Spectrophotometric method for the determination of ionic surfactants by flow-injection analysis with acidic dyes

Eco-favourable Mobile Phase in Thin Layer Chromatographic Analysis of Surfactants: Resolution of Coexisting Alkyl Dimethylbenzyl Ammonium Chloride, Cetyltrimethyl Ammonium Bromide and Triton X 100

A thin-layer chromatographic system comprising of silica gel as stationary phase and a mixture of methanol, 0.1 % aqueous sodium thiocyanate, acetone and ethyl acetate in 7 : 3 : 2 : 3 ratio as eco-favourable mobile phase has been found most efficient for the separation of ternary mixture of surfactants (alkyldimethylbenzylammonium chloride (ADBAC) + cetyltrimethylammonium bromide (CTAB) + Triton X 100). The separation pattern has been presented as densitogram. Chromatographic parameters like ΔRF, separation factor (α) and resolution (RS) for the separation have been calculated. The effect of the presence of foreign substances such as metal cations, metal anions, amino acids and vitamins as impurities on the separation has been examined. The mobility trend of the separated surfactants was also examined by replacing methanol with other alcohols. The detection limits for ADBAC, CTAB and Triton X 100 have been determined. The proposed method has been successfully applied for the identification of ADBAC in the household cleaning product “Lizol”.

Potentiometric determination of cetylpyridinium chloride using a new type of screen-printed ion selective electrodes

A new type of screen-printed ion-selective electrode for the determination of cetylpyridinium chloride (CPC) is presented. These new electrodes involve in situ, modified and unmodified screen-printed ion-selective electrodes for the determination of CPC. The screen-printed electrodes (SPEs) show a stable, near-Nernstian response for 1 x 10(-2) to 1 x 10(-6) M CPC at 25 degrees C over the pH range 2-8 with cationic slope 60.66+/-1.10. The lower detection limit is found to be 8 x 10(-7) M and response time of about 3s and exhibit adequate shelf-life (6 months). The fabricated electrodes can be also successfully used in the potentiometric titration of CPC with sodium tetraphenylborate (NaTPB). The analytical performances of the SPEs are compared with those for carbon paste electrode (CPE) and polyvinyl chloride (PVC) electrodes. The method is applied for pharmaceutical preparations with a percentage recovery of 99.60% and R.S.D.=0.53. The frequently used CPC of analytical and technical grade as well as different water samples has been successfully titrated and the results obtained agreed with those obtained with commercial electrode and standard two-phase titration method. The sensitivity of the proposed method is comparable with the official method and ability of field measurements.

Non-extraction flow injection determination of cationic surfactants using eriochrome black-T

A new, rapid, sensitive, non-extraction batch, and flow injection spectrophotometric method for the determination of cationic surfactants (CSs) such as cetyltrimethyl ammonium bromide (CTAB), tetra-n-butyl ammonium chloride (TBAC) and cetylpyridinium chloride (CPC) is proposed. The method is based on the interaction of cationic surfactants with eriochrome black-T to form an ion-association complex. This complex has strong absorbance at 708 nm. The effects of chemical parameters and FIA variables on the determination of cationic surfactants were studied in detail, especially for CTAB. Under optimum conditions, the two linear calibration ranges of the method are 3.0 x 10(-6) to 5.0 x 10(-3)mol L(-1) CTAB, CPB and DTAB for the batch spectrophotometric method and 2.0 x 10(-6) to 2.0 x 10(-4)mol L(-1) CTAB, CPB and TBC for the flow injection spectrophotometric method. The sample throughput was 35+/-5 samples h(-1) at room temperature. The relative standard deviations for 10 replicates of analysis of (2.0, 0.6 and 0.2)x10(-4)mol L(-1) CTAB were 1.2, 1.3, and 0.8%, respectively. In addition, the influence of potential interfering substances on the determination of cationic surfactants was studied. The proposed method is simple and rapid, using no toxic organic solvents. It was applied to the determination of trace CS in industrial wastewater with satisfactory results.

A multicommuted stop-flow system employing LEDs-based photometer for the sequential determination of anionic and cationic surfactants in water

It has been developed an automatic stop-flow procedure for sequential photometric determination of anionic and cationic surfactants in a same sample of water. The flow system was based on multicommutation process that was designed employing two solenoid micro-pumps and six solenoid pinch valves, which under microcomputer control carry out fluid propelling and reagent solutions handling. A homemade photometer using a photodiode as detector and two light emitting diodes (LEDs) with emission at 470 nm (blue) and 650 nm (red) as radiation sources, which was tailored to allow the determination of anionic and cationic surfactants in waters. The procedure for anionic surfactant determination was based on the substitution reaction of methyl orange (MO) by the anionic surfactant sodium dodecylbenzene sulfonate (DBS) to form an ion-pair with the cetyl pyridine chloride (CPC). Features such as a linear response ranging from 0.35 to 10.5 mg L(-1) DBS (R=0.999), a detection limit of 0.06 mg L(-1) DBS and a relative standard deviation of 0.6% (n=11) were achieved. For cationic surfactant determination, the procedure was based on the ternary complex formation between cationic surfactant, Fe(III) and chromazurol S (CAS) using CPC as reference standard solution. A linear response range between 0.34 and 10.2 mg L(-1) CPC (R=0.999), a detection limit of 0.05 mg L(-1) CPC and a relative standard deviation of 0.5% (n=11) were obtained. In both cases, the sampling throughput was 60 determinations per hour. Reagents consumption of 7.8 microg MO, 8.2 microg CPC, 37.2 microg CAS and 21.6 microg Fe(III) per determination were achieved. Analyzing river water samples and applying t-test between the results found and those obtained using reference procedures for both surfactant types provide no significant differences at 95% confidence level.

Micro-pumping flow system for spectrophotometric determination of anionic surfactants in water

A novel procedure has been developed for spectrophotometric determination of anionic surfactants in water using a solenoid micro-pump as fluid-propulsion device. The proposed method is based on substitution of methyl orange (MO) by anionic surfactants in the formation of an ion-pair with the cetyl pyridine ion (CPC+) at pH 5.0. The flow network comprised four solenoid micro-pumps which, under microcomputer control, enabled sample and reagent introduction, and homogenisation in the reaction zone. The system is flexible and simple to operate and control, and sensitive and precise. The analytical plot for the anionic surfactant was linear between 1.43x10(-6) and 1.43x10(-5) mol L(-1) (0.5 to 5.0 mg L(-1); R=0.997, n=5). The relative standard deviation was 0.8% (n=11) for a sample containing 5.74x10(-6) mol L(-1) (2 mg L(-1)) surfactant. The limit of detection was 9.76x10(-8) mol L(-1) (0.034 mg L(-1)) and the sampling throughput was 60 determinations per hour. The results obtained for washing-water samples were comparable with those obtained by use of the reference method, and no significant differences at the 95% confidence level were observed.

Application of Sequential Injection Analysis to the Determination of Cationic Surfactants Based on the Sensitized Molybdenum-Bromopyrogallol Red Reaction

The aim of this work was to develop a simple, automatic system for the evaluation of cationic surfactants by combining sequential injection analysis and the sensitized effect of cationic surfactants on the reaction between metal ions and chelating dyes. This reaction is based on the increase in absorbance of the complex formed among molybdenum, bromopyrogallol red and increasing concentrations of cationic surfactants. Under optimum conditions, two calibration plots were obtained for a concentration range between 2.50 x 10(-7) mol dm(-3) (detection limit) and 5.00 x 10(-4) mol dm(-3) of cetylpyridinium chloride, used as standard. Solubilization of water insoluble complexes formed for concentrations of cationic surfactants greater than 1.00 x 10(-4) mol dm(-3) were successfully achieved with Triton X-405. RSD values lower than 5.0% were obtained in all cases. The quality of the results obtained for 18 water samples were evaluated by comparison with conventional methods, with no statistically significant differences for a 95% confidence level.

Interaction between sulfonephthalein dyes and chitosan in aqueous solution and its application to the determination of surfactants

A spectrophotometric method for the determination of ionic surfactants with Bromophenol Blue (BPB) based on incorporation into a precipitated chitosan was studied. Cationic surfactants (CS+), such as a quaternary ammonium ion containing a long-chain alkyl group, associate with BPB2- buffered at about pH 9 to form the ion associate (CS+)2 x BPB2-. CS+ associates with anionic surfactants (AS-). In the presence of a definite amount of CS+, an increase in the amount of AS- leads to a decrease in the amount of excess CS+, and therefore to a decrease in the amount of the ion associate of CS+ with BPB2-. The addition of a chitosan dissolved in acetic acid to a solution containing these ion associates leads immediately to precipitation of the chitosan and the incorporation of the ion associates (CS+)2 x BPB2- or CS+ x AS- into the precipitated chitosan. After centrifuging, ionic surfactants can be determined by the following two methods: (1) the absorbance of the supernatant solution is measured at 590 nm. (2) After the supernatant solution is separated, the precipitate is dissolved in an acetic acid solution and the absorbance is measured at 625 nm. Because the color of the precipitate is judged by the naked eye, this can be applied to the visual method. This is a simple and rapid method for the determination of a 10(-6) M order of ionic surfactants.

Simultaneous Determination of Cationic Surfactants and Nonionic Surfactants by Ion-Association Titration

A simultaneous determination of cationic and nonionic surfactants has been developed using ion-association titration. Tetrabromophenolphthalein ethyl ester (TBPE) was used as an indicator. Benzalkonium reacted with TBPE to form a blue ion-associate in the organic phase. When tetrakis(4-fluorophenyl)borate was added dropwise to the solution, the color of the organic phase turned to yellow at the equivalence point. In addition, when a large amount of potassium ion was added to a solution including Triton X-100, Triton X-100 could be determined by the same technique as described above because of formation of the K+-Triton X-100 cation. The proposed method is available for the stepwise determination of cationic and nonionic surfactants in mixtures.

PVC matrix membrane sensor for potentiometric determination of cetylpyridinium chloride

A novel cetylpyridinium chloride-selective membrane sensor consisting of cetylpyridinium-ferric thiocyanate ion pairs dispersed in a PVC matrix placticized with dioctylphthalate is described. The electrode shows a stable, near-Nernstian response for 1 x 10(-3)-1 x 10(-6) mol l-1 cetylpyridinium chloride (CPC) at 25 degrees C over the pH range 1-6 with a cationic slope of 57.5 +/- 0.4. The lower detection limit is 8 x 10(-7) mol l-1 and the response time is 30-60 s. Selectivity coefficients for CPC relative to a number of interfering substances were investigated. There is negligible interference from many cations, anions and pharmaceutical excipients; however, cetyltrimethylammonim bromide (CTMAB) interfered significantly. The determination of 0.5-350 micrograms/ml of CPC in aqueous solutions shows an average recovery of 98.5% and a mean relative standard deviation of 1.6% at 56.0 micrograms/ml. The direct determination of CPC in Ezafluor mouthwash gave results that compare favorably with those obtained by the British Pharmacopoeia method. Precipitation titrations involving CPC as titrant are monitored with a CP sensor. The CP electrode has been utilized as an end point indicator electrode for the determination of anionic surfactants in some commercial detergents.