Adsorption–Photometric Determination of Cationic Surfactant Traces

A procedure has been developed for the adsorption–photometric determination of cationic surfactants in natural water. The procedure is based on the adsorption preconcentration of the cationic surfactants on silica gel, the reaction of the concentrate with the anionic reagent bromothymol blue to form ion pairs on a solid surface, and the photometric determination of excess bromothymol blue in solution. The analytical range is (0.5–5) × 10^–5 M for a 50-mL sample.     

Chromatographic Determination of Silicon and Phosphorus as Molybdic Heteropoly Acids with Preconcentration

The chromatographic behavior of molybdic heteropoly acids of silicon and phosphorus as ion pairs with tetrabutylammonium bromide was studied by ion-pair high-performance liquid chromatography on the C₁₈reversed phase (UV detection at 310 nm). Heteropoly acids were preconcentrated as ion pairs with tetrabutylammonium bromide to increase the sensitivity of the determination. Optimal conditions were selected for the chromatographic determination of silicon and phosphorus in water in the presence of each other. Detection limits for silicon and phosphorus are (1.1 × 0.3) × 10^–3and (6.7 × 1.2) × 10^–3g/mL, respectively. Calibration plots are linear in the concentration ranges 0.01–0.1 g/mL (silicon) and 0.02–0.15 g/mL (phosphorus). The procedure was used for the analysis of distilled water.     

Potentiometric Flow Injection Analysis of Anionic Surfactants in Industrial Products and Wastes

A new sensor for anionic surfactants with a membrane consisting of 33wt% poly(vinyl chloride) (PVC), 66wt% dioctylphthalate (DOP) plasticizer, and 1wt% tridodecylmethylammonium chloride (TDMAC) is developed and used for flow injection analysis. The sensor displays a working response range of 5×10^–7–5×10^–3M dodecylbenzene sulfonate (DBS^–) with a Nernstian slope of 58.5±0.2mV decade^–1, a response time of 30s and a detection limit of 1.5×10^–7M DBS^–. Selectivity measurements with different anionic species indicate good membrane selectivity towards DBS^–. The sensor is used to measure anionic surfactants (DBS^–) in different wastewater samples, commercial detergent products, and for monitoring the rate of surfactant biodegradation in sewage treatment plants. The results obtained agree fairly well with data obtained by the standard extraction-spectrophotometric method. The proposed potentiometric method offers the advantages of simplicity, accuracy, automation feasibility, and applicability to turbid and colored sample solutions.     

Spectrophotometric determination of anionic surfactants in tap and river waters with 1-(10-bromodecyl)-4-(4-aminonaphthylazo)-pyrimidinium bromide

Summary A new cationic dye, 1-(10-bromodecyl)-4-(4-aminonaphthylazo)-pyridinium bromide, was synthesized and evaluated as a new reagent for the determination of anionic surfactants. The reagent reacts with anionic surfactants, such as sodium dodecylsulphate and sodium dodecylbenzenesulphonate, to produce an ion associate in an aqueous medium. The colour change occurs simultaneously, and the colour development is very stable. This makes it possible to determine anionic surfactants directly by spectrophotometry without solvent extraction. The stoichiometric ratio of the ion associate was found to be 1:1 by the mole ratio method. The calibration graph was linear up to 2.5×10^–6 mol/l. The apparent molar absorptivity of the ion associate was 5.3×10⁴ l mol^–1 cm^–1 (at 595 nm). The relative standard deviation (n=10) for 1.2×10^–6 mol/l sodium dodecylsulphate was 4.9%. The proposed method was applied to the determination of anionic surfactants in tap and river waters.     

Multielement determinations in ground water ultrafiltrates using inductively coupled plasma mass spectrometry and monostandard neutron activation analysis

Twelve ultrafiltrates of two ground waters rich in humic substances (up to 97.8 mg CL^–1) and in salinity (up to: cations 44.3 meq L^–1, anions 44.9 meq L^–1) were investigated with ICP-MS and with NAA in parallel. With both techniques 22 elements were analysed in a wide concentration range (mg/L to ng/L). Ultrafiltration at pore sizes from 1000 nm down to 1 nm lowers the humic colloid content as well as the concentration of the colloidborne polyvalent cations. Carbon interferences were studied in detail using artificially prepared model waters. The detection limits of ICP-MS in the ultrafiltrates (0.01 g/L–10 g/L) and in pure analyte solutions (5 ng/L–600 ng/L) are compared with those of NAA for pure water analysis (0.004 ng/L–50 ng/L).Dedicated to Professor Dr. H. Schmidbaur on the occasion of his 60th birthday     

Sorption-photometric determination of anionic surfactants in water

The adsorption of Crystal Violet, anionic surfactants, and their ion associates on nonionic hydrophobic polymer adsorbent Amberlite XAD-16 was studied. A procedure for the sorption-photometric determination of anionic surfactants in water was developed with a detection limit of 0.001–0.003 mg/L at a sample volume of 50 mL.     

Effects of Surfactants on the Spectral Properties of Carbocyanine Dyes in Solutions

The spectral and luminescence properties of an anionic carbocyanine dye were studied under various conditions. These properties were shown to depend on the solvent polarity and additives introduced such as KBr, gelatin, and surfactants. It has been established that the effects of different surfactants (cationic CTAB, anionic SDS, AOT, and nonionic Triton X-100) on the spectral behavior of the dye in solutions are very individual and exhibit a number of features, which cannot be reduced to the rule below CMC–above CMC.     

Rapid separation of humic acid in fresh waters by coprecipitation and flotation

After removal of suspended matter in 1 liter of water by flotation with a cationic surfactant, humic acid at theg/l level is separated from fulvic acid by coprecipitation with milligram quantities of iron(III) hydroxide at pH 7 followed by flotation with anionic surfactants. The iron(III) hydroxide is dissolved in 2M hydrochloric acid, and the acid-insoluble humic acid is filtered off on an ultrafilter and then dissolved in 10 ml of 0.1M potassium hydroxide solution for measurements of absorption spectra, molecular weight distribution and complexing ability. The time required for the separation is ca. 1 h.     

Sorption-Photometric Determination of Cationic Surfactants with the Use of Silica Gel and Dyes (Zincon and Thiazine Red)

Conditions were determined for the formation of colored ion-pair complexes of cationic surfactants with Zincon and Thiazine Red in aqueous solutions and at the surface of silica gel. A photometric method using Zincon with a detection limit of 1 mg/L and a sorption–spectrometric method using Thiazine Red with a detection limit of 2–3 g/L were developed for the determination of trace cationic surfactants in water. The relative standard deviations of the results of analysis in both cases were no more than 10%. A test method with the use of indicator tubes filled with silica gel and Zincon as the reagent is proposed; the detection limit of cationic surfactants is 0.5 g/L (RSD < 25%).     

Some N-alkyl-naphthylazo pyridinium salts as new reagents for the spectrophotometric determination of anionic surfactants

Summary Eleven pyridinium azo dyes with straight-chain alkyl groups C_nH_2n+1–(n=6–18) and bromoalkyl groups BrC_mH_2m–(m=6–12) were synthesized with the intention of developing reagents for the determination of low levels of anionic surfactants in an aqueous medium. The effect of the alkyl chain length of these reagents on the reactivity with anionic surfactants such as sodium dodecylsulphate (SDS), sodium linear-dodecylbenzenesulphonate (DBS), sodium dodecylsulphonate (DS) and sodium laurate (SL) was studied. It was found that the alkyl chain length played an important role in the formation of ion associates and the composition of the ion associates formed. These reagents were classified into four groups with respect to the reactivity with anionic surfactants. The first group (n,m=6) reacts only with DBS. The second group (n,m=8) reacts with SDS, DBS and DS. The third group (n,m=10, 12) reacts with SDS, DBS and DS; however, the colour intensity of the DBS-ion associate was unstable. The fourth group (n=14, 16, 18) reacts with all anionic surfactants examined, and the composition of the ion associates with SDS and DS was 2:1 ([reagent]/[surfactant]) though that of the ion associates of the three reagent groups mentioned above was 1:1. The optimal conditions for the determination of anionic surfactants in river water with 1-octyl-4-(4-aminonaphthylazo)-pyridinium bromide was examined. The calibration graph was linear up to 3×10^–6 mol/l, and the apparent molar absorptivity of the ion associate was 3.8×10⁴ l mol^–1 cm^–1 (at 427 nm). The relative standard deviation for 2.4×10^–6 mol/l SDS was 4.9%. Recoveries of 88–107% were found for 8.0×10^–7 mol/l SDS in river water samples.     

A new method for quantitative mass-spectrometric analysis of solutions

Summary The mass-spectrometric method for the analysis of inorganic solutions is not only a very sensitive technique but also one of broad applicability. The study of the behaviour of solutions of mineral acids chilled to –70°C under a r.f. voltage from 7 to 15 kV indicated that solutions of hydrochloric acids containing 20–32% of hydrogen chloride allow to obtain stable ion currents. The equipment for the analysis of solutions on the spark source mass-spectrometer is designed and the procedure of analysis is described. The detection limits of 47 elements are in the range from 10^–7 to 10^–11 g. The accuracy of the determinations was established by the added-found method. The reproducibility is 0.1–0.34 for content levels of 10^–7–10^–9 g. The analytical possibilities of different spark source mass-spectroscopic methods for the analysis of solutions are compared.     

Interaction of chromophores in cationic/anionic dyes

The spectral properties of dyes containing colored organic cations and anions have been investigated in solvents differing in polarity. It has been established that the color of cationic/anionic dyes in low-polarity solvents is governed by the properties of the ion pairs that are formed. The chromophores in the ion pairs of cationic/anionic dyes interact, and this moves the absorption bands away from each other and redistributes their intensities.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 1, pp. 47–53, January–February, 1989.     

Flow-injection photometric determination of the phenol index of natural waters in the presence of humic acids

Different schemes were considered for extraction preconcentration in the flow-injection determination of a phenol index, the total concentration of phenol and its derivatives that react with 4-aminoantipyrine. Preference was given to the scheme of flow injection analysis with the direct introduction of an extractant into the mixed flow of a sample and a reagent solution followed by phase separation in a chromatomembrane cell. This allowed phenols to be determined in natural and purified waste waters in the concentration range 1.0 to 10.0 µg/L with an RSD 25% and a throughput of 15 samples an hour. The study of the effect of humic acids on the results of determining the phenol index of natural waters showed that humic acids were hydrolyzed to form compounds that made their own contributions to the phenol index which were difficult to take into account.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 1, 2005, pp. 79–84.Original Russian Text Copyright © 2005 by A. Moskvin, Mozzhukhin, Mukhina, L. Moskvin.     

Spectrophotometric determination of cationic and anionic surfactants with anionic dyes in the presence of nonionic surfactants,part II: Development of batch and flow injection methods

On the basis of the changes in absorption spectra of azo dyes on the addition of an organic onium ion, spectrophotometric methods for the determination of organic onium salts and anionic surfactants were developed, and applied to flow injection method. Propyl orange (PO^–) was used for the determination of organic onium ions. Pairs of PO^– and Zeph⁺ (tetradecyldimethyl-benzylammonium ion) or PO^– and nC₁₈TMA⁺ (n-octadecyltrimethylammonium ion) were used for the determination of anionic surfactants. The determination range of organic onium ions were (0–3) × 10^–5 M by a batch method and were (0–2) × 10^–5 M by a flow injection method. The determination ranges of anionic surfactants were (0–2) × 10^–5 M by the batch method, and were (0–5) × 10^–5 M by the flow injection method, and the detection limit corresponding toS/N = 3 was 3 × 10^–7 M by the flow injection method. By the proposed flow injection method, anionic surfactants in water samples were determined.     

Volumetric Properties of Amino Acids and Hen-Egg White Lysozyme in Aqueous Triton X-100 at 298.15 K

The apparent molar volumes, V_,2, of glycine, alanine, -amino-n-butyric acid, valine, leucine, and lysine monohydrochloride have been determined in aqueous solutions of 0.05, 0.1, and 0.4 mol-kg^–1 Triton X-100 (TX-100), and the partial specific volume, v⁰, of hen-egg-white lysozyme in 0.4 mol-kg^–1 TX-100 by density measurements at 298.15 K. These data have been used to calculate the infinite dilution apparent molar volumes, V_2,m⁰, for the amino acids in aqueous TX-100 solutions and the standard partial molar volumes of transfer, _tr V_2,m⁰, of the amino acids from water to the aqueous surfactant solutions. The linear correlation of V_2,m⁰ for a homologous series of amino acids has been utilized to calculate the contribution of the charged end groups (NH₃⁺, COO^–), CH₂ group and other alkyl chains of the amino acids to V_2,m⁰. The results on _tr V_2,m⁰, of amino acids from water to aqueous TX-100 solutions have been interpreted in terms of ion–ion, ion–polar, hydrophilic–hydrophilic and hydrophobic–hydrophobic group interactions. For all the six amino acids studied, the values of _tr V_2,m⁰ from water to all the studied concentrations of aqueous TX-100 are small in spite of their different hydrophobic content, indicating an overall balance in interactions of zwitterionic/hydrophilic groups of amino acids with the hydrophilic groups of TX-100, and of hydrophobic and ionic/hydrophilic groups of the amino acids with hydrophobic groups of TX-100. Comparison of the interactions of the amino acids with nonionic, anionic and cationic surfactants has also been made and discussed. The partial specific volume of transfer of lysozyme from water to aqueous TX-100 solutions also indicates a balance of the hydrophobic and hydrophilic interactions in the protein–nonionic surfactant system.     

Kinetics of diethyl sulfide oxidation by hydrogen peroxide and peroxymonocarbonate in the presence of surfactants

We have studied the effect of different surfactants on the rate of diethyl sulfide (Et₂S) oxidation by hydrogen peroxide and peroxymonocarbonate (HCO ₄ ^- ) in aqueous solutions. In all the studied cases, the rate of the reaction between Et₂S and H₂O₂ decreases as the surfactant concentration increases. The reaction of Et₂S with HCO ₄ ^- is catalyzed by cationic surfactants and inhibited by neutral and anionic surfactants.Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 40, No. 6, pp. 368–372, November–December, 2004.     

Spectrophotometric Determination of Polyoxyethylene Nonionic Surfactants in Ground Waters Using Triple-Stage Solid-Phase Extraction Followed by an Improved Ferric Thiocyanate Complexation Method

A practical spectrophotometric determination method for polyoxyethylene nonionic surfactants in ground waters was established, which is based on a ferric thiocyanate complexation colorimetric method preceded by a triple-stage solid-phase extraction technique using SCX, SAX, and C18 cartridges interconnected. Cationic and anionic surfactants interfere with the determination and were therefore effectively trapped and isolated by the SCX and SAX solid phases, respectively. Nonionic surfactants (NSs) were finally introduced and concentrated in the C18 cartridge. The analyte was quantitatively eluted from the C18 sorbent, and the residue was subjected to the colorimetric determination. The calibration line was linear (r² = 0.9997) up to 200µgL^–1 of heptaoxyethylenedodecylether when analyzing sample sizes of 100mL. Overall recoveries were 95–97% with an RSD of less than 3%. The method was applied to the analysis of river water, and 6.4µgL^–1 of NSs as heptaoxyethylenedodecylether was found by means of the standard addition method. The proposed method is very practical and features minimum consumption of chemicals.     

Determination of pyrimethanil and kresoxim-methyl in soils by headspace solid-phase microextraction and gas chromatography-mass spectrometry

A method using headspace solid-phase microextraction (HS-SPME) then gas chromatography–mass spectrometry with selected ion monitoring (GC–MS, SIM) has been developed for determination of trace amounts of the fungicides pyrimethanil and kresoxim-methyl in soil and humic materials. Both fungicides were extracted on to a fused-silica fibre coated with 85 m polyacrylate (PA). Response-surface methodology was used to optimise the experimental conditions. For soil samples the linear dynamic range of application was 0.004–1.000 g g^–1 for pyrimethanil and 0.013–1.000 g g^–1 for kresoxim-methyl. The detection limits were 0.001 g g^–1 and 0.004 g g^–1 for pyrimethanil and kresoxim-methyl, respectively. HP-SPME–GC–MS analysis was highly reproducible—relative standard deviations (RSD) were between 6.7 and 12.2%. The method was validated by analysis of spiked matrix samples and used to investigate the presence of pyrimethanil and kresoxim-methyl above the detection limits in soil and humic materials.     

Voltammetric behavior of ethopropazine and the influence of sodium dodecylsulfate on its accumulation on gold electrodes

Surfactants are sometimes used to improve the accumulation of some electroactive organic compounds, but anionic surfactants have seldom been utilized for such a purpose yet. In this paper, the influence of the anionic surfactant sodium dodecylsulfate (SDS) on the accumulation of ethopropazine (EPZ) at a polycrystalline gold electrode has been studied. EPZ exhibits an anodic peak at about 0.67 V (vs. SCE) and a shoulder in pH 3.5 citric acid–biphthalate buffer solution. In the absence of SDS, the peak is small and ill defined, but it becomes high and well shaped when SDS is added. This results from the adsorption of EPZ in the SDS membrane, which forms spontaneously on the gold electrode surface. For both cases EPZ shows the same electrode reaction mechanism, which is similar to that of promethazine (PMZ). The influence of other factors, such as pH value, variety and concentration of buffers, other surfactants, accumulation potential and time etc has been discussed. It was found that only the anionic surfactants had an enhancement effect on the EPZ accumulation. Also, the solution should be acidic or neutral so as to maintain the interaction due to its electrostatic nature. The optimum SDS concentration for EPZ accumulation is about 0.1 mM regardless of whether or not an accumulation potential is adopted. When all the experiment conditions are optimized, the peak current of the anodic peak changes linearly with the concentration of EPZ over the range 0.4–4 M, and is thus of analytical significance.