Direct introduction

Mass spectrometry allows analysis by hydrocarbon family for a variety of petroleum cuts as deep as vacuum distillates since we have seen that the molecules must be vaporized. The study of vacuum residues can be conducted by a method of direct introduction which we will address only briefly because the quantitative aspects are ek r metiy difficult to master. Table 3.6 gives some examples the matrices used differ according to the distillation cut and the chemical content such as the presence or absence of olefins or sulfur. 

The direct introduction of a halogen atom (usually bromine) by means of V-haloamine (generally iV-bromosuccinimide) in the allyl position is known as the Wohl-Ziegler reaction ... 

For mixture.s the picture is different. Unless the mixture is to be examined by MS/MS methods, usually it will be necessary to separate it into its individual components. This separation is most often done by gas or liquid chromatography. In the latter, small quantities of emerging mixture components dissolved in elution solvent would be laborious to deal with if each component had to be first isolated by evaporation of solvent before its introduction into the mass spectrometer. In such circumstances, the direct introduction, removal of solvent, and ionization provided by electrospray is a boon and puts LC/MS on a level with GC/MS for mixture analysis. Further, GC is normally concerned with volatile, relatively low-molecular-weight compounds and is of little or no use for the many polar, water soluble, high-molecular-mass substances such as the peptides, proteins, carbohydrates, nucleotides, and similar substances found in biological systems. LC/MS with an electrospray interface is frequently used in biochemical research and medical analysis. 

Direct-inlet probe. A shaft or tube having a sample holder at one end that is inserted into the vacuum system of a mass spectrometer through a vacuum lock to place the sample near to, at the entrance of, or within the ion source. The sample is vaporized by heat from the ion source, by heat applied from an external source, or by exposure to ion or atom bombardment. Direct-inlet probe, direct-introduction probe, and direct-insertion probe are synonymous terms. The use of DIP as an abbreviation for these terms is not recommended. 

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. 

Alkylation a.ndAryla.tion, The direct introduction of carbon—carbon bonds in quinoline rings takes place in low yield and with Htde selectivity. The most promising report involves carboxyHc acids with ammonium persulfate and silver nitrate (31). 

Environmental problems associated with PCBs are the result of a number of factors. Several open uses of PCBs have resulted in thein direct introduction into the environment, eg, organic diluents careless PCB disposal practices have resulted in significant releases into aquatic and marine ecosystems higher chlorinated PCBs are very stable in thein persistence in different environmental matrices and by a variety of processes (Fig. 1) PCBs are transported throughout the global ecosystem and preferentiaHy bioconcentrate in higher trophic levels of the food chain. 

There are several minor routes to pyrimidinethiones from thiocyanato- or amino-pyrimidines or by direct introduction of sulfur, but they are preparatively unimportant. 

The direct introduction of an alkythio substituent into the 5-position of uracils and analogous pyrimidines is possible. The reagent, which is usually made quite easily in situ,... 

The above examples illustrate reactions at an electron-deficient carbon atom. Other 1,1-bielectrophiles allow the direct introduction of a heteroatom into the resultant heterocycle. The most widely applicable and versatile methods for the synthesis of 1,2,5-thiadiazoles and 1,2,5-selenadiazole rely on this approach. 

As atomic fluorescence spectrometer a mercury analyzer Mercur , (Analytik-Jena, Germany) was used. In the amalgamation mode an increase of sensitivity by a factor of approximately 7-8 is obtained compared with direct introduction, resulting in a detection limit of 0,09 ng/1. This detection limit has been improved further by pre-concentration of larger volumes of samples and optimization of instrumental parameters. Detection limit 0,02 ng/1 was achieved, RSD = 1-6 %. 

See 5-4.5.1. Manual operations are particularly hazardous in terms of both frequency and consequence. If possible, direct introduction of powder to a... 

Direct Introduction - This involves locating, in the event tree, support systems (e.g., electric power) before the systems they affect. The event tree is constructed so that systems requiring the support systems are bypassed as failed. This is the technique in WASH-1400. 

Direct Introduction - This method, similar to the preceding, introduces the dependency in the. fault tree higher than the affected subsystems to bypass the "AND" operation of the redundancy. This is also the technique in WASH-1400. An example of this technique is found in the fault tree shown in Figure 3.4.4-9. 

DIRECT INTRODUCTION OE WATER VIA A VAPORIZER CHAMBER/PRECOLUMN SOLVENT SPLIT/GAS DISCHARGE INTEREACE... 

The most convenient method for the preparation of sodium acetylide appears to be by reaction of acetylene with sodium methylsulfinyl carbanion (dimsylsodium). The anion is readily generated by treatment of DMSO with sodium hydride, and the direct introduction of acetylene leads to the reagent. As above, the acetylide may then be employed in the ethynylation reaction. 

Carbonyl derivatives can be made similarly, either by abstracting CO from the solvent, by direct introduction or by oxidative addition to a Vaska-type complex ... 

The following nitrating agents are most frequently used in industry for the direct introduction of the nitro group ... 

Some time ago Tedder (1957) recommended a process which he called direct introduction of the diazonium group , because it replaces the steps of nitration, reduction, and diazotization of an aromatic compound by a one-pot operation with three equivalents of a nitrosating reagent in acidic solution. The first step (Scheme 2-35) is a C-nitrosation and the following steps (Scheme 2-36) are the reduction of the nitroso-arene. 

The reaction of molecular nitrogen with aryl cations, i. e., the reverse reaction of (heterolytic) dediazoniations of arenediazonium ions, is a direct introduction of the... 

Because synthesis of l-(2-deoxy-2-fluoro-)S-D-arabinofuranosyl)cytosine (744, FAC), an elementary arabino type of nucleoside having a growth-inhibitory effect against L 1210 leukemia in mice, through direct introduction of a fluorine atom in the 2 - up (arabino) position was difficult, compound 744 was prepared by condensation of trimethylsilylated A -acetylcytosine with 3-0-acetyl-5-(7-benzoyl-2-deoxy-2-fluoro-D-arabin-ofuranosyl bromide (742), which had been prepared by periodate oxidation of 6-0-benzoyl-3-deoxy-3-fluoro-D-glucofuranose (741). Similar condensa-... 

Kharasch, M.S. and Isbell, H.S. (1931) The chemistry of organic gold compounds. III. Direct introduction of gold into the aromatic nucleus (Preliminary communication). Journal of the American Chemical Society, 53(2), 3053-3059. 

Section 6.4 deals with other EI-MS analyses of samples, i.e. analyses using direct introduction methods (reservoir or reference inlet system and direct insertion probe). Applications of hyphenated electron impact mass-spectrometric techniques for poly-mer/additive analysis are described elsewhere GC-MS (Section 7.3.1.2), LC-PB-MS (Section 7.3.3.2), SFC-MS (Section 13.2.2) and TLC-MS (Section 7.3.5.4). 

The particle-beam, interface has been used for direct introduction of extracts into the mass spectrometer without chromatographic separation [55]. In fact, chromatographic separation is not always essential, especially if structural information is available about the analytes of interest. The main features of this particular approach are ... 

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. 

Direct liquid injection (DLI) has been used even less. Hirter et al. [579] have reported the early analysis of a synthetic antioxidant mixture (Irganox 1010/1076/1098) by means of iRPLC-DLI-QMS with Cl. In early studies, the HPLC effluent was vaporised by laser radiation [593] both El and solvent-mediated Cl spectra were obtained in the on-line mode from analytically difficult molecules. However, the instrumentation was complex the sensitivity was not as good as that obtained by GC-MS and thermal decomposition was observed with other compounds. This direct introduction approach with enrichment was used for the analysis of phthalates. 

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