HPLC analysis of aliphatic sulfonate surfactants using ion-pair detection

A method was developed for the analysis of a number of surfactants which contained no UV-chromophores, using RP-HPLC with Indirect Photometric Detection, IPD. Pyridinium salts such as N-methylpyridinium iodide, N-methyl-2,2'-dipyridinium iodide and N,N'-dimethyl-2,2'-dipyridinium diiodide, were used as the visualization reagents, forming ion-pair complexes with the sulfonate surfactants. This allowed ordinary UV-detection. N-methylpyridinium iodide proved to be a suitable reagent, both with respect to ease of preparation and response. The eluents consisted of mixtures of acetonitrile and water, being 0.1 - 0.25 mM with respect to pyridinium salt. The method was sensitive and exhibited good signal to noise ratios, as well as linear responses over a wide concentration range. All of the analyzed surfactants were separated, including the diastereomeric forms of some of the surfactants.     

Trace humic and fulvic acid determination in natural water by cloud point extraction/preconcentration using non-ionic and cationic surfactants with FI-UV detection

A preconcentration and determination method for humic and fulvic acids at trace levels in natural water samples was developed. Cloud point extraction was successfully employed for the preconcentration of humic acid (HA) and fulvic acid (FA) prior to the determination by using a flow injection (FI) system coupled to a spectrophotometric UV-Vis detector. The quantitative extraction of HA and FA within the pH range 1-12 was obtained by neutralization of the anionic charge on the humic substances with a cationic surfactant, hexadecyltrimethylammonium bromide (CTAB). This generated a hydrophobic species that was subsequently incorporated (solubilized) into the micelles of a non-ionic surfactant polyethylene glycol, tert-octylphenyl ether (Triton X-114). The FI method for HA and FA determination was developed by injection of 100 microl of the extracted surfactant-rich phase using an HPLC pump with spectrophotometric detection at 350 nm. A 50 ml sample solution preconcentration allowed an enrichment factor of 167. The limit of detection (LOD) obtained under the optimal conditions was 5 microg l(-1). The precision for ten replicate determinations at 0.2 mg l(-1) HA was 3.1% relative standard deviation (RSD), calculated from the peak heights. The calibration using the preconcentration system for HA and FA was linear with a correlation coefficient (r2) of 0.9997 at levels near the detection limits up to at least 1 mg l(-1). The method was successfully applied to the determination of HA and FA in natural water samples (river water).     

Chloride analysis in magnesium metal using ion chromatography with conductometric detection

A simple, rapid and accurate method for the determination of chloride in magnesium metal has been developed. The quantitative determination of chloride was accomplished by anion exchange chromatography with conductometric determination. A Metrosep Anion Dual 2 analytical column connected in series with a Metrosep RP guard column was used for chloride separation. A solution containing a mixture of 1.3 mM Na2CO3 and 2 mM NaHCO3 was used as eluent. The method requires a sample dissolution using nitric acid. The limit of detection for the determination of chloride is 50 mg kg(-1) and the relative standard deviation was 5% for the overall method. The recovery of chloride added was 99-102%. No interference was observed from either the closely eluting "system peak" or the nitrate peak in the determination of chloride.     

Trace analysis of ioxynil and bromoxynil using HPLC with electrochemical and UV detection

Summary A method for the determination of residues of bromoxynil and ioxynil in barley matrices is described. Samples are extracted with acetone; partition between water and chloroform/dichloromethane, gel permeation chromatography on a polystyrene-divinylbenzene gel and liquid chromatography on nitrile-modified silica are used for clean up of the sample extracts.The compounds are determined by reversed phase HPLC with electrochemical and UV-detection.Determination limits are in the range of 50 ppb.

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Spurenanalyse von Ioxynil and Bromoxynil unter Verwendung von HPLC mit elektrochemischer und UV-Detektion

Zusammenfassung Eine Methode für die Bestimmung von Rückständen von Bromoxynil und Ioxynil in Gerstenmatrices wird beschrieben. Die Proben werden mit Aceton extrahiert; Verteilung zwischen Wasser und Chloroform/Dichlormethan, Gelchromatographie an Polystyrol-Divinylbenzol-Gel und Flüssigkeitschromatographie an nitrilmodifiziertem Kieselgel werden zur Reinigung der Extrakte verwendet. Die Verbindungen werden mittels Umkehrphasen — HPLC mit elektrochemischer und UV-Detektion bestimmt. Die Bestimmungsgrenzen liegen bei 50 ppb.

     

Investigation of interactions between some anionic dyes and cationic surfactants by conductometric method

The interactions of cationic surfactants with anionic dyes were studied by conductometric method. Benzyltrimethylammonium chloride (BTMACl), benzyltriethylammonium chloride (BTEACl) and benzyltributylammonium chloride (BTBACl) were used as cationic surfactants and indigo carmine (IC) and amaranth (Amr) were chosen as anionic dyes. The specific conductance of dye–surfactant mixtures was measured at 25, 35 and 45 °C. A decrease in measured specific conductance values of dye–surfactant mixture was caused by the formation of non-conducting or less-conducting dye–surfactant complex. The equilibrium constants, K₁, the standard free energy changes, ΔG₁°$\mathrm{\Delta }{G}_1°$, the standard enthalpy changes, ΔH₁°$\mathrm{\Delta }{H}_1°$ and the standard entropy changes, ΔS₁°$\mathrm{\Delta }{S}_1°$ for the first association step of dye–surfactant complex formation were calculated by a theoretical model. The results showed that the equilibrium constants and the negative standard free energy change values for all systems decreased as temperature increased. Also these values decreased for all systems studied with increasing alkyl chains of surfactants due to the steric effect. When the equilibrium constant values, K₁, for the first association step of IC–surfactant and Amr–surfactant systems with the same surfactant were compared, the values of K₁ for IC–surfactant system were higher than that of Amr–surfactant system.     

Trace analysis of pollutants in water using the photothermal interferometry as HPLC detector

A new procedure including high performance liquid chromatography in combination with photothermal interference spectroscopy as detection device (HPLC/PIS) has been proposed, optimized and its figures of merit for pesticide residue analysis are shown. The flowing sample under study is set in one arm of a Mach-Zehnder interferometer, and its refractive index is modulated by a periodically chopped continuous wave argon ion laser. As chopper, an acousto optical modulator has been introduced to switch the excitation laser beam between different lines (457 nm, 488 nm, 514 nm) simultaneously. Thus a multi component analysis can be realized either by using an HPLC-system in front of the PIS device or by a multi line Ar(+)-laser, directly. The limit of detection of the HPLC/PIS system reached 71 microg/l of the pesticide di-nitro-ortho-cresol (DNOC).     

Trace analysis of pollutants in water using the photothermal interferometry as HPLC detector

A new procedure including high performance liquid chromatography in combination with photothermal interference spectroscopy as detection device (HPLC/PIS) has been proposed, optimized and its figures of merit for pesticide residue analysis are shown. The flowing sample under study is set in one arm of a Mach-Zehnder interferometer, and its refractive index is modulated by a periodically chopped continuous wave argon ion laser. As chopper, an acousto optical modulator has been introduced to switch the excitation laser beam between different lines (457 nm, 488 nm, 514 nm) simultaneously. Thus a multi component analysis can be realized either by using an HPLC-system in front of the PIS device or by a multi line Ar⁺-laser, directly. The limit of detection of the HPLC/PIS system reached 71 g/l of the pesticide di-nitro-ortho-cresol (DNOC).     

Trace analysis of surfactants using chromatographic and electrophoretic techniques

Because of the widespread use, increased application of new formulations and immense impact on organisms and ecology surfactants are still in the focus of analytical chemistry. The development of methods with higher selectivity and lower detection limits is important to meet the requirements of greater responsibility for health of people and environment. Efficient separation methods, like HPLC, GC and CE, in combination with sensitive detection, like MS, are to be preferred over collective techniques which can suffer from interfering components. A review on trace analysis of ionic and neutral surfactants including sample preparation steps is presented, considering especially those methods which provide information about homologous and isomeric distribution of surfactant mixtures. Examples for the determination of linear alkylbenzene sulfonates in river water by HPLC and CE are discussed to show the capability of these methods for environmental analyses. As future trends increased applications of LC/MS (very high sensitivity) and also of CE (robustness and possibility for rapid method development) can be predicted.     

Trace analysis of surfactants using chromatographic and electrophoretic techniques

Because of the widespread use, increased application of new formulations and immense impact on organisms and ecology surfactants are still in the focus of analytical chemistry. The development of methods with higher selectivity and lower detection limits is important to meet the requirements of greater responsibility for health of people and environment. Efficient separation methods, like HPLC, GC and CE, in combination with sensitive detection, like MS, are to be preferred over collective techniques which can suffer from interfering components. A review on trace analysis of ionic and neutral surfactants including sample preparation steps is presented, considering especially those methods which provide information about homologous and isomeric distribution of surfactant mixtures. Examples for the determination of linear alkylbenzene sulfonates in river water by HPLC and CE are discussed to show the capability of these methods for environmental analyses. As future trends increased applications of LC/MS (very high sensitivity) and also of CE (robustness and possibility for rapid method development) can be predicted. Received: 30 July 1998 / Revised: 28 October 1998 / Accetped: 1 November 1998     

Head-group-modification-controlled mixing behavior of binary cationic surfactants: conductometric,viscometric, and NMR studies

The mixed-micelle formation by hexadecyltrimethylammonium bromide (HTAB) with hexadecyltriphenylphosphonium bromide (HTPB) and hexadecyltributylphosphonium bromide (HTBB), and by hexadecylpyridinium bromide (HPyBr) with HTPB and HTBB has been studied with the help of conductivity, viscometry, and NMR studies. The conductivity studies showed close-to-ideal mixing in all cases with weak synergistic interactions. The relative viscosity is more sensitive than the conductivity and demonstrated that the micellization of HTAB, HPyBr, HTPB, and HTBB proceeded through the appearance of a minimum, whereas their mixtures showed a strong maximum in each case. NMR measurements suggested that bulky head groups of HTPB and HTBB induce significant steric hindrance in the mixed state upon mixing with HTAB and HPyBr. The appearance of the maximum shown by the relative viscosity in the mixed-micellization process is due to steric compulsions, which may also lead to some structural transitions.     

双波长分光光度法测定溴化十六烷基三甲基铵

以二甲酚橙为显色剂,采用双波长分光光度法测定水中溴化十六烷基三甲基铵。实验确定的测定条件为:最大吸收波长为590 nm,等吸光度点的波长点为509 nm,选择pH为6.86的Na3PO4-Na2HPO4缓冲溶液3.50 mL,0.80 g/L二甲酚橙显色剂2.0 mL,显色时间为5 min。试剂加入顺序对测定结果基本无影响。CTMAB的质量浓度在0~1.2 mg/mL范围内符合比尔定律,标准曲线为ΔA=0.0123ρ 0.0825,相关系数为R2=0.9998,样品加标回收率为99.6%~101.3%。     

Trace analysis of acids and bases by conductometric titration with multiparametric non-linear regression

A chemometric method for analysis of conductometric titration data was introduced to extend its applicability to lower concentrations and more complex acid-base systems. Auxiliary pH measurements were made during the titration to assist the calculation of the distribution of protonable species on base of known or guessed equilibrium constants. Conductivity values of each ionized or ionizable species possibly present in the sample were introduced in a general equation where the only unknown parameters were the total concentrations of (conjugated) bases and of strong electrolytes not involved in acid-base equilibria. All these concentrations were adjusted by a multiparametric nonlinear regression (NLR) method, based on the Levenberg-Marquardt algorithm. This first conductometric titration method with NLR analysis (CT-NLR) was successfully applied to simulated conductometric titration data and to synthetic samples with multiple components at concentrations as low as those found in rainwater (∼10 μmol L⁻¹). It was possible to resolve and quantify mixtures containing a strong acid, formic acid, acetic acid, ammonium ion, bicarbonate and inert electrolyte with accuracy of 5% or better.     

Analysis of ethoxylated alcohol surfactants in water by HPLC

Summary An HPLC procedure for the determination of linear alcohol polyethoxylates in surface water, waste water, and detergents is described. After extraction of the alcohol ethoxylates into an organic phase the alcohol ethoxylates are derivatized with phenyl isocyanate to apply an UV detection. A reversed-phase HPLC procedure is used to separate different ethoxylate species by their different alkyl chain length. A normal phase procedure is employed to separate alcohol polyethoxylates by their different number of ethoxylate groups in the molecule.     

Effect of water hardness on the interaction of cationic dye with anionic surfactants

ABSTRACT

The effect of water hardness causing ions on the critical micelle concentration (cmc) of surfactants was studied using conductivity measurement. Spectrophotometric and conductometric studies of dye and surfactant interaction under the influence of water hardness causing ions were also investigated. It was found that with increasing hardness in water, cmc of the surfactants tends to decrease. The change in the colour of the solution was observed as the degree of hardness increases. Hardness of water can consider as a major contributor of fading or change in colour during washing and cleaning of dyed material. Dye in a surfactant solution containing varying amount of hardness causing ions undergoes a blue shift in the visible region and red shift in ultraviolet region. The comparison between sodium dodecylsulphate (SDS) and saponin natural surfactant showed that turbidity was observed only in the aqueous solution of SDS in the presence of very hard water.     

Trace analysis of halocarbons in water; Direct aqueous injection with electron capture detection

Interest in monitoring halogenated organics in drinking water and natural surface and ground water in the low ppb range continues to grow. There is a tendency to include still more volatile halocarbons, the trace determination of which is known to be rather demanding. This prompted us to re-examine the feasibility of large-volume direct aqueous injection onto capillary columns, coupled with ECD. A primary problem was to avoid simultaneous elution of water with halocarbons, since water suppresses the ground current of the ECD. The following measures contributed to the solution of this problem. Apolar, extremely inert, columns are required to elute water completely, and even before very light halocarbons. Their coatings have to be far thicker (≈? 5 mUm) than commonly employed thick films since they must permit isothermal analysis at a column temperature around 100°C in order to ensure rapid and complete elution of water. Finally, it is essential that sampling be carried out on-column for two reasons: diffusion of water vapor in the injector, resulting in delayed elution, is then eliminated, and peak distortion during splitless injection is avoided. Although we now know that persilylated columns with immobilized coatings withstand routine water injections, more longterm experience is needed to provide detailed recommendations for the handling of these columns.     

HPLC separations with micro-bore columns using high-temperature water and flame ionization detection

Previous work demonstrates that a flame ionization detector (FID) may be used as a detector for high-temperature water separation. However, the relatively high flow rate of the eluent required by standard high-performance liquid chromatography columns causes instability of the FID. In this work, micro-bore columns are packed with poly(styrene-divinylbenzene) (PRP-1) or Daiso gel octadecylsilane-bonded phase particles. Because micro columns require low volume flow rates, the eluent used in high-temperature water chromatography does not cause instability of the FID. Separation of carbohydrates, amino acids, and other organic acids and bases is performed on two micro-bore columns using a homemade high-temperature water chromatograph with FID. Both isothermal and programmed temperatures are used in this work. The limit of detection and the linear range are also determined for amino acids tested.     

On-line sample concentration in micellar electrokinetic chromatography using cationic surfactants

Two on-line sample concentration techniques, sample stacking and sweeping, were evaluated using cationic surfactants as pseudostationary phases in micellar electrokinetic chromatography. As cationic surfactant micelles, tetradecyltrimethylammonium bromide and cetyltrimethylammonium chloride were employed. About 10-fold and 1000-fold increases in detection sensitivity in terms of peak heights were observed by sample stacking and sweeping, respectively, without suppression of the electroosmotic flow. In particular, the concentration limits of detection (S/N=3) for test naphthalenesulfonic acids obtained with sweeping were from 0.96 to 0.47 ppb with UV detection without any preconcentration procedure.     

Single‐breath analysis using a novel simple sampler and capillary electrophoresis with contactless conductometric detection

The analysis of ionic content of exhaled breath condensate (EBC) from one single breath by CE with C⁴D is demonstrated for the first time. A miniature sampler made from a 2‐mL syringe and an aluminum cooling cylinder for collection of EBC was developed. Various parameters of the sampler that influence its collection efficiency, repeatability, and effect of respiratory patterns were studied in detail. Efficient procedures for the cleanup of the miniature sampler were also developed and resulted in significant improvement of sampling repeatability. Analysis of EBC was performed by CE‐C⁴D in a 60 mM MES/l ‐histidine BGE with 30 μM CTAB and 2 mM 18‐crown‐6 at pH 6 and excellent repeatability of migration times (RSD < 1.3% (n = 7)) and peak areas (RSD < 7% (n = 7)) of 12 inorganic anions, cations, and organic acids was obtained. It has been shown that the breathing pattern has a significant impact on the concentration of the analytes in the collected EBC. As the ventilatory pattern can be easily controlled during single exhalation, the developed collection system and method provides a highly reproducible and fast way of collecting EBC with applicability in point‐of‐care diagnostics.