The dimerization of p-hydroxyphenylacetic acid by hydrogen peroxide in the presence of manganesetetrasulfonatophthalocyanine (MnTSPc) has been applied to the determination of hydrogen peroxide in marine surface water samples. As MnTSPc was used as a substitute for horse radish peroxidase, the difficulties caused by possible loss of enzyme activity over time was eliminated. An EDTA-Mn(II) solution containing 2.0×10-3 mol/l EDTA and 1.0×10-6 mol/l Mn(II) ion was used to reduce the interference caused by some metal ions and to increase the sensitivity. The detection limit of the method is 6.3×10-8 mol/l. At a H2O2 concentration of 1.0×10-6 mol/l, the standard deviation is 3.0% (n=6).
A conventional method for the quantitative and simultaneous analysis of a large number of pesticides was proposed using a combination of commercial extraction disks and a quartz-fiber disk. Pesticides contained in air were collected on these disks at a flow rate of 10 l min-1 and extracted by acetone. The extracted solution was analyzed quantitatively with GC/MS. In order to evaluate the accuracy of this method, a recovery test was performed. Forty-five kinds of pesticides were spiked on the quartz-fiber disk at a concentration level of 0.2 μg by collecting 10 m3 of clean air. The recovery efficiencies of almost 40 kinds of pesticides showed more than 80%, and the coefficients of variations were less than 20%. The method was applied to a practical environmental analysis of pesticides, and an appropriate result could be obtained.
A stopped-flow injection system with an immobilized enzyme reactor is proposed for the quantification of L-tartrate in wine. L-Tartrate was oxidized using the secondary activity of D-malate dehydrogenase (D-MDH), which was immobilized on aminopropyl-controlled pore glass beads with glutaraldehyde. NADH produced by D-MDH reaction was detected fluorometrically at 460 nm (excitation at 340 nm). The calibration graph was linear over the range 0.01 - 1.20 mM with a correlation coefficient of 0.999 when the stopped-time was 180 s. The relative standard deviation for ten measurements was 0.81% at the 1.0 mM level. The sample throughput was 12 h-1. The results obtained by the proposed method and an HPLC method are in good agreement with each other. The D-MDH reactor was stable for one month when used daily under the optimal conditions.
A sensitive solid-phase spectrophotometric method for the determination of phenol in tap water or river water samples was developed. The antipyrine dye formed by the reaction between phenol and 4-aminoantipyrine was extracted and concentrated from 50 cm3 of sample solutions on the finely divided anion-exchange resin in the presence of sodium sulfate (14.5 g/50 cm3 of a sample solution) as the salting out reagent. After the resin was collected on a membrane filter by filtration under suction as a colored circular thin layer (ca. 17 mm in diameter), the absorbance of the antipyrine dye fixed on the resin thin layer was measured directly on the membrane filter. Calibration graphs were prepared in the range 0 - 1.0 μg of phenol. The calibration graphs consist of two linear regions, 0 - 0.6 μg and 0.6 - 1.0 μg. The relative standard deviations were 1.9 and 0.2% for five replicate determinations of a blank and 1.0 μg of phenol, respectively. The detection limit, based on three times the standard deviation of the blank, was 25 ng of phenol for 50 cm3 of solution (0.5 ng cm-3). The recovery test was done by adding a 0.2 or 0.4 μg amount of phenol to 50 cm3 of tap water or river water samples and determining phenol by the proposed method with or without separation by distillation of phenol. The recoveries were 90 - 110% and the relative standard deviations were 1.8 - 15% for the tap water samples analyzed with or without distillation and the river water sample with distillation. On the other hand, recoveries were 110 - 120% for the river water sample analyzed without distillation.
The relationship between hydrogen peroxide and nitrate and nitrite by monitoring these substances in rain water was investigated. For the determination of hydrogen peroxide, our previously reported FIA system was applied. For the determination of nitrate and nitrite, an FIA system consisting a copperized cadmium reduction column and 2,3-diaminonaphthalene (DAN) used as fluorescence substance was developed. Under the recommended conditions, it took 8 min to determine the sum of nitrate and nitrite while passing through the copperized cadmium reduction column; it took 6 min under the same condition to determine nitrite without passing through the column. The concentration of nitrate was calculated from the difference between the sum of nitrate and nitrite and nitrite. The detection limit, which was defined by a signal-to-noise ratio of 3, was calculated to be 0.1 μmol dm-3 for nitrite. Also, the relative standard deviation at 20 μmol dm-3 of nitrate was under 1.0% (n = 10). There was no interference from the major substances present in rain. The reaction scheme was based on the monitoring results.
This report describes the application of purge-and-trap (P&T) gas chromatography/mass spectrometry (GC/MS) to analyze carboxylic acids (CAs) using esterification. The optimum analytical conditions were determined based on the esterification recoveries using 10 mmol L-1 of a CAs methanol solution. P&T sampling was carried out with a Curiepoint head-space sampler. The optimum instrumental conditions were: purging, 150°C for 10 min; trap temperature, -10°C; desorption, 358°C for 20 s. A comparison of pyrolysis (Py)-GC/MS, P&T-GC/MS, and solvent extraction-GC/MS was made based on conversions of the CAs into the corresponding CA methylesters. The merits of the P&T method for the other two methods were validated according to quantitative data, the coefficient of variation, and the lower limit of determination calculated from the standard deviation. As a result, we concluded that the P&T method is more useful than the pyrolysis and solvent extraction methods.
A simple and highly sensitive fluorometric high-performance liquid chromatographic method was developed for the determination of busulfan in human serum. After busulfan and 1,6-bis(methanesulfonyloxy)hexane as an internal standard were extracted from serum with ethyl acetate, they were derivatized with 2-naphthalenethiol in an alkaline medium. The derivatives were separated by reversed-phase chromatography on a YMC-Pack C4 column with a mixture of methanol-0.1 M sodium acetate buffer (pH 7.0) (8:2, v/v) as a mobile phase, and were then detected spectrofluorometrically at 370 nm with excitation at 255 nm. Extraction and derivatization efficiencies were 73.9 - 75.1% and greater than 91.1%, respectively. The detection limit for busulfan added to serum was 2 ng (8 pmol) ml-1 serum (330 fmol on column) at a signal-to-noise ratio of three with a linear relationship over the 10 ng - 3.0 μg ml-1 (0.04 - 12 μM) concentration range. The accuracy and precision of this method were within 7.0% and 9.3% even at low concentration (10 ng ml-1). The within- and between-day variations were lower than 9.3% and 10.9%, respectively.
In order to improve electrochemical performance of a glassy carbon (GC) electrode anodized in triethylene glycol (TEG), a GC electrode was anodized in H2O prior to TEG anodization. The effect of this pretreatment was evaluated by comparing electrochemical responses of acetaminophen on HPLC using the following electrodes: a GC electrode anodized in both H2O and TEG (double modified GC electrode); an unmodified GC electrode; GC electrodes anodized in either H2O or TEG. HPLC was carried out for samples containing uric acid and acetaminophen with or without various proteins. The results reveal that the double modified GC electrode has satisfactory sensitivity, reproducibility, and durability in electrochemical detection of acetaminophen by HPLC, compared with other electrodes. In order to demonstrate the advantage of the double modified GC electrode, analysis of acetaminophen from a urine sample was performed by HPLC without carrying out any tedious procedures such as the removal of proteins. In addition, electrochemical analyses of various compounds were performed using the double modified GC electrode in a near-flow injection mode, suggesting that the electrode has potential applications for HPLC analysis of biologically important cationic and neutral compounds.
Nickel diethyldithiocarbamate (nickel DDTC) coprecipitated quantitatively 3 - 90 ng of cadmium in up to 500 cm3 of the sample solution at pH 4.0 - 11.5. The coprecipitant could be easily dissolved with nitric acid (1+1) and acetone, and 3 - 90 ng of cadmium in the final solution (10 cm3) could be determined by electrothermal atomic absorption spectrometry. The peak height of cadmium in atomic absorbance measurements remained almost constant, even if large amounts of nickel DDTC (up to at least 10 mg as nickel amount) were used for the coprecipitation. The detection limit (signal/noise=2) was 1.2 pg cm-3 of cadmium in 500 cm3 of the initial sample solution. The 32 diverse ions investigated did not interfere with the determination in at least a 1000-fold mass ratio to cadmium. The proposed method was successfully applied to the determination of trace amounts of cadmium in river and sea water.
Di-n-butyltin dihalides (Bu2SnY2, Y=Cl, I, OMe) behaved as neutral carriers for anion-selective electrodes. A variety of selectivity patterns have been obtained by using Bu2SnY2 which differ in the electronegative substituents Y on the Sn atom. However, all electrodes containing Bu2SnY2 provided the highest degree of selectivity for the SCN- ion. The interaction of Bu2SnY2 with the SCN- ion was studied in the organic solution by means of 13C NMR spectroscopy. In the case of the addition of NaSCN, a significant increase of the value of 1J(119Sn-13Cα) was observed in the 2.0 M CDCl3 solution of Bu2SnCl2.
A new membrane selenite selective electrode has been developed. The electrode consisted of 4% ion exchanger, QAD 86 PI (dialkyldimethylammonium chloride), as the active material, and 96% SR as the membrane matrix. An analytically useful potential change occurs from 10-6 - 10-1 M selenite ion. The slope of the linear portion is 19 mV/10 fold change in selenite concentration. No interference was observed for SO42-, SO32-, S2-, HPO42-, Cl-, Br- and I- ions. The lifetime of the electrode was about three months. This electrode has been used for the determination of selenium in anodic slime at pH 8 (ammonia buffer) using standard addition method.