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.     

Rapid tool for distinction of wines based on the global volatile signature

A new methodology capable of performing the simultaneous analysis of the main surfactants--linear alkylbenzene sulfonates (LAS), alkyl ethoxysulfates (AES), alkyl sulfates (AS), nonylphenol polyethoxylates (NPEOs) and alcohol polyethoxylates (AEOs)--and their carboxylated metabolites--sulfophenyl carboxylic acids (SPCs) and alkylphenol ethoxycarboxylates (APECs)--in environmental samples has been developed for the first time. Extraction is carried out by solid-phase extraction (SPE) and pressurized liquid extraction (PLE) from water and sediment, respectively. Identification and quantification of the target compounds is performed using a liquid chromatography-mass spectrometry (LC-MS) system equipped with an electrospray interface (ESI) operating in mixed-mode. Optimization of parameters such as pH, ionic strength, temperature and solvents has been carried out in order to obtain recoveries in the range from 70 to 107% for most homologs, while the limits of detection are 0.05-0.5 ng mL(-1) in water and 1-10 ng g(-1) in sediment. The proposed methodology has been applied for the simultaneous determination of all the target compounds in samples taken from aquatic ecosystems in the SW of Spain. Values for LAS, AS, AES, NPEOs and AEOs are up to 38.7, 3.0, 2.9, 5.0 and 1.2 microg L(-1) in waters, and in the ranges of 1.73-12.80, 0.11-0.24, 0.02-0.59, 1.94-2.70 and 0.64-3.64 mg kg(-1) in sediments, respectively. The highest concentrations of metabolites found in water are 149.6 microg L(-1) of SPCs and 3.9 microg L(-1) of APECs.     

Determination of the four major surfactant classes in cleaning products by reversed-phase liquid chromatography using serially connected UV and evaporative light-scattering detection

A method for the simultaneous determination of the most frequently used surfactant families –linear alkyl benzenesulphonates (LAS), alkyl ether sulphates (AES), fatty alcohol ethoxylates (FAE) and oleins (soaps, fatty acid salts) – in cleaning products, has been developed. The common reversed phase octyl (C8), pentafluorophenyl and biphenyl columns were not capable of separating the anionic LAS and AES classes; however, since only LAS absorbs in the UV, these two classes were independently quantified using a C8 column and serially connected UV and ELSD detection. The best compromise to resolve the four surfactant classes and the oligomers within the classes was achieved with a C8 column and an ACN/water gradient. To enhance retention of the anionic surfactants, ammonium acetate, as an ion-pairing agent compatible with ELSD detection, was used. Also, to shift the olein peaks with respect to that of the FAE oligomers, acetic acid was used. In the optimized method, modulation of the mobile phase, using ammonium acetate during elution of LAS and AES, and acetic acid after elution of LAS and AES, was provided. Quantitation of the overlapped LAS and AES classes was achieved by using the UV detector to quantitate LAS and the ELSD to determine AES by difference. Accuracy in the determination of AES was achieved by using a quadratic model, and by correcting the predicted AES concentration according to the LAS concentration previously established using the UV chromatogram. Another approach also leading to accurate predictions of the AES concentration was to increase the AES concentrations in the samples by adding a standard solution. In the samples reinforced with AES, correction of the predicted AES concentration was not required. FAE and olein were quantified using also quadratic calibration.     

Stability of fluorinated surfactants in advanced oxidation processes--A follow up of degradation products using flow injection-mass spectrometry, liquid chromatography-mass spectrometry and liquid chromatography-multiple stage mass spectrometry

The advanced oxidation process (AOP) reagents ozone (O3), O3/UV, O3/H2O2, and H2O2/Fe2+ (Fenton's reagent) were applied to the anionic and the non-ionic fluorinated surfactants perfluorooctanesulfonate (PFOS) and N-ethyl-N-(perfluoroalkyl)-sulfonyl-glycinic acid (HFOSA-glycinic acid) or N-ethyl-N-perfluoroalkyl sulfonylamido-2-ethanol polyethoxylates (NEtFASE-PEG), their methyl ethers (NEtFASE-PEG methyl ether) and partly fluorinated alkyl-ethoxylates (FAEO) dissolved in ultrapure water. To monitor the efficiencies of destruction samples were taken during the treatment period of 120 min. After sample concentration by C18-solid phase extraction (SPE) and desorption MS, coupled with atmospheric pressure chemical ionisation (APCI) or electrospray interface (ESI) was applied for detection. No elimination of PFOS was observed while HFOSA-glycinic acid and AOP treated non-ionic surfactants were eliminated by oxidation. Degradation products could be detected and identified. So PFOS was observed during HFOSA-glycinic acid oxidation. Polyethylene glycols (PEG) and PEG methyl ethers were generated from non-ionic fluorinated surfactants beside their oxidation products--aldehydes and acids--all identified by tandem (MS-MS) or multiple stage mass spectrometry (MSn). AOP treatment of FAEO blend resulted in a mixture of partly fluorinated alcohols, separated and identified using GC-MS.     

Concentration of nonylphenol and its polyethoxylated derivatives by polymer-mediated extraction

Polymer-mediated extraction based on thermoresponsive precipitation of poly(N-isopropylacrylamide) [PNIPAAm] was applied to the concentration of amphiphilic compounds, nonylphenyl polyethoxylates (NPnEOs), in water. Among these nonionic surfactants, NPnEOs possessing the number, n, of ethoxy unit less than 5 were quantitatively recovered in polymer precipitates when a 0.100-g portion of PNIPAAm was used for a 10 ml sample solution. Torelance limit (30 ppm) against a typical industrial anionic surfactant, sodium dodecylsulfate, strongly suggests the potential to use the present method for practical purposes. After preconcentration, trace nonylphenol and mono-ethoxylated nonylphenol (ppb-level) in a river water sample were successfully determined by high-performance liquid chromatography with ultra-violet photometric detection.     

Determination of phenolic xenoestrogens in environmental samples by liquid chromatography with mass spectrometric detection

A method is proposed for the determination of several phenolic xenoestrogens in aqueous and solid environmental samples. The method uses solid-phase extraction (preceded by ultrasonic solvent extraction for solid samples), reversed-phase liquid chromatographic separation, and mass spectrometric detection using both atmospheric pressure chemical ionization and electrospray ionization. This method was developed to support several studies undertaken to obtain aquatic and sedimentary data for rivers and seashores in Spain that are likely to be contaminated by endocrine-disrupting compounds (EDCs) as a consequence of wastewater discharge. Nonylphenol polyethoxylates (NPEOs), nonylphenoxy carboxylates (NPECs), nonylphenol (NP), octylphenol (OP), and bisphenol A (BPA) were determined in various samples of surface water and sediment, collected at different locations upstream and downstream from outfalls of municipal wastewater treatment plants (WWTPs). Seawater and marine sediments were collected in different harbor areas in Spain. Additionally, WWTP influent and effluents were analyzed to monitor the occurrence and transformation of phenolic EDCs during physicochemical and biological treatment. Rather high concentrations of the compounds investigated were found in some samples. Concentrations of NP were < or = 590 microg/kg in sediments and < or = 15 microg/L in water samples. NPEOs and NPECs were found in water samples in concentrations < or = 41 and < or = 35 microg/L, respectively. In solid samples (river sediment), concentrations of NPEO were < or = 818 microg/kg and those of NP1EC were 95 microg/kg.     

Simultaneous extraction and determination of anionic surfactants in waters and sediments

A new method has been developed for the simultaneous determination of the most frequently used anionic surfactants - linear alkylbenzene sulfonates (LAS), alkyl ethoxysulfates (AES) and alkyl sulfates (AS) - in aqueous and sediment samples. Preconcentration and purification of water samples are carried out by means of solid-phase extraction (SPE). The efficiency of two different extraction methods for the analysis of sediments - Soxhlet extraction and pressurized liquid extraction (PLE) - has been compared. Identification and quantification of the target compounds is performed using a liquid chromatography - mass spectrometry (LC-MS) system equipped with an electrospray interface (ESI) in negative ion-mode. Homologue recoveries are 85-123% for SPE, 94-112% for Soxhlet extraction and 81-125% for PLE in the case of LAS, and 60-94% for SPE, 61-109% for Soxhlet extraction and 55-99% for PLE in the case of AES, whereas the limits of detection are 0.1-0.5 ngml(-1) in water and 1-5 ngg(-1) in sediment. This method has been applied to the determination of anionic surfactants in the Guadalete estuary (SW Spain), and LAS concentration levels from 538 to 1014 ngg(-1) in sediments and from 25.1 to 64.4 ngml(-1) in waters have been found. AES values from 168 to 536 ngg(-1) in sediments and from 4.5 to 11.9 ngml(-1) in waters are reported for the first time in European rivers.     

Simultaneous determination of degradation products of nonylphenol polyethoxylates and their halogenated derivatives by solid-phase extraction and gas chromatography-tandem mass spectrometry after trimethylsilylation

An efficient method for the simultaneous determination of the degradation products of nonylphenol polyethoxylates (NPnEOs, n = number of ethoxy units), i.e., nonylphenol (NP), NPnEOs (n = 1-3), nonylphenoxy carboxylic acids (NPnECs, n = 1-2, number of ethoxy units plus an acetate) and their halogenated derivatives (XNP, XNP1EO and XNP1EC; X = Br or Cl), in water samples were developed. After trimethylsilylation with N,O-bis(trimethysilyl)acetamide, all the analytes were determined by gas chromatography-tandem mass spectrometry (GC-MS-MS) with electron ionization (EI). The ion peaks of [M - 85]+ of the derivatives were selected as precursor ions and their product ions showing the highest intensities were used for the quantitative analysis. The instrumental detection limits were in the range from 2.1 to 11 pg. The recoveries of the analytes from the water samples were optimized by using solid-phase extraction (SPE). The deuterated reagents of octylphenol, octylphenol monoethoxylate and octylphenoxyacetic acid were used as the surrogates. The method detection limits (500 ml water sample) using C18 SPE were from 2.5 to 18 ng/l. The recoveries from spiked pure water and the environmental water samples were greater than 78%. The method was successfully applied to environmental samples. Remarkably, the concentrations of the halogenated compounds (CINP, CINP1EO and BrNP1EO) were detected at the hundreds of ng/l levels in the Neya river.     

Separation techniques for the analysis of artists' acrylic emulsion paints

Emulsion paints are complex chemical systems. The main problems in their characterization are related to the similarities in polymer composition and to the presence of many different types of additives. Thus high resolution separations, sensitivity, and response specificity are required to identify simultaneously the polymer matrix and the minor components. Especially surfactants and pigments are thought to affect significantly the properties of the paint layers during ageing and their identification is the first step in evaluating the behaviour of these products in working conditions. Representative samples of acrylic emulsion paints for artists have been investigated by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and size exclusion chromatography-Fourier transform infrared spectroscopy (SEC-FTIR), and the results have been compared. All the analysed samples were bound in ethyl acrylate-methyl methacrylate, poly(EA-co-MMA), or n-butyl acrylate-methyl methacrylate, poly(nBA-co-MMA), copolymers. Two types of nonionic surfactants, ethoxylated fatty alcohols and alkylaryl polyethoxylates, commonly used as emulsifiers and dispersive agents have been identified, together with a number of organic pigments.     

固相萃取净化-正相高效液相色谱测定纺织品中残留的烷基酚和烷基酚聚氧乙烯醚

建立了测定纺织品中烷基酚(AP)和烷基酚聚氧乙烯醚(APnEO)(n2～16)的正相高效液相色谱法。以甲醇为提取溶剂,用索氏抽提法提取纺织品中的AP和APnEO,用正相高效液相色谱法测定,并对提取溶剂、提取方式和净化条件等前处理条件进行优化。该方法的检出限为1.0 mg/kg,回收率为90.4%～104.1%,相对标准偏差为0.64%～4.21%。采用该方法对多种基质纺织品进行检测,可满足残留检测要求。     

Molecularly imprinted polymer for selective extraction of endocrine disrupters nonylphenol and its ethoxylated derivates from environmental solids

Nonylphenol isomers (NP), linear nonylphenol (4-n-NP) and NP short chain ethoxylated derivates (NPEO1 and NPEO2) are degradation products of nonylphenol polyethoxylates, a worldwide used group of surfactants. All of them are considered endocrine disrupters due to their ability to mimic natural estrogens. In this paper, the preparation and evaluation of several 4-n-NP molecularly imprinted polymers (MIPs) for the selective extraction and clean-up of 4-n-NP, NP, NPEO1 and NPEO2 from complex environmental solid samples is described. Among the different combinations tested, a methacrylic acid-based imprinted polymer prepared in toluene provided the better performance for molecularly imprinted SPE (MISPE). Under optimum MISPE conditions, the polymer was able to selectively retain not only linear NP but also the endocrine disruptors NPEO1, NPEO2 and NP with recoveries ranging from 60 to 100%, depending upon the analyte. The developed MISPE procedure was successfully used for the determination of 4-n-NP, NP, NPEO1 and NPEO2 in sediments and sludge samples at concentration levels according to data reported in the literature for incurred samples. Finally, various sludge samples collected at five different sewage treatment plants from Madrid and commercial sludge for agriculture purposes were analysed. The measured concentrations of the different compounds varied from 3.7 to 107.5 mg/kg depending upon the analyte and the sample.     

Matrix Effects on Water Analysis for Alkylphenols Using Solid Phase Extraction Gas Chromatography-Mass Spectrometry

Gas chromatography with mass spectrometry is frequently used for the quantification of many classes of substances, including alkylphenols. Alkylphenol polyethoxylates are nonionic surfactants used in a wide variety of industrial and consumer applications. Alkylphenol polyethoxylates can degrade to alkylphenols, which are endocrine disruptors. In analytical validation procedures, the most common parameters studied are the detection and quantification limits, linearity, and recovery; however, the matrix effects are sometimes neglected. Although some investigators have evaluated matrix effects, there is no consensus on how to evaluate them during method validation. In this study, the matrix effects of alkylphenol polyethoxylates (nonylphenol monoethoxylate, nonylphenol diethoxylate, octylphenol monoethoxylate, octylphenol diethoxylate) and alkylphenols (nonylphenol and octylphenol) were studied using solid phase extraction and gas chromatography-mass spectrometry analysis. For alkylphenol polyethoxylates, the matrix effects ranged from 16 to 4692%, whereas for alkylphenols (nonylphenol and octylphenol), the effects were insignificant. Therefore, constructing an analytical curve in the matrix for alkylphenol polyethoxylates is essential.     

Optimization of a hydrogen bromide fission procedure for nonyl- and dinonylphenol polyethoxylates and their <Emphasis Type="Italic">o</Emphasis>-phosphate esters

Nonyl- and dinonylphenol polyethoxylates (NPEOs, DNPEOs) and their o-phosphate esters are widely used as surfactants in various industrial, agricultural and domestic applications. An HBr-fission procedure was developed for cleaving NPEOs, DNPEOs and their o-phosphate esters to nonylphenol (NP) and dinonylphenol (DNP), and their bromine adducts, thereby facilitating the analysis of NP- and DNP contents in complex NPEO- and DNPEO-containing samples. The procedure includes fission, liquid-liquid extraction and GC-MS analyses of the fission end-products. Using 2 × 2 factorial experimental designs, 2 h cleavage at 120°C was found to provide optimal yields of the target compounds, with minimal unwanted by-products. The calculated accuracy for the cleavage of NP10EO to NP was 95% and the limit of NP/DNP detection of the presented method was 5 mg/L.     

Characterization and quantitative analysis of surfactants in textile wastewater by liquid chromatography/quadrupole-time-of-flight mass spectrometry

A method based on the application of ultra-performance liquid chromatography (UPLC) coupled to hybrid quadrupole-time-of-flight mass spectrometry (QqTOF-MS) with an electrospray (ESI) interface has been developed for the screening and confirmation of several anionic and non-ionic surfactants: linear alkylbenzenesulfonates (LAS), alkylsulfate (AS), alkylethersulfate (AES), dihexyl sulfosuccinate (DHSS), alcohol ethoxylates (AEOs), coconut diethanolamide (CDEA), nonylphenol ethoxylates (NPEOs), and their degradation products (nonylphenol carboxylate (NPEC), octylphenol carboxylate (OPEC), 4-nonylphenol (NP), 4-octylphenol (OP) and NPEO sulfate (NPEO-SO4). The developed methodology permits reliable quantification combined with a high accuracy confirmation based on the accurate mass of the (de)protonated molecules in the TOFMS mode. For further confirmation of the identity of the detected compounds the QqTOF mode was used. Accurate masses of product ions obtained by performing collision-induced dissociation (CID) of the (de)protonated molecules of parent compounds were matched with the ions obtained for a standard solution. The method was applied for the quantitative analysis and high accuracy confirmation of surfactants in complex mixtures in effluents from the textile industry. Positive identification of the target compounds was based on accurate mass measurement of the base peak, at least one product ion and the LC retention time of the analyte compared with that of a standard. The most frequently surfactants found in these textile effluents were NPEO and NPEO-SO4 in concentrations ranging from 0.93 to 5.68 mg/L for NPEO and 0.06 to 4.30 mg/L for NPEO-SO4. AEOs were also identified.     

Determination of fatty alcohol ethoxylates and alkylether sulfates by anionic exchange separation, derivatization with a cyclic anhydride and liquid chromatography

A method for the separation, characterization and determination of fatty alcohol ethoxylates (FAE) and alkylether sulfates (AES) in industrial and environmental samples is described. Separation of the two surfactant classes was achieved in a 50:50 methanol-water medium by retaining AES on a strong anionic exchanger (SAX) whereas most FAE were eluted. After washing the SAX cartridges to remove cations, the residual hydrophobic FAE were eluted by increasing methanol to 80%. Finally, AES were eluted using 80:20 and 95:5 methanol-concentrated aqueous HCl mixtures. Methanol and water were removed from the FAE and AES fractions, and the residues were dissolved in 1,4-dioxane. In this medium, esterification of FAE and transesterification of AES with a cyclic anhydride was performed. Phthalic and diphenic anhydrides were used to derivatizate the surfactants in industrial samples and seawater extracts, respectively. Separation of the derivatized oligomers was achieved by gradient elution on a C8 column with acetonitrile/water in the presence of 0.1% acetic acid. Good resolution between both the hydrocarbon series and the successive oligomers within the series was achieved. Cross-contamination of FAE with AES and vice versa was not observed. Using dodecyl alcohol as calibration standard, and correction of the peak areas of the derivatized oligomers by their respective UV-vis response factors, both FAE and AES were evaluated. After solid-phase extraction on C18, the proposed method was successfully applied to the characterization and determination of the two surfactant classes in industrial samples and in seawater.     

Liquid Chromatographic Determination of Cationic Surfactants in Environmental Samples using a Continuous Post-Column Ion-Pair Extraction Detector with a Sandwich Phase Separator

Abstract

A new detection technique is described for the quantitative analysis of cationic surfactants by HPLC via post-column ion-pair formation. A new sandwich type phase separator, as part of the extraction detector, was successfully introduced. The method was used to determine ditallowdimethylammonium chloride (DTDMAC) in various environmental samples. Detection limits of DTDMAC in river water were about 2 μg/1 (60 ng absolute; S/N = 5) and 10 ng/1 (260 pg absolute; S/N = 5), using methyl orange and 9,10-dimethoxyanthracene-2-sulphonate (DAS) as ion-pairing reagents, respectively. The environmental concentration of DTDMAC found on random samples from two Belgian rivers range from 30 to 40 μg/1. The reproducibility of the determination of DTDMAC in river water was 4.2% (RSD) (n = 20).     

Determination of endocrine-disrupting compounds in environmental samples using gas and liquid chromatography with mass spectrometry

This paper describes certain applications for endocrine-disrupting compounds determination. LC-MS was applied using an electrospray ionization (ESI) technique in positive mode for alcohol polyethoxylates and nonylphenol and octylphenol polyethoxylates (NPEOn and OPEOn), and in negative mode for 4-nonylphenol (4-NP) and 4-octylphenol (4-OP) to determine targeted compounds in wastewater and sludge. GC-MS and GC-MS-MS were used to determine 4-NP, 4-tert.-octylphenol (4-t-OP), bisphenol A, estradiol-17beta, estriol estrone, testosterone, 17alpha-ethynylestradioL cholesterol, coprostan-3-ol, coprostan and coprostan-3-one in both surface water and wastewater after derivatization with N,O-bis(trimethyl-silyl)trifluoroacetamide (BSTFA). Extraction from the water samples was by an SPE technique, using either a copolymeric (Oasis HLB) or C18 silica sorbents, depending on the target contaminants. Extraction from the sludge samples was by a Soxtec system using methanol. Percentage recoveries for most of the selected compounds, using either a copolymeric (Oasis HLB) or C18 silica sorbents, were satisfactory (>60%). Quantification limits for the target compounds were at ppb levels in both water and sludge samples when using LC-ESI-MS in both positive and negative modes. They reached ppt levels in water when using GC-MS (in large volume injection mode) and GC-MS-MS. The results revealed 4-NP, NPEOn and AEOs in sludge samples at a concentration range of 1.3-8.5 microg/g, and NPEOn, OPEOn and other compounds, such as coprostan and bisphenol A, in surface water and/or wastewater samples at concentrations ranging from the ppt to ppb levels.     

All-solid-state potentiometric sensors sensitive to nonionic surfactants based on ionophores containing ethoxylate units

Earlier work of potentiometric Ion-selective electrodes (ISEs) sensitive to nonionic surfactants of the polyethoxylate type is further extended. The ISEs constructed were all-solid-state sensors with plasticized PVC membranes. The sensing material was a tetraphenylborate salt of the barium complex with a polyethoxylate nonionic surfactant. As membrane component, the combinations of two polyethoxylates of the nonylphenoxy type, which differed in the number of oxyethylene units (5 or 12), and two different plasticizers, (o-nitrophenyloctyl ether and o-nitrophenylphenyl ether), were tested. The response of these electrodes to different nonionic surfactants and the interference effect of several species has been evaluated. For all the types of tested electrodes, the sensitivities shown were ca. 30.0 mV dec(-1) and the limit of detection, ca. 10(-5) M, when a nonylphenoxyde with 12 oxyethylene units was used as standard. The membrane with the best response characteristics was then applied in potentiometric titrations of this kind of surfactants in the presence of Ba(2+) ion and using tetraphenylborate as the titrant.     

Influence of Ionic Surfactants on the Properties of Nanoemulsions Emulsified by Nonionic Surfactants Span 80/Tween 80

The instability of nanoemulsions were mainly due to Ostwald ripening. The droplet charge was influenced by the stability of nanoemulsions significantly. In this work, the properties of the shea butter oil-loaded nanoemulsions were investigated in detail with the addition of cationic surfactants (cetyl trimethyl ammonium chloride, 1631; octadecyl trimethyl ammonium chloride, 1831), anionic surfactants (alcohol ethoxysulfate, AES; dodecyl phosphate ester sodium salt, MAP), and zwitterionic surfactants (cocoamidopropyl betaine, CAB; dodecyl hydroxysulfobetaine, 20HD). By increasing the concentration of cationic surfactants, the positively charged nanoemulsions were prepared and the smallest droplets were being formed with 0.05% 1831. Upon the addition of anionic surfactants, a more negative value was obtained and the smallest droplets were being formed with 0.1% AES. The ionic surfactants by increasing the electrostatic interactions between droplets and incorporation into the oil phase improved the stability of the nanoemulsions via lowering the Ostwald ripening rate, and especially improved the high temperature stability. By increasing the concentration of zwitterionic surfactants, a less negative zeta potential was observed and the stability of the nanoemulsions did not improve. The results proved that the electrosteric repulsion had an appreciable impact on the stability of the nanoemulsions.     

Sequential injection immunoassay for environmental measurements

Sequential injection immunoassay systems for environmental measurements based on the selective immunoreaction between antigen and antibody were described. A sequential injection analysis (SIA) technique is suitable to be applied for the procedure of enzyme-linked immunosorbent assay (ELISA), because the washing and the addition of reagent solutions can be automated by using a computer-controlled syringe pump and switching valve. We selected vitellogenin (Vg), which is a biomarker for evaluating environmental risk caused by endocrine-disrupting chemicals in the hydrosphere, and linear alkylbenzene sulfonates (LAS) and alkylphenol polyethoxylates (APEO), which are versatile surfactants, as target analytes in the flow immunoassay systems. For Vg monitoring, SIA systems based on spectrophotometric, chemiluminescence, and electrochemical determinations were constructed. On the other hand, chemiluminescence determination was applied to the detection of LAS and APEO. For APEO, an SIA system combined with surface plasmon resonance (SPR) sensor was also developed. These new sequential injection immunoassay systems are expected to be useful systems for environmental analysis.