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Source: Reprinted with permission from Nickless and Jones [118]. Copyright (1978) Elsevier Science Publishers BV.

Source: Reprinted with permission from Nickless and Jones [118]. Copyright (1978) Elsevier Science Publishers BV.

Note a <0.5% corresponds to the limit of detection (ppm) for SAE 9EO.

chromatography. The performance of the resin in this respect was evaluated by using solutions of a mixture of three model compounds, secondary alcohol ethoxylate 9EO, alkylphenol ethoxylate 9EO and polyethylene glycol 9EO. Recoveries varied from 82% at the 0.01mg L-1 level to 98% at the 1mg L-1 level.

Jones and Nickless [121] continued their study of Amberlite XAD-4 resins by examining polyethoxylated materials before and after passage through a sewage works. Samples from the inlet and outlet of the sewage works and from the adjacent river were subjected to a three-stage isolation procedure and the final extracts were separated into a non-ionic detergent and a polyethylene glycol. The non-ionic detergent concentration was 100 times lower (8ng mL-1) in the river than in the sewage effluent. Thin-layer chromatography and ultraviolet, infrared and NMR spectroscopy were used to identify, in the non-ionic detergent compound, alkylphenol ethoxylates (the most persistent), secondary alcohol ethoxylate and primary alcohol ethoxylate.

4.3.1.7 Polarography

Hunter and Liss [122] used polarography to measure surface active substances in natural waters.

4.3.1.8 Atomic absorption spectrometry

Greff [123] has also described a widely used method for non-ionic detergents based on the benzene extraction of the ammonium tetrathiocyanatocobaltate (II) complex followed by atomic absorption spectrophotometry at 320nm. The method is simple, rapid, well suited to the routine analysis of large numbers of samples, and applicable to surfactant concentrations in the range 0.1-20mg L-1. With this extraction system, it is necessary to saturate the water samples with sodium chloride to improve extraction efficiency. A more serious disadvantage is interference by anionic surfactants.

Courtot Coupez and Le Bihan [124] determined the optimum pH (7.4) for extraction of non-ionic surfactants with the tetrathiocyanatocobaltate (II) ((NH ) [Co(SCN) ])- complex-benzene system. Cobalt in the extract is estimated by atomic absorption spectrometry after evaporation to dryness and dissolution of the residue in methyl isobutyl ketone. The method is applicable to surfactant concentrations in the range 0.02-0.5mg L-1 and is not seriously affected by the presence of anionic surfactants.

The detergent concentration is determined over the range 0-0.44ppm by reference to a calibration graph. The average recovery is 60%. Interference of anionic detergents at concentrations of less than 10mg L-1

is prevented by extraction from an ammonium chloride medium.

Arpino et al. [125] performed microdeterminations of non-ionic ethoxylated surfactants in surface waters by precipitation with tungstophosphoric acid as described by Burttschell [126] and by the precipitation of tetrathiocyanatocobaltate (II) detergent ion pair, followed by determination of cobalt in the precipitate by atomic absorption spectrometry as described by Courtot Coupez and Le Bihan [124]. Both methods were found by Arpino et al. [125] to give erratic results.

Crisp et al. [127] have described a method for the determination of non-ionic detergent concentrations between 0.05 and 2mg L-1 in natural waters including sea water based on solvent extraction of the detergent-potassium tetrathiocyanatozincate (II) complex followed by determination of extracted zinc by atomic absorption spectrometry. Surfactant molecules are extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate (II) and the determination is completed by atomic absorption spectrometry. With a 150mL water sample the limit of detection is 0.03mg L-1 (as Triton X-100). The method is relatively free from interference by anionic surfactants; the presence of up to 5mg L-1 of anionic surfactant introduces an error of no more than 0.07mg L-1 (as Triton X-100) in the apparent non-ionic surfactant concentration.

Only sulphide, iron (III), aluminium (III) and chromium (III) ions interfere at concentrations likely to be found in contaminated waters. There is, however, no interference from sulphide at up to 100mg L-1 if the water is treated with 30% hydrogen peroxide, shaken and allowed to stand for 10min before addition of the zinc thiocyanate. Interference from up to 100mg L-1 concentrations of iron (II), aluminium (III) or chromium III is suppressed by addition of 1g of EDTA (disodium salt dihydrate) prior to the addition of the zinc thiocyanate reagent; the EDTA is unnecessary, however, if the metals are present mainly as a suspension of the hydroxides.

The performance of this method in the presence of anionic surfactants is of special importance, since most natural or waste water samples which contain non-ionic surfactants also contain anionic surfactants. The presence of up to 5mg L-1 linear alkylbenzene sulphonate increases the apparent concentration of non-ionic surfactant by a maximum of 0.07mg L-1 (as Triton X-100). Soaps, such as sodium stearate, do not interfere with the recovery of Triton X-100 (1.00mg L-1 when present at the same concentration (i.e. 1.00mg L-1)). Cationic surfactants, however, form extractable ion-association compounds with the tetrathiocyanatozincate ion and interfere with the method.

4.3.1.9 Miscellaneous

Various attempts have been made to develop titration methods for nonionic surfactants. Wickbold [128] has described a method in which the surfactants are extracted from aqueous samples (mixed with sodium bicarbonate) by the passage of nitrogen (50-60L h-1) saturated with ethyl acetate through the sample, covered by a layer of ethyl acetate for 5min. After evaporation of the extract and dissolution of the residue in 5mL of methanol and 40mL of water, and adjustment of the pH to 4.6, 30mL of precipitation reagent (a 1:2 mixture of 29% aqueous barium chloride and a solution containing 1.7g of basic bismuth (III) nitrate, 65g of potassium iodide and 220mL of acetic acid per litre) is added. The precipitate formed is dissolved in 30mL of hot ammonium tartrate solution (12.4g of tartaric acid and 18mL of 25% aq. ammonia per litre) and after adjustment of the pH to 4.6 is titrated potentiometrically (platinum and calomel electrodes) with 0.5mN-pyrrolidine-l-carbodithioate. Tsuji et al. [42] have described a potentiometric titration method for non-ionic surfactants utilizing cholinesterase. This method utilizes the phenomenon that non-ionics weaken the inhibitory effect of the cholinesterase-butyrylthiocholine system.

La Noce [48] has described methods for determining non-ionic surfactants gravimetrically, turbidimetrically and colorimetrically by precipitation as a metal complex and determination of the metal (Mo, W, Bi or Co) by thin-layer chromatography, or by infrared spectroscopy.

McCracken and Datyner [129] have determined non-ionics in aqueous solution by a method based on foam entrainment. The method involves measuring the weight of foam plus liquid entrained by passage of a regulated air flow during a given time. This weight can be correlated with the initial concentration of detergent, e.g. with measurement at 25°C; the relationship is almost rectilinear for 0.015 to 0.06% of detergent.

Wickbold [46] has described a method for separating non-ionics from surface water at a gas-water interface in which a 4L sample is treated with sodium bicarbonate (10g) in a glass tower (830mm x 99mm) and ethyl acetate (200mL) is used for the collection of the surfactant from a stream of nitrogen (90-100L h-1). After evaporation of the combined organic phases, the surfactant is determined by any suitable procedure.

Continuous automated extraction techniques for removal of low concentrations of non-ionics from water have been developed [130, 131]. In this system the sample is mixed with solvent and passed through a vertical coil partly packed with glass ballotini. Separation of these phases begins in the upper (empty) part of this coil and is completed by means of a double-weir separator, liquid control being by means of phase-sensing electrodes and solenoid valves. The system has been used for extracting 5-25^g amounts of non-ionic detergent from effluents containing concentrations of up to 0.1ppm, with typical extraction efficiencies of 95-100%.

Linhart [132] has described a method for separating detergents into cationic, anionic and non-ionic types on a mixed bed of a cation-exchange resin (e.g. Lewatit S1020, H+ form) and an anion-exchange resin (Lewatit M5020, OH- form). He then determined the detergents by a polarographic procedure. This method is based on the damping of the polarographic maximum of oxygen by the surfactants and on the fact that in mM potassium chloride it is not the molarity but the percentage by weight of the surfactants that is proportional to this damping. The proportionality (which is rectilinear over the range 0-100mg L-1) applies equally to anionic, cationic and non-ionic surfactants containing up to 90 ethoxy units and to polyoxyethylene glycols containing >400 ethoxy units.

The British Standard method [15] for non-ionic detergents is based on either colorimetry by extraction with chloroform and measurement of the colour formed with ammonium cobaltothiocyanate or by thin-layer cnromatography after extraction with chloroform with location of the spots with a modified Burger reagent and comparison with standards.

4.3.1.10 Preconcentration

Nickless and Jones [118] and Musty and Nickless [119, 120] evaluated Amberlite XAD-4 resin as an extractant for down to 1^g L-1 of polyethylated or secondary alcohol ethoxylates, [((R))OCH CH ]OH surfactants and their degradation products from water samp2les. 2 This resin was found to be an efficient adsorbent for extraction of polyethoxylated compounds from water except for polyethylene glycols of molecular weight less than 300. Flow rates of 100mL min-1 were possible using 5g of resin, and interfering compounds can be removed by a rigorous purification procedure. Adsorption efficiencies of 80-100% at 10^g L-1 were possible for non-ionic detergents using distilled-water solutions. The main purpose of the work of Nickless and Jones [118] was the investigation of secondary alcohol ethoxylate as it proceeds through the water system. Associated with this is polyethylene glycol, a likely biodegradation product. Alkylphenol ethoxylate was also considered, but only as possible interferent that should be differentiated in order to allow fuller characterization of secondary alcohol ethoxylate residues.

Inaba [133] described improvements in the tetrathiocyanatocobalt (II) dipotassium salt method to achieve greater sensitivity and simplicity in the determination of polyoxyethylene-type non-ionic surfactants. The amount of cobalt (II) extracted into the organic phase (toluene) was determined by using 4-(2-pyridylazo)-resorcinol as a spectrophotometric reagent. The molecular absorptivity of cobalt (II)-PAR complex was 33 times larger than that of the thiocyanato complex. Octaethyleneglycol mono-n-dodecylether was used as a standard polyoxyethylene-type non-ionic surfactant. Absorbance of the organic phase increased with increasing thiocyanate and/or cobalt (II) concentration, when the aqueous phase contained no potassium chloride salt. Interferences from coexisting substances such as linear alkylbenzene sulphonates and humic acid were eliminated during the toluene preconcentration step. Preliminary ion-exchange procedures were recommended for samples with high salinity (sea water) and/or high concentrations of interfering substances. The applicability of the method was demonstrated by the analysis of several highly polluted Japanese lakes and marshes.

4.3.2 Sea water

4.3.2.1 Spectrophotometric method

The picrate Spectrophotometric method described by Favretto et al. [105] (Section 4.3.1.1) has been applied to the determination of polyethylene non-ionic detergents in sea water.

A mean value of 93 ± 1% was obtained in recovery experiments on C E (at an aqueous concentration of 0.10mg L-1) extracted from synthetic se1a2 w9 ater by means of the above procedure. Therefore, a multiplication factor of 1.07 was adopted in correcting for the extraction losses.

Crisp [134] has described a method for the determination of non-ionic detergent concentrations between 0.05 and 2mg L-1 in fresh, estuarine and sea water based on solvent extraction of the detergent-potassium tetrathiocyanatozincate (II) complex followed by determination of extracted zinc by atomic absorption spectrometry. A method is described for the determination of non-ionic surfactants in the concentration range 0.05-2mg L-1. Surfactant molecules are extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate (II) and the determination is completed by atomic absorption spectrometry. With a 150mL water sample the limit of detection is 0.03mg L-1 (as Triton X-100). The method is relatively free from interference by anionic surfactants; the presence of up to 5mg L-1 of organic surfactant introduces an error of no more than 0.07mg L-1 (as Triton X-100) in the apparent non-ionic surfactant concentration.

4.3.2.2 Atomic absorption spectrometry

Courtot Coupez and Le Bihan [135] determined non-ionic detergents in sea and fresh water samples at concentrations down to 0.002ppm by benzene extraction of the tetrathiocyanatocobaltate (II) ((NH ) [Co(SCN) ])-detergent ion pair followed by atomic absorption spectr4o2photometr4ic determination of cobalt.

4.3.3 Potable waters 4.3.3.1 Mass spectrometry

Ventura et al. [136] identified [(alkoxy)polyethoxy] carboxylates in potable waters by mass spectrometry and mass determination using fast ion atom bombardment. Non-ionic detergents were used as internal standards in this method.

4.3.4 Waste waters

4.3.4.1 Spectrophotometric methods

Baleux [137] has described a spectrophotometric method for non-ionic polyoxyethylene surfactants in effluents using an iodide-iodine reagent. Although the method is especially applicable to waste effluent it is less satisfactory for the determination of the surfactants in natural waters.

The levels of cationic and non-cationic polymetric flocculants (used for sludge dewatering in sewage works) in waste water were measured by Hanasaki et al. [138]. Test solution, tannic acid solution and inorganic salt (sodium nitrate or sodium chlorate) solution were incubated for 1h at room temperature and the transmittance measured with a spectrophotometer at 554nm (more sensitive than 830nm). Transmittance was independent of temperature between 10 and 30°C and was not affected by ferric ion concentrations up to 200mg L-1. Determinations should be made at pH7 or less as transmittance decreased rapidly at higher pH values.

4.3.4.2 Gas chromatography

Reubecker [139] developed a procedure for the determination of alkylethoxylated surfactants in waste water. The method of determination involved concentration of the alkylethoxylated surfactants on an anionexchange resin, elution with ethanolk hydrochloric acid, hydrolysis of the surfactant to alkylethoxy, which was then extracted from the remaining ionic species, and conversion to the corresponding alkylbromides, which were determined by gas chromatography.

4.3.4.3 Atomic absorption spectrometry

Grasso and Buffalo [140] determined down to 0.1mg L-1 non-ionic detergents in waste by atomic absorption spectrometry. This technique was based on the formation of an insoluble cadmium surfactant phosphotungstic acid complex in acid media. A high-performance liquid chromatographic microfiltration apparatus was used to recover this precipitate before dissolving it in acetone and measuring the cadmium absorbance signal by flame atomic absorption spectrometry. A calibration curve, plotted using nonylphenol containing 10 units of ethylene oxide per mole, as standard compound, was used for calculating the amount of non-ionic surfactant in the sample. This amount was expressed as the equivalent amount of the same standard. Strontium chloride was required to overcome the interference of phosphates on calcium absorbance signals.

Gallago et al. [141] used indirect atomic absorption spectrometry to determine down to 100^g L-1 anionic detergents in waste water by flow injection continuous liquid extraction. A membrane phase separator designed for the continuous extraction of anionic surfactants is described. The detergent-1,10-phenanthroline copper (II) ion pair was extracted into methyl isobutyl ketone through two layers of Fluoropore membranes (1.0^m pore size). The concentration of detergent was determined indirectly by atomic absorption spectrometric determination of copper. The relative standard deviation was 0.8% over the range 100-500^g L-1. The method was highly selective and showed good agreement with the methylene blue method.

4.3.4.4 Miscellaneous

Zoller and Ramono [142] have developed procedures for facilitating the application of existing analytical methods for the determination of non-anionic detergents, in waste waters. They determined the ratio between biodegradable and non-biodegradable non-ionics in the sample and correlated the analytical data with the information available on production, formulation and use of non-ionic detergents. Using the hydrophilic cobaltothiocyanate method, with certain modifications, average factorized calibration curves were obtained.

4.3.5 Trade effluents

4.3.5.1 Flow injection analysis

Bos et al. [143] give details of equipment and a procedure for the determination of both ionic and non-ionic surfactants by flow injection analysis with tensammetric detection. A mercury coated gold electrode is used. Both surfactant types can be determined in the concentration range 10-100^M with an accuracy of ±4%. Sample rate is roughly 60 per hour.

4.3.5.2 High-performance liquid chromatography

Cassidy and Niro [116] have applied high-speed liquid chromatography combined with infrared spectrometry to the analysis of polyoxyethylene surfactants and their decomposition products in industrial process waters. Molecular sieve chromatography combined with infrared spectrometry gives a selective method for the analysis of trace concentrations of these surfactants. These workers found that the liquidsolid chromatography and reversed-phase chromatography are useful for the characterization and analysis of fatty free acids.

4.3.6 Sewage effluents

4.3.6.1 Spectrophotometric methods

Dozanska [144] has described a Spectrophotometric method involving reaction with cobalt thiocyanate or tungstophosphoric acid for the determination on non-ionic detergents in sewage. Stephanou and Giger [145] carried out quantitative determinations of nonylphenolethoxylates and nonylphenol in sewage effluents by capillary gas chromatography.

Waters et al. [146] investigated the scope and limitations of the Wickbold active substances procedure for the determination of non-ionic substances in sewage. The method was found to be unsuitable for sewage which gives low recoveries.

4.3.6.2 High-performance liquid chromatography

Boyd-Boland and Pawliszyn [147] have used solid-phase microextraction coupled with high-performance liquid chromatography to determine alkylphenol ethoxylate (Triton X-100) surface active agent in sewage effluent samples. These workers used normal phase gradient elution and detection by ultraviolet absorbance at 220nm to determine alkylphenol ethoxylates (Triton X-100) surface active agent in sewage effluent samples. Carbowax-template resin or Carbowax-divinylbenzene coatings on the column allowed successful analysis of the ethoxylates with a linear range of 100-0.1mg L-1. Limits of detection were in the low microgram per litre range.

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