Solvent-minimized extraction for determining halonitromethanes and trihalomethanes in water

Trihalomethanes in water samples: Recent update on pretreatment and detection methods

Trihalomethanes (THMs) are classified as volatile organic compounds, considered to be a disinfection by-product during water disinfection process. THMs have been shown to be cytotoxic, genotoxic and mutagenic, with a risk of cancer when they contact with people directly. To protect public health and monitor water quality, it is important to monitor and measure THMs in drinking water. Therefore, it is crucial to develop fast, accurate, highly sensitivity and green analysis methods of THMs in various complicated matrices. Here, this review presents an overall summary of the current state of the pretreatment and detection methods for THMs in various sample matrices since 2005. In addition to the traditionally used pretreatment methods for THMs (such as headspace extraction, microwave-assisted extraction, liquid-liquid extraction), the new-developed methods, including solid-phase extraction, QuEChERS and different microextraction methods, have been summarized. The detection methods include gas chromatography-based methods, sensors and several other approaches. Additionally, benefits and limitations of different techniques were also discussed and compared. This study is anticipated to offer fruitful insights into the further advancement and widespread applications of pretreatment and detection technologies for THMs as well as for related substances.

Effervescence-assisted spiral hollow-fibre liquid-phase microextraction of trihalomethanes, halonitromethanes, haloacetonitriles, and haloketones in drinking water

A new analytical method was optimized to determine 18 disinfection by-products (DBPs) in drinking water, including four different chemical groups. For this purpose, spiral-shaped hollow-fibre liquid phase microextraction with 1-octanol as the acceptor solvent assisted by effervescence was applied using a homemade supporting device that was specifically designed for this application. The device was printed in a 3D printer and allows for an increased fibre surface even with a low sample volume, which significantly facilitates the extraction. The samples were analysed by gas chromatography coupled to both an electron capture detector and a mass spectrometer for the quantification and unequivocal identification of the analytes, respectively. Effervescence was generated using citric acid and bicarbonate at a molar ratio 1:2, which significantly improves the extraction efficiency and reduces mechanical operations, since stirring and modifiers are not required. The results showed enrichment factors ranging from 13.1 to 140.1. Satisfactory recoveries (80-113 %) were obtained, with relative standard deviations from 3 to 15 % and good linearity. The detection limits (ng L^-1) ranged from 10 to 35 (trihalomethanes), 12 to 220 (halonitromethanes), 17 to 79 (haloacetonitriles) and 10 to 16 (haloketones). The applicability of the method was assessed in 6 local water distribution systems.

Simultaneous analysis of haloacetonitriles, haloacetamides and halonitromethanes in chlorinated waters by gas chromatography-mass spectrometry

Nitrogenous classes of disinfection by-products (DBPs), such as haloacetamides (HAAms), haloacetonitriles (HANs) and halonitromethanes (HNMs), while generally present at lower concentrations in disinfected waters than carbonaceous DBPs, such as trihalomethanes or haloacetic acids, have been shown to be more detrimental to human health. While several methods have been shown to be suitable for the analysis of some nitrogenous DBPs (N-DBPs) in disinfected waters, many are unable to quantify HAAms, the most detrimental to health of these three N-DBP classes. Here, we report the first method for the simultaneous analysis of twenty-five N-DBPs (nine HANs, nine HNMs and seven HAAms) in disinfected waters using liquid-liquid extraction followed by gas chromatography-mass spectrometry. The use of a programmable temperature vaporiser injector minimises degradation of the thermally labile HNMs, while avoiding the concomitant decreases in HANs and HAAms which occur when using lower injector temperatures. Extraction parameters, including sample pH, solvent volume, salt addition and sample pre-concentration, were investigated to determine the optimal conditions across all target N-DBPs. Good detection limits were achieved for all analytes (0.8-1.7 μg L^-1) and both laboratory and instrumental runtimes were significantly reduced compared to previous methods. The method was validated for the analysis of N-DBPs in drinking, swimming pool and spa waters, and concentrations of up to 41 μg L^-1 of some N-DBPs were measured in some pools.

Regulated and emerging disinfection by-products in recycled waters

Disinfection is an integral component of water treatment performed daily on large volumes of water worldwide. Chemical disinfection may result in the unintended production of disinfectant by-products (DBPs) due to reactions between disinfectants and natural organic matter present in the source water. Due to their potential toxicity, levels of DBPs have been strictly regulated in drinking waters for many years. With water reuse now becoming more common around the world DBPs are increasingly becoming a concern in recycled waters, where a much larger amount and variety of compounds may be formed due to a higher abundance and diversity of organic material in the source waters. Regulation of DBPs in recycled waters is limited; generally, drinking water regulations are applied in place of specific guidelines for recycled waters. Such regulations are set for only 11, commonly observed, compounds of the 600+ that may, potentially, be found. In this review an overview of current research in this area is provided, the types of compounds that have been observed, methods for their analysis and possible regulation are also discussed. Through this review it is evident that there is a knowledge gap for the occurrence of DBPs in recycled waters, especially when comparing this information to that available for drinking waters. The concentrations of DBPs observed in recycled waters are seen to be higher than those in drinking water, though still within potable threshold limits. It is clear that there is a need for the analysis and understanding of a larger suite of compounds in recycled waters, as these will most likely be the source of future, global renewable water.

Monitoring trihalomethanes and nitrogenous disinfection by-products in blending desalinated waters using solid-phase microextraction and gas chromatography

A simple and efficient method has been developed for the extraction and determination of 16 common volatile halogenated disinfection by-products (DBPs) (four trihalomethanes, six haloacetonitriles, and six halonitromethanes) in blending desalinated waters, using headspace solid-phase microextraction and gas chromatography with flame ionization detector (HS-SPME/GC-FID). After the optimization using factorial designs of the HS-SPME parameters (optimum: carboxen/polydimethylsiloxane such as fiber, extraction time of 60 min at 30°C, pH 7, addition of 40% (w/v) of sodium chloride, and desorption time of 2 min at 250°C), quantification limits ranged from 3.03 to 40.8 µg L^-1, and relative standard deviation (inter-day) were lower than 9.7% for all the target DBPs. Adequate relative recoveries (with the exception of chloronitromethane) were obtained even when spiking waters at low levels (25 µg L^-1), with values between 83.1% and 119% for ultrapure water, and between 87.4% and 115% for blending desalinated waters, supporting in this way the applicability of the method. The influence of various dechlorinating agents on the stability of 16 DBPs in water was evaluated, with ammonium chloride being the most suitable inhibitor of residual chlorine and carrying out the analytical determination of DBPs within 48 h after sampling. Different blending desalinated water samples collected in the South of Tenerife Island (Spain) were successfully analyzed.

Effect of Metal Ions on the Formation of Trichloronitromethane during Chlorination of Catechol and Nitrite

Catechol, nitrite, and dissolved metals are ubiquitous in source drinking water. Catechol and nitrite have been identified as precursors for halonitromethanes (HNMs), but the effect of metal ions on HNM formation during chlorination remains unclear. The main objective of this study was to investigate the effect of metal ions (Fe, Ti, Al) on the formation of trichloronitromethane (TCNM) (the most representative HNM species in disinfected water) on chlorinating catechol and nitrite. Trichloronitromethane was extracted by methyl tert-butyl ether and detected by gas chromatography. The results show that metal ions promoted the formation of TCNM and that the enhancement efficiency followed the order of Fe > Ti > Al. Trichloronitromethane formation increased greatly within 2 h, and a basic condition (pH 8-9) favored TCNM formation more than acidic or neutral conditions. The conjoint effect of the metal-ion mixtures was shown to be similar to that of the single metal ion having the highest promoting effect on TCNM formation. Our results strongly suggest that metal ions play a significant role in enhancing TCNM formation.

Simultaneous determination of dorzolomide and timolol in aqueous humor: a novel salting out liquid-liquid microextraction combined with HPLC

A Snovel method for the simultaneous separation and determination of two antiglaucoma drugs namely, dorzolamide hydrochloride (DOR) and timolol maleate (TIM) in aqueous humor samples (AH) was developed by using salting-out assisted liquid-liquid microextraction (SALLME) combined with HPLC-UV method. Box-Behnken experimental design and response surface methodology were employed to assist the optimization of SALLME conditions, including salt concentration, the pH of sample solution and vortex time as variable factors. The optimal extraction conditions were as follows: to 50 µL of AH sample, 100 µL of phosphate buffer (100 mmol L(-1), pH 11.9), 90 µL of acetonitrile (ACN) and 0.11 g of (NH4)2SO4 salt were added into an Eppendorf vial (1 mL) then vortexed for 1.1 min. As an effort to miniaturize SALLE system, a 1 mL syringe adapted with a capillary tube was employed as the phase separation device. Once the phase separation occurred, the upper layer could be narrowed into the capillary tube by pushing the plunger; thus, the collection of the upper layer solvent was simple and convenient. By miniaturization, the consumption of the organic solvent was decreased as low as possible. The chromatographic separation was achieved on Gemini C18 column using a mobile phase of ACN: 30 mmol L(-1) potassium dihydrogen phosphate buffer containing 0.1% triethylamine, pH 3.5 (20:80, v/v) at a flow rate of 1 mL min(-1) and UV detection at 254 and 295 nm for DOR and TIM, respectively. Mepivacaine hydrochloride was used as an internal standard. The described method showed better separation with enhanced sensitivities than the previously reported methods with limits of quantitation of 8.75 and 10.32 ng mL(-1) in aqueous solution and 15.97 and 23.53 ng mL(-1) in AH for DOR and TIM, respectively. The simple, rapid and eco-friendly SALLME-HPLC method has been successfully applied for the simultaneous pharmacokinetic studies of DOR and TIM in rabbit AH.

Eco-friendly microextraction method for the quantitative speciation of 13 haloacetic acids in water

This paper describes the first micro liquid-liquid extraction (MLLE) gas chromatography-mass spectrometry (GC-MS) method for the speciation of emerging iodinated acetic acids, along with conventional chlorinated and brominated acids in water. The haloacetic acids (HAAs) were derivatised using 3 reagents for their methylation, both in aqueous and organic media. The acidic methanol derivatisation in aqueous medium provided the best efficiency, requiring minimal sample manipulation. The derivatisation yield was improved through the use of microwave energy that drastically reduced reaction time (2 min). The HAA methyl esters were finally extracted using 250 μL of methyl tert-butyl ether. This MLLE combined with the use of a large-volume sample injection coupled to a programmed temperature vaporiser-GC-MS improved the sensitivity of the method and minimised the generation of hazardous residues in accordance with the principles of "Green Chemistry". Detection and quantification limits (excepting tribromoacetic acid) within the range of 0.01-0.15 μg/L and 0.03-0.5 μg/L, respectively, were obtained and the relative standard deviation was lower than 10%. The eco-friendly method was applied to the speciation of the 13 HAAs in treated (chlorinated and chloraminated water) and untreated water. Up to 8 HAAs were found at detectable levels in treated water. The highly toxic monoiodoacetic acid was detected in almost all the chloraminated water.

An optimized analytical method for the simultaneous detection of iodoform, iodoacetic acid, and other trihalomethanes and haloacetic acids in drinking water

An optimized method is presented using liquid-liquid extraction and derivatization for the extraction of iodoacetic acid (IAA) and other haloacetic acids (HAA9) and direct extraction of iodoform (IF) and other trihalomethanes (THM4) from drinking water, followed by detection by gas chromatography with electron capture detection (GC-ECD). A Doehlert experimental design was performed to determine the optimum conditions for the five most significant factors in the derivatization step: namely, the volume and concentration of acidic methanol (optimized values  = 15%, 1 mL), the volume and concentration of Na2SO4 solution (129 g/L, 8.5 mL), and the volume of saturated NaHCO3 solution (1 mL). Also, derivatization time and temperature were optimized by a two-variable Doehlert design, resulting in the following optimized parameters: an extraction time of 11 minutes for IF and THM4 and 14 minutes for IAA and HAA9; mass of anhydrous Na2SO4 of 4 g for IF and THM4 and 16 g for IAA and HAA9; derivatization time of 160 min and temperature at 40°C. Under optimal conditions, the optimized procedure achieves excellent linearity (R(2) ranges 0.9990-0.9998), low detection limits (0.0008-0.2 µg/L), low quantification limits (0.008-0.4 µg/L), and good recovery (86.6%-106.3%). Intra- and inter-day precision were less than 8.9% and 8.8%, respectively. The method was validated by applying it to the analysis of raw, flocculated, settled, and finished waters collected from a water treatment plant in China.