Acids In Aqueous Samples Research Articles

Luminescence Lifetime-Based Sensing Platform Based on Cyclometalated Iridium(III) Complexes for the Detection of Perfluorooctanoic Acid in Aqueous Samples.

Luminescence lifetimes are an attractive analytical method for detection due to its high sensitivity and stability. Iridium probes exhibit luminescence with long excited-state lifetimes, which are sensitive to the local environment. Perfluorooctanoic acid (PFOA) is listed as a chemical of high concern regarding its toxicity and is classified as a "forever chemical". In addition to strict limits on the presence of PFOA in drinking water, environmental contamination from industrial effluent or chemical spills requires rapid, simple, accurate, and cost-effective analysis in order to aid containment. Herein, we report the fabrication and function of a novel and facile luminescence sensor for PFOA based on iridium modified on gold surfaces. These surfaces were modified with lipophilic iridium complexes bearing alkyl chains, namely, IrC6 and IrC12, and Zonyl-FSA surfactant. Upon addition of PFOA, the modified surfaces IrC6-FSA@Au and IrC12-FSA @Au show the largest change in the red luminescence signal with changes in the luminescence lifetime that allow monitoring of PFOA concentrations in aqueous solutions. The platform was tested for the measurement of PFOA in aqueous samples spiked with known concentrations of PFOA and demonstrated the capacity to determine PFOA at concentrations >100 μg/L (240 nM).

Enrichment behavior of electrospun PVDF nanofiber membranes for simultaneous spectrophotometric determination of mixed organic acids in water

Electrospun nanofiber membranes (ENMs) of polyvinylidene fluoride which is known as solid phase extraction materials were fabricated through electrospinning technology. Different electrospinning conditions including polymer content, spinning voltage and flow rate were investigated. The optimal operation conditions for electrospun process were set at 12% of PVDF mass fraction, 12 kV of spinning voltage, 0.5 mL h−1 of flow rate, 15 cm of receiving distance, 22 °C of spinning temperature and 45% of environmental humidity. The self-made ENMs were introduced into a combined method of radial electric focusing solid phase extraction enrichment, ultrasonic elution, UV-Vis detection and PLS calculation for determining benzoic acid, phthalic acid and p-toluene sulfonic acid in aqueous samples simultaneously. The calculation results of unknown sample show that the concentrations of benzoic acid, phthalic acid and p-toluene sulfonic acid were 4.416 mg L−1, 4.976 mg L−1 and 5.27 mg L−1, respectively. The relative standard deviation values of each component are all less than 2% with a relative recovery of 84–119%. The ENMs illustrate their fascinating application prospects in determining trace complex materials in aqueous samples.

Simultaneous spectroscopic determination of trace mixed organic acids in aqueous samples using magnetic solid phase extraction coupled with chemometrics method

The polyaniline-coated magnetite/silica nanomaterials (Fe 3 O 4 @SiO 2 /PANI) were synthesized and successfully applied as an effective sorbent for preconcentration of several typical organic acids from environmental water samples. The properties of Fe 3 O 4 @SiO 2 /PANI were characterized by FT-IR and XPS. These magnetic materials can enrich trace organic acids effectively by solid-phase extraction. Three kinds of organic acids including benzoic acids, phthalic acids and p -toluene sulfonic acids were selected as target analytes for magnetic solid phase extraction (MSPE). Various experimental parameters of the MSPE were investigated and optimized. After the desorption process, the elution was detected by UV-Vis spectrophotometer. The spectroscopic data were analyzed through partial least squares (PLS) method which facilitate quantitation of mixture from complex data. The enrichment factor of benzoic acids, phthalic acids and p -toluene sulfonic acids reached 19.53, 20.31 and 16.89 respectively. A wide measurement range of 10 μg L -1 to 50 mg L -1 was obtained. The LOD was 0.8 μg L -1 . The spiked recoveries in the range of 94%-101% with RSD ( n =8) lower than 4%. The results illustrated that the combined approach of MSPE and PLS has great applied potential for mixture of trace compounds in different field because of its high efficiency, easy to operate conditions, speediness and simplicity.

Shell thickness controlled hydrophilic magnetic molecularly imprinted resins for high-efficient extraction of benzoic acids in aqueous samples

Hydrophilic magnetic molecular imprinted resins (MMIRs) were firstly fabricated by one-pot copolycondensation of resorcinol, melamine, and formaldehyde in the pores of Fe3O4 @mSiO2. The porous structure of mSiO2 limited copolycondensation. After the removal of mSiO2, controllable imprinting shell thickness (about 5 nm) was formed, reducing the probability of embedded sites, favoring the efficient adsorption. Moreover, the reaction time (3 h) was just 1/5−1/8 of those synthesized by conventional heating method. The transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), vibrating sample magnetometer (VSM), thermo-gravimetric analysis (TGA), water contact angle analysis, and Brunauer‒Emmett‒Teller (BET) analysis indicated the successful preparation of MMIRs with excellent hydrophilic property, and magnetic separation characteristics. Steady-state adsorption studies showed that the resultant MMIRs had specific recognition for benzoic acids, GA, protocatechuic acid (PCA), vanillic acid (VA), 4-hydroxybenzoic acid (4-HBA), salicylic acid (SA), and benzoic acid (BA). MMIRs combination with high-performance liquid chromatography–ultraviolet (HPLC–UV) were then directly used for selective extraction and determination of benzoic acids in river water, fruit juices, and human serum. Obtained limits of detection (LOD) and recoveries were in the range of 0.02–1.0 μg/mL, and 81.8–108.7%, respectively, and the batch-to-batch relative standard deviation (RSD) was 5.9%. The proposed strategy showed excellent hydrophilicity and specificity, which was promising for detection of benzoic acids in real aqueous samples.

A cotton thread fluidic device with a wall-jet pencil-drawn paper based dual electrode detector

A simple and sensitive device is presented based on the use of pencil-drawn paper based electrochemical detector placed at the end of a cotton thread fluidic channel in wall-jet configuration. This innovative and fast responding electroanalytical system can be adopted for both single and dual electrode electrochemical detection, this last achieved by applying two different potentials at two independent working electrodes drawn on the opposite faces of the paper based detector. Its performance was preliminarily optimized by adopting hexacyanoferrate(II) as probe species undergoing reversible electrochemical processes. These devices were then used for the single electrode detection of ascorbic acid in aqueous samples and the dual electrode detection of orthodiphenols in extra virgin olive oils (EVOOs). In fact, these devices enable hydrophilic orthodiphenols, typically present in EVOOs (extracted by a 80:20% v/v acetonitrile/water mixture), to be discriminated from hydrophilic monophenols instead present in almost all vegetable oils. Flow-injections runs were conducted by using a 0.01 M H2SO4 + 0.5 KCl running electrolyte allowing the rapid and selective detection of hydrophilic orthodiphenols with satisfactory sensitivity and a low enough detection limit (2 μM). Different real samples of EVOOs and sunflower oils were analyzed. Abundant enough contents of orthidiphenols were found in EVOO samples, while no trace of these antioxidants was found in sunflower oils.

A sensitive and specific solid-phase extraction-gas chromatography-tandem mass spectrometry method for the determination of 11 haloacetic acids in aqueous samples.

A method for the analysis of 11 haloacetic acids in water samples has been developed. It involves enrichment of the target analytes from water samples by solid-phase extraction, derivatization to methyl esters, and gas chromatography coupled with tandem mass spectrometry determination. Gas chromatography conditions were optimized for a good separation of all haloacetic acids in a short runtime. Data were acquired in the multiple reaction monitoring mode. Six solid-phase extraction sorbents among the most widely used in environmental analysis were tested. Bakerbond SDB was retained because it has been shown to provide the best results for a large class of targeted haloacetic acids. The performances of the developed method have been assessed according to the French Standard NF T 90-210. The calibration curves for all the studied haloacetic acids had consistent slopes with r2 values > 0.99. Quantification limits between 0.01 and 0.50 µg l-1 were achieved. Satisfactory repeatability (relative standard deviation ≤ 14.3%) and intermediate precision (relative standard deviation ≤ 15.7%) were obtained. Applied to the analysis of 15 untreated water samples collected from three rivers, the method allowed the detection of five haloacetic acids including monochloroacetic acid (in 100% of the samples, <0.5-1.85 µg l-1), dichloroacetic acid (87%, <0.05-0.22 µg l-1), trichloroacetic acid (93%, <0.05-0.52 µg l-1), dibromoacetic acid (53%, <0.01-0.40 µg l-1), tribromoacetic acid (20%, <0.05-0.14 µg l-1), and bromodichloroacetic acid (6%, < 0.05 µg l-1).

Hollow-fiber liquid-phase microextraction based on carrier-mediated transport for determination of urinary methyl hippuric acids

ABSTRACTHollow-fiber liquid-phase microextraction based on carrier-mediated transport for analysis of methyl hippuric acids in aqueous samples is described. Under optimized conditions, relative recoveries of 83%–98% and limits of detection of 2–3 µg L−1 were obtained, with linear calibration curves for the three isomers in the range of 10–50,000 µg L−1. The method was applied for the determination of urine samples of volunteers at various working environments.

Hollow Fiber Supported Liquid Membrane Extraction Combined with HPLC-UV for Simultaneous Preconcentration and Determination of Urinary Hippuric Acid and Mandelic Acid

This work describes a new extraction method with hollow-fiber liquid-phase microextraction based on facilitated pH gradient transport for analyzing hippuric acid and mandelic acid in aqueous samples. The factors affecting the metabolites extraction were optimized as follows: the volume of sample solution was 10 mL with pH 2 containing 0.5 mol·L−1 sodium chloride, liquid membrane containing 1-octanol with 20% (w/v) tributyl phosphate as the carrier, the time of extraction was 150 min, and stirring rate was 500 rpm. The organic phase immobilized in the pores of a hollow fiber was back-extracted into 24 µL of a solution containing sodium carbonate with pH 11, which was placed inside the lumen of the fiber. Under optimized conditions, the high enrichment factors of 172 and 195 folds, detection limit of 0.007 and 0.009 µg·mL−1 were obtained. The relative standard deviation (RSD) (%) values for intra- and inter-day precisions were calculated at 2.5%–8.2% and 4.1%–10.7%, respectively. The proposed method was successfully applied to the analysis of these metabolites in real urine samples. The results indicated that hollow-fiber liquid-phase microextraction (HF-LPME) based on facilitated pH gradient transport can be used as a sensitive and effective method for the determination of mandelic acid and hippuric acid in urine specimens.

Fiber Optic SPR-Based Uric Acid Biosensor Using Uricase Entrapped Polyacrylamide Gel

In this letter, we report a fiber optic biosensor based on surface plasmon resonance (SPR) for the detection of uric acid in aqueous samples. The sensing probe is prepared by successive coatings of silver and silicon layers over a small unclad length of the plastic clad silica optical fiber in the middle. Thereafter, the probe is dipped in a polyacrylamide gel containing enzyme uricase to immobilize it using a gel entrapment method. The sensor is characterized using a wavelength interrogation method. The SPR spectra corresponding to different concentrations of uric acid in the range of 0-0.9 mM are recorded. A red shift in the resonance wavelength is observed with an increase in the concentration of uric acid around the probe. In addition, the sensitivity of the proposed biosensor is studied in relation to parameters, such as concentration and pH of the uric acid solution. Finally, the sensor is highly selective and possesses better limit of detection and limit of quantification.

Erratum to: Perfluoroalkyl acids in aqueous samples from Germany and Kenya.

Erratum to: Perfluoroalkyl acids in aqueous samples from Germany and Kenya.

Low Density Solvent Ion Pair Dispersive Liquid–Liquid Micro‐Extraction – An Economic Method for Extraction of Phthalic Acids

A simple and economic analytical method based on low density solvent ion‐pair dispersive liquid–liquid micro‐extraction using high performance liquid chromatography–diode array detection has been used for the determination of phthalic acid, terephthalic acid, and iso‐phthalic acid in aqueous samples. In this work, 0.75 mL methanol (as a disperser solvent), 90 μL toluene (as an extraction solvent), and 15 μL tri‐butyl amine (as an ion pair reagent) were injected into aqueous phase. After centrifuging (at 4000 rpm for 5 min), the analyte ion pairs were extracted into toluene. The collected toluene was withdrawn and transferred into a microtube. The transferred toluene was evaporated under a stream of nitrogen at room temperature to dryness. Then, 10 μL of the mobile phase was added to the microtube to re‐dissolve the residues. Under the optimized conditions, limits of detection and quantification were calculated in the range of 0.12–0.34 and 0.37–1.06 ng mL−1, respectively. The linear range of the developed method was obtained as 0.37–10000 ng mL−1. Enrichment factors and extraction recoveries were from 82 to 98% and 411–492, respectively. Finally, different aqueous samples such as tap water, mineral water, cola, lemon juice, vinegar, and dextrose and NaCl injection solutions were analyzed successfully by the developed procedure and the selected analytes were found in some of them in the range of 6.2–72 ng mL−1.

Perfluoroalkyl acids in aqueous samples from Germany and Kenya.

Continuous monitoring of chemicals in the environment is important to control their fate and to protect human health, flora, and fauna. Perfluoroalkyl acids (PFAAs) have been detected frequently in different environmental compartments during the last 15years and have drawn much attention because of their environmental persistence, omnipresence, and bioaccumulation potential. Water is an important source of their transport. In the present study, distributions of PFAAs in river water, wastewater treatment plant (WWTP) effluent, and tap water from eastern part of Germany and western part of Kenya were investigated. Eleven perfluorocarboxylic acids (PFCAs) and five perfluorosulfonic acids (PFSAs) were analyzed using liquid chromatography/tandem mass spectrometry. Sum of mean concentrations of eight PFAAs detected in drinking tap water from Leipzig was 11.5ngL-1, dominated by perfluorooctanoic acid (PFOA, 6.2ngL-1). Sums of mean riverine concentrations of PFAAs detected in Pleiße/White Elster, Saale, and Elbe (Germany) were 24.8, 54.3, and 26.8ngL-1, respectively. Annual flux of PFAAs from River Saale was estimated to be 164 ± 23kga-1. The effluent of WWTP in Halle was found to contain four times higher levels of PFAAs than river water and was dominated by perfluorobutane sulfonate (PFBS) with 32 times higher concentration than the riverine level. It advocates that WWTPs are the point source of contaminating water bodies with PFAAs, and short-chain PFAAs are substituting long-chain homologues. Sums of mean riverine concentrations of PFAAs in Sosiani (Kenya) in samples from sparsely populated and densely populated areas were 58.8 and 109.4ngL-1, respectively, indicating that population directly affected the emissions of PFAAs to surface waters. The discussion includes thorough review and comparison of recently published literature reporting occurrence of PFAAs in aqueous matrices. Graphical abstract Perfluoroalkyl acids in aqueous matrices.

Method for quantifying NSAIDs and clofibric acid in aqueous samples, lumpfish (Cyclopterus lumpus) roe, and zebrafish (Danio rerio) eleutheroembryos and evaluation of their bioconcentration in zebrafish eleutheroembryos.

Pharmaceuticals such as nonsteroidal anti-inflammatory drugs (NSAIDs) and lipid regulators are being repeatedly detected at low concentrations (pg · mL-1-ng · mL-1) in the environment. A large fraction of these compounds are ionizable. Ionized compounds show different physico-chemical properties and environmental behavior in comparison to their neutral analogs; as a consequence, the quantification methods currently available, based on the neutral molecules, might not be suitable to detect the corresponding ionized compounds. To overcome this problem, we developed a specific analytical method to quantify NSAIDs and lipid regulators (i.e., ibuprofen, diclofenac, naproxen, and clofibric acid) and their ionized compounds. This method is based on three steps: (1) the extraction of the organic compounds with an organic solvent assisted with an ultrasonic probe, (2) the cleaning of the extracts with a dispersive SPE with C18, and (3) the determination of the chemical compounds by GC-MS (prior derivatization of the analytes). We demonstrated that the proposed method can successfully quantify the pharmaceuticals and their ionized compounds in aqueous samples, lumpfish eggs, and zebrafish eleutheroembryos. Additionally, it allows the extraction and the cleanup of extracts from small samples (0.010g of wet weight in pools of 20 larvae) and complex matrixes (due to high lipid content) and can be used as a basis for bioaccumulation assays performed with zebrafish eleutheroembryos in alternative to OECD test 305.

A validated LC–MS/MS method for fast detection of thiodiglycolic acid in aqueous samples

ABSTRACTA novel sensitive screening method based on liquid chromatography–tandem mass spectrometry (LC–MS/MS) has shown the feasibility of separation and detection of thiodiglycolic acid in aqueous samples. The analysis of this compound is of interest since it is specific microbiological metabolite of thiodiglycol, which is precursor and degradation product of chemical warfare agent sulfur mustard. The LC–electrospray ionisation (ESI)–MS method provides a sensitive and direct approach for thiodiglycolic acid identification and quantification using non-extracted non-derivitised samples from aqueous solutions. Chromatographic separation of the thiodiglycolic acid was produced using a reverse phase LC column with gradient mobile phases consisting of 0.1% formic acid in water and acetonitrile. Identification and quantification of species were achieved using ESI–tandem MS monitoring two precursor-to-product ion transitions for thiodiglycolic acid. The method demonstrates linearity over at least two orders of magnitude and detection limit of 10 ng...mL–1 in environmental water samples.

Batch and flow injection spectrophotometric methods for the determination of barbituric acid in aqueous samples via oxidative coupling with 4-aminoantipyrine

A batch and flow injection (FI) spectrophotometric methods are described for the determination of barbituric acid in aqueous and urine samples. The method is based on the oxidative coupling reaction of barbituric acid with 4-aminoantipyrine and potassium iodate to form purple water soluble stable product at λ 510 nm. Good linearity for both methods was obtained ranging from 2 to 60 μg mL−1, 5–100 μg mL−1 for batch and FI techniques, respectively. The limit of detection (signal/noise = 3) of 0.45 μg mL−1 for batch method and 0.48 μg mL−1 for FI analysis was obtained. The proposed methods were applied successfully for the determination of barbituric acid in tap water, river water, and urine samples with good recoveries of 99.92% and 100.67% for batch and FI method, respectively.

Analysis of picric acid and picramic acid in water samples by ultra performance hydrophilic interaction chromatography-tandem mass spectrometry

An ultra performance liquid chromatography/tandem mass spectrometry (UPLC-MS/ MS) method was developed for the determination of picric acid and its reductive transformation product picramic acid in aqueous samples. A hydrophilic interaction liquid chromatography (HILIC) column (Acquity UPLC BEH HILIC; 100 mm x 2.1 mm, 1.7 microm) was used for the separation. Surface water samples could be injected into the UPLC system just after being filtered through a 0.2 microm membrane. The satisfactory recoveries of picric acid and picramic acid were in the range of 89% - 107%. Waste water samples were purified by solid phase extraction (SPE), and then were analyzed. The recoveries of picric acid and picramic acid in waste water were 72%-101%. The reproducibility of the method was good with the RSDs of 4.9% - 14.7%. The limits of detection (LODs) of picric acid and picramic acid were 0.1 microg/L and 0.3 microg/L, respectively. This proposed method is rapid, highly specific and suitable for the confirmation and quantitative determination of picric acid and picramic acid in surface water and waste water.

Application of NaClO‐treated multiwalled carbon nanotubes as solid phase extraction sorbents for preconcentration of trace 2,4‐dichlorophenoxyacetic acid in aqueous samples

Multiwalled carbon nanotubes functionalized by oxidation of original multiwalled carbon nanotubes with NaClO were prepared and their application as solid phase extraction sorbent for 2,4-dichlorophenoxyacetic acid (2,4-D) was investigated systemically, and a new method was developed for the determination of trace 2,4-D in water samples based on extraction and preconcentration of 2,4-D with solid phase extraction columns packed with NaClO-treated multiwalled carbon nanotubes prior to its determination by HPLC. The optimum experimental parameters for preconcentration of 2,4-D, including the column activating conditions, the amount of the sorbent, pH of the sample, elution composition, and elution volume, were investigated. The results indicated 2,4-D could be quantitatively retained by 100 mg NaClO-treated multiwalled carbon nanotubes at pH 5, and then eluted completely with 10 mL 3:1 (v/v) methanol-ammonium acetate solution (0.3 mol/L). The detection limit of this method for 2,4-D was 0.15 μg/L, and the relative standard deviation was 2.3% for fortified tap water samples and 2.5% for fortified riverine water sample at the 10 μg/L level. The method was validated using fortified tap water and riverine water samples with known amount of 2,4-D at the 0.4, 10, and 30 μg/L levels, respectively.

Application of headspace solid-phase microextraction followed by gas chromatography–mass spectrometry to determine short-chain alkane monocarboxylic acids in aqueous samples

In this study, a procedure was developed to determine short-chain alkane monocarboxylic acids (SCMAs) in aqueous samples using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography (GC) coupled with mass spectrometry (MS). A Stabilwax-DA capillary column (30 m × 0.32-mm inner diameter, 0.50-μm film thickness) was used for GC separation and a 60-μm poly(ethylene glycol) fiber was used to isolate SCMAs from water and introduce them into the gas chromatograph. Parameters of HS-SPME, analyte desorption, and GC-MS analysis were selected and an analytical procedure was proposed. Limits of quantitation were on the order of about 0.2 mg L-1. As an example of the application of the procedure, SCAMs were determined in municipal wastewater at different steps of treatment.

Determination of perfluorocarboxylic acids in aqueous matrices by ion-pair solid-phase microextraction–in-port derivatization–gas chromatography–negative ion chemical ionization mass spectrometry

A rapid, selective and simple analytical procedure using tetrabutylammonium as ion pair in conjunction with solid-phase microextraction followed by in-port derivatization–GC–negative ion chemical ionization mass spectrometry was developed. The procedure allows an accurate determination of perfluoroalkylcarboxylic acids in aqueous samples at ng L −1 levels (i.e. method detection limit 20 ng L −1 for perfluorodecanoic acid) improving previous GC methods in terms of analysis time and sensitivity. Ammonia as reagent gas in the negative ion chemical ionization mass spectrometry increased the sensitivity at least 3-fold compared to methane for perfluorocarboxylic acid butyl esters. The developed procedure was successfully applied to effluents from wastewater treatment plants (i.e. 0.05–8.2 μg L −1) and harbor seawaters.

HPLC method with on-line SPE preconcentration for quantification of permethric acid sorption to goethite

Pesticide metabolites are often found to be more mobile in soil than their parent compounds. Pyrethroids are bound strongly to soil and therefore sorption of the pyrethroid metabolite permethric acid (PA) to a typical soil sorbent, goethite, was investigated. An on-line solid-phase extraction (SPE)-HPLC-UV procedure was developed for quantification of trans- and cis-permethric acid in aqueous samples. Limits of detection (LOD) were 500 times lower than those obtained with conventional HPLC-UV, resulting in LODs of 1.4 and 0.3 nM for the trans- and cis-isomers, respectively. Sorption of nanomolar concentrations of PA to goethite was found to be specific up to less than 1% surface coverage. In this range the data was described by a Langmuir equation with K ads = 7.1 × 10−9 L/mol and Γmax = 7.1 × 10−9 mol/m2 for total PA (trans + cis) at pH = 3. K ads, cis (1.4 × 106 L/mol) was approximately twice K ads, trans (7.9 × 105 L/mol). At higher PA concentrations the slope of the sorption isotherm increased, which is ascribed to hydrophobic interactions between adsorbed and dissolved PA molecules. Based on comparison with reported K om values, metal oxides are expected to have a relatively greater significance to the retention of PA than soil organic matter.