Analytical and Bioanalytical Chemistry (v.356, #5)

Ion-exchange LC and spectroscopic supporting techniques have been successfully used to study the kinetics and mechanism of oxidation reactions of sele-nomethionine (SeMet). Oxidation of selenomethionine with both cyanogen bromide (CNBr) and hydrogen peroxide (H2O2) proceeds through a stable intermediate which undergoes cyclization and C-Se bond cleavage to form 2-amino-4-butyrolactone. This stable intermediate was identified by IR spectroscopy as methionine dihydroxy selenide. The CH3-Se moiety of SeMet formed methyl selenic acid upon reaction with H2O2 and methyl selenocyanate (CH3SeCN), characterized by GC-MS, for the reaction with CNBr. Both reactions were of apparent first order with respect to the concentration of SeMet. A rate constant (k1) of 4.0×l0−3s−1 for the reaction of SeMet with H2O2 and 4.0 ×10−4s−1 for the reaction with CNBr were determined at a temperature of 22°C. Oxidation of methionine (Met) gives disparate kinetics and oxidation products from SeMet. Thus the differential rate method can be utilized to quantitatively separate SeMet in biological samples in the presence of much higher concentrations of Met.

Aldehydes and ketones readily react with 2,4-dinitrophenylhydrazine (2,4-DNPH) to form the corresponding hydrazones. This reaction has been frequently used for the quantification of airborne carbonyl compounds. Since unsymmetrical aldehydes and ketones are known to form isomeric 2,4-dinitrophenylhydrazones (syn/ anti-isomers), the influence of isomerization on the practicability and accuracy of the 2,4-DNPH-method using 2,4-dinitrophenylhydrazine-coated solid sorbent samplers has been studied with three ketones (methyl ethyl ketone (MEK), methyl isopropyl ketone (MIPK), and methyl isobutyl ketone (MIBK)). With all three ketones the reaction with 2,4-DNPH resulted in mixtures of the isomeric hydrazones which were separated by HPLC and GC and identified by mass spectroscopy and 1H nuclear magnetic resonance spectroscopy. The isomers show similar Chromatographic behaviour in HPLC as well as in GC, thus leading to problems in quantification and interpretation of Chromatographic results.

Selective spectrofluorometric determination of lithium(I) with quinizarin by extraction into tributyl phosphate by L. Cuadros Rodríguez; C. Jiménez Linares; M. Román Ceba (320-325).
A method for the determination of trace amounts of lithium at the ppb level has been described based on the reaction of lithium(I) with 1,4-dihydro-xyanthraquinone (quinizarin) in alkaline medium, extraction into tributyl phosphate (TBP) and measurement of the fluorescence of the organic phase. A linear calibration was found in the concentration range of 9–250 ppb of lithium in aqueous solutions (λexc = 590 nm, λem = 670 nm) with a RSD of 2.7% for 100 ppb of lithium. After a prior treatment with potassium carbonate the method is highly specific for the analysis of lithium in presence of other inorganic ions. The proposed procedure has been applied for the determination of lithium in mineral waters, drugs and vegetables.

N-Dansyl-N′-ethylthiourea (DET) forms fluorescent chelates with a large number of heavy metal ions. The influence of the pH-value on the luminescence of DET and its metal chelates was investigated. The addition of Cu(II) to DET causes a bathochromic shift of the emission maximum, which is linearly dependent on the Cu(II) concentration. Low detection limits and a wide linear range of detection are achieved by HPLC using RP 18 columns as stationary phase. Also presented are first measurements of fluorescence decay times of the ligand as well as some complexes.

The interfering effects of various foreign ions on the determination of arsenic were studied by hydride generation inductively coupled plasma atomic emission spectrometry (HG-ICP-AES). There were serious inhibiting interferences by Cu, Pb, Co, Au, Pd and Ni. However, by using cyanide as a complexing agent these interferences could be completely eliminated over a wide range of interferent concentration. The optimum chemical parameters for continuous arsine generation were studied. A major advantage of this technique is that it only needs low acid concentrations and produces less hazardous waste. Sensivity, selectivity and accuracy of the determination of arsenic by HG-ICP-AES were investigated. The detection limit (in 1 mol/1 HCl medium) for arsenic(III) was 0.82 ng/ml. The relative standard deviation for ten determinations of a solution containing 50 ng/ml arsenic was 1.3%.

A liquid-liquid extraction procedure for the elimination of high levels of sulfate is described. The proposed method allows the ion-chromatographic determination of ppb concentrations of phosphate in the presence of a 20 000-fold excess of sulfate. The liquid anion exchange resin Amberlite LA-2 was selected to retain sulfate from the sample solution acidified by acetic acid as well as cation-exchange cartridges in the H-form. The detection limit for phosphate was 0.03 mg/L.

Carbohydrates have been separated on POLYSPHER®CH OH columns using pulsed amperometric detection (PAD) and UV detection (λ =196 nm) in series and pure water as mobile phase. Nearly baseline separations have been obtained for the glycoprotein carbohydrates of sialic acid (N-acetylneuraminic acid, NANA), N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc). As carbohydrates dissolved and eluted with pure water are present in the neutral form they are not detectable with PAD in contrast to carbohydrate anions formed at high pH values. Therefore an additional NaOH post column reagent has been continuously pumped through a mixing chamber into the mobile phase to form carbohydrate anions resulting in improved detection limits. Monosaccharides as well as glycoprotein carbohydrates could be detected in the μg/ml-range. This method has been applied successfully to the analysis of sugars in fruit juice. With only 2 μl of juice per 50 ml water, the determination of the main constituents, sucrose, glucose and fructose, was possible in a few minutes without sample preparation.

A method for the fast routine analysis of the total content of volatile organic compounds in wallcoverings and paper products was developed, using headspace gas-chromatography for quantification. 57 wallcoverings of different types were investigated. Typical components were toluene, methyl-ethyl ketone, methyl-iso-butyl ketone, n-butyl acetate and iso-butyl acetate, all compounds being used as industrial solvents. The TVOC concentrations are calculated in toluene-carbon equivalents and ranged from 0.31 μ/g to 1789 μ/g with an average value of 123.22 μg/g and a median of 20.37 μg/g. To obtain an estimation of VOC-concentrations in indoor air, 10 selected wallcoverings were also analyzed in a 1 m3 climate test chamber. A correlation between headspace data and chamber concentrations could not be observed, which might be a result of increased analytical uncertainties at low emission rates under chamber conditions.

Determination of thallium in soils by flame atomic absorption spectrometry by Teruo Asami; Chizuru Mizui; Takeshi Shimada; Masatsugu Kubota (348-351).
A method is described for the determination of T1 in soils by FAAS, involving extraction of T1 from 5 g of soil by digestion with HClO4/HNO3 followed by separation of the extracted T1 into 5 mL of diisopropylether from HBr solution, including Ce(SO4)2. T1 in the organic phase is determined by direct aspiration into the spectrophotometer. The percentage relative standard deviation (% RSD) for 5 replicate samples is about 1%. The detection limits (S/N = 3) of this method are 0.001 mg/L for aqueous solution and 0.02 mg/kg DW for soil, when 50 mL of soil solution corresponding to 2.5 g soil are used. The T1 concentration even of unpolluted soils can be determined. The method was shown to be unaffected by the presence of various ions in soil and was able to recover nearly 100% T1 added to soils. The arithmetic mean (range) of 18 Japanese unpolluted surface soils was 0.33 (0.10–0.56)mgT1/kgDW.

Comparative studies of high-performance liquid Chromatographic and liquid chromatographic/mass spectrometric methods for the quantitative determination of glibenclamide in patient serum are described. The 4-methylcyclohexyl analogue of glibenclamide [N-(4-(β-5-chloro-2-methoxybenzamidoethyl)benzenesulfonyl-N′-(4-methyl-cyclohexyl)-urea] is used as internal standard for both methods. After acidification of the sample, the analyte and internal standard are extracted with chloroform. For HPLC analysis, the glibenclamide and internal standard are derivatized to a highly fluorescent amine with 7-chloro-4-nitrobenzo-2-oxa-l,3-diazole (NBD-chloride). The glibenclamide derivative is detected by a fluorescence detector. For APCI LC/MS assay, a derivatization of the analyte is not required and the compounds are measured by selected ion monitoring (SIM). The accuracy, precision, and recovery of the compared methods are presented and discussed.

Silver compounds are used in pharmaceutical and ayurvedic medicines. A method is proposed for the extraction separation of silver from Cu, Cd, Zn, Ni, Pt (IV) and Au (III) from nitrate solution using triphenylphosphine sulphide as an extractant. The recovery of silver is tested both volumetrically and/or by ICP-AES technique.

An electrochemical method was developed for the determination of traces of hemoglobin (Hb) by adsorption square wave voltammetric stripping at a bare silver microelectrode. Under optimum conditions the proposed method provided a linear response over the hemoglobin concentration range 5 to 100 nmol/L. The detection limit was 3 nmol/L. The relative standard deviation was 4.5% for 6 successive determinations at 50 nmol/L Hb. Other chemicals present in the sample did not interfere.