Problems caused by the activity of Al2O3-PLOT columns in the capillary gas chromatographic analysis of volatile organic compounds

Summary Al₂O₃-PLOT columns are used with great advantage for the analysis of volatiles, because of the increased capacity ratio and selectivity compared to WCOT-columns. Their applicability is limited to relatively non-polar components with relatively low boiling points i. e. eluting before n-decane.In the analysis of the halocarbons in stratospheric air, the decomposition of certain compounds was observed. In this study the stability of a number of volatile organic compounds was determined in function dependence of the column temperature using a two-dimensional GC-system.A possible reaction mechanism for the decomposition is proposed and confirmed for several chlorinated ethanes.     

Surface and wastewater quality monitoring: combination of liquid chromatography with (geno)toxicity detection,diode array detection and tandem mass spectrometry for identification of pollutants

Identification of unknown water pollutants with liquid chromatography and tandem mass spectrometry (LC–MS–MS) is often more complex and time consuming than identification with gas chromatography and mass spectrometry (GC–MS). In order to focus the identification effort on relevant compounds, unknown peaks need to be selected carefully. Based on its frequency of occurrence in the LC–Diode Array Detection (LC–DAD) chromatograms of surface and infiltrated waters, an unknown peak was selected for identification with LC–MS–MS. This compound was identified as hexamethoxymethylmelamine (HMMM), a chemical often used in the coating industry. This is the first time the presence of this chemical in surface waters has been reported. In addition to HMMM, two other structurally related compounds were found to be present in the investigated surface water. A standard mixture of HMMM and its by-products did not exhibit (geno)toxicity under the test conditions applied in this study. In another example, a genotoxic fraction of an industrial wastewater was isolated and examined by LC–MS–MS using a modern quadrupole–orthogonal acceleration-time-of-flight mass spectrometer (Q-TOF). Four compounds were detected. The structures of two compounds present are proposed to be 9-amino-2-hydroxy-acridine and 9-hydroxy-acridine-N-oxide or its structural isomer dihydroxy-acridine. Confirmation with standards could not be carried out, as pure compounds are not available. The other two compounds (structural isomers) could not be identified based on the data available within this study.     

A continuous preconcentration/extraction method for organic trace analysis by capillary gas chromatography

Summary A slightly modified steam distillation-extraction device is described for the continuous extraction and preconcentration of organic traces in aqueous samples, prior to capillary G.C.-analysis. The quantitative performance, both theoretically and practically, is studied using phenols as the test substances. The final recovery is determined by the flow-ratio of the water and the extracting solvent and by the extraction coefficient. The process is found to be highly reproducible even at low concentration levels (ppb’s). Using 30 ml. samples with a concentration of 30 ppb (1:10^9), 100 % recoveries are obtained for the phenolic substances studied, with a relative standard deviation of about 3 %, both for methylene chloride and ethylacetate as the extracting solvents. Using methylene chloride as the extracting solvent, for phenol a maximum recovery of 80 % was obtained. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Selective removal of water in purge and cold-trap capmary gas chromatographic analysis of volatile organic traces in aqueous samples

The design and features of an on-line purge and cold-trap pre-concentration device for rapid analysis of volatile organic compounds in aqueous samples are discussed. Excessive water is removed from the purge gas by a condenser or a water permeable membrane in order to avoid blocking of the capillary cold-trap. Synthetic mixtures covering concentrations ranging from tenths to tens of ppb's and different chemical classes are used to study the effect of various process factors on the efficiency and selectivity of water removal as well as on the purging recovery. The importance of the concentration of the solutes, the flow rate in conjunction with the volume of the purge gas, and the temperature of the condenser, the cold-trap and the sample is emphasized. Theoretical models describing the purge process and the blocking of the cold-trap agree fairly well with the highly reproducible experimental results (σ = 2–4%). Both the condenser and the Nafion membrane successfully remove water, although some compounds, dependent on volatility and polarity, are partly or completely lost. It is shown that non-polar volatile organic compounds are efficiently enriched so that recoveries between 80–100% and a detection limit of 1 ppt can be obtained. The applicability of the system is illustrated on some examples.     

Automated analysis of polar pesticides in water by on-line solid phase extraction and gas chromatography using the co-solvent effect

In order to meet the requirements of analyzing very low concentrations of pesticides in water (typically at 0.1 μg/l or less), samples have to be concentrated prior to GC-analysis. Samplie pre-concentration by off-line methods based on solid phase extraction (SPE) or liquid-liquid extraction are very time consuming and cumbersome. Moreover, the quantitative performance of the analytical method as a whole in terms of accuracy and reliability is seriously hindered by elaborate, manually performed sample pre-treatment steps. This paper describes an automated method based on solid phase extraction and capillary gas chromatography. The technique was applied for the analysis of 31 polar organophosphorus and organonitrogen pesticides. A commercially available HPLC/GC instrument is modified, using the LC-part for solid phase extraction. The sample, of which only a few ml's is required to obtain sufficiently low detection limits, is delivered by a robotic large volume autosampler. After solid phase extraction and elution, the eluate is transferred into the GC via a so called “loop type interface”. In this paper the instrumentation and analytical methodology is described, as well as the main validation results. The quantitative performance (i.e. recovery and repeatability) of the most polar solutes like metamitron and dimethoate appears to be better than obtained with off-line SPE as a result of the more beneficial ratio between the amount of sorbent and the sample volume. As the loop-type interface causes losses of the most volatile compounds, a co-solvent is added. This co-solvent provides sufficient trapping capacity in the capillary pre-columns to allow quantitative analysis of even the most volatile pesticides. Moreover a better separation of early eluting compounds is also established.     

High-performance liquid chromatography--ToxPrint: chromatographic analysis with a novel (geno)toxicity detection.

In order to aid the monitoring of the overall quality of (surface) waters a new analytical approach has been developed, combining on-line solid-phase extraction, HPLC separation and effect-related detection. Compounds present in surface water or wastewater samples are extracted on-line with Oasis [poly(divinylbenzene-co-N-vinylpyrrolidone)] material and directly fractionated by reversed-phase HPLC. The eluent of the total chromatogram is collected on a microtitre plate in fractions of 1 min each. After evaporation and re-dissolvation in a suitable solvent, the (geno)toxicity of the individual fractions before and after enzymatic activation with S9, is determined with the umu test. In this way, harmful compounds can be detected and localized in the HPLC-diode array detection trace even without their identity and exact concentration being known at that moment. The method was developed using two test compounds, 4-nitroquinoline-N-oxide and 2-aminoanthracene. Compounds with mutagenic properties comparable to those of the test compounds can be detected from 0.1 microg/l, which is a concentration relevant for surface waters. The new analytical approach was successfully applied to various types of model samples, as well as real wastewater.     

Detector Systems in Capillary Gas Chromatography

Expressions for the minimum detectable amount Q_o and the minimum analyte concentration C_o as functions of the chromatographic parameters are derived for both mass and concentration sensitive detectors. The effects of pressure drop, column inner diameter, and film thickness are given. The minimum analyte concentration for mass flow sensitive detectors, C_o^m, can be reduced considerably by selecting the carrier gas velocity well above its optimum value (related to H_min), however, at the cost of long columns and long analysis times. For Q_o the improvements can be neglected, and so the analysis can best be performed at u_opt. When the flow rate in the detector, F_d, is equal to the column flow rate F_c, the maximum permissible detector volume of concentration sensitive detectors is proportional to d_c² up to d_c³, and so narrow bore columns require detectors of extremely small volume. Make-up gas has to be added when the actual volume is too large, thus worsening the detectability. Another approach, vacuum operation of the detector cell, appears to be very attractive. On the other hand, when wide bore columns are used in combination with small volume concentration sensitive detectors, very small values of Q_o^c and C_o^c are obtainable when the abundant carrier gas can be removed before entering the detector cell. Digital noise filtering can further reduce the obtainable Q_o and C_o values, especially for broad peaks and thus for wide bore columns.