Ian Fowlis

Extraction of polycyclic aromatic hydrocarbons from highly contaminated soils using microwave energy

Microwave energy, generated in a commercial microwave system designed for extraction of organic samples, has been used for the extraction of polycyclic aromatic hydrocarbons (PAHs) from highly contaminated land samples. Initial studies used a native soil and compared a 20 min microwave extraction with a 6 h conventional Soxhlet extraction (both using dichloromethane) with comparable results. The low concentration of PAHs found in the soil resulted in large relative standard deviation (sr) values for the individual PAHs (maximum of 60.9% for microwave extraction). A second soil, with higher PAH levels, was microwave extracted using both dichloromethane and different compositions of an acetone–hexane mixture and compared with Soxhlet extraction. The results indicate that microwave extraction using pure acetone is a more efficient procedure than other combinations studied. A repeatability study gave an sr value for the total PAHs extracted of 2.4%(n= 6). A central composite experimental design was used to elucidate optimum operating parameters but variations in temperature, extraction time and solvent volume were found to have little effect on recovery. The over-all sr for the design was 5.34% illustrating no statistical significance in recovery. A third, Laboratory of the Government Chemist, test soil was used which indicated that the soil matrix was the greatest factor affecting PAH recovery.

Automated determination of s-triazine herbicides using solid-phase microextraction

Solid-phase microextraction (SPME) allows the determination of pollutants in aqueous solution by the adsorption of analytes onto stationary-phase coated fused-silica fibres followed by thermal desorption in the injection system of a capillary column gas chromatograph. This technique has been fully automated using a Varian 8100 autosampler and 3400 gas chromatograph fitted with a nitrogen-phosphorus flame thermionic detector. Fibres coated with 7-μm and 100-μm film thicknesses were used to evaluate the adsorption and desorption of four s-triazines. The resulting gas chromatographic peaks desorbed from the fibres were shown to be comparable to those obtained with direct manual injection. The 7-μm fibre, designed for the analysis of semi-volatile analytes was used to investigate the effect of desorption temperature and on-column focusing temperatures on peak response. The desorption temperature was found to be non-critical and an optimum focusing temperature of 40°C was used throughout the analysis. Evaluation of the 100-μm film fibre demonstrated its potential to adsorb greater quantities of analyte from solution and this study established that an adsorption time of 15 min gave an equilibrium distribution of the solutes between the stationary and liquid phases. With the thicker film fibre it was noted that the effectiveness of the desorption process was reduced at temperatures below 140°C. The linear dynamic range of the technique was evaluated over three orders of magnitude. To enhance method sensitivity, the fibre was used to extract a 0.1 ppb solution of herbicide by repeatedly adsorbing and desorbing from the same solution and focusing the combined solutes at the front of the analytical column prior to elution and analysis.

Simultaneous quantitation of sixteen organochlorine pesticides in drinking waters using automated solid-phase extraction, high-volume injection, high-resolution gas chromatography

A method is described for the simultaneous determination of sixteen organochlorine pesticides in drinking water using automated solid-phase extraction followed by high-volume (80 microliters) capillary column gas chromatography using electron capture detection. The fully automated extraction method followed by high-volume injection permits rapid sample analysis compared to previously described procedures since no further pre-concentration of the analytes is necessary after they have been eluted from the octadecyl solid-phase extraction cartridge. The lowest detectable concentrations of the pesticides are between 1-5 ng l(-1), relative recoveries range from 92-105% in tap water spiked at 100 ng l(-1) and the relative standard deviations are in the range 5-12%.

Evaluation and application of static headspace–multicapillary column-gas chromatography–ion mobility spectrometry for complex sample analysis

An evaluation of static headspace-multicapillary column-gas chromatography-ion mobility spectrometry (SHS-MCC-GC-IMS) has been undertaken to assess its applicability for the determination of 32 volatile compounds (VCs). The key experimental variables of sample incubation time and temperature have been evaluated alongside the MCC-GC variables of column polarity, syringe temperature, injection temperature, injection volume, column temperature and carrier gas flow rate coupled with the IMS variables of temperature and drift gas flow rate. This evaluation resulted in six sets of experimental variables being required to separate the 32 VCs. The optimum experimental variables for SHS-MCC-GC-IMS, the retention time and drift time operating parameters were determined; to normalise the operating parameters, the relative drift time and normalised reduced ion mobility for each VC were determined. In addition, a full theoretical explanation is provided on the formation of the monomer, dimer and trimer of a VC. The optimum operating condition for each VC calibration data was obtained alongside limit of detection (LOD) and limit of quantitation (LOQ) values. Typical detection limits ranged from 0.1ng bis(methylthio)methane, ethylbutanoate and (E)-2-nonenal to 472ng isovaleric acid with correlation coefficient (R(2)) data ranging from 0.9793 (for the dimer of octanal) through to 0.9990 (for isobutyric acid). Finally, the developed protocols were applied to the analysis of malodour in sock samples. Initial work involved spiking an inert matrix and sock samples with appropriate concentrations of eight VCs. The average recovery from the inert matrix was 101±18% (n=8), while recoveries from the sock samples were lower, that is, 54±30% (n=8) for sock type 1 and 78±24% (n=6) for sock type 2. Finally, SHS-MCC-GC-IMS was applied to sock malodour in a field trial based on 11 volunteers (mixed gender) over a 3-week period. By applying the SHS-MCC-GC-IMS database, four VCs were identified and quantified: ammonia, dimethyl disulphide, dimethyl trisulphide and butyric acid. A link was identified between the presence of high ammonia and dimethyl disulphide concentrations and a high malodour odour grading, that is, ≥ 6. Statistical analysis did not find any correlation between the occurrence of dimethyl disulphide and participant gender.

Extraction of polycyclic aromatic hydrocarbons from highly contaminated soils : a comparison between Soxhlet, microwave and supercritical fluid extraction techniques

A direct comparison between Soxhlet, microwave-assisted extraction and supercritical fluid extraction is made. Each technique was used to extract sixteen polycyclic aromatic hydrocarbons (PAHs) from a native, contaminated soil. The total amounts of PAHs found were 297.4, 422.9 and 458.0 mg kg–1 using Soxhlet, microwave-assisted extraction and supercritical fluid extraction. The merits and disadvantages of each extraction technique is discussed.

Analysis of Listeria using exogenous volatile organic compound metabolites and their detection by static headspace–multi-capillary column–gas chromatography–ion mobility spectrometry (SHS–MCC–GC–IMS)

Listeria monocytogenes is a Gram-positive bacterium and an opportunistic food-borne pathogen which poses significant risk to the immune-compromised and pregnant due to the increased likelihood of acquiring infection and potential transmission of infection to the unborn child. Conventional methods of analysis suffer from either long turn-around times or lack the ability to discriminate between Listeria spp. reliably. This paper investigates an alternative method of detecting Listeria spp. using two novel enzyme substrates that liberate exogenous volatile organic compounds in the presence of α-mannosidase and d-alanyl aminopeptidase. The discriminating capabilities of this approach for identifying L. monocytogenes from other species of Listeria are investigated. The liberated volatile organic compounds (VOCs) are detected using an automated analytical technique based on static headspace–multi-capillary column–gas chromatography–ion mobility spectrometry (SHS–MCC–GC–IMS). The results obtained by SHS–MCC–GC–IMS are compared with those obtained by the more conventional analytical technique of headspace–solid phase microextraction–gas chromatography–mass spectrometry (HS–SPME–GC–MS). The results found that it was possible to differentiate between L. monocytogenes and L. ivanovii, based on their VOC response from α-mannosidase activity.

Source, impact and removal of malodour from soiled clothing

Static headspace--multi-capillary column--gas chromatography--ion mobility spectrometry (SHS-MCC-GC-IMS) has been applied to the analysis of malodour compounds from soiled clothing (socks and T-shirts), pre- and post washing, at low temperature (20°C). Six volatile compounds (VCs) (i.e. butyric acid, dimethyl disulfide, dimethyl trisulfide, 2-heptanone, 2-nonanone and 2-octanone) were identified. After sensory evaluation of soiled garments they were subjected to laundering with non-perfumed washing powder. The efficiency of the laundering process was evaluated by determining the reduction of each detected volatile compound (VC) post-wash (damp) for socks and T-shirts; VC concentration reductions of between 16 and 100% were noted, irrespective of sample type. Additionally the T-shirt study considered the change in VC concentration post-wash (dry) i.e. after the drying process at ambient temperature. Overall VC concentration reductions of between 25 and 98% were noted for T-shirt samples pre-wash to post-wash (dry). Finally, a potential biochemical metabolic pathway for the formation of malodour compounds associated with bacteria in axillary sweat is proposed.