Neutral loss purpose

FIA-MS-MS in parent or neutral loss mode on triple quad instruments can also be applied to screen mixtures of unknown compounds quite rapidly, so that compound classes can be recognised. Yet despite the information about molecular weight and the structural information by product ions, MS-data systems in their commercial form up to the mid-1990s provided no structural information for identification purposes in the form of libraries comparable with the NIST-library of El spectra in GC-MS analysis. It can be hoped that troubles arising out of the lack of computer-searchable library data for identification will be overcome with the gradual increase in trap applications in MS-MS mode. The situation in identification is set to change [36]. 

Constant Neutral Loss Scan (MS/MS) Determination of precursor/product ion combinations that exhibit a specific, characteristic loss of a portion of a molecular ion. Particularly useful when the characteristic species (loss) is neutral and cannot be detected directly by the mass spectrometer. Analysis of glutathione conjugates via neutral loss of 129 is an example. For the purposes of this book, NLS is used to describe these types of MS/MS experiments. 

In industrial production of acid-modified starches, a 40% slurry of normal com starch or waxy maize starch is acidified with hydrochloric or sulfuric acid at 25—55°C. Reaction time is controlled by measuring loss of viscosity and may vary from 6 to 24 hs. For product reproducibiUty, it is necessary to strictly control the type of starch, its concentration, the type of acid and its concentration, the temperature, and time of reaction. Viscosity is plotted versus time, and when the desired amount of thinning is attained the mixture is neutralized with soda ash or dilute sodium hydroxide. The acid-modified starch is then filtered and dried. If the starch is washed with a nonaqueous solvent (89), gelling time is reduced, but such drying is seldom used. Acid treatment may be used in conjunction with preparation of starch ethers (90), cationic starches, or cross-linked starches. Acid treatment of 34 different rice starches has been reported (91), as well as acidic hydrolysis of wheat and com starches followed by hydroxypropylation for the purpose of preparing thin-hoiling and nongelling adhesives (92). 

The other isolation methods evaluated employed solid adsorbents to isolate the model solutes (6-8). The first of these used XAD-4, a macroreticular, polystyrene-divinylbenzene resin (Rohm and Haas), into which trimethylamine groups had been introduced (9). The purpose of the resulting quaternary ammonium functional groups was to allow more efficient adsorption of acidic compounds without an appreciable loss of capacity for hydrophobic compounds. This feature is important because the vast majority of the organic matter in potable water is neutral or acidic in nature (JO). 

Crude Oil Conditioning—Crude oils with high levels of phosphatides and trace metals are usually treated with food-grade phosphoric acid for 4 to 8 hours before refining. The purpose of the acid pretreatment is to (1) help precipitate phosphatidic materials (2) precipitate natural calcium and magnesium as insoluble phosphate salts (3) inactivate trace metals, such as iron, copper, and others that may be present in the oil (4) reduce the neutral oil losses and (5) improve the color and flavor stability of the finished deodorized oil. 

It is often preferable for physiological purposes to use buffer systems other than the boric acid-borate mixtures. L. Michaelis has found that mixtures of veronal (diethylbarbituric acid) with its sodium salt show a satisfactory buffer action in the neighborhood of pH = 8.0. Pure commercial samples of the sodium salt of veronal are readily available, and may be used frequently without previous recrystallization. Buffer mixtures can be prepared by adding hydrochloric acid to the salt. This compound is water-free, and should suffer no loss in weight when dried at 100°. A 0.1 N solution in water requires exactly an equivalent quantity of 0.1 N hydrochloric acid when neutralized against methyl red. A stock solution should contain 10.30 g. of the sodium salt per 500 c.c. Only carbon dioxide free water should be used. 

The second addition of acetic acid serves the purpose of neutralizing the last traces of ammonia in the mother liquor and reduces losses of valuable silver in the mother liquor. 

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