Optimization strategies of in-tube extraction (ITEX) methods.

Microextraction techniques, especially dynamic techniques like in-tube extraction (ITEX), can require an extensive method optimization procedure. This work summarizes the experiences from several methods and gives recommendations for the setting of proper extraction conditions to minimize experimental effort. Therefore, the governing parameters of the extraction and injection stages are discussed. This includes the relative extraction efficiencies of 11 kinds of sorbent tubes, either commercially available or custom made, regarding 53 analytes from different classes of compounds. They cover aromatics, heterocyclic aromatics, halogenated hydrocarbons, fuel oxygenates, alcohols, esters, and aldehydes. The number of extraction strokes and the corresponding extraction flow, also in dependence of the expected analyte concentrations, are discussed as well as the interactions between sample and extraction phase temperature. The injection parameters cover two different injection methods. The first is intended for the analysis of highly volatile analytes and the second either for the analysis of lower volatile analytes or when the analytes can be re-focused by a cold trap. The desorption volume, the desorption temperature, and the desorption flow are compared, together with the suitability of both methods for analytes of varying volatilities. The results are summarized in a flow chart, which can be used to select favorable starting conditions for further method optimization.

In-Tube Extraction-GC-MS as a High-Capacity Enrichment Technique for the Analysis of Alcoholic Beverages.

An in-tube extraction (ITEX) method for the GC-MS analysis of volatile constituents of alcoholic beverages was developed and applied in the analysis of 46 beers from six varieties, Alt, Helles, Kölsch, Pilsener beer, Schwarzbier, and wheat beer, which are popular in Germany. The extraction performance of nine different sorbent materials was evaluated. The best overall sensitivity was achieved using Tenax TA, with method detection limits down to 0.01 µg L-1, whereas the widest linear range was possible with PDMS, covering almost 5 orders of magnitude. This is the first application of PDMS in ITEX as a high-capacity extraction device and highlights the importance of choosing the appropriate sorbent material for the analytical task at hand. A satisfying chemometric discrimination of all analyzed beer varieties was possible, and alcohol-free beers could clearly be separated from regular beers, also.

Fingerprinting of red wine by headspace solid-phase dynamic extraction of volatile constituents.

Headspace solid-phase dynamic extraction (HS-SPDE) was investigated for its applicability in quality control analysis of wine volatiles using gas chromatography-mass spectrometry. In total, 196 German red wines were analysed and 22 flavour-relevant alcohols and esters were quantified. The method detection limits were between 0.1 and 9.3 µg L(-1), allowing the dilution of the samples to decrease matrix and competition effects. Quantification resulted in a concentration range from about 1 µg L(-1) linalool up to 380 mg L(-1) 2-methyl-1-propanol. The measurement uncertainty budget was determined for all compounds in a "top-down" approach and was between 2.5 and 7.9%, with an average of 5.5%. A surveillance of the extraction performance of the HS-SPDE devices showed constant results for up to 400 extractions using one extraction needle tip. A chromatogram library for quality and authenticity control of wine samples was created using commercially available chromatogram comparison software.

Solvent-free microextraction techniques in gas chromatography.

Microextraction techniques represent a major part of modern sample preparation in the analysis of organic micropollutants. This article provides a short overview of recent developments in solvent-free microextraction techniques. From the first open-tubular trap techniques in the mid-1980s to recent packed-needle devices, different implementations of in-needle packings for microextraction are discussed with their characteristic benefits, shortcomings and possible sampling modes. Special emphasis is placed on methods providing full automation and solvent exclusion. In this context, in-tube extraction and the needle trap are discussed, with an overview of current research on new sorbent materials, together with the requirements for more efficient method development.

Compound-specific chlorine isotope analysis: a comparison of gas chromatography/isotope ratio mass spectrometry and gas chromatography/quadrupole mass spectrometry methods in an interlaboratory study.

Chlorine isotope analysis of chlorinated hydrocarbons like trichloroethylene (TCE) is of emerging demand because these species are important environmental pollutants. Continuous flow analysis of noncombusted TCE molecules, either by gas chromatography/isotope ratio mass spectrometry (GC/IRMS) or by GC/quadrupole mass spectrometry (GC/qMS), was recently brought forward as innovative analytical solution. Despite early implementations, a benchmark for routine applications has been missing. This study systematically compared the performance of GC/qMS versus GC/IRMS in six laboratories involving eight different instruments (GC/IRMS, Isoprime and Thermo MAT-253; GC/qMS, Agilent 5973N, two Agilent 5975C, two Thermo DSQII, and one Thermo DSQI). Calibrations of (37)Cl/(35)Cl instrument data against the international SMOC scale (Standard Mean Ocean Chloride) deviated between instruments and over time. Therefore, at least two calibration standards are required to obtain true differences between samples. Amount dependency of δ(37)Cl was pronounced for some instruments, but could be eliminated by corrections, or by adjusting amplitudes of standards and samples. Precision decreased in the order GC/IRMS (1σ ≈ 0.1‰), to GC/qMS (1σ ≈ 0.2-0.5‰ for Agilent GC/qMS and 1σ ≈ 0.2-0.9‰ for Thermo GC/qMS). Nonetheless, δ(37)Cl values between laboratories showed good agreement when the same external standards were used. These results lend confidence to the methods and may serve as a benchmark for future applications.

In-tube extraction of volatile organic compounds from aqueous samples: an economical alternative to purge and trap enrichment.

A novel in-tube extraction device (ITEX 2) for headspace sampling was evaluated for GC/MS analysis of aqueous samples. Twenty compounds of regulatory and drinking water quality importance were analyzed, including halogenated hydrocarbons, BTEX compounds (benzene, toluene, ethylbenzene, xylenes), fuel oxygenates, geosmin, and 2-methylisoborneol. Five commercially available sorbent traps were compared for their compound specific extraction yield. On the basis of the results, a mixed bed trap was prepared and evaluated. The extraction parameters were optimized to yield maximum sensitivity within the time of a GC run, to avoid unnecessary downtime of the system. Method detection limits of 1-10 ng L(-1) were achieved for volatile organic compounds (VOCs), which is much lower than demands by regulatory limit values. The performance of the ITEX system is similar to that of purge and trap systems, but it requires lower sample volumes and is less prone to contamination, much simpler, more flexible, and affordable. Average relative standard deviations below 10% were achieved for all analytes, and recoveries from spiked tap water samples were between 90% and 103%, mostly. The extraction is nonexhaustive, removing a fraction of 7% to 55% of the target compounds, depending on the air-water partitioning coefficients. The method was also tested with nonsynthetic samples, including tap, pond, and reservoir water and different soft drinks.