Inductively coupled plasma Information sources

Generally, extensive prior information is known about the sample in terms of the elemental composition and in these cases methods of analysis can be selected that will provide the desired result. However, if this information is not available or else a more general survey of ultratrace elements is required, then AES with an inductively coupled plasma source is the only atomic spectrometric technique that can provide these data at ultratrace levels. 

For these techniques, a dissolved sample is usually employed in the analysis to form a liquid spray which is delivered to an atomiser e.g. a flame or electrically generated plasma). Concerning optical spectrometry, techniques based on photon absorption, photon emission and fluorescence will be described (Section 1.2), while for mass spectrometry (MS) particular attention will be paid to the use of an inductively coupled plasma (TCP) as the atomisation/ionisation source (Section 1.3). The use of on-line coupled systems to the above liquid analysis techniques such as flow injection manifolds and chromatographic systems will be dealt with in Section 1.4 because they have become commonplace in most laboratories, opening up new opportunities for sample handling and pretreatment and also to obtain element-specific molecular information. 

A. Montaser, Inductively Coupled Plasma Mass Spectrometry , 1st edition, Wiley-VCH, Weinheim, 1998—source of information on ICP-MS spectrometry. 

Barba and his colleagues sampled the three outcrops of limestone to determine their distinctive signatures. This information was compared to lumps of calcium carbonate found in the finished plaster in the city. The group of scientists used several different techniques to examine the samples. The major element composition of the geological samples was determined by XRF. The major element composition of the lumps was determined by SEM-EDS. Trace element composition was determined by LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry) to measure the elemental composition of the plaster and the limestone. This methodology is well suited for analyses of very small lumps with microscopic spot sizes. The LA-ICP-MS method is able to analyze a large number of trace and rare earth elements with speed, precision, and high resolution, especially in cases where the major chemical composition does not appear to be particularly distinctive. The instrument worked extremely well for the characterization and determination of the provenance of the Ume plaster source material. 

Some of the problems In forensic analysis related to sample matrix and detection limits can be found In other analytical laboratories as well. Besides the enhancement and suppression effects on analyte signals described by Mr. Mldklff In the previous section. Dr. Watters and Ms. Wood of the National Bureau of Standards provide some specific Information regarding matrix effects on spectral background. Background level and spectral structure comprise the chief source of measured signal when blanks are being measured for detection limit estimation. Their example Is taken from Inductively coupled plasma (ICP) spectrometry. 

The spectrometry method also outperforms the diffraction technique both in precision and accuracy, perhaps by a factor of two to six. The diffraction technique is at best a rather insensitive, slow technique, giving somewhat poor quantitative accuracy. On the other hand, it will be realized that the information given by the X-ray diffraction method is unique, and no other technique is able to provide such data. This is not true of the X-ray fluorescence method, since there are many other techniques available to the analytical chemist today for the quantitation of elements. Atomic absorption, inductively coupled plasma emission, and solid-source mass spectrometry are all examples of competing methods. 

Plasma source mass spectrometry is a powerful analytical technique for trace element analysis with species selectivity when coupled with a suitable chromatographic sample introduction method. It combines the ability of the analytical plasma to atomize and ionize samples efficiently, with the sensitivity and selectivity of mass spectrometry. Following the commercial introduction of inductively coupled plasma mass spectrometry (ICP-MS) instrumentation in 1983, interest in plasma source MS increased rapidly. The enormous popularity of ICP-MS is not surprising considering the low levels of detection possible for a wide range of elements. In addition, multielement capability and the availability of isotope ratio information help make plasma source MS particularly... 

Plasma torches and thermal ionization sources break down the substances into atoms and ionized atoms. Both are used for measurement of accurate isotope ratios. In the breakdown process, all structural information is lost, other than an identification of elements present (e.g., as in inductively coupled mass spectrometry, ICP/MS). 

Electron ionization usually gives some molecular ions and sometimes these are abundant. Often it is difficult to be certain which ion, if any, is the molecular ion. For this rea.son, it is advantageous to obtain both El and Cl spectra, the first giving good structural information and the second good molecular mass information. g Plasma torches and thermal ionization sources break down the substances into atoms and ionized atoms. Both are used for measurement of accurate isotope ratios. In the breakdown process, all structural information is lost, other than an identification of elements present (e.g., as in inductively coupled mass spectrometry, ICP/MS),... 

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