Solid-phase extraction combined with dispersive liquid-liquid microextraction for the determination for polybrominated diphenyl ethers in different environmental matrices

pH-controlled dispersive liquid-liquid microextraction for the analysis of ionisable compounds in complex matrices: Case study of ochratoxin A in cereals

A new sample preparation procedure, termed pH-controlled dispersive liquid-liquid microextraction (pH-DLLME), has been developed for the analysis of ionisable compounds in highly complex matrices. This DLLME mode, intended to improve the selectivity and to expand the application range of DLLME, is based on two successive DLLMEs conducted at opposite pH values. pH-DLLME was applied to determination of ochratoxin A (OTA) in cereals. The hydrophobic matrix interferences in the raw methanol extract (disperser, 1mL) were removed by a first DLLME (I DLLME) performed at pH 8 to reduce the solubility of OTA in the extractant (CCl(4), 400μL). The pH of the aqueous phase was then adjusted to 2, and the analyte was extracted and concentrated by a second DLLME (extractant, 150μL C(2)H(4)Br(2)). The main factors influencing the efficiency of pH-DLLME including type and volume of I DLLME extractant, as well as the parameters affecting the OTA extraction by II DLLME, were studied in detail. Under optimum conditions, the method has detection and quantification limits of 0.019 and 0.062μg kg(-1), respectively, with OTA recoveries in the range of 81.2-90.1% (n=3). The accuracy of the analytical procedure, evaluated with a reference material (cereal naturally contaminated with OTA), is acceptable (accuracy of 85.6%±1.7, n=5). The applicability of pH-DLLME to the selective extraction of other ionisable compounds, such as acidic and basic pharmaceutical products was also demonstrated. The additional advantages of pH-DLLME are a higher selectivity and the extension of this microextraction technique to highly complex matrices.

Development, validation, and application of a liquid chromatography-tandem mass spectrometry method for the determination of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol in human hair

The tobacco-specific nitrosamine metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) is a valuable biomarker for human exposure to the carcinogenic nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in tobacco and tobacco smoke. In this work, an efficient and sensitive method for the analysis of NNAL in human hair was developed and validated. The hair sample was extracted by NaOH solution digestion, purified by C(18) solid-phase extraction (SPE) and molecularly imprinted solid-phase extraction, further enriched by reverse-phase ultrasound-assisted dispersive liquid-liquid microextraction (USA-DLLME) into 1.0 % aqueous formic acid, and finally analyzed by liquid chromatography-electrospray ionization tandem mass spectrometry. Good linearity was obtained in the range of 0.24-10.0 pg/mg hair with a correlation coefficient of 0.9982, when 150 mg hair was analyzed. The limit of detection and lower limit of quantification were 0.08 and 0.24 pg/mg hair, respectively. Accuracies determined from hair samples spiked with three different levels of NNAL ranged between 87.3 and 107.7 %. Intra- and inter-day relative standard deviations varied from 4.1 to 8.5 % and from 6.9 to 11.3 %, respectively. Under the optimized conditions, an enrichment factor of 20 was obtained. Finally, the developed method was applied for the analysis of NNAL in smokers' hair. The proposed sample preparation procedure combining selectivity of two-step SPE and enrichment of DLLME significantly improves the purification and enrichment of the analyte and should be useful to analyze NNAL in hair samples for cancer risk evaluation and cancer prevention in relation to exposure to the tobacco-specific carcinogen NNK.

Determination of phthalate esters in water samples by ionic liquid cold-induced aggregation dispersive liquid-liquid microextraction coupled with high-performance liquid chromatography

A novel method, termed ionic liquid cold-induced aggregation dispersive liquid-liquid microextraction (IL-CIA-DLLME), combined with high-performance liquid chromatography (HPLC) was developed for the determination of three phthalate esters in water samples. Several important parameters influencing the IL-CIA-DLLME extraction efficiency, such as the type of extraction and disperser solvent, the volume of extraction and disperser solvent, temperature, extraction time and salt effect, were investigated. Under optimal extraction conditions, the enrichment factors and extraction recoveries ranged from 174 to 212 and 69.9 to 84.8%, respectively. Excellent linearity with coefficients of correlation from 0.9968 to 0.9994 was observed in the concentration range of 2-100 ng mL(-1). The repeatability of the proposed method expressed as relative standard deviations ranged from 2.2 to 3.7% (n=5). Limits of detection were between 0.68 and 1.36 ng mL(-1). Good relative recoveries for phthalate esters in tap, bottled mineral and river water samples were obtained in the ranges of 91.5-98.1%, 92.4-99.2% and 90.1-96.8%, respectively. Thus, the proposed method has excellent potential for the determination of phthalate esters in the environmental field.

Development of analytical procedures for trace-level determination of polybrominated diphenyl ethers and tetrabromobisphenol A in river water and sediment

The aim of this work was to develop procedures for the simultaneous determination of selected brominated flame retardants (BFRs) in river water and in river bed sediment. The target analytes were polybrominated diphenyl ethers (PBDEs) and tetrabromobisphenol A (TBBPA). To determine dissolved BFRs, a novel mixed-mode solid-phase extraction procedure was developed by combining a hydrophobic sorbent (C(18)) with a silica-based anion exchange sorbent, so as to overcome the negative artefact induced by dissolved organic carbon. Extraction recoveries exceeded 73% for most analytes, except for BDE-183 and BDE-209 (57%). As regards suspended sediment and river bed sediment, extraction was carried out by means of ultrasonication (recoveries: 73-94%). These procedures, combined to gas chromatography coupled to negative chemical ionisation mass spectrometry (GC-NCI-MS), enabled the determination of BFRs at trace level: 3-160 pg L(-1) in river water, 5-145 pg g(-1) in bed sediment. These methods were applied to the determination of PBDEs and TBBPA in a suburban river (near Paris, France). PBDEs were systematically detected in the water column (SigmaBDEs, 2,300-4,300 pg L(-1)); they partitioned between the dissolved and particulate phases and BDE-209 was the dominant congener, followed by BDE-99 and BDE-47. TBBPA was detected in the dissolved phase only (<35-68 pg L(-1)). All selected BFRs were ubiquitous in bed sediments and levels ranged from 3,100 to 15,100 pg g(-1) and from 70 to 280 pg g(-1) (dry weight), for SigmaBDEs and TBBPA, respectively.