Multielement method

Mass spectrometry is the only universal multielement method which allows the determination of all elements and their isotopes in both solids and liquids. Detection limits for virtually all elements are low. Mass spectrometry can be more easily applied than other spectroscopic techniques as an absolute method, because the analyte atoms produce the analytical signal themselves, and their amount is not deduced from emitted or absorbed radiation the spectra are simple compared to the line-rich spectra often found in optical emission spectrometry. The resolving power of conventional mass spectrometers is sufficient to separate all isotope signals, although expensive instruments and skill are required to eliminate interferences from molecules and polyatomic cluster ions. 

Atomic emission spectrometry (AES) is also called optical emission spectrometry (OES). It is the oldest atomic spectrometric multielement method which originally involved the use of flame, electric arc or spark excitation. Recently there has been considerable innovation in new sources plasma sources and discharges under reduced pressure. Littlejohn et al. (1991) have reviewed recent advances in the field of atomic emission spectrometry, including fundamental processes and instrumentation. 

By the late 1960 s a number of laboratories were using the method. Among others, Kneip etal. [1] reported AAS analyses of matter collected on filters from urban and rural air. Thompson et al. [2] reported the use of AAS in a study of sample preparation methods used in the continuing development of the multielement methods in use by the United States Environmental Protection Agency. 

Despite the availability of neutron activation, X-ray fluorescence and spectrographic multielement methods, atomic absorption continues to be very important. It has advantages of versatility and ease of calibration for laboratories with single element or variable analytical requirements. The high capital cost of the equipment makes the other methods competitive only for multielement, multisample programs. 

In both total and sequential dissolutions, the result is a solution containing the components of rocks and soils. This solution is then analyzed by different methods. Mostly, spectroscopic methods are used atomic absorption and emission spectroscopic methods, ultraviolet, atom fluorescence, and x-ray fluorescence spectrometry. Multielement methods (e.g., inductively coupled plasma optical emission spectroscopy) obviously have some advantages. Moreover, elec-troanalytical methods, ion-selective electrodes, and neutron activation analysis can also be applied. Spectroscopic methods can also be combined with mass spectrometry. 

Official Methods of Analysis of AOAC International, 17th edn. Rev 1, AOAC International, Gaithersburg, MD, USA, Official Method 986.15. Arsenic, Cadmium, Lead, Selenium, and Zinc in Human and Pet Foods - Multielement Method (2002)... 

Coherent forward scattering (CFS) atomic spectrometry is a multielement method. The instrumentation required is simple and consists of the same components as a Zeeman AAS system. As the spectra contain only some resonance lines, a spectrometer with just a low spectral resolution is required. The detection limits depend considerably on the primary source and on the atom reservoir used. When using a xenon lamp as the primary source, multielement determinations can be performed but the power of detection will be low as the spectral radiances are low as compared with those of a hollow cathode lamp. By using high-intensity laser sources the intensities of the signals and accordingly the power of detection can be considerably improved. Indeed, both Ip(k) and Iy(k) are proportional to Io(k). When furnaces are used as the atomizers typical detection limits in the case of a xenon arc are Cd 4, Pb 0.9, T11.5, Fe 2.5 and Zn 50 ng [309]. They are considerably higher than in furnace AAS. 

As all elements present in the radiation source emit their spectrum at the same time, from the principles of AES it is clear that it is a multielement method and is very suitable for the determination of many elements under the same working conditions. Apart from simultaneous determinations, so-called sequential analyses can also be carried out, provided the analytical signals are constant. Sequential and... 

Hence, it is important to have test methods that can determine metals, both at trace levels and at major concentrations. Thus test methods have evolved that are used for the determination of specific metals as well as the multielement methods of determination using techniques such as atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry, and X-ray fluorescence spectroscopy. 

Trace elements were determined on the 88 crude oils by neutron activation analysis using the multielement method of Shah, et and Filby and... 

Atomic emission spectroscopy with inductive coupled exitation (ICP-AES), although quite costly, is important for multielement determination with high sample rate. Neutron activation analysis (NAA) is a powerful detection method but costly in terms of both financial and work expenditures. X-ray fluorescence (XRF) methods are perfect multielement methods with high sampling rate. ICP-MS is also applied. 

Multielement flame emission spectroscopy is a relatively new development, although multielement methods have been used in arc-spark emission spectroscopy for some years. Several multielement methods are available, including scanning, direct reading techniques similar to those employed in arc-spark emission spectroscopy and the more recently developed vidicon detector tubes. Vidicon detectors are described in Chapter 3. 

Methods of quality control (QC) of convenience reagents vary according to type. Simple solutions are controlled by analysis and for standard solutions an accuracy of 0.1% is required wherever attainable. Multielement metal standards are prepared from high-purity starting materials that have been well analyzed, and are tested by a multielement method to ensure that no extraneous contamination has occurred. Prepared reagent mixtures for specific applications and test kits are subject to both QC analysis of the individual components and then, after preparation, have to meet performance criteria. 

Further methods are atomic fluorescence [32,33] or multielement methods like inductively coupled plasma (ICP), eventually in combination with mass spectrometry [32], X-ray fluorescence [32], and neutron activation [32]. However, all of these methods are unfit for clinical chemical laboratories. Spectrophotometric, chromatographic, and enzymatic methods have lost their significance, but in recent years electrochemical methods have gained importance [21,32], particularly stripping voltammetry [34]. 

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]. 

Despite the recognizable advantages of compound methods, work is increasingly being carried out on the (further) development of multielement methods with high powers of detection, especially for micro samples. Table 2 shows a survey of modem instrumental multianalyte methods. 

In contrast, transition metal analysis in wine is not a trivial matter. Metals such as aluminum, cobalt, iron, or nickel impact the taste of wine and lead to unwanted clouding [334], and health organizations impose strict thresholds for toxic elements such as lead, cadmium, copper, and zinc. Thus, there is a great demand for a fest, simple, and sensitive multielement method for determining transition metals in wine. In the wine matrix, some of the metals are complexed. Therefore, the organic matrk has to be eliminated. Widely distributed sample... 

Precursor ion scan, where Q2 is set to the target ion mass, while Ql scans over a user-defined mass range to select the precursor ions that enter the cell and react with the coUision/reaction gas. An example of this is the monitoring of the by-product " Nldj ion in the determination of Hg using NH3 as a reaction gas for a multielement method. In this example, NH3 is the optimum reaction gas for the majority of the other elements, but by measuring the NH4 ion, Hg can also be determined in the same suite. 

The real benefit of the universal collision/reaction cell approach is that it can be used in both the collision cell and the reaction cell modes. This means the operator has the flexibility of operating the system in three different modes all in the same multielement method—in the standard mode for elements where interferences are not present in collision mode for removal of minor interferences and in dynamic reaction mode for the most severe polyatomic spectral interferences. 

Efficiency of the DD method is related to the use of precise and highly sensitive multielement methods of elemental analysis, which are computerized because the number of elementary computing operations exceeds 10 for DD analysis of a substance comprising, e.g., 5 elements. About 20 years ago, a device that strongly enhanced the possibilities of DD method was devised at the Boreskov Institute of Catalysis SB RAS, Novosibirsk. This device, called stoichiograph, successfully operates until now. 

Many laboratories employ radiochemical separation techniques to isolate groups of elements from the sample after irradiation. The combination of simple group separations and high-resolution gamma-ray spectroscopy reduces substantially the analysis time and analytical costs, and makes the technique nearly a true multielement method. Additional effort is being expended to automate these group separations to further decrease analytical costs. 

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