The stability of non-ionic surfactants and linear alkylbenzene sulfonates in a water matrix and on solid-phase extraction cartridges

The stability of nonylphenol ethoxylates (NPEO), alcohol ethoxylates (AEO), coconut diethanol amides (CDEA) and linear alkylbenzene sulfonates (LAS) in a water matrix and preconcentrated on SPE cartridges was studied. A stability study was carried out in a water matrix (spiked ground water and real-world waste water) comparing different pretreatment procedures (addition of sulfuric acid to pH = 3, preservation with 1% and 3% of formaldehyde). When stored in a water matrix serious qualitative and quantitative changes occurred in waste water during the period of time studied (30 days). The losses of C₁₂–C₁₄ alcohol ethoxylates ranged from 72% to 88% when the sample was preserved with acid and from 17% to 86% when the sample was preserved with formaldehyde (3%). Simultaneously, an enrichment of the shorter alkyl chain homologues (C₇EO and C₁₀EO) was observed. The losses of NPEO were from 45% (sample preserved by acidification or by addition of 3% of formaldehyde) to 85% (sample preserved with 1% of formaldehyde). Additionally, an increase in concentration of polyethylene glycols (PEGs) and formation of different acidic forms, such as monocarboxylated (MCPEGs) and dicarboxylated polyethylene glycols (DCPEGs) were observed. The stability of surfactants preconcentrated on SPE cartridges was studied as a function of storage time and storage conditions (room temperature, 4?°C and –20?°C). The results indicate that disposable SPE cartridges can be recommended for the stabilization of non-ionic surfactants and LAS. Storage at –20?°C is feasible for long periods (up to ¶3 months for ground water and up to 2 months for waste water), while storage at 4?°C can be recommended for a maximum of 1 month. When cartridges were kept at –20?°C the losses of AEOs (n = 12, 13 and 14), preconcentrated from waste water, ranged from 17 to 29% (after 60 days) and other compounds suffered small losses (maximum of 14% for C₁₃LAS). At room temperature, after 7 days, the losses were less than 11%, indicating that shipping of samples by mail can be done without any special requirements.     

Determination of linear alkylbenzene sulfonates by ion-pair solid-phase extraction and high-performance liquid chromatography

In this paper, the potential use of multiwalled carbon nanotubes (MWCNTs) as solid phase extraction (SPE) adsorbent was evaluated for preconcentration of linear alkylbenzene sulfonates (LAS) using ion-pair (IP)-SPE with tetrabutylammonium hydroxide (TBAH). The LAS homologues present in the aqueous sample were ion-paired with TBAH and the solution was passed through the MWCNT cartridges. The analytes retained in the cartridge were eluted with methanol and the concentrated methanol extract was analysed by HPLC-UV. In order to obtain the satisfactory recovery of LAS homologues, various parameters including the type and amount of the ion-pair reagents, the desorption and enrichment conditions such as the effect of eluent and its volume, pH, the flow rate, the ultrasonic time of sample, and the volume of sample solution were systematically optimized. Under the optimal conditions, LAS homologues could be easily extracted by the proposed SPE cartridge. The favorable limits of detection (LOD) for LAS homologues were in the range from 0.02 to 0.03 μg L⁻¹, and the relative standard deviations (RSDs) were 1.55-2.54% for 10 μg L⁻¹ LAS (n = 6). The proposed method has been successfully applied for the analysis of LAS homologues in aqueous environmental samples. A comparison study with ion-pair solid extraction on MWCNTs, C8 and C18 as adsorbents for LAS demonstrated that ion pair-based solid extraction on MWCNTs adsorbent was advantageous over C8 and C18, the widely used traditional adsorbents.     

Evaluation of eggshell membrane-based bio-adsorbent for solid-phase extraction of linear alkylbenzene sulfonates coupled with high-performance liquid chromatography

The potential of eggshell membrane (ESM) as a novel solid-phase extraction bio-adsorbent was investigated in the present study. The ESM with a unique structure of intricate lattice network showed a predominant ability to capture linear alkylbenzene sulfonates (LAS) as a model of organic pollutants by the hydrophobic interactions between ESM and LAS molecular at pH very close to the isoelectric point of ESM, which was similar to the most widely used trapping mechanism for SPE. Under the optimal conditions, the breakthrough capacities of the ESM packed cartridge for C10–C13 LAS homologues were found to be 30, 53, 50, and 43 μg g⁻¹, respectively. On the basis of high-performance liquid chromatography separation and UV detection of LAS homologues, the proposed system could respond down to 0.027 ng mL⁻¹ of LAS with a linear calibration range from 0.2 to 100 ng mL⁻¹, showing a good LAS enrichment ability of eggshell membrane biomaterial with high sensitivity, and could be successfully used for the detection of residual LAS in environmental water samples. The reproducibility among columns was satisfactory (RSD among columns is less than 10%). A comparison study with ESM, C8 and C18 as adsorbents for LAS demonstrated that ESM-based bio-adsorbent was advantageous over C8 and C18, the widely used traditional adsorbents.     

Highly stable magnetic multiwalled carbon nanotube composites for solid-phase extraction of linear alkylbenzene sulfonates in environmental water samples prior to high-performance liquid chromatography analysis

The magnetic multiwalled carbon nanotubes (MMWCNTs) have been successfully prepared using a one-pot chemical coprecipitation method, in which magnetic nanoparticles (MNPs) were deposited onto multiwalled carbon nanotubes (MWCNTs) by in situ high temperature decomposition of the magnetic precursor of iron(III) in ethylene glycol media. A novel procedure for extraction of linear alkylbenzene sulfonates (LAS) as a model compound was thus developed in an off-line extraction system with detection by HPLC. The procedure includes the separation and preconcentration of LAS homologues onto MMWCNTs at pH 7.0 and their subsequent detection after sonication elution, followed by the separation of the MMWCNTs from the aqueous phase by external magnetic field and washing with ultra pure water. With a sample volume of 500 mL and 100 mg MMWCNTs sorbents, an enrichment factor of about 500, and a detection limit of 0.013-0.021 μg L(-1) were obtained within a linear range of 0.5-100 μg L(-1), together with a correlation coefficient of 0.9938-0.9998 for four LAS homologues. A precision of 2.4-5.6% was obtained for six replicate determinations of 50 μg L(-1) LAS. The recoveries of LAS homologues spiked in environmental water samples ranged from 87.3 to 106.3%, demonstrating the utility of the MMWCNTs adsorbents in a series of water samples. Stability testing demonstrated that the MMWCNTs remained 95.0% recovery for the target LAS even after a run of 50 adsorption and desorption cycles, showing their super operational stability. The MMWCNTs are promising adsorbents, suitable for the long-term repetitive sorption/desorption of target compounds in environmental water samples.     

Freely dissolved concentrations of anionic surfactants in seawater solutions: Optimization of the non-depletive solid-phase microextraction method and application to linear alkylbenzene sulfonates

A solid-phase microextraction method (SPME) has been optimized for the analysis of freely dissolved anionic surfactants, namely linear alkylbenzene sulfonates (LAS), in seawater. An effect of the thermal conditioning treatment on the polyacrylate fiber coating was demonstrated for both uptake kinetics and sorption isotherm linearity. Thermal conditioning at 120 °C yielded linear sorption isotherms and reproducible SPME measurements for several individual LAS compounds, with detection limits at the low microgram per liter range. Sorption of LAS to the conditioned SPME fiber was independent of LAS co-solutes in mixtures. The method has been applied to study the precipitation of LAS in seawater, and solubility data for a wide range of individual LAS constituents is presented for the first time. Hence, the developed SPME method for the anionic LAS has shown to be a useful tool in complex matrices. The advantage of the SPME analyses in complex matrices is, besides its simplicity, that it also leads to clean extracts for chromatographic analyses.     

Carboxyl modified multi-walled carbon nanotubes as solid-phase extraction adsorbents combined with high-performance liquid chromatography for analysis of linear alkylbenzene sulfonates

Recently, multi-wall carbon nanotubes (MWCNTs) as adsorbents of solid-phase extraction are attractive because they can be used for enrichment of organic compounds and metal ions at trace levels. In this study, we use the carboxyl modified multi-wall carbon nanotubes (CMMWCNTs) as adsorbents of solid-phase extraction for extraction of linear alkylbenzene sulfonates (LAS), which are widely used anion surfactant with different homologues, and detected by HPLC-UV. The effect of eluent and its volume, sample pH and flow rate, sample volume and the ultrasonic time of sample, the content of the electrolyte (NaCl) were investigated and optimized. The detection limit for LAS homologues was 0.02-0.03 μg L⁻¹ with R.S.D. (n = 6) ranging from 2.04 to 10.03%. The recoveries of LAS homologues in the spiked environmental water samples ranged from 84.8 to 106.1%. The proposed method has been applied successfully to the analysis of LAS in aqueous environmental samples, which demonstrates that CMMWCNTs-based solid-phase extraction is a precision and convenient enrichment method and can be used for analysis of LAS homologues in water samples.     

Molecularly imprinted solid-phase extraction of naphthalene sulfonates from water

A new polymeric sorbent synthesised by exploiting molecular imprinting technology has been used to selectively extract naphthalene sulfonates (NSs) directly from aqueous samples. In the non-covalent molecular imprinting approach used to prepare this polymer, 1-naphthalene sulfonic acid (1-NS) and 4-vinylpyridine (4-VP) were used as a template molecule and functional monomer, respectively, and both dissolved in a mixture of methanol/water (4:1) as porogen together with the cross-linker ethylene glycol dimethacrylate. The new non-covalent molecularly imprinted polymer (MIP) prepared in aqueous environment was used as a sorbent in solid-phase extraction (SPE) to selectively extract a group of naphthalene mono- and disulfonates. When one litre of a standard aqueous solution, which contained a mixture of eight NSs, was percolated through the SPE cartridge, all the NSs were retained on the MIP because of the cross-reactivity of the polymer. Recoveries were higher than 80% for all the compounds even after a clean-up step with methanol (MeOH). The MIP was also used to analyse water from the Ebro river.     

Determination of alkylphenols and linear alkylbenzene sulfonates in sediments applying accelerated solvent extraction (ASE)

A time and solvent saving method (accelerated solvent extraction, ASE) for the extraction of anionic surfactants as linear alkylbenzene sulfonates (LAS) and alkylphenols from sediments is presented. The analytes are extracted by methanol at 100° C and 150 atm within 10 min of static and 5 min of dynamic extraction. The presence of methanol and a maximum pressure of 150 atm are essential for the complete extraction of anionic surfactants, whereas the extraction of alkylphenols is independent of both parameters. The extraction of alkylphenolethoxylates yielded only unsatisfactor results. It was demonstrated that the ASE extraction is selective for LAS surfactants, while matrix substances, which are extracted by the methanol extraction and interfere with the target analytes during the HPLC-run, remain in the sample. Thus, a further clean-up procedure of the ASE extract is not necessary.     

Determination of alkylphenols and linear alkylbenzene sulfonates in sediments applying accelerated solvent extraction (ASE)

A time and solvent saving method (accelerated solvent extraction, ASE) for the extraction of anionic surfactants as linear alkylbenzene sulfonates (LAS) and alkylphenols from sediments is presented. The analytes are extracted by methanol at 100 degrees C and 150 atm within 10 min of static and 5 min of dynamic extraction. The presence of methanol and a maximum pressure of 150 atm are essential for the complete extraction of anionic surfactants, whereas the extraction of alkylphenols is independent of both parameters. The extraction of alkylphenolethoxylates yielded only unsatisfactor results. It was demonstrated that the ASE extraction is selective for LAS surfactants, while matrix substances, which are extracted by the methanol extraction and interfere with the target analytes during the HPLC-run, remain in the sample. Thus, a further clean-up procedure of the ASE extract is not necessary.     

New extraction method for the analysis of linear alkylbenzene sulfonates in marine organisms. Pressurized liquid extraction versus Soxhlet extraction

A new method has been developed for the determination of linear alkylbenzene sulfonates (LAS) from various marine organisms, and compared with Soxhlet extraction. The technique applied includes the use of pressurized liquid extraction (PLE) for the extraction stage, preconcentration of the samples, purification by solid-phase extraction (SPE) and analysis by liquid chromatography with fluorescence detection. The spiked concentrations were added to the samples (wet mass of the organisms: Solea senegalensis and Ruditapes semidecussatus), which were homogenized and agitated continuously for 25 h. The samples were extracted by pressurized hot solvent extraction using two different extraction temperatures (100 and 150 degrees C) and by traditional Soxhlet extraction. The best recoveries were obtained employing pressurized hot solvent extraction at 100 degrees C and varied in the range from 66.1 to 101.3% with a standard deviation of between 2 and 13. Detection limit was between 5 and 15 microg kg(-1) wet mass using HPLC-fluorescence detection. The analytical method developed in this paper has been applied for LAS determination in samples from a Flow-through exposure system with the objective of measuring the bioconcentration of this surfactant.     

Determination of linear alkylbenzene sulfonates and their polar carboxylic degradation products in sewage treatment plants by automated solid-phase extraction followed by capillary electrophoresis-mass spectrometry.

Linear alkylbenzene sulfonates (LAS) were determined by solid-phase extraction (SPE), followed by capillary electrophoresis and mass spectrometry detection (CE-MS). The linear range of the proposed method varied from 33 to 316 and from 215 to 2057 micrograms L-1, depending on the compound, with limits of detection ranging from 4.4 to 23 micrograms L-1 when 200 ml of wastewater were preconcentrated. The analysis and confirmation of the polar carboxylic metabolites of LAS, the sulfophenyl carboxylic acids (SPC) was also achieved, and their presence was detected in both, influent and effluents of the sewage treatment plant (STP). [M - H]- ions were used for CE-MS confirmation and quantification. CE-MS diagnostic ions were the same ones used in LC-electrospray (ESI)-MS and corresponded to m/z 297, 311, 325 and 339 for C10LAS, C11LAS, C12LAS and C13LAS, respectively. For SPC identification, diagnostic ions corresponded to m/z 215 to 369 (with 14 mass unit steps) for C2 to C13SPC, respectively. LAS were determined in wastewater samples of the influent and effluent of three sewage treatment plants (STP), two of them using biological treatment with secondary settlement and receiving mainly domestic wastewater whereas one of the plants was operated with physiochemical treatment and received mainly industrial wastewater. The concentration levels of total LAS varied from 1000 to 1900 micrograms L-1 in the influents of STP, whereas in the effluents the concentrations varied from 125 to 360 micrograms L-1.     

Bioconcentration of linear alkylbenzene sulfonates and their degradation intermediates in marine algae

Sorption experiments using different homologues of linear alkylbenzene sulfonate (LAS) and sulfophenylcarboxylic acid (SPC) on several marine microalgae have been carried out. The steady state seems to be reached in the first 4 hours. Longer exposure times lead to biodegradation of the compound and, therefore, to an overestimation of the bioconcentration factor. Sorption coefficients are higher for Nannochloropsis gaditana, for example, 1,293 Lkg(-1) for C11-LAS and 525 Lkg(-1) for C11-SPC versus 727 Lkg(-1) for C11-LAS and 28 Lkg(-1) for C11-SPC for Dunaliella salina. For both algae an increase in the sorption coefficient is observed when the polarity of the compound decreases (C5-SPC相似文献   

Stability of fluoroquinolone antibiotics in river water samples and in octadecyl silica solid-phase extraction cartridges

Airborne particulate matter has been sampled at a location close to a metallurgical plant in North-Rhine-Westphalia, Germany, and first results on the chromium(VI) content in the collected dust are presented. A special procedure using a scrubber as sampling device was used to preserve Cr(VI) during the sampling procedure. The scrubber solution which consisted of 0.1 mol L^–1 TRIS-buffer solution was adjusted to a slightly alkaline pH of 8.6 to reduce the oxidation potential of Cr(VI) and to avoid possible oxidation of Cr(III) to Cr(VI), for example by oxygen (or ozone at ambient concentrations). After sampling Cr(VI) was pre-concentrated on an anion-exchange material and eluted with aqueous 0.6 mol L^–1 sodium perchlorate solution. After elution, a species-selective complex of Cr(VI) with diphenylcarbazide (DPC) was prepared; this was extracted into n-hexanol and quantified by UV–visible spectrophotometry. A detection limit of 0.9 ng m^–3 for Cr(VI) in ambient aerosols can be achieved with this method.     

Screening method for linear alkylbenzene sulfonates in sediments based on water Soxhlet extraction assisted by focused microwaves with on-line preconcentration/derivatization/detection

A screening method for linear alkylbenzene sulfonates (LAS) in sediments has been developed. Soxhlet extraction with water assisted by focused microwaves provides recoveries better (>90%) than obtained by conventional Soxhlet extraction (70-80%). Coupling of the extractor with an on-line preconcentration/derivatization/detection manifold through a flow injection (FI) interface allows a fully automated screening approach. A yes/no answer can be obtained in less than 2 h (for the whole analytical process), a short time compared with the at least 24 h of Soxhlet extraction (without final detection). Due to the use of water as leaching agent, the proposed method is environmentally friendly.     

Determination of linear alkylbenzene sulfonates in water samples by liquid chromatography-UV detection and confirmation by liquid chromatography-mass spectrometry

A high-performance liquid chromatographic (HPLC) method was developed for the separation and determination of individual (C₁₀-C₁₃) linear alkylbenzene sulfonates (LAS). New sets of conditions have been established for routine analysis of individual chemical forms of four LAS surfactants, i.e. C₁₀-C₁₃ LAS. Under a condition set using a mobile phase containing 1.5 mM ammonium acetate in methanol/water 80:20 (v/v) mixture, detection limits obtained were in the range 1.5 ppb (for C₁₀ LAS) to 11.5 ppb (for C₁₃ LAS). This offers the advantages of significant improvement in resolution, short separation time and using less amount of common salt under isocratic condition. In addition, the use of simple mobile phase containing a simple low amount of salt cannot deposit at the entrance of mass spectrometric detector. The method is applicable to the simultaneous determination of LAS surfactants in various water samples. LAS surfactants presented in these samples were also successfully confirmed by using electrospray mass spectrometry.     

Determination of non-ionic surfactants and polar degradation products in influent and effluent water samples and sludges of sewage treatment plants by a generic solid-phase extraction protocol

Non-ionic polyethoxylated surfactants (nonylphenol polyethoxylates, alcohol polyethoxylates), their breakdown products (polyethylene glycol, polyethoxylated nonylphenol carboxylates and polyethoxylated alcohol carboxylates) and other compounds were identified and measured in various waste-water treatment samples (influent, effluent and sludge). A generic protocol involving the use of sequential solid-phase extraction (SSPE) with octadecylsilica and styrene-divinylbenzene cartridges in series and differential elution was used. Fractionated extracts were analyzed by liquid chromatography-mass spectrometry (LC-MS) using atmospheric pressure chemical ionization (APCI) in the positive and negative ionization modes. For sewage treatment plant (STP) sludge, the extraction protocol involved lyophilization of the sludge followed by sonication with MeOH-CH2Cl2 (7 + 3) and final clean-up using the SSPE protocol. Limits of detection for target analytes ranging from 1.1 to 4.1 micrograms L-1 for water samples and from 0.11 to 0.28 mg kg-1 for sludge were achieved. The results obtained demonstrated the inefficient removal of the target analytes in physico-chemical STPs whereas their elimination factors in STPs with biological treatment reached average values of 77, 92 and 98% for alcohol polyethoxylates, nonylphenol polyethoxylates (NPEOs) and polyethylene glycols (PEGs), respectively. Quantitative elimination of coconut fatty acid diethanolamide (CDEA) surfactants in the activated sludge process occurred. In contrast, total removal of NPEOs led to the formation of persistent and toxic metabolites such as nonylphenol which was present in treated effluent as well as in sludge samples with average concentrations ranging from 15.0 to 251.2 micrograms L-1 and from 13.5 to 74.2 mg kg-1, respectively. Polyethoxylated carboxylates and short chain NPEOs were also detected at similar levels in the effluents and sludges. In addition, a linear correlation between the total phenolic concentration (Total Ph) measured by the 4-aminoantipyrine method and the total concentration of nonylphenolic compounds (Total NP) measured by SSPE-LC-APCI-MS was observed.     

Application of probe sonication extraction for the determination of linear alkylbenzene sulfonates from sewage sludge. Comparison with other extraction methods

A new method based on probe sonication extraction (USP) prior to high performance liquid chromatography (HPLC) has been developed for the determination of linear alkylbenzene sulfonates (LAS) from sewage sludge. The optimized method was designed to be cost effective compared to existing extraction methods (ultrasonic assisted extraction, Soxhlet or pressurized liquid extraction) which may require large quantities of organic solvents, or costly instrumentation or equipment.The main factors affecting the extraction efficiency (extractant volume, ultrasounds power and extraction time) were optimized using compost sludge. The detection limit of total LAS in the sludge was 10 mg kg^− 1. The extraction of C₁₀-C₁₃ homologues is carried out using an extraction time of 7 min with 10 mL of methanol. Liquid chromatography with fluorescence (FL) detector is used for determination of LAS homologues. A mobile phase acetonitrile-water containing 0.1 M NaClO₄ (65:35) and isocratic elution was used. Compounds were eluted over 6 min at a flow rate of 1 mL/min. Polar interferences are eluted between 0 and 2 min and no purification of the samples is required prior to the final determination by high performance liquid chromatography (HPLC). The recoveries of LAS in spiked sewage sludge were between 84.0% and 97.0%, which reflect the efficiency of the method for extraction of these analytes from sewage sludge. Concentration levels found were between 11,858 mg kg^− 1 for digested sludge and 2379 mg kg^− 1 for compost sludge.     

Lab-on-valve for the automatic determination of the total content and individual profiles of linear alkylbenzene sulfonates in water samples

Methods for the total content and individual determination of linear alkylbenzene sulfonates (LAS) in water samples based on the use of a lab-on-valve (LOV) module alone or coupled to CE equipment, respectively, have been developed. The total content of LAS has been determined by intrinsic absorption measurements (DA method) and after reaction with a methyl orange-cetylpyridine chloride mixture (MO method) with detection limits (LODs) of 21 ng/L and 15 microg/L, respectively, quantification limits (LOQs) of 70 ng/L, 50 microg/L, and development times of 100 and 124 s, respectively. The method for individual separation-quantification of LAS at very low concentration is based on automatic SPE preconcentration in the LOV module coupled on-line with the CE equipment. The LODs and LOQs thus obtained range between 1-21 and 4-70 ng/L, respectively, with linear dynamic ranges from the LOQ to 10 microg/L. Preconcentration factors of 10,000 and high efficiency to eliminate interferents by SPE enable application of the method to treated effluent, waste, surface and sea waters.     

Bromate assay in water by inductively coupled plasma mass spectrometry combined with solid-phase extraction cartridges

Based on selective sorption of bromide, bromoacetic acids (BAA) and bromomethanes on solid-phase extraction (SPE) cartridges, a sensitive and convenient method was developed for the determination of bromate in waters by inductively coupled plasma mass spectrometry (ICP–MS). Dionex OnGuard Ag and reversed-phase (RP) cartridges were tested for retention characteristics for bromide, BAA and bromomethanes. When a sample acidified with nitric acid was passed through an RP cartridge, BAA and bromomethanes were retained, afterwards bromide was absorbed as a precipitate of silver bromide and bromate was unretained when the nearly neutral sample passed a combination of Ag and H cartridges. After SPE pretreatment the recovery of bromate was 96–106%, and bromide remaining in the aqueous phase was found to be less than 0.06 g L^–1 when the original bromide concentrations were less than 5 mg L^–1. Effectiveness of stacked Ag and H cartridges in removing bromide from chloride-containing samples was also examined. Common cations and other anions did not interfere with bromate determination. The detection limit for bromate is 57 ng L^–1. This method has been applied to analyse waters from various sources, and the recovery of the spiked bromate was in the range of 92–107%.     

Extractive spectrophotometric determination of non-ionic surfactants in water

The solvent extraction of non-ionic surfactants with potassium chloride and tetrabromophenolphthalein ethyl ester potassium salt has been studied, and a method developed for determining trace amounts of non-ionic surfactants in water spectrophotometrically. Various non-ionic surfactants of general type RO(CH(2)CH(2)O)(n)H (where R is an alkyl or alkylphenyl group and n is the number-average degree of polymerization) are extracted quantitatively into o-dichlorobenzene from the water sample, and reacted in the organic phase with tetrabromophenolphthalein ethyl ester potassium salt to give a coloured product, the absorbance of which is measured at 620 nm.