Capillary gas chromatography of pesticide residues in foods: Application of a split/splitless inlet system

Residue mixtures of pesticides in foods which were difficult to separate by packed-column gas chromatography were determined by capillary gas chromatography and electron capture detection. Manual injections of sample and reference standard were made with a 10 μL syringe on a septum-enclosed, split/ splitless inlet system. Optimal peak height repeatability (± 3%( was achieved with three-μL injections which were made within time periods of four hours or less. The average linearity coefficient (slope( obtained for detector response as a function of solution concentration was 1.1.     

SIAmate-a compact and modular sequential injection analysis controller

A number of sequential injection analysis (SIA) measurement methods have been developed during the last years. Almost all have been used in laboratory conditions with good results, but very few have been implemented as on-line methods, applied to non-stop measurements, producing immediate results for process control. The transfer of an SIA system from laboratory to an industrial facility [J. Ruzicka, Anal. Chim. Acta 261 (1992) 3] requires a whole new range of details to be taken into account. Some SIA platform related topics will be discussed. There are numerous ways of building an SIA system that meets the needs of the industry. One alternative, SIAmate, is presented.     

Sequential extraction of phosphorus in soil and sediment using a continuous-flow system

Distribution and mobility of phosphorus in soil and sediment are usually studied by sequential extraction. In the extraction procedure, a sample is treated with a series of reagents to distinguish the phases to which phosphorus is associated such as carbonate and iron or manganese oxides, etc. There have been a number of extraction schemes presented for phosphorus. At present, all of the existing schemes are carried out batchwise. Phosphorus contents derived from all sequences are operationally defined and depend on experimental conditions.An extraction procedure, which is a continuous-flow-based technique, was recently proposed by our group for metals in soils and sediments. The extraction is carried out in a closed chamber through which extractants are passed sequentially. In this paper, the system was investigated using the extraction scheme of Hieltjes and Lijklema to study distribution of phosphorus in three certified reference materials (CRMs). A number of fractions were collected for each reagent for subsequent colorimetric determination. The results are compared with those obtained from a batch extraction. The summation of phosphorus contents of all phases were compared with the certified values and with the values obtained from total digestion. These results have demonstrated that the continuous extraction system developed is also applicable for fractionation of phosphorus. Advantage and disadvantage are discussed.     

Synthesis of novel fused isoxazoles and isoxazolines by sequential Ugi/INOC reactions

We report the synthesis of novel fused isoxazoles and isoxazolines by employing an unprecedented Ugi/INOC synthetic sequence. The coupling of the Ugi multicomponent reaction with the intramolecular N-oxide cyclization provides access to unique heterocyclic ring systems in two steps from easily available starting materials in moderate to good overall yields.     

Unified gas and supercritical fluid chromatography on 50 μm i.d. Columns

A unified approach to sequential gas and supercritical fluid Chromatography using 50 μm i.d. open tubular columns is described. Sample introduction is performed by means of a rotary injection valve. In order that linear velocities can be optimized independently, a second rotary valve in the chromatographic oven is used to direct the flow of column eluate to the flame ionization detector through either fused silica tubing in GC, or a frit restrictor in SFC. Applications of sequential GC-SFC on a 50 μm i.d. open tubular column are demonstrated, and comparisons made between sequential GC-SFC on 50 and 100 μm i.d. columns.     

Investigation of parameters affecting the on-line combination of supercritical fluid extraction with capillary gas chromatography

Two different injectors, a split/splitless injector and a programmed temperature vaporizer (PTV) injector were investigated as the interface in on-line supercritical fluid extraction (SFE)-capillary gas chromatography (cGC). The parameters affecting the chromatographic peak shapes as well as the quantitative performance of the interfaces in on-line SFE-cGC were identified and studied. Particular attention was paid to the case where modified extraction fluids were used. Experiments were performed on two different samples. The first sample consisted of PAHs spiked on sand at different concentration levels. The other sample was a polymeric material.     

Sequential injection system with higher dimensional electrochemical sensor signals Part 1. Voltammetric e-tongue for the determination of oxidizable compounds

A sequential injection analysis (SIA) system was developed with the aim of obtaining an automatic and versatile way to prepare standards needed in the study of systems with higher dimensional sensor signals. To illustrate this, different analytical techniques were used in determinations of several analytes. Automated potentiometric calibrations of different potentiometric sensors, with and without interference, were carried out. Useful determinations of selectivity coefficients with two degrees of freedom were obtained. Simultaneous voltammetric determinations have also been done. Firstly, simultaneous determinations of lead and cadmium, using epoxy-graphite composite as the working electrode, have enabled a separate calibration for each metal to be obtained. Next, a voltammetric electronic tongue was designed and applied to the determination of oxidizable species. The use of artificial neural networks has solved the overlapped signal of ascorbic acid, 4-aminophenol and 4-acetamidophenol (paracetamol). A set of 63 data points was prepared automatically and has facilitated the training of an electronic tongue for these three analytes. Accurate predictions of test solutions, in the range of 12–410 μM for ascorbic acid, 17–530 μM for 4-aminophenol and 10–420 μM for paracetamol, have been achieved with RMSEs lower than 0.10 μM.     

A comparison of sequential extraction techniques for determining arsenic fractionation in synthetic mineral mixtures

The sequential extraction methods according to Tessier et al. [1], Borovec et al. [2], Zhang and Moore [3] and Hall et al. [4] have been tested for their suitability for arsenic fractionation in samples of artificially prepared mineral mixtures. Mixtures containing different amounts of As-containing phases were prepared so that their compositions corresponded to weathering products on As-bearing ore deposits. A comparison of different procedures on simple mineral mixtures containing calcium arsenate (CaHAsO₄·H₂O), As-bearing goethite (FeOOH) and arsenopyrite (FeAsS) showed that only the results of the Hall method satisfactorily correspond to the expected arsenic distribution. A detailed verification of the Hall method was subsequently carried out on most complex synthetic mineral mixtures with varying amounts of As-containing kaolinite and carbonate, calcium arsenate, As-bearing goethite and arsenopyrite. The results confirm that the Hall method cannot be fully employed for an accurate As speciation but may be applied for a route identification of As distribution between "labile", "medium-labile" and "residual" forms in heavily polluted soils.     

Sequential injection analysis for benzophenone-4 and phenylbenzimidazole sulphonic acid in sunscreen sprays by solid-phase extraction coupled with ultraviolet spectrometry

A sequential injection UV method was developed to determine benzophenone-4 (BZ4) and phenylbenzimidazole sulphonic acid (PBS) simultaneously, these being the most commonly used UV-filters in aqueous formulations used as sunscreen sprays. The selective elution of both was performed by on-line solid-phase extraction, by retention on a SAX microcolumn and separation by varying the pH of elution. The sensitivity obtained was 0.042±0.001 ml μg⁻¹ for PBS and 0.0159±0.0003 ml μg⁻¹ for BZ4. The limit of detection was 1.6 μg ml⁻¹ for PBS and 0.6 μg ml⁻¹ for BZ4. The R.S.D. of the results was 1-6% for PBS and 1-12% for BZ4. The method was validated using commercial sunscreen formulations with concentrations determined by a liquid chromatographic procedure. The two procedures gave comparable results. Automation of the method means the amount of reagents used and residues generated are decreased. The system allows the required analysis sequence to be programmed using suitable software.     

Facile peptide thioester synthesis via solution-phase tosylamide preparation

Preparation of peptide thioester is essential for native chemical ligation and block condensation. Our novel methodology involves conversion of the carboxylic acid of a peptide into a thioester using p-toluenesulfonyl isocyanate, followed by alkylation, then thiol substitution. Our methodology can also be used for the preparation of glycopeptide thioesters. Furthermore, it is possible to carry out the reaction as a sequential peptide chemical ligation.