Supported liquid membrane microextraction with high-performance liquid chromatography–UV detection for monitoring trace haloacetic acids in water

Comparison of three sorbents for thin film solid phase microextraction of haloacetic acids from water

Water disinfection inevitably leads to disinfection byproduct formation, such as haloacetic acids. Many disinfection byproducts reportedly have adverse health effects and, in many instances, including four haloacetic acids, are classified as potential carcinogens. As the global awareness of these compounds increases, more regulatory bodies include certain disinfection byproduct groups in their regulations. Rugged, fast, and cheap analytical quantification methods are therefore crucial. In this paper, a thin film extraction method for haloacetic acids is outlined. Thin films were synthesized in-house using a spin coating procedure, which allowed for easy adjustment of the sorbent choice and film geometry. PDMS, Carboxen®, and HLB were of interest and their extraction potential for HAAs from spiked water was tested in three film variations. PDMS films impregnated with HLB or Carboxen® improved the extraction drastically compared to PDMS films. Specifically, HLB impregnated films achieved excellent extraction efficiencies for tri-substituted analytes (51% for BDCAA, 77% for CDBAA, and 92% TBAA), which are often present at extremely low concentrations in water. In addition to the extraction experiment, a computational model was applied to compare PDMS and HLB. Trends observed in the computational data reflected in the experimental results, showing the validity of the model and confirming that physisorption through hydrogen bonding was mainly responsible for successful extraction.

Enhanced detection of monoiodoacetic acid at ng/L level by ion chromatography with novel derivatization-free pretreatment

Concerns have recently arisen regarding the formation of carcinogenic and genotoxic iodinated haloacetic acids (HAAs), such as monoiodoacetic acid (MIAA), during the disinfection of iodine-containing water with chloramine. Existing detection methods for MIAA rely on either labor-intensive derivatization operations or expensive instruments, making analysis challenging. To bypass these issues, this study proposed a novel two-step liquid-liquid extraction strategy to enrich MIAA and then pioneered the integration of common ion chromatography (IC) with an ultraviolet detector to measure trace MIAA precisely. This novel approach achieved a remarkable 155.6-fold enrichment of MIAA and significantly reduced the need for water and chemicals, hence enhancing its efficiency and environmental friendliness. Besides, this method effectively removed coexisting anions and separated MIAA from other interferents by adjusting IC column and eluent conditions. The method detection limit of MIAA is an impressive 21.44 ng/L, and the recoveries in synthetic and real water samples ranged from 85 to 113%, with maximum deviations of 7.59%. We validated the reliability of our approach by comparing it with the USEPA 552.3 method. In conclusion, this IC-based method proves to be a robust and environment-benign solution for detecting trace MIAA in complex water components.

Derivatization-free multi-step extraction for trace haloacetic acids analysis with ion chromatography: Performance and mechanisms

Haloacetic acids (HAAs) are a type of disinfection byproducts commonly found in drinking water with carcinogenic, mutagenic, or teratogenic risks to humans. Currently, the analytical methods of trace HAAs are either labor-intensive or very expensive. We herein propose a facile multiple-step extraction strategy for HAAs analysis with common ion chromatography (IC). This study is based on a fundamental water chemistry principle that HAAs become protonated featuring positive logK_ow values (> 0.34) under pH < pK_a but deprotonated featuring negative logK_ow values (< -2.37) under pH > pK_a. By taking advantage of the species and property switches, HAAs can be extracted and enriched into methyl tert-butyl ether first at pH < 0.5 and then back-extracted into neutral water and enriched again. Equally important, interfering anions in IC chromatogram are eliminated because they have negative logK_ow values. Verification results show that HAAs were enriched by 11.4 times in average while interfering anions were almost eliminated (> 99%). Although similar to USEPA Method 552.3 in method detection limits (0.033-0.246 μg/L), recoveries (70%~110%), and relative standard deviations (< 9.91%), this method took ≤ 70 min to run a batch of samples without derivatization, which takes over 2 h. The methodology may be applicable to other pollutants that also have contrasting K_ow values at different pH.

Hollow fibre supported liquid membrane extraction for BTEX metabolites analysis in human teeth as biomarkers

The use of human teeth as biomarkers has been previously applied to characterize environmental exposure mainly to metal contamination. Difficulties arise when the contaminants are volatile or its concentration level is very low. This study presents the development of a methodology based on the transport through hollow fibre membrane liquid-phase microextraction (HF-LPME), followed by HPLC-UV measurement, to determine three different metabolites of BTEX contaminants, mandelic acid (MA), hyppuric acid (HA), and methylhippuric acid (4mHA). The driving force for the liquid membrane has been studied by using both non-facilitated (pH gradient 2-12) and facilitated transport (ionic and non-ionic carriers). Enrichment factors of several hundreds were accomplished. Different ionic and non-ionic water insoluble compounds were used as metabolite carriers for the facilitated transport at HF-LPME. Three organic solvents were used to constitute the liquid membrane, dodecane, dihexyl ether and n-decanol. Other parameters affecting the extraction process, such as extraction time, stirring speed, acceptor buffer and salt content were optimised in spiked solutions and selected those that presented the best enrichment factors for all analytes. Final conditions were established for donor solution as 20mL, pH2 of 0.5M NaCl, the OLM (Organic Liquid Membrane) as n-decanol and the acceptor solution as 40μL of 1M NaOH. The selected extraction time was 20h with stirring speed of 500rpm. Validation of the optimised method included the determination of individual linearity range (MA: 0.002-5.7μg; HA: 0.01-7.9μg; 4mHA 0.002-5.3μg), limits of detection (MA: 1.6ng; HA: 0.2ng; 4mHA 0.2ng), repeatability (RSD 7-10%) and reproducibility (5-8%). The developed method was applied to the analysis of MA, HA and 4mHA in teeth samples of 8 workers exposed to BTEX.

Tributyl phosphate assisted hollow-fiber liquid-phase microextraction of short-chain fatty acids in microbial degradation fluid using capillary electrophoresis-contactless coupled conductivity detection

A tributyl phosphate assisted hollow-fiber liquid-phase microextraction coupled with capillary electrophoresis-contactless coupled conductivity detection (HF-LPME/CE-C⁴D) method has been developed for trace analysis of common short-chain fatty acids (SCFAs) without derivatization. Under the optimum conditions, ten SCFAs including a pair of isomers were well separated from their homologous FAs and the main coexisting inorganic anions within 40 min. Tributyl phosphate assisted HF-LPME produced excellent purification and enrichment for the model sample with high-salt matrix, microbial degradation fluid, and the limits of detection could reach 0.072-0.67 ng/mL (S/N = 3). Owing to its high sensitivity, good linearity, and acceptable recovery, this proposed method provided a sensitive and environment-friendly alternative for trace analysis of SCFAs in complicated samples.

Hollow fibre liquid phase micro-extraction by facilitated anionic exchange for the determination of flavonoids in faba beans (Vicia faba L.)

INTRODUCTION

Flavonoids are polyphenolic compounds found ubiquitously in foods of plant origin. They are commonly extracted from plant materials with ethanol, methanol, water, their combination or even with acidified extracting solutions. The disadvantages of these methods are the use of high quantity of organic solvent, the possible loss of analytes in the different steps and the laborious process of the techniques. In addition, the complexity of the phenolic mixtures present in plant materials requires a preliminary clean-up and fractionation of the crude extracts.

OBJECTIVE

To develop a hollow fibre liquid phase micro-extraction (HF-LPME) method for a one step clean-up and pre-concentration of flavonoids.

METHODOLOGY

Two flavonoids (catechin and rutin) has been extracted by HF-LPME and analysed by HPLC. The related driving force for the liquid membrane has been studied by means of facilitated and non-facilitated transport. Different ionic and non-ionic water insoluble compounds [trioctylamine (TOA), tributyl phosphate (TBP), trioctylphosphine oxide (TOPO) and methyltrioctylammonium chloride (aliquat 336)] were used as carriers. The liquid membrane was constituted by a solution of n-decanol in the presence or absence of carriers.

RESULTS

Maximum enrichment factors were obtained with n-decanol/aliquat 336 (20%) as organic liquid membrane, sodium hydroxide (NaOH) (0.1 M) as donor solution, sodium chloride (NaCl) (2 M) as acceptor solution and 3 h as extraction time. Under these conditions, good results for validation parameters were obtained [for linearity, limit of detection (LOD), limit of quantitation (LOQ) and repeatability].

CONCLUSIONS

The developed method is simple, effective and has been successfully applied to determine catechin and rutin in ethanolic extracts of faba beans.

Recent advances in applications of capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D): an update

Capillary electrophoresis with a capacitively contactless conductivity detector (CE-C⁴D) is becoming a significant useful technique for the analysis of analytes in various fields such as pharmaceutical, biomedical, food and environmental. This review is an update describing the recent developments in the application of CE with a C⁴D detector.

Electro membrane extraction combined with capillary electrophoresis for the determination of amlodipine enantiomers in biological samples

Electro membrane extraction as a new microextraction method was applied for the extraction of amlodipine (AM) enantiomers from biological samples. During the extraction time of 15  min, AM enantiomers migrated from a 3  mL sample solution, through a supported liquid membrane into a 20  μL acceptor solution presented inside the lumen of the hollow fiber. The driving force of the extraction was 200  V potential, with the negative electrode in the acceptor solution and the positive electrode in the sample solution. 2-Nitro phenyl octylether was used as the supported liquid membrane. Using 10  mM HCl as background electrolyte in the sample and acceptor solution, enrichment up to 124 times was achieved. Then, the extract was analyzed using CD modified CE method for separation of AM enantiomers. Best results were achieved using a phosphate running buffer (100  mM, pH 2.0) containing 5  mM hydroxypropyl-α-CD. The range of quantitation for both enantiomers was 10-500  ng/mL. Intra- and interday RSD (n=6) were less than 14%. The limits of quantitation and detection for both enantiomers were 10 and 3  ng/mL respectively. Finally, this procedure was applied to determine the concentration of AM enantiomers in plasma and urine samples.

Optimisation and comparison of several microextraction/methylation methods for determining haloacetic acids in water using gas chromatography

This article presents the different modes and configurations of liquid-phase microextraction (LPME) through comparison with headspace solid-phase microextraction (HS-SPME) for the simultaneous extraction/methylation of the nine haloacetic acids (HAAs) found in water. This is the first analytical case reported of solvent bar extraction-preconcentration-derivatisation assisted by an ion-pairing transfer for HAAs. In this method, 5 muL of the organic extractant, decane, was confined within a hollow-fibre membrane that was placed in a stirred aqueous sample containing the derivatising reagents (dimethylsulphate with a tetrabutylammonium salt). With heating at 45 degrees C in the HS-SPME method, some organic solvents (extractant, excess of derivatising reagent) are also volatilised and compete with the esters on the fibre (the fibre is damaged and it can be reused only 50-60 times). In addition, the HS-SPME method provides inadequate sensitivity (limits of detections between 0.3 and 5 microg/L) to quantify HAAs at the level usually found in drinking waters. Alternative headspace LPME methods for HAAs require heating (45 degrees C, 25 min) to derivatise and volatilise the esters but, by using solvent bar microextraction (SBME), the extraction/methylation takes place at room temperature without degradation of HAAs to trihalomethanes. Adequate precision (relative standard deviation of approximately 8%), linearity (0.1-500 microg/L) and sensitivity (10 times higher than the HS-SPME alternative) indicate that the SBME method can be a candidate for routine determination of HAAs in tap water. Finally, the SBME method was applied for the analysis of HAAs in tap and swimming pool water and the results were compared with those of a previous validated headspace gas chromatography-mass spectrometry method.

Micro-scale membrane extraction of glyphosate and aminomethylphosphonic acid in water followed by high-performance liquid chromatography and post-column derivatization with fluorescence detector

A carrier-mediated supported liquid membrane micro-extraction using single hollow fiber membrane suitable for the determination of the herbicide glyphosate and its main metabolite aminomethylphosphonic acid in water is reported. A solution of 0.20 M Aliquat-336, a cationic carrier, in di-n-hexyl ether was selected as the supported liquid. A 20 microL of 1.0 M potassium chloride as the acceptor phase was filled in the membrane lumen. The membrane was immersed in a 20 mL of pH 9.0 sample solution. After 60-min extraction, the acceptor phase was analyzed by high-performance liquid chromatography with post-column derivatization. The enrichment factors were found to be 853 and 136 for glyphosate and aminomethylphosphonic acid, respectively. The method detection limits are 0.22 microg/L for glyphosate and 3.40 microg/L for aminomethylphosphonic acid. The procedure was validated and showed good accuracy and precision over a large linear dynamic range. The validated method was tested for the analysis of both analytes in spiked groundwater with good success.