Pressure-assisted electrokinetic injection for on-line enrichment in capillary electrophoresis–mass spectrometry: A sensitive method for measurement of ten haloacetic acids in drinking water

Development and validation of a GC-MS/MS method for the determination of iodoacetic acid in biological samples

Iodoacetic acid (IAA) is a halogenated disinfection by-product of growing concern due to its high cytotoxicity, genotoxicity, endocrine disruptor effects, and potential carcinogenicity. However, the data on distribution and excretion of IAA after ingestion by mammals are still scarce. Here, we developed a reliable and validated method for detecting IAA in biological specimens (plasma, urine, feces, liver, kidney, and tissues) based on modified QuEChERS sample preparation combined with gas chromatography-tandem triple quadrupole mass spectrometry (GC-MS/MS). The detection method for IAA exhibited satisfactory recovery rates (62.6-108.0%) with low relative standard deviations (RSD < 12.3%) and a low detection limit for all biological matrices ranging from 0.007 to 0.032 ng/g. The study showed that the proposed method was reliable and reproducible for analyzing IAA in biological specimens. It was successfully used to detect IAA levels in biological samples from rats given gavage administration. The results indicated that IAA was found in various tissues and organs, including plasma, thyroid, the liver, the kidney, the spleen, gastrointestinal tract, and others, 6 h after exposure. This study provides the first data on the in vivo distribution in and excretion of IAA by mammals following oral exposure.

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.

Pressure-assisted electrokinetic injection for the stacking of biogenic amines gives enhancement factor up to 1000 in CE with UV detection

Pressure-assisted electrokinetic injection (PAEKI) was applied for stacking of positively charged biogenic amines (BAs) to improve the sensitivity of capillary electrophoresis (CE). It is well known that the essential step for PAEKI is finding a stationary state of the running buffer such that the movement of the running buffer due to electroosmotic flow (EOF) is counterbalanced by external pressure in the opposite direction of the EOF under a given electric field. In order to find the balance point systematically and integrally, we studied the velocity of the whole BGE in the capillary by the impetus of opposite direction pressure (-0.1 to -0.6 psi), and the velocity of EOF with different voltages. According to the two sets of linear data, the EOF of CE coupled with PAEKI could be counterbalanced at the opposite direction pressure (-0.1 psi) and voltage (7.8 kV). In this study, the injection time was extended up to 0.35 min for all BAs and 0.70 min for the direct ultraviolet (UV) detection of BAs. Compared with hydrodynamic injection (HDI), the enrichment factors for sample injection times of 0.35 min and 0.70 min were 480-fold and 970-fold, respectively. The limits of detection (LODs) (S/N = 3) of indirect and direct UV detection were respectively 8.7-24.3 nmol L^-1 and 0.4-4.5 nmol L^-1, which reaches the sensitivity of high-performance liquid chromatography-mass spectrophotometry (HPLC-MS). With appropriate sample dilution, PAEKI can be used in the analysis of BAs in chicken.

Kinetic analysis of an enzymatic hydrolysis of p-nitrophenyl acetate with carboxylesterase by pressure-assisted capillary electrophoresis/dynamic frontal analysis

An enzymatic hydrolysis of p-nitrophenyl acetate with carboxylesterase was analyzed by capillary electrophoresis/dynamic frontal analysis (CE/DFA). A plateau signal was expected with the anionic product of p-nitrophenol by the CE/DFA applying in-capillary reaction and the continuous CE resolution of the product from the substrate zone. However, the plateau height was not sufficient, and/or the plateau signal fluctuated and drifted. Therefore, a pressure assist was utilized in the CE/DFA to detect the product zone fast and to average the fluctuated plateau signal by mixing in a laminar flow. The plateau signal became relatively flat and its height was developed by the pressure-assisted capillary electrophoresis/dynamic frontal analysis (pCE/DFA). The plateau height was used for the Michaelis-Menten analysis, and a Michaelis-Menten constant was determined as KM = 0.83 mmol L-1. An enzyme inhibition was also examined with bis(p-nitrophenyl) phosphate by adding it in the separation buffer. The height of the plateau signal decreased by the inhibition, and a 50% inhibitory concentration was determined as IC50 = 0.79 μmol L-1. The values of KM and IC50 obtained in this study agreed well with the reported values. Since the proposed pCE/DFA includes electrophoretic migration of the substrate zone in a capillary, it is also noticed that the deactivation of the enzyme by ethanol on the preparation of the substrate solution can be avoided, as well as the exclusion of the inhibition by the product.

Enrichment-free analysis of anionic micropollutants in the sub-ppb range in drinking water by capillary electrophoresis-high resolution mass spectrometry

Reversed-phase liquid chromatography (RPLC) used for water analysis is not ideal for the analysis of highly polar and ionic contaminants because of low retention. Capillary electrophoresis (CE), on the other hand, is perfectly suited for the separation of ionic compounds but rarely applied in environmental analysis due to the weak concentration sensitivity when coupled to mass spectrometry (MS). However, novel interface designs and MS technology strongly improve the sensitivity. Here, a method is presented enabling the screening of anionic micropollutants in drinking water without sample pretreatment by coupling of CE to an Orbitrap mass spectrometer by a nanoflow sheath liquid interface. Targeted analysis of halogenated acetic acids, trifluoromethanesulfonic acid, and perfluorooctanoic and perfluorooctanesulfonic acid was conducted in drinking water samples which were chlorinated for disinfection. A bare fused silica capillary with an optimized background electrolyte (BGE) for separation consisting of 10% acetic acid with 10% isopropanol with large volume sample injection and optimized interface parameters offer limits of quantification in the range of < 0.1 to 0.5 μg/L with good linearity (R² > 0.993) and repeatability (14% standard deviation in area). Concentrations of the target analytes ranged from 0.1 to 6.2 μg/L in the water samples. Masses corresponding to halogenated methanesulfonic acids have been found as suspects and were subsequently verified by standards. Mono-, dichloro-, and bromochloro methanesulfonic acid were quantified in a range of 0.2 to 3.6 μg/L. Furthermore, five sulfonic acids, four organosulfates, and the artificial sweeteners acesulfame and cyclamate as well as inorganics such as halides, halogenates, phosphate, and sulfate could be determined as suspects among more than 300 features in a non-targeted screening. Overall, this approach demonstrates the great potential of CE-nanoESI-MS for the screening of ionic contaminants in environmental samples, complementary to chromatographic approaches.

A fully-automated analyzer for determining haloacetic acid concentrations in drinking water

A fully-automated, on-line, real-time analyzer has been developed for preconcentration and analysis of haloacetic acids (HAAs). Preconcentration of HAAs is achieved by sample acidification and solid phase extraction onto a hydrophobic polymeric resin using sequential injection analysis (SIA). The HAAs preconcentrate is then analyzed using post-column reaction-ion chromatography (PCR-IC), which is selective for HAAs. Systematic optimization of SIA preconcentration parameters are described followed by detailed method detection limit (MDL), accuracy, precision, and linearity studies. MDL values for the individual HAA9 species range from 0.4 to 0.9 μg L(-1). Side-by-side comparison studies of HAAs analysis in 14 real-world drinking water samples from Alabama, Arkansas, Kentucky, Minnesota, Missouri, Mississippi, New York, Pennsylvania and Tennessee are presented that compare the optimized SIA-PCR-IC to USEPA Method 552.3. Trace levels of HAAs detected in select samples are reported, and the bias values calculated between the two methods are typically less than 5 μg L(-1) for eight of the nine individual HAAs.

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.

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2010-2012)

CE has been alive for over two decades now, yet its sensitivity is still regarded as being inferior to that of more traditional methods of separation such as HPLC. As such, it is unsurprising that overcoming this issue still generates much scientific interest. This review continues to update this series of reviews, first published in Electrophoresis in 2007, with updates published in 2009 and 2011 and covers material published through to June 2012. It includes developments in the field of stacking, covering all methods from field amplified sample stacking and large volume sample stacking, through to isotachophoresis, dynamic pH junction and sweeping. Attention is also given to online or inline extraction methods that have been used for electrophoresis.

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.

Influence of pH and ozone dose on the content and structure of haloacetic acid precursors in groundwater

This study investigated the effects of pH (6-10) and ozone dose [0.4-3.0 mg O(3)/mg dissolved organic carbon (DOC)] on the content and structure of haloacetic acid (HAA) precursors in groundwater rich in natural organic matter (NOM; DOC 9.85 ± 0.18 mg/L) during drinking water treatment. The raw water was ozonated in a 2 L glass column. NOM fractionation was carried out using XAD resins. HAA formation potential (HAAFP) was determined according to standard EPA Method 552. NOM characterization revealed it is mostly hydrophobic (65 % fulvic and 14 % humic acids). Hydrophobic NOM significantly influences HAA formation, as confirmed by the high HAAFP (309 ± 15 μg/L). Ozonation at pH 6-10 led to changes in NOM structure, i.e. complete humic acid oxidation, and increased the hydrophilic NOM fraction content (65-90 % achieved using 3.0 mg O(3)/mg DOC). The highest degree of NOM oxidation and HAA precursor removal was achieved at pH 10 (up to 68 % HAAFP). Ozonation pH influenced the distribution of HAA precursor content, as increasing the pH from 6 to 10 increased the reactivity of the hydrophilic fraction, with the HAAFP increasing from 19.1 ± 6.0 μg/mg DOC in raw water to 152 ± 8 μg/mg DOC in ozonated water. The degree of HAA precursor removal depends on the dominant oxidation mechanism, which is related to the applied ozone dose and the pH of the oxidation process. Ozonation at pH 10 favours the mechanism of radical NOM oxidation and was the most effective for HAAFP reduction, with the efficacy of the process improving with increasing ozone dose.