRF resulted mainly from the characteristic features of the method its high detection power, its universal calibration curve, which eliminates the need for matrix-dependent standard samples or standard-addition procedures, the simple preparation of the sample films, and of course the possibility of multielement determination. 

The results of uranium isotope ratio measurements by MC-TIMS (TRITON Thermo Fisher Scientific) on a single uranium oxide reference particle (10 pan) are illustrated in Figure 8.5.9,144 The high precision of multiple ion counters and high detection power in the MC-TIMS are... 

SNMS 1 0-1 00 0.3-3 ion implanted standards +/+ surface analysis poor detection power... 

Detection limits (DLs) are the most common figure used to compare analytical techniques (or methods) from the detection power point of view. DLs depend on the analyte and, for some techniques, also on the matrix. Further, DLs depend on the quality of the instrumentation (which is being continuously improved). Therefore, here just some approximate ranges will be given. DLs obtained by AAS are of the order of mg 1 (ppm). These figures are much improved by using ETAAS in this case, typical DLs are usually lower than 1 pgC (ppb). ICP-OES can be considered half way as it offers DLs usually... 

For analysis of solutions, ICP-mass spectrometry (ICP-MS) is very promising (Houk et al., 1980 Houk, 1986 Bacon et al., 1990). Recent advances in separation and preconcentration techniques are discussed by Horvath et al. (1991). Bacon et al. (1990) report that although ICP-MS is a multi-element technique, recent papers tend to concentrate on a small number of target elements. With isotope dilution mass spectrometry (IDMS), detection limits are further reduced (Heumann, 1988) IDMS is also suitable for accurate speciation in very low concentration levels of elements (Heumann, 1990). For the direct analysis of solid samples, glow discharge mass spectrometry (GD-MS) (Harrison etal., 1986) is of interest. Tolg (1988) has suggested that a substantial improvement in the absolute detection power of GD-MS, as applied to micro analysis, can be expected, at least in comparison with the ICP as ion source. 

Hydride generation may result in a detection limit for arsenic of around 0.8 ng ml-1 by AAS under optimized conditions.2 Over recent years, this impressive detection power has resulted in the development of automated, flow-injection-based hydride generation systems for the determination of arsenic in plants3 and soil... 

A problem with AAS is that the detection power differs greatly among elements. The LoD for Cd, for example, is approximately 20 times better than for... 

If the procedures described above are adhered to, analytical problems can normally be circumvented. As the levels of most trace elements in muscle tissue and milk are very low, it may well happen that they are often at or below the LoDs of the technique resorted to, which for ET-AAS is usually reported to be in the order of 5-25 p,g kg-1, or even lower. Cadmium is usually present at levels below 5 p,gkg 1 (with the exception of horse meat), often below 1 p,gkg 1. Since the detection power for Cd is much better than for Pb, the LoD is typically in the order of <1-5 p,g kg-1. For control purposes this is entirely sufficient. For intake calculations however, results below the LoDs are impossible to quantify. For this purpose, better LoDs are needed. Since this may be very difficult to achieve,... 

The level of As is very low in most foods. The exception is seafood, for example, plaice, which often has an As concentration of >10 mg kg-1. As mentioned above, FAAS is not the first choice for this kind of determination. Dry ashing in combination with HG-AAS is well suited for this purpose and has sufficient detection power for the analysis of concentrations well below 0.05 mg kg-1, levels that can be found in pork and beef. ET-AAS after MW digestion is also suitable for seafood, but lacks the detection power necessary for the analysis of other foodstuffs. Contaminated chemicals can be a problem, and it is advisable to have new batches checked before use. 

As already discussed above, Q-ICP-MS may still require matrix removal and preconcentration because the Q mass analyzer is unable to resolve most of the spectral interferences affecting the analytical masses of PGEs. Moreover, the detection power might be inadequate for the performance of reliable measurements in some samples. PGEs determination is hampered by mass interferences and requires high analytical selectivity and sensitivity. Double-focussing SF-ICP-MS with mass resolution capabilities higher than those afforded by Q instruments (currently up to 10,000) can properly deal with most mass interferences that have... 

Conventional FAAS is chracterized by poor detection power. Serious interferences from hydride-forming elements such as As, Sb, and Se are well known. Hydride generation techniques may circumvent these problems, providing an excellent tool to determine those elements at trace and ultratrace levels this is particularly useful for the determination of Se in milk samples [54-56]. Other... 

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