Multielement reliability

ICP-OES is one of the most successful multielement analysis techniques for materials characterization. While precision and interference effects are generally best when solutions are analyzed, a number of techniques allow the direct analysis of solids. The strengths of ICP-OES include speed, relatively small interference effects, low detection limits, and applicability to a wide variety of materials. Improvements are expected in sample-introduction techniques, spectrometers that detect simultaneously the entire ultraviolet—visible spectrum with high resolution, and in the development of intelligent instruments to further improve analysis reliability. ICPMS vigorously competes with ICP-OES, particularly when low detection limits are required. 

A reliable authenticity assessment is concluded from the simultaneous consideration of multielement IRMS and enantioselective analysis. The differences of the stable isotope ratios of linalool and linalyl acetate are depicted as a three-dimensional plot of A values (d values of linalool minus d values of linalyl acetate for oxygen, hydrogen and carbon) (Fig. 17.15). This plot shows that the commercial samples S1-S5 are different from all the other samples investigated. Linalool and linalyl acetate of S1-S5 definitely are not genuine lavender oil compounds. 

An alternative to quantitative analysis by ICP-MS is semiquantitative analysis, which is generally considered as a rapid multielement survey tool with accuracies in the range 30-50%. Semiquantitative analysis is based on the use of a predefined response table for all the elements and a computer program that can interpret the mass spectrum and correct spectral Interferences. This approach has been successfully applied to different types of samples. The software developed to perform semiquantitative analysis has evolved in parallel with the instrumentation and, today, accuracy values better than 10% have been reported by several authors, even competing with typical ones obtained by quantitative analysis. The development of a semiquantitative procedure for multielemental analysis with ICP-MS requires the evaluation of the molar response curve in the ICP-MS system (variation of sensitivity as a function of the mass of the measured isotope) [17]. Additionally, in the development of a reliable semiquantitative method, some mathematical approaches should be employed in order to estimate the ionisation conditions in the plasma, its use to correct for ionisation degrees and the correction of mass-dependent matrix interferences. 

Traceability of examination results is necessary to ensure reliability and the spatio-temporal comparability which is increasingly needed in the health services. The required global multielement reference examination system hitherto has been provided in a piecemeal fashion, but with the newly established Joint Committee on Traceability in Laboratory Medicine (JCTLM), coordinating all stakeholders with CIPM/BIPM, IFCC, ILAC, and WHO in the lead, the sparse resources should be distributed in a prioritised and structured way. 

Extractive pre-concentration techniques have been used for some time in trace metal analysis of seawater. In particular, the ammonium pyrrolidinecarbodithioate-methyl isobutyl ketone (APCD-MIBK) system has found moderate use (1-7). Because of the potential for multielement analysis of a single extract and the apphcabihty of the technique for shipboard use, this method was evaluated for the analysis of Cu, Cd, Pb, Ni, and Zn at natural levels in coastal waters. The results presented for those five metals show that this method is a reliable and valuable analytical tool for trace metal analysis in seawater if the limitations of the method are realized and the proper precautions are taken. 

In each case a position-sensitive detector records the difffactograms over a range of 20 which typically extends from 10° to 60°. The scanning mode enables so-called QEXAFS (Q for quick) data to be recorded . Often, because of the small concentrations of active sites present in inorganic catalysts — in the Ti/Si02 ones discussed below, for example, Ti/Si ratios seldom exceed 1 50 — it is not possible to acquire reliable XAFS data in the transmission mode. It then becomes essential to use a sensitive, multielement fluorescence detector such as the 13-element germanium one that we and our collaborators at Daresbury have routinely used ". ... 

The analytical chemists must augment the possibilities of their methods with respect to robustness, reliability, detection limits, and multielement capabilities. Methods for the extraction of arsenic compounds from environmental samples without changing the species must be improved, too. Moreover, techniques that allow the direct determination of arsenic compounds (without prior extraction) should be developed to get a clearer picture of arsenic in our environment. 

These mercury-free electrodes, under particular conditions, provide reliable quantification of trace elements. However, multielement analysis is usually complicated by intermetallic interference, multiple ASV peaks, large backgrovmd contribution due to the relatively low cathodic potential limit (caused by reduction of hydrogen ions, or water). 

ICP-AES is a mature technique of analysis, and the number of papers reporting its use for biological analyses is large in comparison with ICP-MS. Recent years have seen a marked decrease in the expected reference intervals of many elements in body fluids [29] and led to the realization that many previous analyses were in error [30]. No analytical technique has been immune from error, but the enthusiasm for multielement analyses, in the absence of appropriate, certified multielement reference materials, has certainly caused ICP-AES its share of problems. It is fruitless to dwell on past mistakes. The intent here is to provide the reader with several leading references that can be consulted for sample preparation and reliable analysis by ICP-AES of biological fluids and tissues. These are listed in Table 1 [69-78]. 

NAA is a multielement method with a high detection limit of 10 —10 g also in small samples. A neutron source and a y-spectrometer are necessary. Radiation of Na, K, and P disturbs direct measurements of total arsenic. A time-consuming separation by digestion and extraction is necessary. As a reference method to prove the reliability of the own results it might be a good tool [71,75,156,157]. 

Note that in spite of the mathematical definitions cited, detection limits are rather nebulous quantities. Because they depend on many variables, a factor of 2—3 times uncertainty in the values can be anticipated. They can vary significantly between various manufacturers instrumentation and are especially sensitive to different modes of sample introduction. They can also be modified by the optimization for the determination of specific elements. When performing multielement analyses, a compromise of optimization must be tolerated. This compromise usually results in the achievement of optimal detection limits for only a few elements, with the remainder often being a factor of 2—3 times their optimized values. Also, because detection limits are so dependent on operating parameters, it is prudent to frequently (i.e., with each batch of samples analyzed) compute detection limits to reliably report ultra-trace concentration levels. Care must be taken to not report too many significant figures when stating detection limits, so as to be consistent with the probability level selected in the computation. Typical published detection limits for various types of instrumentation are tabulated in Table 10.1. 

Fingerprint analysis in forensic science has been used to source the provenance of metals and cannabis crops as well as parts of weapons, housebreaking tools and safes. In many crime cases there is often no need for full quantification, as semiquantitative results are sufficient for reliable comparison of the results with archived multielement data (or spectra) from other samples. 

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