Gas-chromatographic determination of deltamethrin in crops

A rapid and economical method is described for the determination of deltamethrin in wheat, rice, peanuts and corn. It is based on simultaneous extraction and clean-up on a column packed with alumina and silica gel using n-hexane-ethyl ether (8:2, v/v), followed by a derivatization step and gas-chromatographic analysis. Recoveries from fortified cereal and peanut samples were determined at four concentration levels and ranged from 73 to 109%. The detection limits were 0.01 to 0.03 mg/ kg. This method simplifies the traditional procedures in terms of sample size, solvent consumption and analysis time. Received: 25 March 1997 / Revised: 3 June 1997 / Accepted: 4 June 1997     

Performance comparison between packed column supercritical fluid chromatography (SFC) and HPLC using cyclandelate as the model analyte

A reproducible and fast method has been developed for the assay of cyclandelate in bulk and drug forms using packed column supercritical fluid chromatography using dicyclohexyl phthalate (DCHP) as internal standard. The drug and the internal standard were resolved by elution with supercritical fluid carbon dioxide doped with 14.29% (v/v) methanol on an RP-C₁₈ column and detected spectrophotometrically at 228 nm. Chromatographic figures of merit using C₈, C₁₈, cyano and phenyl columns have been assessed. Parallel experiments have been performed by HPLC and the data have been compared. Supercritical fluid extraction using CO₂ modified with a small amount of methanol was found to give quantitative analytical recoveries of cyclandelate from a dosage form. SFC has been shown to be a viable, faster alternative technique to HPLC generating less disposable waste. Received: 20 June 1997 / Revised: 20 October 1997 / Accepted: 26 October 1997     

Spectrophotometric method for the determination of 1,2-propylene glycol

A spectrophotometric method is proposed for the determination of 1,2-propylene glycol. It is based on the ADH/ AlDH catalyzed oxidation of propylene glycol by NAD⁺. The NADH formed is measured at 340 nm. Alcohol dehydrogenase from equine liver was found to be much more effective than that of yeast. No enantiomeric selectivity for s(+) propylene glycol was observed. A linear relation was found in the concentration range from 5 to 50 mg/L. The method achieves a correlation coefficient of r = 0.996 and a relative standard deviation of 1.37%. The limit of quantitation was calculated to 9.6 mg/L. Since the total reaction volume was restricted to 800 μL, only 2.8 units of AlDH and 8 units of ADH were sufficient to develop the final absorption within 30 min. Received: 16 April 1997 / Revised: 19 June 1997 / Accepted: 25 June 1997     

Development of an enzyme-linked immunosorbent assay for gentamicin in human blood serum

An enzyme-linked immunosorbent assay (ELISA) for the quantitative detection of gentamicin in human blood serum was developed. Peculiarities of the adsorption on the microtitre plate surface of the gentamicin-protein conjugate were investigated. Different conditions of the competition stage of the analysis were studied and conditions for gentamicin monitoring in human blood serum in the clinical range were optimized. The matrix effect on the assay results, the specificity of the analytical system and the stability of the reagents were examined. The method permits gentamicin concentrations to be determined in human blood serum, diluted 1/1000, in the linear range from 1 to 30 ng/mL. The assay is characterized by high sensitivity (0.5 ng/mL), good reproducibility (CV < 12%) and good correlation with PFIA (r = 0.943). Received: 17 June 1997 / Revised: 30 September 1997 / Accepted: 2 October 1997     

Development of an enzyme-linked immunosorbent assay for gentamicin in human blood serum

An enzyme-linked immunosorbent assay (ELISA) for the quantitative detection of gentamicin in human blood serum was developed. Peculiarities of the adsorption on the microtitre plate surface of the gentamicin-protein conjugate were investigated. Different conditions of the competition stage of the analysis were studied and conditions for gentamicin monitoring in human blood serum in the clinical range were optimized. The matrix effect on the assay results, the specificity of the analytical system and the stability of the reagents were examined. The method permits gentamicin concentrations to be determined in human blood serum, diluted 1/1000, in the linear range from 1 to 30 ng/mL. The assay is characterized by high sensitivity (0.5 ng/mL), good reproducibility (CV < 12%) and good correlation with PFIA (r = 0.943). Received: 17 June 1997 / Revised: 30 September 1997 / Accepted: 2 October 1997     

Liquid chromatographic isolation of coplanar PCB congeners on an activated carbon stationary phase

A rapid and uncomplicated method for the fractionation of PCBs leading to an isolation of the highly toxic non-ortho substituted PCBs is described. The liquid chromatographic separation was achieved on a stationary phase consisting of activated carbon and Celite 545. Using eluents with different polarity, isolation of the non-ortho substituted PCBs in a single fraction was achieved. The fractions were analysed by GC/MS. The method was tested by the determination of non-ortho substituted PCBs in technical mixtures (Aroclor 1254 and Aroclor 1242). The results were compared with those obtained by using an HPLC fractionation on a porous graphitic carbon column. Finally, the micro-column fractionation was used for the determination of non-ortho substituted PCBs in native soil samples. Received: 5 March 1997 / Revised: 4 June 1997 / Accepted: 6 June 1997     

Spectrophotometric reaction rate method for the determination of molybdenum by its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide

A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied to the determination of molybdenum in plant materials and steels. Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997     

Spectrophotometric reaction rate method for the determination of molybdenum by its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide

A kinetic spectrophotometric method for the determination of molybdenum is based on its catalytic effect on the oxidation of pyrogallol red with hydrogen peroxide. The decrease of the absorbance of pyrogallol red in the presence of hydrogen peroxide with time from 0.5 to 4.5 min is proportional to the concentration of Mo(VI) over the range 0.010–0.500 μg/mL. The limit of detection is 0.008 μg Mo/mL. The precision and the effect of the presence of more than forty ions on the molybdenum determination are reported. Probable interferences are completely removed by a cation exchange resin. The procedure was successfully applied to the determination of molybdenum in plant materials and steels. Received: 28 April 1997 / Revised: 16 June 1997 / Accepted: 18 June 1997     

Determination of alkaline phosphatase activity in human sera by mid-FTIR spectroscopy

Fourier transform infrared spectroscopy is applied to the determination of alkaline phosphatase (ALP) activity in human sera. 4-nitrophenylphosphate was found to be an excellent ALP substrate for FT-IR spectroscopic detection. The developed method is based on the acquisition of two FT-IR spectra: one recorded immediately after mixing the sample and assay solution and the other after an incubation time of 10 min. Spectral changes in the mid IR range due to the enzymatic reaction could be correlated to the ALP activity in the sample. Experimental conditions were established such that the clinically relevant range for determination of ALP activity in human sera (50 to 900 U/L) was covered. The method was applied to the analysis of ALP activities in standard solutions as well as in human sera yielding results which agreed well with those obtained by a standard reference method. Received: 20 June 1997 / Accepted: 16 September 1997     

Conductometric determination of quaternary ammonium salts by sodium perchlorate and vice versa

A conductometric method is proposed for the determination of quaternary ammonium salts (chloride or bromide), based on the poor solubility of the relative perchlorates. A comparison between expected and found values shows that the method is suitable, rapid, and easy for quantities in the range from 0.2 to 5 g. The error depends on the solubility of the relative perchlorate. The apparent and tentative solubility product of the studied compounds were calculated. The obtained values allowed to propose benzyltributyl ammonium chloride (BTBA Cl) as precipitant for the conductometric titration of perchlorate. This easy, rapid and accurate determination can be used to analyze the perchlorate ion even in concentrated solutions and to determine stability constants for complex formation in aqueous solutions. Received: 11 June 1997 / Revised: 8 October 1997 / Accepted: 11 October 1997     

Substrate inhibition in an enzymatic ordered bireactant system: non-linear modelling of the kinetics of hypoxanthine-guanine-phosphoribosyltransferase

Hypoxanthine-guanine-phosphoribosyltransferase (HGPRT; EC 2.4.2.8) was determined as an enzyme following an ordered bireaction in the presence of substrate inhibition due to hypoxanthine. This kind of inhibition has not been postulated for HGPRT so far. The mechanism and the kinetic constants of the reaction of HGPRT from Saccharomyces cerevisiae were investigated by initial velocity studies involving a non-linear regression analysis. In addition, two kinds of experimental designs were compared: the variation of hypoxanthine concentrations over wide ranges at different of fixed levels of 5-phosphoribosyl-1-pyrophosphate, and the use of five appropriate sets of experimental conditions each characterized by different hypoxanthine and 5-phosphoribosyl-1-pyrophosphate concentrations. Both experimental designs were consistent with an ordered bi bi mechanism including a dead-end-complex between the enzyme and hypoxanthine. Received: 25 April 1997 / Revised: 9 June 1997 / Accepted: 16 June 1997     

Potentiometric stripping determination of heavy metals using a graphite-reinforcement carbon vibrating electrode

Potentiometric stripping determination of Cd, Cu and Zn using a vibrating electrode (VE) is presented. A simple VE was constructed by using a piezoelectric bimorph oscillator and an inexpensive graphite-reinforcement carbon (GRC) rod (a mechanical pencil). Experimental results obtained with the simple VE follow the equation valid for quantitative application of potentiometric stripping analysis (PSA) in large solutions. It was found that the GRC vibrating electrode is suitable for multielement trace analysis of small samples of 0.05 mL. The relative standard deviations for divalent metals are better than 2%. Received: 3 February 1997 / Revised: 2 June 1997 / Accepted: 7 June 1997     

Accurate and rapid estimation on spectral interferences in routine analysis by ICP-AES: use of mutual interference coefficients

A practical method to estimate spectral interferences and to select optimum analytical lines in ICP-AES is suggested. Depending on the matrix composition and the amounts of the analyte, the analytical lines suffering from little interferences and the limit of determination can be determined from calculation using spectral interference coefficients. For this calculation, the spectral interference coefficients, which are defined as apparent mass of the analyte equivalent to the spectral interference from unit mass of the interferent, are obtained experimentally for 639 emission lines of 68 elements. There is a good correlation between the coefficients obtained on two spectrometers having different resolutions. Received: 24 June 1997 / Revised: 4 December 1997 / Accepted: 24 January 1998     

ICP-MS – A powerful analytical technique for the analysis of traces of Sb, Bi, Pb, Sn and P in steel

The determination of Sb, Bi, Sn, Pb and P in steel using quadrupole- and double-focusing-sector-field-ICP-MS is described. Simple and fast methods for sample preparation were developed with regard to requirements of ICP-MS. Several certified steel reference materials were analyzed in order to verify the accuracy and precision of the applied methods. Received: 22 April 1997 / Revised: 19 June 1997 / Accepted: 23 June 1997     

Trace analysis of metals in plant samples with inductively coupled plasma – mass spectrometry

An analytical method for the quantitative determination of Al, Ti, V, Cr, Co, Ni, Cu, Zn, Mo, Cd, Ti and Pb in plant samples by ICP-MS has been developed. Spectral interferences, plant matrix effects, precision and accuracy are discussed. Results are demonstrated for selected samples concerned with the mass balance of heavy metals after utilization of non-food vegetable materials in a power plant. Received: 7 January 1997 / Revised: 2 June 1997 / Accepted: 18 June 1997     

The potential of gas chromatography with microwave-induced plasma atomic emission detection (GC-MIP-AED) as a complementary analytical technique in environmental screening analysis of aqueous samples

With GC-MIP-AED as a complementary analytical technique to GC-MS, the reliable identification of many organic pollutants in water samples of the Nitra river has been made possible due to the additional information on the elemental composition of organic pollutants it provides. Some compounds, which have been identified by GC-MS in the scan mode after a MS-library search, can be confirmed by their element responses. Even where the identification of substances cannot be confirmed by their empirical formulas calculated by GC-MIP-AED due to insufficient peak intensities, integration problems or chromatographic interferences, it can be facilitated by the presence of one or more heteroatoms. Quantitative data of selected organic pollutants from GC-MIP-AED screening analysis after compound independent calibration can be obtained more easily than, and in good agreement with, quantitative results provided by target analysis (e.g. GC-MS in the SIM-mode). New self-developed macros are helpful tools for acquiring information on the elemental composition and concentration of organic pollutants analyzed by GC-MIP-AED. Received: 3 March 1997 / Revised: 11 June 1997 / Accepted: 11 June 1997     

Capillary gas-chromatographic method for determining non-derivatized sterols – some results for duplicate 24 h diet samples collected in 1994

A gas-chromatographic method for the determination of non-derivatized sterols in duplicate 24 h diet was developed and validated. In the spring and autumn of 1994, 123 people participated in a duplicate 24 h diet study. Each participant collected one duplicate of the food and drink consumed in a continuous 24 h period. The first analytical step involved hydrolysis of the test portion, to which an internal standard solution was added. The sterols were extracted with cyclohexane and determined by capillary gas chromatography with flame ionization detection. Samples were analyzed for cholesterol, coprosterol, brassicasterol, campesterol, stigmasterol and β-sitosterol. The quality control checks showed that the sterol contents of 26 lyophilized subsamples were unstable. In these cases, non-lyophilized subsamples were taken for analysis. The mean intake for all participants was: for cholesterol 202 mg/day per person, for campesterol 27 mg/day per person, for stigmasterol 15 mg/day per person and for β-sitosterol 102 mg/day per person. The mean intake for brassicasterol could not be calculated because too many values were below the limit of detection. Coprosterol could not be detected in the samples. Received: 14 May 1997 / Revised: 18 June 1997 / Accepted: 20 June 1997     

The potential of gas chromatography with microwave-induced plasma atomic emission detection (GC-MIP-AED) as a complementary analytical technique in environmental screening analysis of aqueous samples

With GC-MIP-AED as a complementary analytical technique to GC-MS, the reliable identification of many organic pollutants in water samples of the Nitra river has been made possible due to the additional information on the elemental composition of organic pollutants it provides. Some compounds, which have been identified by GC-MS in the scan mode after a MS-library search, can be confirmed by their element responses. Even where the identification of substances cannot be confirmed by their empirical formulas calculated by GC-MIP-AED due to insufficient peak intensities, integration problems or chromatographic interferences, it can be facilitated by the presence of one or more heteroatoms. Quantitative data of selected organic pollutants from GC-MIP-AED screening analysis after compound independent calibration can be obtained more easily than, and in good agreement with, quantitative results provided by target analysis (e.g. GC-MS in the SIM-mode). New self-developed macros are helpful tools for acquiring information on the elemental composition and concentration of organic pollutants analyzed by GC-MIP-AED. Received: 3 March 1997 / Revised: 11 June 1997 / Accepted: 11 June 1997     

A new proposal for a parameter-free integration software

An algorithm is presented that has successfully been utilized in practice for several years. It improves data analysis in chromatography. The program runs in an extremely reliable way and evaluates chromatographic raw data with an acceptable error. The algorithm requires a minimum of preliminaries and integrates even unsmoothed noisy data correctly. Received: 7 April 1997 / Revised: 23 May 1997 / Accepted: 4 June 1997     

Flow-injection analysis based on a membrane separation module and a bulk acoustic wave impedance sensor – determination of the volatile acidity of fermentation products

A novel flow-injection analysis (FIA) system has been developed for the rapid determination of the volatile acidity of some fermentation products like vinegars and juices. The proposed method is based on the diffusion of volatile acids, mainly acetic acid, across a PTFE gas-permeable membrane from an acid stream into an alkaline stream, and the acids trapped in the acceptor solution are determined online by a bulk acoustic wave impedance sensor based on changes in the conductivity of the solution. It exhibited a linear frequency response up to 10 mmol · L^–1 acetic acid with a detection limit of 50 μmol · L^–1, and the precision was better than 1% (RSD) at a through-put of 72 h^–1. The effects of operating voltage for the detector, cell constant of the electrode, composition of acceptor stream, flow rates and temperature on the FIA performance were also investigated. Received: 2 June 1997 / Revised: 7 July 1997 / Accepted: 12 July 1997