Determination of organochlorine pesticides by gas chromatography with solid-phase microextraction

Summary A study of different extraction techniques for the determination of a selected group of organochlorine compounds in surface waters is presented. Comparison of liquid-liquid extraction (LLE) with solid-phase extraction (SPE) and solid-phase microextraction (SPME) with fibers of different polarity shows that SPME with a recently commercialised fiber of polydimethylsiloxane divinylbenzene allows these compounds to be determined in surface waters with good extraction efficiencies. Extraction time, effect of temperature, ionic strength and pH were optimised, allowing quantification in agricultural effluents in the range 1.0–60 ng·L⁻¹.     

The identification of tricyclic neuroleptics and sulphonamides by high-performance thin-layer chromatography

Circular high-performance thin-layer chromatography (HPTLC) has been used to differentiate a series of twelve tricyclic neuroleptics, using both normal phase and reverse phase procedures. The use of normal phase systems also allows the resolution of geometric isomers of chlorprothixene, clopenthixol and flupenthixol. Thirteen sulphonamides and Trirnethoprim may also be distinguished using HPTLC.     

HPLC of antibiotics. 1. Streptolydigin and related compounds

Two new acyltetramic acids related to streptolydigin have been isolated from fermentations of Streptomyces lydicus. The principal members of this complex were resolved by TLC on silica gel. However, the methods of detection, permanganate spray or bioautography, were not suitable for both crude fermentation broths and purified extracts. Gas chromatography is unsuitable for the detection of either underivatized or silylated streptolydigins. High performance liquid chromatography (HPLC) particularly on triethylaminoethyl cellulose is rapid and sensitive and is the method of choice for the analysis of both crude and purified samples. Using high performance liquid chromatography, two components were detected in the complex, which are not observed using any of the other chromatographic procedures.     

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.     

Sorption behavior of acidic herbicides on carbon nanotubes

Carbon nanotubes and graphitized carbon are investigated as adsorbents for solid phase extraction of dicamba and 2,4,5-T, two phenoxyalkanoic acid herbicides. These adsorbents have much greater adsorption capability than that of C₁₈ bonded silica, which was also tested for comparison studies. The adsorption capacity increases remarkably at lower pH of the sample solution. Freundlich isotherms were applied to analyze the data. Our studies suggest that carbon nanotubes have great potential applications in environmental analysis.     

Application of the microwave acid digestion method to the decomposition of rock samples

The microwave acid digestion method was applied to the decomposition of rock samples and optimum conditions were investigated. Samples of 10–100 mg were decomposed by changing the amount and composition of acid, heating time and number of reheating steps and then the concentrations of Si, Fe, Mn, Na, K and Mg in these samples were measured. The concentrations agreed with reported values when 10 mg of sample were decomposed by heating for 60 s with 0.3 ml of concentrated HNO₃ and 0.1 ml of concentrated HF. Similarly, 100 mg of sample were also decomposed successfully by heating for 45–110 s with 0.3–1.0 ml of concentrated HNO₃ and 0.4–0.7 ml of concentrated HF. It is concluded that the microwave acid digestion method decomposes rock samples with a very short heating time and with small amount of reagents compared with methods using conventional sealed PTFE vessels, which require several hours for the heating step and several millilitres of reagents.     

Optimization of selenium determination in plant samples by hydride generation and axial view inductively coupled plasma atomic emission spectrometry

The use of hydride generation coupled with axial view inductively couple plasma atomic emission spectrometry was presented for the determination of selenium in plant samples. The chemical factors affecting potentially the hydride generation efficiency (hydrochloric acid, sodium borohydride and sodium hydroxide concentrations) were assessed through investigation of chemical interference, accuracy and repeatability. The accuracy of measurements was not affected by elements present in high concentration in the plant matrix (K, Ca, Mg, and P). No interference was also observed with transition metals. Using a real sample (maize) with standard additions, decreases of recoveries were sometimes observed for 0.1% (m/v) NaOH, and attained 13.8% in the most unfavourable case. The final accuracy of the method was verified by using two certified reference materials: CRM 402 (white clover) and CRM 279 (sea lettuce). No statistically significant differences were obtained between the measured concentrations and the certified values. The optimized method was found sensitive (detection limit 0.15 μg l⁻¹), reliable and repeatable (R.S.D. between 1.3% and 4.0%).     

Trace analysis of volatile polar organics by direct aqueous injection gas chromatography

Summary Procedures for the quantitative analysis of industrial effluents which involve concentration by solvent extraction or the purge-and-trap method are time-consuming, labor-intensive, and prone to error. Direct aqueous injection gas chromatography using an electron-capture detector for the analysis of volatile halocarbons at the ppb level is in routine use in many laboratories. We now discuss the development of a similar protocol for the analysis of volatile polar organics such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and tretrahydrofuran using a flame-ionization detector.     

Determination of Polyvinyl Alcohol Using Gel Filtration Liquid Chromatography

Gel filtration chromatography using a TSKgel G2000 SW column coupled with differential refractive index detection was used to analyse five grades of polyvinyl alcohol. Limits of detection and quantification for the assay were 0.14 mg mL^–1, 0.47 mg mL^–1 respectively. The inter and intra-day co-efficient of variance were both <7%. There was a significant difference (p<0.05, n=5) between the calibration curves across the five grades of PVA due to a refractive index range of 13.0790 –1.3181 (n=3). The assay accuracy was 98.99% ± 8.97% (n=5) and 90.60% ± 7.87% (n=5) of a spiked PVA sample was recovered from a commercial formulation.     

Presence of nonylphenol, octyphenol and bisphenol a in two aquifers close to agricultural, industrial and urban areas

Active endocrine disruptors (nonylphenol, octylphenol and bisphenol A) were analysed in 2 aquifers and the corresponding surface waters. They are compounds widely used in industrial processes. The objective of this study was to determine the leaching potential of these compounds in groundwaters and to eventually correlate these levels with surface water samples. The areas sampled were agricultural, close to large cities and with an important industrial activity in the surrounding area. Samples (200 mL) were extracted using off-line SPE with polymeric OASIS 60 mg cartridges. Analyses were performed by gas chromatography-mass spectrometry (GC-MS) using selected ion monitoring (SIM) and full scan for quantification and unequivocal identification, respectively. This paper reports the detection limit for the compounds studied (from 0.001 to 0.030 μg L⁻¹), and method performance as regards to linearity (0.01–1.3 μg L⁻¹), reproducibility (less than 9%) and recovery (84 to 95%). The results from a monitoring program revealed the presence of the target compounds in all samples analysed, at levels of 0.07 and 1.9 μg L⁻¹. The presence of these compounds in groundwater was attributed basically to degradation of inert ingredients present in the formulation of many pesticides or to the increasing application of sludge in agricultural practice, although the infiltration of industrial run-off and wastewater disposal cannot be disregarded.