Quantitative Mass Spectrometric Techniques

Two factors must be taken into account to obtain quantitative data. It is necessary to use a sufficient delay between rf pulses to ensure that all nuclei are fully relaxed before the next rf pulse is applied (relaxation agents may be added), and the effect of NOE must be eliminated. Consequently, C s-NMR is normally not readily quantifiable. Precision of phosphate assays by NMR is consistently within 0.2-0.6%, comparable to results obtained using chromatographic methods. 

NMR is occasionally used to quantify the relative ratios of the individual components in mixtures. The latter is only possible when the areas of the individual signals generated by individual components can be measured separately. Analysis can be conducted without sample preparation, without destroying the sample and, unlike many methods like chromatography, it does not require a prior standardisation step. Low-resolution FTNMR also permits quantitation, after standardisation. 

In order to overcome the limitations of extraction methods, Schilling et al. [199] used a direct, quantitative procedure that identifies type and quantity of each additive present in stabilised polyolefin samples. High-field (11.7 T), high-resolution NMR and selective signal suppression techniques can discriminate between additives with similar molecular structure and provide a quantitative measure of each compound. 

The best accuracy achievable in extensive studies of NMR of known mixtures is 1%. For analysis the accuracy is commonly poorer, about 1-5%. In case of extruded polymer samples some precaution should be taken to minimise the event of sample to sample variations in additive concentration. Solid NMR speetra of filled vulcanisates allow direct quantitative analysis of the polymeric components without prior sample work-up [200]. 

In many cases, NMR has proven to be the most generally useful method for the study of phosphorous-containing antioxidants. Quantitation is straightforward once the proper experimental conditions have been defined. Typically, at least 1 g of polymer/additive material may be needed to provide enough nuclei to be observed. 

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Applications Table 8.58 shows the main fields of application of inorganic mass spectrometry. Mass-spectrometric techniques find wide application in inorganic analysis, and are being used for the determination of elemental concentrations and of isotopic abundances for speciation and surface characterisation for imaging and depth profiling. Solid-state mass spectrometry is usable as a quantitative method only after calibration by standard samples. 

A recent modification of mass spectrometric technique involves the use of a spark source. A spark is struck by means of a high voltage between two rods of the material under examination. Under this drastic treatment many substances decompose completely into their elements and give positive ions. The ion detector is usually a photographic plate which shows a line mass spectrum. A number of exposures are taken for each sample and a quantitative estimate of the presence of an element in the sample can be made from the exposure time. 

The application of SIMS, SNMS, SSMS and GDMS in quantitative trace analysis for conducting bulk material is restricted to matrices where standard reference materials (SRMs) are available. For quantification purposes, the well characterized multi-element SRMs (e.g., from NIST) are useful. In Table 9.5 the results of the analysis by SNMS and the RSCs (relative sensitivity coefficients) for different elements in a low alloy steel standard (NBS 467) are compared with those of SSMS. Both solid-state mass spectrometric techniques with high vacuum ion sources allow the determination of light non-metals such as C, N, and P in steel, and the RSCs for the elements measured vary from 0.5 to 3 (except C). RSCs are applied as a correction factor in the analytical method used to obtain... 

Multi-element trace analysis is an important prerequisite for the quality assurance of foodstuffs with respect to the characterization of non-essential, toxic and essential (nutrient) elements as pollutions or as mineral elements relevant to health. Contamination with heavy metals such as Cd, Pb or Hg has become a serious problem with increasing environmental (artificial) contamination e.g., due to industrial pollution. The increasing use of inorganic mass spectrometric techniques (especially of ICP-MS) in the analysis of foodstuffs for multi-element analysis of trace elements or the detection of selected elements and species at a low concentration level has resulted from advances in very sensitive and quantitative measurements of metals, metalloids and several non-metals, including their speciation. 

Quantitative Analysis Using Mass Spectrometric Techniques... 

With this background this report will now review the chemical, infrared, ultraviolet, and mass spectrometric techniques as applied to the qualitative and quantitative measurements of organic azides. Additionally, a discussion of the o.r.d./c.d. properties of alkyl azides will be included in this chapter. 

Technique of Quantitative Mass Spectrometric Analysis Chemical... 

Quantitative Mass Spectrometric Analysis Chemical and Biological Applications, Integrated Ion-Current (IIC) Technique cf... 

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