Zwitterionic ion-exchangers represnt a new direction in the development of stationary phases for different modes of high-performance liquid chromatography. The combination of positively and negatively charged sites in a single particle, or within the functional groups of a single molecule attached the surface of an adsorbent, provides unique opportunities to vary the selectivity of the separation. The classification of zwitterionic ion-exchangers based on their structure, distribution of oppositely charged groups, and their applications is considered.
A simple and sensitive extraction-spectrophotometric method for the determination of barium is reported. The 18C6-barium-Rose Bengal (18C6-Ba-RB) ternary complex was quantitatively extracted into dichloromethane, and its absorbance was measured at 565 nm. The calibration graph is linear over a barium concentration range of 0.083 - 4.70 µg ml-1. The limit of detection of barium was 17.7 ng ml-1. The relative standard deviation (RSD) of ten replicate measurements was 2.19% for a 0.83 µg ml-1 barium solution. The interference effects of various cations and anions were also studied and reported. The described method provides a simple and reliable means for determination of trace amounts of barium in real samples.
A new material: magnesia-zirconia composite modified by an alkylphosphonate can be used as a reversed-phase stationary phase for high-performance liquid chromatography. The new material was characterized by elemental analysis, FTIR and 13C solid state NMR spectrometry. The pH stability of the new material was investigated using biphenyl and N,N′-dimethylaniline as probes with methanol-water (60:40, v/v) as a mobile phase, after the column was continuously purged with solutions at extreme pH 2 and pH 11. The chromatographic performance of the new material was studied by using polycyclic aromatic hydrocarbons (PAHs) and basic compounds as probes. The results indicate that the new material is of high pH stability and can be used for separation of PAHs and basic compounds.
A method for the extraction and determination of butyltin species in aqueous samples by solid-phase microextraction (SPME) combined with a capillary gas chromatography-flame photometric detector (GC-FPD) is described. The butyltin species was converted to its hydride form by sodium tetrahydroborate (NaBH4) in a closed headspace vial prior to extraction. A laboratory-assembled SPME device including a fused-silica fiber and a modified microsyringe protection part was used throughout the experiment. The extraction was an equilibrium process that depended on the butyltin species partitioning between the liquid phase and the fiber. When the equilibrium was reached, the fiber was directly transferred to a GC column under the protection of a microsyringe, where the analyte was thermally desorbed inside the heated injector and subsequently, separated in a HP-1 capillary column and detected by a laboratory-made flame photometric detector using quartz surface-induced tin emission. The detection limits based on the signal equal to 3 times of the base-line noise were 0.2 µg/L, 0.2 µg/L, 0.1 µg/L and 0.02 µg/L for monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT) and tetrabutyltin (TeBT), respectively. The recovery ranged from 85% to 117%. The proposed method has been applied to determination of butyltin species in various aqueous samples.
The determination of phenol and p-cresol in urine has been suggested as a suitable biomarker for the monitoring of benzene exposure of pump workers employed in petrol stations. A method for efficiently extracting a wide variety of drugs from urine for toxicological analysis by gas chromatography is presented. The sensitivity of the method is sufficient to monitor normal levels of phenol and p-cresol after exposure to benzene vapors. The detection limit of the method is low enough to measure urinary phenol and p-cresol at a concentration of 0.1 mg/l. The overall recoveries of urinary phenol and p-cresol relative to the internal standard, DPA, ranged between 95 and 96.5%. Our gas chromatographic method is a rapid, precise and economical one suitable to measure the metabolite benzene also in routine monitoring of phenol and p-cresol.
A computer program was developed for the identification and quantification of organic contaminants on silicon wafer surfaces and related materials based on GC/MS spectral data. Information, such as the retention time (RT), mass number and peak intensity, was stored on 359 chemical compounds in the database. Some empirical equations were presented for calculating the existence probabilities of certain organic compounds. This method was confirmed for the identification and quantification of ultratrace organic contaminants on silicon wafer surfaces and related materials.
Two multivariate calibration methods, artificial neural networks (ANN) and partial least-squares (PLS), have been applied to the quantitative determination of iron species in solid mixtures by X-ray absorption near-edge structure (XANES). XANES spectra were successfully resolved by both methods, and the iron compounds in solid mixtures were quantified, even though the spectra of different compounds showed serious overlap. When iron compounds that were not contained in the model mixtures were subjected to the calibration model, ANN recognized the patterns of their XANES spectra as the nearest spectra of model compounds in shape, and gave more robust results than PLS. The self-absorption effect on the calculated values from XANES measured in the fluorescence mode was examined by comparing with transmission mode; it turned out that a spectral distortion by a self-absorption effect is irrelevant to the prediction performance of these multivariate calibration methods. The present study demonstrated that ANN and PLS are applicable to the chemical speciation of elements by XANES measured in the fluorescence mode.
A novel approach for a library search of the mass spectrum of a mixture is proposed, which is a hybrid of retrieval and calibration techniques developed in chemometrics. An index, called weighted reference existence index, has been developed to obtain a set of possible reference spectra corresponding to the spectrum of a mixture. A non-negative least-squares regression is then used to calculate the contributions of the components in the mixture. The real components and their relative quantities can be determined from the regression coefficients of a non-negative least-squares regression. Both simulated and real data are used to evaluate the proposed method, and the results are quite satisfactory.
A non-conducting polymer film of 3-aminophenol, in which horseradish peroxidase was immobilized, has been prepared on a carbon paste electrode containing both ferrocene as a mediator and horseradish peroxidase by the electrochemical polymerization. The response currents of this hydrogen peroxide sensor linearly increased with increasing the concentration of hydrogen peroxide of 0.6 to 20 μmol dm-3; the straight line had a slope equal to 10.1 mA mol-1 dm3 (r= 0.999). This hydrogen peroxide sensor may be available for the fabrication of other biosensors, e.g. glucose and cholesterol sensors, which are not influenced by easily oxidizable species, L-ascorbic acid and uric acid.
A simple, rapid, specific and sensitive method for the assay of dibazol using a bulk acoustic wave technique is described. PVC film containing various activants was coated on one electrode of a piezoelectric quartz crystal to fabricate a dibazol bulk acoustic wave (BAW) sensor for the assay of dibazol. Neither a sample pretreatment nor separation was required. The logarithm of the frequency shift of the dibazol BAW sensor shows a linear relationship to the logarithm of the concentration of dibazol over the range 4.0 × 10-8 - 9.0 × 10-4 M with a detection limit of 4.0 × 10-8 M. In this work, three kinds of ion-pair complexes, namely, dibazol with dicyclohexylnaphthalene sulfonate (DDCHNS), diisobutylnaphthalene sulfonate (DDBNS) and tetraphenylborate (DTPB), were synthesized and investigated. The influencing factors were also examined and optimized. A comparison of the BAW sensing technique with other methods for assaying dibazol was made.
The photodegradation of pentachlorophenol in water was examined with a high-pressure mercury lamp. A number of photodegradation products of pentachlorophenol, such as less-chlorinated phenols through reductive dechlorination, and catechol and trihydroxylated products via the addition of hydroxyl radicals, were observed as major products. Moreover, polychlorinated biphenylethers, hydroxylated polychlorobiphenylethers and polychlorinated dibenzo-p-dioxins as minor products were also formed by dimerization process during the photolysis of pentachlorophenol. These compounds were identified by gas chromatography-mass spectrometry. The degradation rate of PCP in water was measured against the UV-irradiation time. After the irradiation for 15 min, 75% of PCP was converted into a number of products through reductive dechlorination and oxidation. On the basis of the identified products, the photodegradation pathways of PCP under UV irradiation were proposed.
Gas chromatograph/mass spectrometer (GC/MS) and gas chromatograph/atomic emission detector (GC/AED) with temperature programmable pyrolyzer were used for analysis of pressure sensitive adhesives in adhesive tapes. Evolved gas analysis (EGA) profile of the adhesives was obtained by this temperature-programmed pyrolyzer directly coupled with MS via a deactivated metal capillary tube. The EGA profile suggested the optimal thermal desorption condition for additives and the subsequent optimal pyrolysis temperature for the remaining polymeric material. Rubbers were identified from pyrograms with the assistance of a new polymer library. The additives were selectively detected by monitoring hetero elements and these screening results of GC/AED enabled one to easily find additive peaks in complex chromatograms of GC/MS with interference of tackifier. The additives were able to be identified by the corresponding GC/MS data. Furthermore, the EGA profile gave significant data for crosslinking agents by using specific ion monitoring.
A kinetic spectrophotometric method was developed for the determination of sulbutiamine based on the catalytic effect on the reaction between sodium azide and iodine in an aqueous solution. Sulbutiamine at concentrations of 0.5 to 20 µg/ml was determined by measuring the decrease in the absorbance of iodine at 348 nm by a fixed-time method. The decrease in the absorbance in the first 5 min from the initiation of the reaction is related to the concentration of the drug. The detection limit of the procedure was 0.2 µg/ml. The relative standard deviation for the replicate determination (n = 10) of 4 µg/ml was 1.05%. The proposed procedure was successfully utilized in the determination of the drug in pharmaceutical preparations and human serum.