W. Engewald

Trace determination of priority pesticides in water by means of high-speed on-line solid-phase extraction-liquid chromatography-tandem mass spectrometry using turbulent-flow chromatography columns for enrichment and a short monolithic column for fast liquid chromatographic separation.

An integrated on-line SPE-HPLC-MS/MS system has been developed for the rapid analysis of various trace level priority pesticides in surface and drinking water. Eleven pesticides were included in this study, with various phenylureas, triazines and organophosphorous species among them. Use of turbulent-flow chromatography columns (TFC, 50 x 1 mm, 30-50 microm particle size) as extraction cartridges enables fast on-line SPE at high sampling flow-rate (5 ml/min). Polymeric and carbon based TFC columns (Oasis HLB, Cyclone, Hypercarb) allow complete extraction with good recoveries from water volumes up to 50 ml. On-line coupling to HPLC is performed with re-mixing of the organic TFC eluate with water in front of the analytical column to ensure efficient band focussing. For fast HPLC analysis, a short monolithic column is applied in combination with highly selective API-MS/MS detection. Matrix effects on the APCI-MS/MS signal were found to be reduced by the system to an acceptable minimum. Limits of detection, determined for 10-ml samples of river water were in the range between 0.4 and 13 ng/l typically, except trifluralin (approximately 280 ng/l), which is less susceptible to ionization under atmospheric pressure conditions. At an enriched water volume of 10 ml, the whole SPE-HPLC-MS/MS procedure requires less than 14 min. The method was successfully applied to the analysis of drinking and surface water samples taken from several sampling sites around the city of Leipzig, Germany. Concentrations measured (maximum: 16 ng/l simazine in river water) were far below the concentration limits scheduled by law.

Trace analysis of technical nonylphenol, bisphenol A and 17α-ethinylestradiol in wastewater using solid-phase microextraction and gas chromatography–mass spectrometry

To enable high sample throughput, an automated solid-phase microextraction (SPME) method coupled with GC-MS for the trace analysis of technical nonylphenol, bisphenol A and 17alpha-ethinylestradiol was developed. The extraction performance of different SPME fibre coatings was examined, with polyacrylate proving most suitable. Although study of the extraction time showed that the analytes have not reached equilibrium after 3 h, as a compromise an extraction time of 1 h was applied in all the experiments with detection limits between 0.04 and 1 microg l(-1) for wastewater effluent. The mean reproducibility of the technique is 8% RSD. Carry-over effects are negligible. The linearity of calibration curves ranges over three orders of magnitude. The method was tested for determining the analytes in influents and effluents of constructed wetland plants and in model wastewater used in laboratory experiments.

Zur Desaktivierung von Glaskapillaren mittels Silanisierung

SummaryThe deactivation of glass capillaries by silanization with different agents under various reaction conditions has been investigated. It was found the effectiveness of the silanization procedure can be improved if the treatment is performed with pure hexamethyldisilazane for a period of about 20 hours at temperatures approaching 300°C.ZusammenfassungDie Desaktivierung von Glaskapillaren duch Silanisierung mit verschiedenen Reagenzien bei unterschiedlichen Reaktionsbedingungen wurde untersucht. Es zeigte sich, daß die Wirksamkeit der Silanisierung wesentlich verbessert werden kann, wenn die Behandlung der Glaskapillaren mit reinem Hexamethyldisilazan etwa 20 Stunden lang bei 300°C erfolgt.

Application of spectral libraries for high-performance liquid chromatography-atmospheric pressure ionisation mass spectrometry to the analysis of pesticide and explosive residues in environmental samples.

The coupling of high-performance liquid chromatography (HPLC) and atmospheric pressure ionisation mass spectrometry (API-MS) seems to be the method of choice if good separation and selective detection of semi-volatile, thermolabile, and polar substances is required. Libraries of mass spectra will make the identification of unknown substances in complex environmental samples easier and more user-friendly. Unfortunately, existing GC-MS libraries are not applicable to HPLC-API-MS analysis. Thus, new and extensive mass spectral libraries were constructed. Several investigations of chromatographic (composition and salt concentration of the eluent) as well as mass spectrometric (orifice voltage) parameters and a few applications of real environmental samples are used to discuss the possibilities and limits of these libraries.

Determination of gadolinium in river water by SPE preconcentration and ICP-MS

An analytical scheme was developed for the determination of Gd-diethylenetriaminepentaacetate (Gd-DTPA), Gd and the other rare earth elements (REE) in river water by inductively coupled plasma (quadrupole) mass spectrometry (ICP-Q-MS). The preconcentration step was essential, since the limits of detection of this multielemental analytical technique are higher than the trace concentrations of the interesting elements in river water. Solid phase extraction (SPE) with different commercially available complexing agents (Chelex 100, Toyopearl and ethylhexylphosphates) was employed for the preconcentration of REE. The investigations revealed that complex stability (varying in dependence of the pH value) has a strong influence on the degree of the enrichment of Gd-DTPA. Based on acidified water samples (pH<3) a procedure using ethylhexylphosphates was proposed for the preconcentration of Gd and REE from surface water samples. For this purpose C(18)-cartridges loaded with ethylhexylphosphates were used, resulting in an enrichment factor of 40.

On the signal response of various pesticides in electrospray and atmospheric pressure chemical ionization depending on the flow-rate of eluent applied in liquid chromatography–tandem mass spectrometry

The API-MS signal response of several pesticides (atrazine, simazine, isoproturon, diuron, chlorfenvinphos, chlorpyrifos, alachlor, trifluralin) depending on the flow-rate of eluent entering the MS interface was investigated. The investigations were based on API-MS-MS analyses of standard pesticide mixtures in the flow injection mode (FIA) at systematically varied eluent flow-rates using both an ESI interface (Turboionspray) and a heated nebulizer type APCI source. In the result, the individual compounds included in this study showed significant differences in their signal response behaviour depending on the flow-rate of eluent applied. The most hydrophobic compounds among the investigated pesticides (chlorpyrifos and trifluralin) showed drastic losses of sensitivity with increasing eluent flow-rate in both ESI and APCI, while more hydrophilic compounds like atrazine, simazine and isoproturon showed the expected signal response (concentration-sensitive in ESI, mass-flow-sensitive in APCI) at least within a certain range of flow-rates (200-600 microl/min in ESI, 200-2000 microl/min in APCI). These findings lead to the conclusion that application of a programmed HPLC eluent flow-rate may be advantageous to achieve maximum sensitivity of API-MS detection for all pesticides of interest. This is exemplified by the implementation of a flow gradient into an online SPE-HPLC-APCI-MS/MS method for improved analysis of pesticides in drinking water.

Molekülstruktur und Retentionsverhalten. VIII. Zum Retentionsverhalten höherer Alkylbenzole bei der Gas-Verteilungs-Chromatographie

SummaryThe retention indices of alkylbenzenes with 9–14 carbon atoms have been determined on glass capillaries coated with squalane, Ucon LB 550 X, Ucon 50 HB 280 X polar, and carbowax 20 M, respectively. The relationships between the retention behaviour and the structure within homologous series of straight chain mono- and p-dialkylbenzenes, of isomeric straight chain p-dialkylbenzenes which differ in the length of the side chains, of isomeric mono- and p-dibutylbenzenes with branched side chains, and of polymethylbenzenes are discussed in terms of homomorphic factors (HS), index differences between different liquid phases (ΔI) and index differences per methylene group (ICH2).ZusammenfassungDie Retentionsindices von Alkylbenzolen der C-Zahlen 9 bis 14 wurden an Glaskapillaren, welche mit Squalan, Ucon LB 550 X, Ucon 50 HB 280 X polar und Carbowax 20 M imprägniert waren, gemessen. Anhand der aus den Retentionsindices abgeleiteten Homorphiefaktoren (HS), Index-differenzen zwischen unterschiedlich polaren Trennflüssigkeiten (ΔI), und der Indexzunahme pro CH2-Gruppe (ICH2) werden Zusammenhänge zwischen gas-chromatographischem Retentionsverhalten und Molekülstruktur am Beispiel homologer Reihen geradkettiger Mono- und p-Dialkylbenzole, isomerer unverzweigter p-Dialkylbenzole mit unterschiedlich langen Seitenketten, isomerer verzweigter Butyl- und p-Dibutylbenzole sowie der Polymethylbenzole diskutiert.

Analytical characterization of natural waxes employing pyrolysis–gas chromatography–mass spectrometry

Abstract Three natural waxes (bleached beeswax, lanolin, yellow carnauba wax) were investigated by means of pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Pyrograms were obtained showing very characteristic signal patterns. Mass spectrometric detection enabled the structural identification of the pyrolytically formed fragments. For a more detailed investigation of the thermal degradation behaviour of waxy materials, relevant model compounds were selected. Hexadecylpalmitate, cholesterylstearate, heptadecanoic acid and 1-hexacosanol were examined under identical Py–GC–MS conditions. From the resulting product distribution general statements were able to be derived according to the thermal degradation pathways of typical wax constituents. The findings obtained from the model compounds were then applied to the interpretation of the real wax pyrograms. As a result, conclusions according to their origin from corresponding wax constituents were drawn for the majority of pyrolysis products. Thus, the extended potential of the method for the compositional analysis of natural waxes is demonstrated.

Advances in the analysis of natural waxes provided by thermally assisted hydrolysis and methylation (THM) in combination with GC/MS

Abstract THM–GC/MS was applied to the analysis of natural waxes (bleached beeswax, lanolin, yellow carnauba wax). By means of flash heating the wax samples in the presence of tetramethylammonium hydroxide (TMAH) as an alkaline derivatization reagent, the wax constituents, mainly high molecular weight esters, were hydrolyzed and converted into their methyl derivatives. Subsequent GC analysis of the methylation products resulted in chromatograms showing very specific signal patterns for each of the materials investigated. Mass spectrometric detection of the yielded methyl derivatives enabled the identification of more than ninety compounds present in the wax samples, i.e. fatty acids, hydroxy fatty acids, fatty alcohols, diols and sterols, respectively. Additionally to the analysis of real wax samples, several wax-relevant compounds (waxy esters, fatty acids, fatty alcohols) were studied with regard to their methylation behaviour. The investigations show that THM–GC/MS is able to overcome problems that arise from conventional Py–GC analysis of waxes, where thermal fragmentation can lead to rather non-specific pyrolysis products. Therefore, THM–GC/MS is an advantageous technique for the comprehensive analysis of natural waxes.

Thermally assisted hydrolysis and methylation – a simple and rapid online derivatization method for the gas chromatographic analysis of natural waxes

Abstract Thermally assisted hydrolysis and methylation (THM) provides an interesting alternative to other derivatizing sample preparation techniques because of its simplicity and rapidness. The paper presents THM–GC/MS data obtained from standard compounds (cholesteryl stearate, 2-hydroxypalmitic acid) and several types of wax (candelilla wax, beer wax, lanolin, beeswax) using tetramethylammonium hydroxide (TMAH) as reagent. Application of tetramethylammonium acetate (TMAAc) instead of TMAH enables selective analysis of free fatty acids in the presence of esters. Comparison of the results with those obtained from Py–GC/MS illustrates that THM provides a much higher extent of information. The thermochemolytic behaviour of several wax compounds is discussed. THM yields may differ from compound to compound due to specific thermal and chemical behaviour. While structurally simple wax esters, e.g. cholesteryl stearate, gave very efficient conversion within a wide temperature range between 350 and 600°C, compounds of less thermal stability (e.g. 2-hydroxyfatty acids) yielded substantial amounts of pyrolysis products (aldehydes) even at the lowest temperature applied (350°C). Some phytosterols present in candelilla wax showed less affinity to TMAH and were only partly converted into methyl ethers. Various applications of THM–GC/MS are described: analysis of lipid based leather polish, identification of wax content in spots in ancient Egyptian textiles, profiling of pharmaceutical lanolin batches, characterization of aging processes in lanolin. Fingerprints and characteristic marker compounds were employed for discrimination and identification purposes.