Issei Kasahara

Application of organic solvent-soluble membrane filters in the preconcentration and determination of trace elements: spectrophotometric determination of phosphorus as phosphomolybdenum blue

A simple and rapid preconcentration technique, based on collecting trace elements on a membrane filter and dissolving the membrane filter in an organic solvent, has been applied to the spectrophotometric determination of phosphorus in water. Phosphorus, 0.5-7 mug in 50-500 ml of water sample, is collected as phosphomolybdenum blue on a nitrocellulose or acetylcellulose membrane in the presence of n-dodecyltrimethylammonium bromide, the membrane is dissolved in 5 ml of dimethyl-sulphoxide (DMSO), and the absorbance of the DMSO solution is measured at 710 nm against a reagent blank. Moderate concentrations of silicate, anionic and non-ionic surfactants and high concentrations of sodium chloride do not interfere. Interference from arsenate can be eliminated by reducing the arsenate to arsenite. Condensed and organic phosphates can be determined if they are first converted into orthophosphoric acid by digestion with persulphate. The limit of determination is 0.002 mug of phosphorus in 100 ml of sample.

Bis[2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulpho propylamino)phenolato]cobaltate(III) as a counter ion for the extraction and spectrophotometric determination of long-chain quaternary ammonium salts and tertiary alkylamines in the presence of each other

Abstract The singly charged complex anion bis[2-(5-bromo-2-pyridylazo)-5-( N -propyl- N -sulphopropylamino)phenolato]cobaltate(III) is intensely purple-violet and is stable over the pH range 1–13. Its absorption spectrum remains the same over this pH range. At pH2, it forms extractable ion pairs with long-chain quaternary ammonium ions and protonated alkylamines. Only the quaternary ammonium ions are extracted into chloroform at pH 11, hence separate extractions allow both types to be determined. The absorbance of the organic phase is measured at 594 nm. The apparent molar absorptivity is 7.0 × 10 4 l mol −1 cm −1 . Calibration graphs for zephiramine, benzethonium and hexadecylpyridinium ions are linear over the range 0.1–2 × 10 −6 M. The only interference found was from anionic surfactants. The method is applied to hair and fabric conditioners.

An application of bis[2-(5-chloro-2-pyridylazo)- 5-diethylaminophenolato]cobalt(III) chloride to the extraction and spectrophotometric determination of sulphonated and sulphated surfactants

Bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt(III) is proposed for the extraction and spectrophotometric determination of sulphated and sulphonated surfactants. The complex and the surfactants form ion-pairs which are extracted into benzene from O.1M hydrochloric acid. The absorbance of the benzene phase is measured at 560 nm against a reagent blank. Less than 25 mug of sodium di-(2-ethylhexyl) sulphosuccinate in 50-200 ml of sample solution is determined reproducibly by the proposed method. When applied to river water samples, the proposed method gives results which agree very well with those obtained by the standard Methylene Blue method. However, the proposed method is simpler and more sensitive than the Methylene Blue method.

Transportation and fate of cationic surfactant in river water.

The degradation, sorption, transportation and material balance of cationic surfactants discharged from domestic waste into river water was studied. Ion-pair solid-phase extraction behavior showed that the sorption of cationic surfactants as an ion-pair with anionic surfactant onto river sediment was so strong that little cationic surfactant was found in the bulk water. Cationic surfactant was found in river sediment at more than 500 times higher concentration than that in the bulk water. The degradation of the cationic surfactant was very slow in river water and much slower in the sediment. A material balance of cationic surfactant was estimated for a river running through Toyama City by measuring the flow rate and the concentration of cationic surfactant in the water at several points. It was found that more than 30% of cationic surfactant introduced to the river was lost during the river running through ca. 3 km in 3 h. This reduction probably comes from a quick transfer of the cationic surfactant from river water to sediment and water weed by means of adsorption or precipitation with suspending solids.

Spectrophotometric determination of anionic surfactants in sea-water based on ion-pair extraction with bis[2-(5-trifluoromethyl-2-pyridylazo)-5-diethylaminophenolato]cobalt(III) as counter ion

A simple and sensitive spectrophotometric method was developed for the extraction and spectrophotometric determination of low levels of anionic surfactants in sea-water. Anionic surfactants are extracted into toluene as an ion-pair with bis[2-(5-trifluoromethyl-2-pyridylazo)-5-diethylaminophenolato]cobalt(III){[Co(CF3-PADAP)2]+} and the absorbance of the organic phase is measured at 560nm. The cobalt complex cation is inert and stable over a wide pH range, and has a large molar absorption coefficient (Iµ= 1.06 × 104 m2 mol–1 at 573 nm in water and Iµ= 5.83 × 103 m2 mol–1 at 560 nm in toluene). The Beer–Lambert law was obeyed over the concentration range 0.01–0.4 mg dm–3 of sodium dodecyl sulfate (SDS) and the detection limit was 0.005 mg dm–3 on a 3σb basis. The relative standard deviations for artificial sea-water spiked SDS were about 2%. Electrolytes in sea-water do not interfere. The proposed method is simpler and more sensitive than the conventional Methylene Blue method even when the degradation products of anionic surfactants are present. The method was applied to the determination of anionic surfactants in sea-water samples without interference from matrix substances.

Membrane solubilization with tetramethylammonium hydroxide for the preconcentration and electrothermal atomic absorption spectrometric determination of trace amounts of arsenic in water

Solubilization of a mixed cellulose ester membrane filter (MF) with tetramethylammonium hydroxide (TMAH) is proposed for the preconcentration and electrothermal atomic absorption spectrometric (ETAAS) determination of trace amounts of arsenic in water. Arsenic at not more than 0.4 µg in 100 ml of sample solution was retained on the MF by filtration as an ion associate of arsenomolybdate and tetraphenylphosphonium ions.The ion associate was dissolved in a small volume of TMAH together with the MF. After being made up to 2 ml with water, the arsenic in the concentrate was determined by ETAAS in the presence of zirconyl nitrate as a chemical modifier. This method is very simple and rapid. The detection limit, defined as three times the standard deviation of the blank, was 0.04 µg l–1. Inorganic matrix components in river waters, Na+, K+, Ca2+, Mg2+, SO42–, NO3– and silicate at high concentrations did not interfere with the determination. Trace components, phosphate at 0.3 mg l–1, dodecyl sulfate at 14 mg l–1 and aluminium at 5 mg l–1, also did not interfere with the determination. The proposed method was applied to the analysis of river water samples.

Membrane filters for the concentration of trace elements in water: distribution of ion pairs between membrane filter and aqueous phases

The sorption of ion pairs on membrane filters (MFs) has been studied by taking the membrane filter as one of the homogeneous phases. The sorbability of some ionic species and the sorption abilities of different types of MF were evaluated in terms of the sorption constant defined by Ksor,CA = [(C+,A-)f]/[C+][A-], where C+, A- and (C+,A-) refer to the cation, anion and the ion pair, respectively, and f refers to the filter phase. The values of Ksor,CA were determined for many combinations of ionic complexes of cobalt(III) with pyridylazophenols, either as cations or anions, and oppositely charged organic ions having different alkyl chain lengths, with MFs made of different materials: nitrocellulose (NC; Toyo Advantec), acetylcellulose (AC; Fuji Film), regenerated cellulose (RC; Toyo Advantec) and polyethersulphone (PS; Toyo Advantec). For a given cobalt complex ion, the value of log Ksor,CA increased linearly with the increasing number of carbons in the counter ion. Membrane filters made of different materials showed different sorption abilities, the order being NC greater than PS greater than RC greater than AC. It was shown that the surface area of the MF is of greater significance than the volume of the matrix of the MF in determining the sorption constant.

A transparent membrane filter for the solid-phase spectrophotometric determination of trace cationic surfactant in water

The use of a transparent membrane filter is proposed for a simple and rapid solid-phase spectrophotometric determination of trace cationic surfactant in water. Cationic surfactant is retained on the membrane filter during filtration as an ion-pair with an intensely colored inert anionic cobalt complex, bis[4-hydroxy-3-(8-quinolyl)azo-1-naphthalenesulfonato]cobaltate(III). The absorbance of the colored membrane filter is measured directly at 593 nm against a reagent blank. A linear calibration was obtained for 0.8–4.0 × 10–6 mol dm–3 of benzyldimethyltetradecylammonium ion as a standard material. Inorganic major ions in natural water at mg dm–3 or higher concentrations and sodium dodecylsulfate at 0.4 mg dm–3 did not interfere with the determination. The recoveries of the cationic surfactant added to river water and tap water were quantitative.

Determination of arsenic by inductively coupled plasma atomic emission spectrometry after pre-concentration on an acid-soluble membrane filter as arsenomolybdate in the presence of a quaternary ammonium salt

A simple pre-concentration technique, based on collecting trace analytes on a membrane filter and dissolving the filter and the analytes in a suitable solvent, has been applied to the determination of arsenic in water by inductively coupled plasma atomic emission spectrometry. Arsenic, in the range 1–50 µg in a 100–500-ml sample, is collected on a nitrocellulose membrane filter as an ion associate of arsenomolybdate with tetrapentylammonium ion. The membrane filter and the arsenomolybdate are dissolved in a small volume of concentrated sulphuric acid, diluted to 2–10 ml and aspirated into the nebuliser. Arsenic is determined from the emission intensity at 228.812 nm. Moderate concentrations of silicate, phosphate and cadmium and high concentrations of sodium chloride do not interfere. Enrichment factors as high as 250 can be easily attained by the proposed pre-concentration technique. The detection limit, defined as three times the standard deviation of the blank, is 0.3 µg l–1 with 250-fold pre-concentration.

Sensitive and selective extraction-spectrophotometric determination of trace amounts of palladium(II) as a mixed complex with 2-(5-methyl-2-pyridylazo)-5-diethylaminophenol and bromide

A sensitive, selective and reproducible, spectrophotometric method has been developed for the determination of trace amounts of palladium, based on the extraction of palladium as a mixed complex with 2-(5-methyl-2-pyridylazo)-5-diethylaminophenol and bromide ion from 0.1 M sulphuric acid into toluene. The mixed complex has an absorption maximum at 553 nm. The reagent blank was made negligible by back-extracting the excess of reagent with 1 M sulphuric acid. Relative standard deviations were 0.3–1.3%. Beers law was obeyed in the concentration range 0.008–0.32 µg ml–1 of Pd and the detection limit was 0.4 ng ml–1 on a three times the standard deviation of the blank basis. High concentrations of foreign ions, with the exception of AuIII, PtII, VV and WVI, do not interfere with the determination. The proposed method was applied successfully to the determination of palladium in some alloy, catalyst and environmental samples.