Direct sample introduction mass spectrometry materials

DIRECT SAMPLE INTRODUCTION MASS SPECTROMETRY (DSIMS) ANALYSIS OF SURROGATES IN CONTACT WITH PERMEABLE MATERIALS... 

Also, direct determination of additives by means of laser desorption in solid polymeric materials rather than in polymer extracts has been reported [266], Takayama et al. [267] have described the direct detection of additives on the surface of LLDPE/(Chimassorb 944 LD and Irgafos P-EPQ) after matrix (THAP)-coating. As shown in Scheme 7.13, direct inlet mass spectrometry is also applicable to transfer TLC-MS and TLC-MS/MS analyses without the need for prior analysis. For direct sample introduction a small amount of the selected... 

The main advantages of the ms/ms systems are related to the sensitivity and selectivity they provide. Two mass analyzers in tandem significantly enhance selectivity. Thus samples in very complex matrices can be characterized quickly with Htde or no sample clean-up. Direct introduction of samples such as coca leaves or urine into an ms or even a gc/lc/ms system requires a clean-up step that is not needed in tandem mass spectrometry (28,29). Adding the sensitivity of the electron multiplier to this type of selectivity makes ms/ms a powerhil analytical tool, indeed. It should be noted that introduction of very complex materials increases the frequency of ion source cleaning compared to single-stage instmments where sample clean-up is done first. 

Smith and Udseth [154] first described SFE-MS in 1983. Direct fluid injection (DFT) mass spectrometry (DFT-MS, DFI-MS/MS) utilises supercritical fluids for solvation and transfer of materials to a mass-spectrometer chemical ionisation (Cl) source. Extraction with scC02 is compatible with a variety of Cl reagents, which allow a sensitive and selective means for ionising the solute classes of interest. If the interfering effects of the sample matrix cannot be overcome by selective ionisation, techniques based on tandem mass spectrometry can be used [7]. In these cases, a cheaper and more attractive alternative is often to perform some form of chromatography between extraction and detection. In SFE-MS, on-line fractionation using pressure can be used to control SCF solubility to a limited extent. The main features of on-line SFE-MS are summarised in Table 7.20. It appears that the direct introduction into a mass spectrometer of analytes dissolved in supercritical fluids without on-line chromatography has not actively been pursued. 

Different analytical procedures have been developed for direct atomic spectrometry of solids applicable to inorganic and organic materials in the form of powders, granulate, fibres, foils or sheets. For sample introduction without prior dissolution, a sample can also be suspended in a suitable solvent. Slurry techniques have not been used in relation to polymer/additive analysis. The required amount of sample taken for analysis typically ranges from 0.1 to 10 mg for analyte concentrations in the ppm and ppb range. In direct solid sampling method development, the mass of sample to be used is determined by the sensitivity of the available analytical lines. Physical methods are direct and relative instrumental methods, subjected to matrix-dependent physical and nonspectral interferences. Standard reference samples may be used to compensate for systematic errors. The minimum difficulties cause INAA, SNMS, XRF (for thin samples), TXRF and PIXE. 

The introduction of inductively coupled plasma (ICP) in inorganic mass spectrometry means that there is an effective ion source operating at atmospheric pressure. Whereas solid mass spectrometric techniques allow direct analysis of solid samples in ICP-MS, the determination of trace impurities or isotope ratios in solid samples is often carried out after digestion and dissolution of the material. For the determination of trace impurities and isotope ratios in liquids, an additional nebulization... 

This section provides a simplified introduction to the methods by which calibration solutions containing analytical (or reference) standards, with or without internal standards, are used in practice to measure amounts of analytes in unknown samples. The main deficiency of this brief account is its lack of any attempt to take into account experimental uncertainties (both random and systematic) and thus the level of confidence in the results thus obtained. While this book is directed towards analyses in which mass spectrometry is used as the chromatographic detection technique, most of the following discussion is applicable also to other detectors the main exception concerns use of isotope-labeled surrogate internal standards, for which only mass spectrometry can provide adequate detection. A much more complete account of this material, including a discussion of the associated random and systematic errors, is given in Section 8.5. 

Samples analyzed by El mass spectrometry must be converted to gas phase. For pure gases or volatile liquids the samples may be introduced directly through a small orifice that allows an appropriate amount of material into the vacuum chamber. A small amount of a solid sample can be placed in a melting point capillary tube and inserted into the mass spectrometer at the end of a metal rod, called a direct insertion probe (DIP).The temperature at the tip of the probe can be varied to promote sublimation of the sample. Another common method of sample introduction is gas chromatography, which is the ideal choice for samples that are impure. 

Rabek [51] and others [52] have described laser-induced decomposition of polymers. Comprehensive reviews have appeared on the interaction of laser radiation with solid materials and its significance in analytical chemistry [53,53a]. Various reviews cover the subjects of optical and mass spectrometry performed directly on the laser plume [54,55]. Moenke-Blankenburg [38] has described laser ablation for sample introduction. Advances in laser ablation of materials were recently reported [56,57]. 

Numerous ambient direct ionization methods have been introduced for use with mass spectrometry over the last several years.< - °) A major advantage of these methods is speed of analysis, which is achieved not only by the fast insertion and ionization of the sample, but by the elimination of most sample preparation and chromatographic separations. However, this presents a problem in materials analysis and for mixtures in general because of the complexity of the mass spectra that result from direct analysis of complex mixtures. The atmospheric solids analysis probe (ASAP)< > mass spectrometry (MS) method offers some separation related to volatility by control of the heated gas used to effect vaporization, but this is not sufficient for many mixtures. Ion mobility spectrometry (IMS) offers rapid gas-phase separation of ions based on differences in charge state and collision cross section (CCS) (size/shape). Here we explore the utility of a commercial IMS/MS instrument with ASAP sample introduction for analysis of complex mixtures. 

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