Volatile buffer

FAB ionization has been used in combination with LC/MS in a technique called continuous-flow FAB LC/MS (Schmitz et al., 1992 van Breemen et al., 1993). Although any standard HPLC solvent can be used, including methyl-ferf-butyl ether and methanol, the mobile phase should not contain nonvolatile additives such as phosphate or Tris buffers. Volatile buffers such as ammonium acetate are compatible at low concentrations (i.e., <10 mM). Continuous-flow FAB has also been used in combination with MS/MS (van Breemen et al., 1993). The main limitationsof continuous-flow FAB compared to other LC/MS techniques for carotenoids, such as ESI and APCI, are the low flow rates and the high maintenance requirements. During use, the 3-nitrobenzyl alcohol matrix polymerizes on the continuous-flow probe tip causing loss of sample signal. As a result, the continuous-flow probe must be removed and cleaned approximately every 3 hr. 

FAB ionization has been used in combination with LC/MS in a technique called continuous-flow FAB LC/MS (van Breemen et al., 1991b). Although any standard HPLC solvents may be used, including ethyl acetate, methanol, and water, the mobile phase should not contain nonvolatile additives such as phosphate or Tris buffers. Volatile buffers such as ammonium acetate are compatible. The low flow rate of... 

The combination of XRF with electrophoresis can constitute a quasi-on-line coupling technique. Great efforts have been made to develop on-line analysis techniques with XRF. Mann et reported a technique of on-line SRXRF detection of metal ions, such as Fe, Co, Cu, and Zn, in their high binding-constant complexes for capillary electrophoresis (CE) separation. An X-ray transparent polymer coupling is used to create a window for the on-line X-ray detection. In contrast to ICP-MS, this detection technique is not limited by sample or the buffer volatility or atomization efficiency. Simultaneous XRF and UV absorbance detection can be used to provide on-line determination of metal/chelate ratios. A bench-top energy-dispersive micro X-ray fluorescence system was also combined with the CE apparatus constructed by a thin-walled fused-silica capillary for elemental analysis of the species containing Fe, Co, and Cu, for example. This coupled technique used for metalloprotein speciation analysis can avoid the compromise between optimal separation and sensitive detection, which must be taken into account in the HPLC-ICP-MS procedure. In addition, this detection scheme is non-destructive, so the separated material can be recovered for additional characterization. 

Nltropropane. As much as 9100 t of 2-nitropropane once were consumed for use in coatings annually. Concern about toxicity and a general movement to low volatile organic compound (VOC) coatings have resulted in almost the complete disappearance of this use for 2-nitropropane. However, derivatives such as 2-meth5l-2-nitro-l-propanol (used in tire cord adhesive) and 2-amino-2-methyl-l-propanol (a pigment dispersant and buffer), have served as an outlet for 2-nitropropane production. 

Textiles. Citric acid acts as a buffer in the manufacture of glyoxal resins which are used to give textiles a high quaUty durable-press finish (see Amino resins). It has been reported to increase the soil-release property of cotton with wrinkle-resistant finishes and is used as a buffer, a chelating agent, and a non-volatile acid to adjust pH in disperse dying operations (182—193). 

The impurities present in aromatic nitro compounds depend on the aromatic portion of the molecule. Thus, benzene, phenols or anilines are probable impurities in nitrobenzene, nitrophenols and nitroanilines, respectively. Purification should be carried out accordingly. Isomeric compounds are likely to remain as impurities after the preliminary purifications to remove basic and acidic contaminants. For example, o-nitrophenol may be found in samples ofp-nitrophenol. Usually, the ri-nitro compounds are more steam volatile than the p-nitro isomers, and can be separated in this way. Polynitro impurities in mononitro compounds can be readily removed because of their relatively lower solubilities in solvents. With acidic or basic nitro compounds which cannot be separated in the above manner, advantage may be taken of their differences in pK values (see Chapter 1). The compounds can thus be purified by preliminary extractions with several sets of aqueous buffers... 

An amount of enzyme preparation equivalent to 900 mg of wet cells was made up to 25 ml with the above potassium phosphate buffer solution. 150 mg (1.15 mmol) of 5-fluorouracil and 1.0 gram of thymidine (4.12 mmol) were dissolved in 15 ml of the above potassium phosphate buffer solution. The mixture was incubated at 37°C for 18 hours. After this time, enzyme action was stopped by the addition of four volumes of acetone and one volume of peroxide-free diethyl ether. The precipitated solids were removed by filtration, and the filtrate was evaporated under nitrogen at reduced pressure until substantially all volatile organic solvent had been removed. About 20 ml of aqueous solution, essentially free of organic solvent, remained. This solution was diluted to 100 ml with distilled water. 

Erythorbates are safe products and there are no harmful breakdown products, although when early formulations utilized ammonia as a PH buffer (and neutralizer for part of the carbon dioxide), copper corrosion problems resulted. However, erythorbates are not steam-volatile,and consequently there is no post-boiler oxygen scavenging potential available. Thus, in the event of complete breakdown of the product at high pressure, oxygen-induced, ammonia corrosion of copper may continue unchecked. 

A further longer term wet lay-up alternative is through the use of volatile corrosion inhibitors (VCIs) such as dicyclohexylamine acetate. These are dissolved in the water at a temperature below 60 °C, and the water is circulated for 4 to 5 hours. The boiler does not need to be completely filled because the VCI migrates to all parts of the boiler and reaches equilibrium in each of the void spaces. With traditional lay-up chemicals, the oxygen scavenger may become depleted easily (which is why the reserve usually is so high) and corrosion protection is quickly lost however, with VCI programs, there is always a volatile buffer available that maintains equilibrium and hence corrosion protection. 

One of the functions of an LC-MS interface is to remove the mobile phase and this results in buffer molecules being deposited in the interface and/or the source of the mass spectrometer with a consequent reduction in detector performance. Methods involving the use of volatile buffers, such as ammonium acetate, are therefore preferred. 

Reference has been made to the problems associated with the presence of highly involatile analytes. Many buffers used in HPLC are inorganic and thus involatile and these tend to compromise the use of the interface, in particular with respect to snagging of the belt in the tunnel seals. The problem of inorganic buffers is not one confined to the moving-belt interface and, unless post-column extraction is to be used, those developing HPLC methods for use with mass spectrometry are advised to utilize relatively volatile buffers, such as ammonium acetate, if at all possible. 

Involatile inorganic buffers, when used as mobile-phase additives, are the prime canse of blocking of the pinhole. The situation can be alleviated either by replacing them by a more volatile alternative, such as ammonium acetate, or by nsing post-colnmn extraction to separate the analytes from the buffer, with the analytes, dissolved in an appropriate organic solvent, being introduced into the mass spectrometer. 

If a buffer is present in the HPLC mobile phase, and this is essential for true thermospray ionization, it should ideally be volatile and this may necessitate modifying existing HPLC methodology. 

An involatile ion-pairing reagent would be deposited in the electrospray interface and lead to a reduction in performance. Some interfaces have been specifically designed to minimize this by removing the line-of-sight between the spray and the entrance to the mass spectrometer, and are thus more tolerant to involatile buffers. The performance of the interface will be improved by the use of volatile alternatives. 

The soluble tryptic peptides of 130 mg a chain of Hb-St. Claude were separated on 0.9 x 60 cm columns of Chromobead resin type P (Technlcon Instruments, Dowex 50-X4) at 37°C using the procedure described earlier (16). The method uses a gradient of volatile pyrldlne-acetlc acid buffers of differing molarities and pH as follows first gradient, 666 ml 0.1 M, pH 3.1, and 333 ml 1.0 M, pH 5.0 and second gradient, 166 wl 1.0 M, pH 5.0, and 332 ml 2.0 M, pH 5.0. The amino acid composition of Isolated fragments was determined with a Splnco model 121 automated amino acid analyzer (Beckman Instruments)... 

The choice of the chromatographic system depends on the chemical character of the extracts being separated. The mobile phase should accomplish all requirements for PLC determined by volatility and low viscosity, because nonvolatile components (e.g., ion association reagents and most buffers) should be avoided. It means that, for PLC of plant extracts, normal phase chromatography is much more preferable than reversed-phase systems. In the latter situation, mixtures such as methanol-ace-tonitrile-water are mostly used. If buffers and acids have to be added to either the... 

Eluent components should be volatile. Solvents such as ethyl acetate, isopropyl ether, diethylketone, chloroform, dichloromethane, and toluene as modifiers and n-hexane as diluent are recommended for normal phase chromatography. For reversed-phase systems, methanol or acetonitrile are used as modifiers. Such components as acetic acid or buffers, as well as ion association reagents, should be avoided. 

UV/VIS, F RI ECD, ELCD ELSD, MS UV-grade non UV-absorbing solvents No mobile phase gradients Conducting mobile phase Volatile solvents and volatile buffers... 

Solvents used successfully in TSP operation include water, methanol, acetonitrile, propan-2-ol, dichloro-methane and hexane. Any volatile buffer may be employed as an electrolyte, but involatile buffers and inorganic acids such as phosphate salts are to be avoided. This poses some limits on the analysis. 

Multiple hyphenation ( hypemation ) provides comprehensive spectroscopic information from a single separation. The first doubly hyphenated HPLC-NMR-MS appeared in 1995 [661], and its value is now accepted meanwhile fully integrated on-line LC-NMR-MS and MSn systems (QMS, QTTMS) are commercially available. On-line LC-NMR-MS coupling is by no means trivial. For example, the sensitivity of NMR is limited, while MS is incompatible with non-volatile buffers. The... 

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