Pervaporation-flow injection with chemiluminescence detection for determination of iodide in multivitamin tablets.

This paper describes the use of a pervaporation (PV) technique in a flow injection (FI) system for selective improvement in iodide analysis. Iodide in the sample zone is oxidized to iodine, which permeates through a hydrophobic membrane. Detection of the diffused iodine is achieved using the chemiluminescent (CL) emission at 425nm that results from the reaction between iodine and luminol. The method was applied for the analysis of some pharmaceutical products, such as nuclear emergency tablets and multivitamin tablets. Ascorbic acid present in multivitamin samples interfered seriously with the analysis, and off-line sample treatment using anion exchange resin was employed to successfully remove ascorbic acid before the analysis. Ascorbic acid was flushed from the column using 0.4M sodium nitrate followed by elution of iodide with 2M sodium nitrate. The detection limit (3S.D.) of the system was 0.5mgl(-1), with reproducibility of 5.2% R.S.D. at 5mgl(-1). Sample throughput was determined as 30injectionsh(-1). There was good agreement between iodide concentrations from extracted samples determined using four different methods, i.e., PV-FI, gas diffusion-flow injection, potentiometry and ICP-MS. A comparison of the analytical features of the developed pervaporation system with these of the previously reported chemiluminescence gas diffusion-flow injection previously reported is also described.

MHC variation and tissue transplantation in fish.

Major histocompatibility complex (MHC) genes were originally discovered because of their role in tissue rejection in mammals and have subsequently been implicated in the incidence of autoimmune diseases and resistance to infectious diseases. Here we present the first demonstration that a gene defined by molecular sequence in the fish MHC, specifically a class II locus, plays an important role in tissue rejection. This effect in the endangered Gila topminnows appears to be additive and depends on the number of MHC alleles shared between the host and the recipient fish of the scale transplants. In addition, there was lower success of scale transplants in MHC-matched individuals in a population with high microsatellite variation than in a population with low variation. This suggests that other loci, presumably other MHC loci, play a significant role in transplantation success in fishes, as they do in mammals.

Determination of Henry's law constants of phenols by pervaporation-flow injection analysis.

A novel dynamic nonequilibrium technique for the determination of Henry's law constant (HLC) of phenols based on pervaporation-flow injection (PFI) is described. A linear relationship between HLC and the amount of phenol measured by a detector in the acceptor line of a PFI system was demonstrated. This relationship was constructed using five frequently encountered phenols (phenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 2-chlorophenol, and 2,3-dimethylphenol) and used for the determination of the HLC of three other phenols (2,4,6-trichlorophenol, 2-methylphenol, and 3-methylphenol). The HLC of all eight phenols were also determined by the single equilibrium static technique (SEST). Fairly good agreementwas observed between both techniques regarding the HLC of 2,4,6-trichlorophenol, 2-methylphenol, and 3-methylphenol. On the basis of the results obtained, it was concluded that the PFI technique offers considerable advantages over SEST in terms of precision, speed, labor intensity, and possibilities for automation.

A polymer membrane potentiometric sensor for silver.

Four new sulfur-containing compounds based on pyridine, benzene, 1,8-naphthyridine and 1,10-phenanthroline have been synthesized. These molecules have been incorporated into a polymeric matrix as neutral carriers and evaluated as silver sensors. Two of the compounds (pyridine and benzene) show high selectivity for Ag(+). The sensor with the pyridine-based compound, in particular, shows near-Nernstian response and good sensitivity towards Ag(+) with a short response time (<10s), making it ideal for use in flow analysis.

Gas diffusion with preconcentration for the determination of fluoride in water samples by flow injection.

The preconcentration of fluoride is achieved on-line by converting it to trimethylsilane which then diffuses through a gas permeable membrane to be absorbed in a stationary sodium hydroxide acceptor stream. This stream is enclosed in the sample loop of an injection valve and after preconcentration, the fluoride sample is flushed into a flow injection manifold for spectrophotometric analysis by the zirconium/alizarin S procedure at 520 nm. The method is suitable for fluoride analysis in the range 0.1-10 mg/l at a sampling rate of 17/hr. Phosphate does not interfere and aluminium and iron can be tolerated at 200 and 500 times the fluoride concentration, respectively. The LOD was calculated to be 0.055 mg/l and LOQ was found to be 0.18 mg/l.

Speciation of dissolved phosphorus in environmental samples by gel filtration and flow-injection analysis.

A study of the factors affecting separation and detection of dissolved organic and inorganic phosphorus species found in waters sediments is reported. The system involved the use of gel filtration and flow injection analysis (FIA). Orthophosphate and myo-inositol hexakisphosphate, as model solutes representative of low molecular weight P (LMWP) and high molecular weight P (HMWP), were separated on a Sephadex G25 column incorporated into a flow-injection manifold which utilized photo-oxidation and spectrophotometry for detection of dissolved reactive phosphorus (DRP) and dissolved organic phosphorus (DOP). The influence of eluent pH and ionic strength on adsorption and anionic exclusion of the model solutes is described, and the optimum eluent composition and sample size are described. The method was used to determine LMWP and HMWP in natural and waste waters, and in sediment extracts. Potential limitations of this approach are discussed.

Determination of sulfur dioxide in wines and beverages by flow injection analysis with reductive amperometric detection and electrolytic cleanup.

A new flow injection method is described for the determination of sulfur dioxide in red and white wines and other beverages. A dual-electrode electrochemical detector eliminates interferences by reduction at an upstream coulometric electrode before reductive detection of sulfur dioxide at the amperometric electrode. The data for free and total sulfur dioxide in wines and other beverages agree well with those obtained by the standard aspiration-oxidation method.

A fast response membrane-based pH indicator optode.

A cellulose acetate based optode membrane containing 4-dimethylamino-4'-octylazobenzene as an acid-base indicator is described. Other essential components of the membrane for a fast-responding and durable sensor are diethyl phthalate, triethyleneglycol and potassium tetrakis(4-chlorophenyl)borate. Factors affecting the sensor behaviour are discussed and an application in a flow-cell is demonstrated.

Determination of calcium in waters, milk and wine by discontinuous-flow analysis.

The flow-based analysis method, discontinuous-flow analysis (DFA), was used for the determination of total calcium in drinking water, milk and wine by titration with ethyleneglycoltetraacetic acid. The detector is a coated-wire calcium-selective electrode. The titration can be cycled continuously with a cycle time of about 1 min. This can be carried out with a single sample or with different samples using an autosampler. The method for waters and wine is simple, fast and highly reproducible. For milk, a back-titration method was used because of the complex matrix of the sample.

Reutilization of fatty acid carbons for lung lipid synthesis.

The utilization of glucose, palmitate, and oleate for the synthesis of lung lipids was studied in isolated rat lungs. Lungs were ventilated with 5% CO2 in air and perfused for 100 min with a Krebs-Ringer bicarbonate buffer (pH 7.4), containing 3% fatty acid-free albumin and either 5.6 mM [U-14C]glucose or 0.25 mM [1-14C]palmitate, or 0.25 mM [1-14C]-oleate. At the end of 100 min of perfusion with these precursors, between 73 and 85% of total lipid 14C was recovered as phospholipid. Glucose carbon was mainly incorporated into triglyceride fatty acids (TG-FA) and phosphatidylcholine fatty acids (PC-FA) of 16- and 18-carbon chain length. After perfusion with [14C]palmitate and [14C]oleate, only 65 and 20% of 14C was recovered as PC 16-carbon and 18-carbon FA, respectively. The remaining 14C was mainly recovered as FA shorter than the 14C precursors. Schmidt degradation analysis of lipid FA demonstrated considerable labeling of alkyl carbons on perfusion with the carboxyl-labeled precursors, indicating that FA degradation products were used for synthesis of lipid FA. This process was enhanced on addition of glucose to the perfusate.