Capillary electrochromatography-mass spectrometry of zwitterionic surfactants

This work describes the on-line hyphenation of a packed capillary electrochromatography (CEC) column with an internally tapered tip coupled to electrospray ionization-mass spectrometry (ESI-MS) and atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) for the analysis of betaine-type amphoteric or zwitterionic surfactants (Zwittergent). A systematic investigation of the CEC separation and MS detection parameters comparing ESI and APCI is shown. First, a detailed and optimized manufacturing procedure for fabrication of the CEC-MS column with a reproducible internally tapered tip (7-9 microm) is presented. Next, the optimization of the separation parameters by varying the C(18) stationary-phase particle size (3 versus 1.5 microm), as well as mobile-phase composition including acetonitrile (ACN) volume fraction, ionic strength, and pH is described. The optimized separation is achieved using 3-microm C(18) packing with 75% ACN (v/v), 5 mM Tris at pH 8.0. Optimization for on-line CEC-ESI-MS detection is then done varying both the sheath liquid and spray chamber parameters while evaluating the use of random versus structured factorial table experimental designs. The more structured approach allows fundamental analysis of individual ESI-MS parameters while minimizing CEC and MS equilibration time between settings. A comparison of CEC-ESI-MS to CEC-APCI-MS using similar sheath and spray chamber conditions presents new insight for coupling of CEC to APCI-MS. The sheath liquid flow rate required to maintain adequate sensitivity is much higher in APCI source (50 microL/min) as compared to the ESI source (3 microL/min). The on-line mass spectra obtained in the full scan mode show that fragmentation in the two sources occurs at different positions on the Zwittergent molecules. For ESI-MS, the protonated molecular ion is always highest in abundance with minor fragmentation occurring due to the loss of the alkyl chain. In contrast, the APCI-MS spectra show that the highest abundant ion resulted by elimination of propane sulfonate from the Zwittergent molecule. A comparison of the sensitivity between the two sources in positive ionization SIM mode shows that CEC-ESI-MS provides an impressive limit of detection (LOD) of 5 ng/mL, which is at least 3 orders of magnitude lower than CEC-APCI-MS (LOD 100 microg/mL). Finally, the optimized CEC-MS methods comparing ESI and APCI are applied for separation and structural characterization of a real industrial zwittergent sample, Rewoteric AM CAS.     

Effect of nonionic surfactants on the solubilization of alachlor

The ability of nonionic surfactants to solubilize the pesticide alachlor was studied. Two homologue series, octylphenol ethoxylates (Triton X-114, Triton X-100 and Triton X-102) and ethoxylated decyl alcohols (Neodol 91-5E, Neodol 91-6E and Neodol 91-8E) were used at concentrations 3 critical micelle concentration (CMC) and 6 CMC. The rate of solubilization of a sufficient quantity of alachlor (for saturation) in aqueous solution containing the micelles of nonionic surfactant was recorded. The experimental data were fitted to a first-order kinetic model. The rate constant, saturation concentration and enhancement factor were estimated for each surfactant system. The effect of surfactant structure, CMC concentration, pesticide structure and its physicochemical properties on the effectiveness of solubilization was determined. In terms of solubilization capability, the nonionic surfactants of each homologue series can be ranked as follows: Neodol 91-8E>Neodol 91-6E>Neodol 91-5E and Triton X-102>Triton X-100>Triton X-114. The more hydrophilic Neodol series was proved more efficient in alachlor solubilization than Triton series. The enhancement factor values ranged from 1.064 to 1.995 at 3 CMC and 1.320 to 2.919 at 6 CMC. The results will be used mainly for micellar-enhanced ultrafiltration since the extent of solubilization is a critical factor.     

Biomimetic synthesis of oriented hydroxyapatite mediated by nonionic surfactants

Highly oriented organization of hydroxyapatite (HAP) nanorods was achieved through a simple reflux method using mixtures of triblock copolymer pluronic P123 and tween-60 as the mediated agents. Raft-like organized complexes were prepared when the nanorods were only directed by the mixed surfactants. Bundles of nanorod-like HAP crystals were obtained when urea was used as the cosurfactant. These HAP nanorods with a large amount of uniform 4?nm worm-like mesopores were arranged in parallel to each other along the c axis of HAP. The raft-like complexes might be mediated by the reverse lamellar micelles. And the added urea transformed the reverse lamellar micelles into hexagonal ones due to its association with the surfactant molecules by hydrogen bonds, resulting in the formation of bundles of nanorod-like HAP crystals. The regulation of the oriented HAP complexes in morphology extends the understanding of biomineralization and permits controllable design of biomimetic materials. In addition, the c-axis oriented raft-like HAP complex has great potential in selective bio-absorption and separation.     

Capillary electrophoretic separations of proteins using nonionic surfactant coatings

Capillary zone electrophoretic separations of proteins have been achieved by using nonionic surfactant coated capillaries. Capillaries were prepared by derivatization of the silica surface with octadecylsilane followed by the deposition of a layer of nonionic surfactant from an aqueous solution above the critical micelle concentration. This coating is of sufficient thickness and hydrophilicity to reduce both protein adsorption and electroosmotic pumping. This hydrophilic coating reduces electroosmotic pumping 5-8-fold while resolving proteins quickly and efficiently with good recovery. The coating provides a stable and reproducible means of deactivation, while the rate of electroosmotic pumping stays relatively constant throughout the pH range 4-11. This allows the pH to be varied to enhance selectivity without adversely affecting the flow rate.     

HPLC/ESI-quadrupole ion trap mass spectrometry for characterization and direct quantification of amphoteric and nonionic surfactants in aqueous samples

An amphoteric (cocamidopropylbetaine, CAPB) and a nonionic (alcohol polyethoxylate, AE) surfactant were characterized by electrospray ionization quadrupole ion trap mass spectrometry (ESI-MS) as to their homologue distribution and ionization/fragmentation chemistry. Quantitative methods involving reversed-phase gradient HPLC and (+)ESI-MSn were developed to directly determine these surfactants in hydroponic plant growth medium that received simulated graywater. The predominant homologues, 12 C alkyl CAPB and 9 EO AE, were monitored to represent the total amount of the respective surfactants. The methods demonstrated dynamic linear ranges of 0.5-250 ng (r2 > 0.996) for CAPB and 8-560 ng (r2 > 0.998) for AE homologue mixture, corresponding to minimum quantification limits of 25 ppb CAPB and 0.4 ppm AE with 20-microL injections. This translated into an even lower limit for individual components due to the polydispersive nature of the surfactants. The procedure was successfully employed for the assessment of CAPB and AE biodegradation in a hydroponic plant growth system used as a graywater bioreactor.     

Separation of nonionic surfactants by capillary electrophoresis and high-performance liquid chromatography

Fatty alcohol ethoxylates (FAEs) are applied in commercial formulations (laundry detergents) as complex mixtures of alkyl and ethoxylate homologues. Therefore, efficient analytical methods are required for product control. Capillary electrophoresis, a modern analytical separation technique, was used to separate FAEs in technical products and household formulations after derivatization with phthalic anhydride. The well-established high-performance liquid chromatography was used as reference and supplementary method. UV detection after derivatization with phenyl isocyanate or light scattering detection has been carried out. Sample components have been identified by standard addition or by comparison to known products. The peak pattern can be considered as a "fingerprint" of the product and is characteristic for a defined composition.     

Simultaneous quantitative analysis of anionic, cationic, and nonionic surfactants in water by electrospray ionization mass spectrometry with flow injection analysis

A rapid method is described for the quantitative analysis of anionic, cationic, and nonionic surfactants in water samples by flow injection analysis coupled to electrospray ionization mass spectrometry (FIA/ESI-MS). All surfactants were isolated by liquid-liquid extraction and quantified using labeled triethoxylated nonylphenol ([13C6]-NP3EO) and sodium dibutylnaphthalenesulfonate as internal standards. FIA/ESI-MS was performed by alternating both positive and negative ionization modes, which allows simultaneous analysis of most common surfactants in a short time. Quality parameters of the method, such as linear range, repeatability, reproducibility, and limits of detection were studied. This method was applied to the analysis of wastewater treatment plant effluents from Catalonia (NE Spain).     

Determination of anionic and nonionic surfactants, their degradation products, and endocrine-disrupting compounds in sewage sludge by liquid chromatography/mass spectrometry

A comprehensive analytical method based on reversed-phase liquid chromatography and mass spectrometry using both atmospheric pressure chemical ionization and electrospray ionization has been developed for the simultaneous determination of anionic and nonionic surfactants, their polar degradation products, and endocrine-disrupting compounds (EDCs) in sewage sludge. Extraction of target compounds, with recovery rates from 86% to nearly 100% for polyethoxylates and from 84 to 94% for polar degradation products, was achieved applying ultrasonic solvent extraction with a mixture of methanol/ dichloromethane (7:3, v/v). Cleanup of sample extracts was performed on octadecyl solid-phase extraction cartridges. Determination of less polar compounds: alcohol ethoxylates (AEOs), nonylphenol ethoxylates (NPEOs), coconut diethanol amides, poly(ethylene glycol)s, and phthalate esters was accomplished by reversed-phase LC-APCI-MS in positive ionization mode, while more polar compounds: nonylphenolcarboxylates, nonylphenol (NP), octylphenol, and bisphenol Awere analyzed by ion-pair LC-ESI-MS under negative ionization conditions. This protocol was successfully applied to the trace determination of anionic and nonionic surfactants, polar degradation products, and EDCs in sewage sludge collected from different sewage treatment plants. The analysis revealed the presence of NP at high concentration levels ranging from 25 to 600 mg/kg. Polyethoxylates (AEOs and NPEOs) were also found in all samples at parts-per-million levels (10-190 mg/kg AEOs and 2-135 mg/kg NPEOs, respectively).     

Study of mixed micelles and interaction parameters for polymeric nonionic and normal surfactants

Surface tension (ST) measurements were carried out on various binary mixtures of the "normal" surfactants, such as nonionic surfactant, hexaethylene glycol mono-n-dodecyl ether(C12EO6), and cationic surfactant, tetradecyltrimethylammonium bromide (TTAB), and polymeric copolymer, Pluronic F127, F127(PPO)-g-PVP, and F127(PEO)-g-PVP. In all cases mixed micellar aggregates were formed and critical micellar concentrations of binary mixtures containing different mole fractions of the surfactants were measured using surface tension measurement. In the region where mixed micelles are formed, the interaction of two "normal" surfactants and three "polymeric" nonionic surfactants showed synergistic behavior and the results were analyzed using a interaction parameter, beta, which characterized the interaction in the mixed micelle and introduced by a regular solution theory. The regular solution theory can be applied to describe the interaction between TTAB and C12EO6, and graft polymeric surfactants systems. The results discussed in this paper indicated that regular solution theory has broader extent of application.     

Comparison of amphiphilic polyurethane nanoparticles to nonionic surfactants for flushing phenanthrene from soil

Amphiphilic polyurethane (APU) nanoparticles were synthesized through crosslinking polymerization of nano-aggregates of urethane acrylate nonionomer (UAN). The efficiency of in situ extraction of sorbed phenanthrene from aquifer material was tested using soil columns and compared with that of surfactants such as Triton X-100, Brij 30, and Tween 80. The extraction efficiency of those washing materials strongly depended on their concentration, flow rate, and the degree of sorption within soil column. That is, the extraction efficiency increased with the decrease of flow rate and the degree of sorption and the increase of the concentration. Even though the surfactants are superior to APU nanoparticles at solubilizing phenanthrene, at the same flow rate (0.02 mL/min) and concentration (4000 mg/L), the effectiveness of in situ soil washing of APU nanoparticles was about two times higher than those of surfactants. This is because, at the lower flow rates, the degree of sorption of APU nanoparticles was lower than that of surfactants, owing to the chemically crosslinked nature of APU nanoparticles.     

Effect of nonionic surfactants on biodegradation of phenanthrene by a marine bacteria of Neptunomonas naphthovorans

Biodegradation of three nonionic surfactants, Tergitol 15-S-X (X=7, 9 and 12), and their effects on the biodegradation of phenanthrene by marine bacteria, Neptunomonas naphthovorans, were studied. The experimental outcomes could be fit well with the first-order biodegradation kinetics model. It was observed that the biodegradability of these surfactants decreased with an increase in the chain length of the hydrophilic moiety of the surfactant. When surfactant concentrations initially present were less than 250mgcarbon/L, biodegradability of Tergitol 15-S-X surfactants is around 0.3. Reduced biodegradability of Tergitol 15-S-7 and Tergitol 15-S-9 was observed when their concentrations initially present were increased to 322 and 371mgcarbon/L, respectively. In general, biodegradation of phenanthrene was enhanced with increasing solubilization of phenanthrene by these surfactants. However, with the same initial concentration of phenanthrene, biodegradability of phenanthrene was found to decrease with an increase in surfactant concentration. For these three surfactants, more than 80% of the phenanthrene was degraded when surfactant concentrations initially present were 200mg/L. However, less than 30% of phenanthrene could be degraded, if initial surfactant concentrations were increased to 1000mg/L. Interestingly, the concurrent biodegradation of the surfactants reduced their effective concentrations for micelle formation and, hence, contribute to the higher bioavailability of phenanthrene by gradually releasing phenanthrene molecules into the aqueous phase.     

Crystallization of strontium carbonate in alcohol or water solution containing mixed nonionic/anionic surfactants

The crystallization of strontium carbonate is performed in aqueous solution or alcohol/water solution in the presence of mixed nonionic/anionic surfactants Pluronic F127/sodium dodecyl sulfate. With an increase of the volume ratio of ethanol/water, SrCO₃ pancakes transform into flowers, and then to irregular flakes. X-ray diffraction (XRD) pattern reveals that both of pancake-like and flower-like SrCO₃ particles are orthorhombic phases. Larger pancakes with porous structure are produced when the content of ethylene glycol reaches a relatively high value. Results indicate that -OH groups of alcohol play an important role in morphological controlling of SrCO₃.     

Selective adsorption and partitioning of nonionic surfactants onto solids via liquid chromatograph mass spectra analysis

The sorption characteristics of three Triton series surfactants (Triton-100, Triton-305, and Triton-405) from aqueous solution onto four different solids with a wide range of organic matter (OM) content were studied through the liquid chromatograph mass spectrometry (LC-MS) analysis. The examined surfactant concentrations ranged from below to above the critical micelle concentration (CMC) of the selected surfactants. A parameter, Phi, defined as the ratio of the average ethylene oxide (EO) number of surfactant on the adsorbed phase to that in the aqueous solution, was used to distinguish the controlling mechanism (adsorption or partitioning) of surfactants from aqueous solution onto the solids. For solids with very low OM content, adsorption was the primary mechanism and the Phi values were found to be larger than 1.0 and might reduce to 1.0 with the increasing surfactant concentration. On the other hand, the Phi values for solids with very high content of OM were equal to or less than 1.0 and remained constant as the surfactant concentrations varied, in which partitioning was the most likely dominant mechanism. For solids with an intermediate content of OM, adsorption and partitioning mechanisms coexisted and the Phi values could be larger or less than 1.0 and decreased with the increasing surfactant concentration.     

Soil washing using various nonionic surfactants and their recovery by selective adsorption with activated carbon

The performance of activated carbon in soil washing and subsequent selective adsorption for surfactant recovery from the washed solution was investigated. Sandy loam soil contaminated with phenanthrene at 200 mg kg(-1) was washed with four different nonionic surfactants: Tween 40, Tween 80, Brij 30 and Brij 35. The efficiency of soil washing was highest when using Brij 30 with the highest solubilizing ability for phenanthrene and low adsorption onto soil. In the selective adsorption step, surfactant recovery was quite effective for all surfactants ranging from 85.0 to 89.0% at 1 g L(-1) of activated carbon (Darco 20-40 mesh). Phenanthrene removal from the solution washed with Brij 30 was only 33.9%, even though it was 54.1-56.4% with other surfactants. The selectivity was larger than 7.02 except for Brij 30 (3.60). The overall performance considering both the washing and surfactant recovery step was effective when using Tween 80 and Brij 35. The results suggest that higher solubilizing ability of surfactants is a requirement for soil washing but causes negative effects on phenanthrene removal in the selective adsorption. Therefore, if a surfactant recovery process by selective adsorption is included in soil remediation by washing, the overall performance including the two steps should be considered for properly choosing the surfactant.     

Interaction of tritium atoms with solid composite targets: Adsorption layers of nonionic surfactants on hydrophobic supports

The capability of tritium atoms to penetrate deep into solids was used for revealing nonuniformity of coating of polymeric [polyethylene, poly(ethylene terephthalate)] supports by adsorption layers of a nonionic surfactant Brij-35, formed by adsorption from aqueous solutions. The permeability to atomic tritium of Brij-35 adsorption layers on polyethylene appeared to be close to that obtained for hydrocarbon fragments of cationic surfactants in adsorption layers on the water/air boundary. A decrease in the coefficients of attenuation of the tritium atom flow at formation of adsorption polylayers was revealed. This decrease suggests less ordered structure of the polylayers relative to the monolayer. The developed approach involving preparation of adsorption coatings of tritium-labeled surfactants, their treatment with tritium atoms, and subsequent removal of the surfactant from the support, with the autoradiographic detection of tritium distribution on the plate in all the steps of the work, can be used for studying the structure of surfactant adsorption layers on flat solid surfaces.     

Analysis of cationic surfactants by microbore high-performance liquid chromatography-electrospray mass spectrometry

In the work reported here, a state-of-the-art analytical method for the quantitative analysis of cationic surfactants in environmental matrixes is described. High-performance liquid chromatography on-line coupled via an electrospray interface to a mass spectrometer (HPLC-ESP-MS) is used for the determination of ditallowdimethylammonium chloride (DTDMAC) and two of its most important substitution products, diethylester dimethylammonium chloride (DEEDMAC) and Diesterquaternary (DEQ). Using the analytical method developed in our laboratory, it is possible to determine single homologues of these surfactants as well as the first hydrolysis products of DEQ and DEEDMAC. In combination with our extraction procedure, which is based on ion-pair extraction, cationic surfactants were determined in environmental samples (sewage influent, sewage effluent, river water); concentrations ranged from 0.4 to 140 μg/L. The linear dynamic range of the HPLC-ESP-MS method, which is an injected amount between 0.4 and 30 ng, is well suitable for the analysis of these samples, as well as the performance of the quantification through external standards.     

Capillary electrophoresis to mass spectrometry interface using a porous junction

A new capillary electrophoresis interface to electrospray ionization mass spectrometry (CE/ESI-MS) is introduced in which the electrical connection to the CE capillary outlet/ESI electrode is achieved by transfer of small ions related to the background electrolyte (BGE) through a porous section near the CE capillary outlet. In this design, only a small section of the capillary wall is made porous. The porous section is created by first thinning a small section of the capillary wall by drilling a well into it and then etching the remaining thin wall porous. This design has two advantages over previous designs (in which the whole circumference of the capillary was made porous): first, the capillary interface is more robust because only a small section of it is made porous, and therefore, no liquid junction is needed to secure the porous section. The electrical connection is achieved simply by inserting the capillary outlet containing the porous junction into the existing ESI needle and filling the needle with the BGE. Second, the time required to make the fused silica porous is reduced from approximately 1 h to a few minutes. In addition, there is no dead volume associated with the porous design, and because the actual metal/liquid contact occurs outside of the CE capillary, bubble formation due to redox reactions of water at the electrode does not affect CE/ESI-MS performance. The performance of this interface is demonstrated by the analyses of peptide and protein mixtures.     

The effects of nonionic surfactants on the tris(2,2'-bipyridyl)ruthenium(II)--tripropylamine electrochemiluminescence system

The electrochemistry and electrogenerated chemiluminescence (ECL) of Ru(bpy)3(2+) (bpy = 2,2'-bipyridyl) were studied in the presence of the nonionic surfactants Triton X-100, Thesit, and Nonidet P40. The anodic oxidation of Ru(bpy)3(2+) produces ECL in the presence of tri-n-propylamine in both aqueous and surfactant solutions. Increases in both ECL efficiency (> or =8-fold) and duration of the ECL signal were observed in surfactant media. A shift to lower energies of the Ru(bpy)3(2+) ECL emission by approximately 8 nm was also observed. The one-electron oxidation of Ru(bpy)3(2+) to Ru(bpy)3(3t) occurs at + 1.03 V vs Ag/AgCl in aqueous buffered (0.2 M potassium phosphate) solution as found by square wave voltammetry. This potential did not shift in surfactant systems, indicating that the redshifts in ECL emission are due to stabilization of ligand pi* orbitals in the metal-to-ligand charge-transfer excited state. These results are consistent with hydrophobic interactions between Ru(bpy)3(2+) and the nonionic surfactants.     

Liquid chromatography-tandem mass spectrometry determination of nonionic organophosphorus flame retardants and plasticizers in wastewater samples

A comprehensive method for the determination of nonionic organophosphorus flame retardants/plasticizers in wastewater samples by solid-phase extraction (SPE) with liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) is presented. It allows the determination of 11 organophosphorus compounds, trialkyl and trichloralkyl phosphates, triaryl phosphate, and biphosphates together with triphenylphosphine oxide (TPPO). Limits of quantification after SPE of 100 mL of water are between 3 and 80 ng/L, which are adequate for most aqueous samples. The sensitivity of the LC-ESI-MS approach allows direct injection of aqueous sample without preceding extraction for concentrations in the low microg/L range. The method was finally applied to municipal wastewater samples, showing the occurrence of six phosphoric acid triesters and TPPO in both raw and treated municipal wastewaters.