Instrumental techniques comparison

There may be circumstances in which an electroanalytical method, as a consequence of the additional chemicals required, has disadvantages in comparison with instrumental techniques of analysis however, the above-mentioned advantages often make electroanalysis the preferred approach for chemical control in industrial and environmental studies. Hence, in order to achieve a full understanding of what electroanalysis can do in these fields first, it will be treated more systematically in Part A second, some attention will be paid in Part B to electroanalysis in non-aqueous media in view of its growing importance and finally, the subject will be rounded off in Part C by some insight into and some examples of applications to automated chemical control. 

Fig. 2.9. Comparison of analytical multi-stage techniques (left) and direct instrumental techniques (right)...

Over sixty years have passed since the beginning of the development of the mass spectrometer as a modern analytical instrument. In comparison, FTMS is a relatively new technique, first introduced by Comisarow and Marshall in 197 1 (8). Perhaps it is an indication of the technique s high potential that FTMS has developed so rapidly. However, it should not be surprising, by analogy with the long development of sector instruments, that its full potential has not yet been realized. 

Only in one test (the fourth round-robin) were the identified chemicals quantified (4), and then only to facilitate the evaluation of sample preparation methods. The quantitative results varied widely. Weaknesses were revealed in the procedures because all the chemicals were polar and adsorptive. Comparison of the quantitative results as a means of deciding upon the best sample preparation procedures proved to be an unreasonable approach, however, as the total variance in the results was clearly the product of several factors the sample preparation procedure, the quantitative method, and the instrumental technique. Nevertheless, the exercise proved to have considerable educational value. The test revealed weaknesses in the existing ROPs (6) and the methods were subsequently improved to cover the gaps (7). 

Having identified the materials as potentially containing opiates, the next phase in the analysis is to confirm the identity of which opiates are present and, where necessary, to carry ont a comparison of samples. In order to identify which drugs are contained in a sample, without employing expensive instrumental techniques, thin layer chromatography can often be used. 

CRM for road dust (BCR-723) containing 81.3 2.5 Jg/kg Pt, 6.1 1.9 ig/ kg Pd, and 12.8 1.3 Jg/kg Rh, was introduced [49, 228]. It is widely used for quality control of results obtained in the analysis of environmental materials (e.g., airborne particulate matters, dusts, soils, and sediments). Comparison of results obtained using different analytical procedures and interlaboratory studies are recommended when there is a lack of suitable CRM (e.g., in examination of clinical samples). The use of standards based on real matrices (e.g., saliva, plasma, ultrafiltrates, and lung fluids) instead of synthetic solutions is recommended in such analyses. Difficulties with the identification and quantification of different metal species in examined samples make the reliability of results of great importance. The use of various instrumental techniques for examination of particular samples can be helpful. The application of chromatography, mass spectrometry, and electrochemistry [199] HPLC ICP MS and HPLC MS/MS [156] ESI MS and MALDI [162] micellar electrokinetic chromatography, NMR, and MS [167] AAS, ESI MS, and CD spectroscopy [179] SEC IC ICP MS and EC ESI MS [180] and NMR and HPLC [229] are examples of such approaches. 

The nose is an extremely sensitive detector of odors it can be matched only by the most sensitive instrumental techniques. Many smells are identified by comparison with pure compounds diluted by odor-free air until they are near the odor threshold limit. However, with the introduction of flame photometric detectors it has been possible to measure the concentration of the sulfur compounds giving rise to odors in the ppb range with the aid of preconcentration (by a fector of 10 to 10. ... 

McAlister, J.J., Svehla, G. Whalley, W.B. (1988) A comparison of various pre-treatment and instrumental techniques for the mineral characterisation of chemically weathered basalt. Microchemical Journal 38, 211-231. 

The position of ICP-AES among other instrumental techniques for trace analysis is well established. Although instrumentation is still developing it is more in respect to reduce laborious introductions of dilferent types of corrections than increase the quality of analysis. As an interesting example in this respect a comparison of ICP-AES analysis of soil and sediment standard reference materials done in 1985 (Liese, 1985a) and 1998 (Leivuori, 1998) may be done. In 1985 the content of 21 elements in IAEA soil, five and 19 elements in IAEA SL-1 has been determined after introduction of two type of corrections. The accuracy was 0.1-18% and precision below 10%. In 1998 in a sediment standard reference material (NIST-SRM-2704 - Buffalo River Sediment) ten elements were determined (for the rest of the elements in this study ETAAS is preferred) with accuracy of 0.1-16% and precision below 10%. The same result is obtained if a comparison of analysis of plant standard reference materials is done (Liese, 1985a Kos et al., 1996 Djingova et al., 1998). 

Chemical analysis of hazardous substances in air, water, soil, sediment, or solid waste can best be performed by instrumental techniques involving gas chromatography (GC), high-performance liquid chromatography (HPLC), GC/mass spectrometry (MS), Fourier transform infrared spectroscopy (FTIR), and atomic absorption spectrophotometry (AA) (for the metals). GC techniques using a flame ionization detector (FID) or electron-capture detector (BCD) are widely used. Other detectors can be used for specific analyses. However, for unknown substances, identification by GC is extremely difficult. The number of pollutants listed by the U.S. Environmental Protection Agency (EPA) are only in the hundreds — in comparison with the thousands of harmful... 

This exercise affords students the opportunity to use several instrumental techniques to which they have previously been introduced in the laboratory in order to conduct a comparison of soil types with respect to determining the ratio of Cr(III) to Cr(VI). The exercise includes pH measurement, calibration of an UV vis spectrophotometer, calibration of an atomic absorption spectrophotometer in the flame mode (FIAA), and sample preparation techniques. 

For higher precision, the scale is magnified with an optical microscope. Accuracies of 0.2 pm are possible in this way. Precision techniques for subdivision of scales and special instruments for comparisons have been developed. The highest precision can be reached by observing differences in interference fringes, set up by monochromatic light between the ends of the objects to be compared. For the maintenance of the standard meter a precision of 1 in 10 is possible as mentioned in Appendix 8. 

Photon activation analysis, as well as other instrumental techniques, is generally quantified by comparison of activities in the sample with those in a reference material of known elemental composition that was irradiated simultaneously. In photon activation analysis this is necessary particularly because some accelerator parameters and nuclear data for the photoreactions involved are either unknown or not precisely determinable. In addition, some machine parameters of the accelerator cannot be assumed constant throughout the exposure period and might show uncontrolled variation. The use of... 

There are a number of mathematical techniques commonly used with data obtained from instrumental techniques. These enable the verification of the instrumental analysis with respect to reliability and reproducibility of response, comparison of retention time data, and the determination of the concentration of active component (to greater or lesser degrees of accuracy and with slight variation depending on the type of analytical technique used). 

Table 3 Comparison of some attributes of instrumental techniques commonly employed for soil analysis ...

A comparison with a hard-model evaluation based on nonlinear regression techniques shows excellent agreement. The proposed ANN method is of a general nature and, in principal, can be adopted to any instrumental technique used in equilibria studies including extraction. 

PTR-MS and SIFT-MS have a clear advantage over most other techniques for direct analysis of gas mixtures as no derivatization, adsorption onto traps followed by desorption steps, or other sample pretreatment steps are required before the sample is admitted to the analytical instrument. A comparison between the two techruques relevant to breath-sampling has been presented recently [220]. Both technologies allow irmnediate quantification of an analyte in a gas rruxture in real time whether it be a breath sample or an envirormrental sample. As discussed in Sect. 8.4 (PTR-MS) and 8.5 (SIFT-MS), there are three main differences between these two techruques ... 

Why are comparisons of particle sizes between different instrumental techniques only qualitative ... 

Steroids have been extensively investigated using instrumental techniques such as overpressured layer chromatography (2,4,17,34,55), parallel development TLC (56), programmed multiple development [57], and automated multiple development/AMD (58). Each technique has been reported to furnish a significant improvement in separation selectivity in comparison with development in conventional TLC chamber systems. 

The two instrumental techniques are compared in Table 24.1 on the basis of their calibration statistics and the standard error of performance (SEP) with a confirmation set. NIR would appear to have an edge over FT/IR on all counts correlation is better, equations are more robust (higher F values), and there are lower errors. If one adds to this comparison two time factors, NIR emerges as a clear winner, as is shown in Table 24.1. 

Among the various methods used for studying thermal and thermo-oxidative degradation of PES, thermogravimetric analysis (TGA) and pyrolysis gas chromatography-mass spectroscopy (PGC-MS) have been used most frequently. These instruments enable comparisons of the relative thermal stability and thermal decomposition temperature, and give information about the degradation mechanism [9,24]. TGA also is an excellent technique for product characterization and quality control. 

With X-ray fluorescence stoichiometry can be determined to 0.01-0.1 % when suitable standards are available. Precise lattice parameters and pycnometric density determinations have been used to determine deviations from stoichiometry or nonstoichiometry in Bertholide-type compounds. Other instrumental techniques such as nuclear magnetic resonance and comparison of ferroelectric Curie temperatures have also found applications. ... 

Unsaturation may also be determined by spectroscopic techniques like IR, NIR, and NMR. NIR in particular may be more convenient if other parameters are determined simultaneously. Instrumental techniques are tailored to specific products and are usually verified by comparison to the wet chemical methods. 

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