Analytical separation, aqueous

Of the many molybdenum sulfides which have been reported, only MoS, M0S2 and M02S3 are well established. A hydrated form of the trisulfide of somewhat variable composition is precipitated from aqueous molybdate solutions by H2S in classical analytical separations of molybdenum, but it is best prepared by thermal decomposition of the thiomolybdate, (NH4)2MoS4. MoS is formed by heating the calculated amounts of Mo and S in an evacuated tube. The black M0S2, however, is the most stable sulfide and, besides being the principal ore of Mo,... 

The suspension of microbial cells in a solvent such as aqueous acidic acetonitrile is a procedure used routinely in soft ionization mass spectrometric investigations of microorganisms. This is particularly the case in MALDI-MS studies where whole-cell suspensions have been analyzed directly without separating the cellular residue. By contrast, ESMS is usually carried out with cell-free supernatants after analyte separation by LC. Some workers71 report that partial lysis of the cells occurs due to the acidic conditions employed in such techniques and that this results in the release of proteins and peptides from... 

This is a more recently developed technique which is a hybrid between HPLC and capillary electrophoresis. The capillary is packed with HPLC media and the mobile phases are aqueous buffers. A voltage is applied to generate an electroendosmotic flow and the analytes separate by interaction with the stationary phase and electrophoretic forces no pump being required as for HPLC. Improved separation efficiencies have been reported. 

Normal-phase HPLC has also found application in the analysis of pigments in marine sediments and water-column particulate matter. Sediments were extracted twice with methanol and twice with dichloromethane. The combined extracts were washed with water, concentrated under vacuum and redissolved in acetone. Nomal-phase separation was performed with gradient elution solvents A and B being hexane-N,N-disopropylethylamine (99.5 0.5, v/v) and hexane-2-propanol (60 40, v/v), respectively. Gradient conditions were 100 per cent A, in 0 min 50 per cent A, in 10 min 0 per cent A in 15 min isocratic, 20 min. Preparative RP-HPLC was carried out in an ODS column (100 X 4.6 mm i.d. particle size 3 jum). Solvent A was methanol-aqueous 0.5 N ammonium acetate (75 25, v/v), solvent B methanol-acetone (20 80, v/v). The gradient was as follows 0 min, 60 per cent A 40 per cent A over 2 min 0 per cent A over 28 min isocratic, 30 min. The same column and mobile phase components were applied for the analytical separation of solutes. The chemical structure and retention time of the major pigments are compiled in Table 2.96. 

Various liquid chromatographic techniques have been frequently employed for the purification of commercial dyes for theoretical studies or for the exact determination of their toxicity and environmental pollution capacity. Thus, several sulphonated azo dyes were purified by using reversed-phase preparative HPLC. The chemical strctures, colour index names and numbers, and molecular masses of the sulphonated azo dyes included in the experiments are listed in Fig. 3.114. In order to determine the non-sulphonated azo dyes impurities, commercial dye samples were extracted with hexane, chloroform and ethyl acetate. Colourization of the organic phase indicated impurities. TLC carried out on silica and ODS stationary phases was also applied to control impurities. Mobile phases were composed of methanol, chloroform, acetone, ACN, 2-propanol, water and 0.1 M sodium sulphate depending on the type of stationary phase. Two ODS columns were employed for the analytical separation of dyes. The parameters of the columns were 150 X 3.9 mm i.d. particle size 4 /jm and 250 X 4.6 mm i.d. particle size 5 //m. Mobile phases consisted of methanol and 0.05 M aqueous ammonium acetate in various volume ratios. The flow rate was 0.9 ml/min and dyes were detected at 254 nm. Preparative separations were carried out in an ODS column (250 X 21.2 mm i.d.) using a flow rate of 13.5 ml/min. The composition of the mobile phases employed for the analytical and preparative separation of dyes is compiled in Table 3.33. 

A method capable of quantifying SPC in raw bovine milk was developed. In this procedure the sample was centrifuged at -4°C and the top fat layer removed. The defatted milk was depro-teinated with TCA, and the supernatant was washed sequentially with dichloromethane, hexane, and ethyl acetate. An aliquot of the separated aqueous layer was prepared for the HPLC analysis by mixing with DSA and filtering. The analyte was quantified with an electrochemical detector. Recoveries achieved were 76-80% (116). 

Analyte in aqueous samples extracted by purge and trap a measured volume of sample purged with helium volatile analytes transferred into the vapor phase and trapped on a sorbent trap analyte thermally desorbed and swept onto a GC column for separation from other volatile compounds detected by HECD, ECD, or MSD. 

Columns lengths of 10-25 m with a 0.32-mm ID and 10-/tm film thickness are available commercially. These phases are ideal for the separation of analytes in aqueous solutions or trace analysis of residual water, because the hydrophobic nature of the polymer allows water to be eluted as a sharp peak. The upper operational temperature of 250°C makes these phases a good choice for the separation of polar light hydrocarbons and alcohols. At subambient temperatures oxygenated gases such as CO and C02 are separated without tailing. 

The excellent reproducibility that can be achieved in repetitive separations carried out over long periods of time, due in part to the stability of the various stationary phases to many aqueous mobile phase conditions. Thus, it is not uncommon with the current generation of pressure-stable HPLC sorbents for little change in the resolution to arise after more than 1000 repetitive analytical separations. 

The interaction of the polymeric analyte molecules (charged or uncharged) with the polymeric sieving media (uncharged or charged) is a general and principal method for analytical separation of water-soluble polymers. Transfer of this technique to water-insoluble polymers by applying the technique of non-aqueous capillary electrophoresis (NACE) seems feasible. 

An example for the separation for flavonoids with HP-RPC is the screening method employed for the systematic identification of glycosylated flavonoids and other phenolic compounds in plant food materials by Lin et al20 These authors used an analytical 4.6 mm x 250 mm 5 pm C18 silica column at 25 °C with linear gradient elution (eluent A (0.1% FA in water and eluent B 0.1% FA in ACN) at 1.0 ml min-1. DAD was performed at 270, 310, 350, and 520 nm to monitor the UV/VIS absorption. The LC system was directly coupled to an ESI mass spectrometer without flow splitting and the mass spectra acquired in the positive and negative ionization mode. The same analytical scheme (aqueous MeOH extraction, reversed-phase liquid chromatographic separation, and diode array and mass spectrometric detection) can be applied to a wide variety of samples and standards and therefore allows the cross-comparison of newly detected compounds in samples with standards and plant materials previously identified in the published literature. 

In dialysis, size exclusion is the main separation mechanism, while osmotic pressure and concentration difference drive the transport across two typically aqueous phases. While dialysis is used in some analytical separations, dialysis for the removal of toxins from blood (hemodialysis) is the most prominent application for hollow fiber technology in the biomedical field. The hemodialyzers are used to treat over one million people a year and have become a mass produced, disposable medical commodity. While the first hemodialyzers were developed from cellulosic material (Cuprophane, RC, etc.), synthetic polymers such as polyacrylonitrile, poly(ether) sulfone, and polyvinyl pyrrolidone are increasingly used to improve blood compatibility and flux. Hemodialyzer modules consist of thousands of extremely fine hollow fibers... 

Sterol Analyses. The overall analytical procedure for each 2 cm subcore section Is schematically represented in Figure 3, After homogenization and lyophilization, approximately 1 g of each sediment was mixed with 37.5 ml of chloroform, 75 ml of methanol and 30 ml of a buffered aqueous solution (pH=7). The sediment-solvent slurry was then sonicated for 3-5 minutes and the extract decanted to a separatory funnel. Seventy five ml of water was then added to the funnel, resulting In separate aqueous and organic phases. The chloroform layer was then removed and the aqueous phase washed five times with chloroform. The chloroform fractions were then combined and the volume reduced to 10 ml under nitrogen at 37°C. The entire extraction was repeated until the chloroform phase was visually colorless (6-9 extractions). 

Flow analysis is associated with wet chemical methods and samples are generally collected and transported to the laboratory for analysis. After optional preparative step(s), e.g., dilution, dissolution, extraction, depro-teinisation, or analyte separation/concentration, the resulting aqueous test sample is accommodated in a cup in the sampler tray of the flow analyser for further handling. This practice has been adopted since the appearance of the first commercially available flow analysers, as shown in Fig. 2.3. 

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