New phase separator for extraction-spectrophotometric determination of anionic surfactants with Malachite Green by flow injection analysis

A simple flow injection spectrophotometric method for the determination of anionic surfactants in river water was studied. A three-channel flow system was assembled. The distilled water as a carrier and 5x10(-5) mol l(-1) Malachite Green (MG) dissolved in 0.1 mol l(-1) CH(3)COONa-CH(3)COOH buffer solution (pH 5) were delivered at 1.94 ml min(-1). The mixed solvent (toluene+methylisobutyl ketone (MIBK)=1+1) was pumped at 0.78 ml min(-1). Other conditions were the extraction coil 0.5 mm i.d.x3 m, the reaction temperature 20 degrees C and the sample size 200 mul. The calibration graph was linear in the range 0.1-0.4 ppm at 626 nm. The detection limit (S/N=3) was 18 ppb and a sample frequency of 20 h(-1) was attained. The relative standard deviation (n=7) for 0.4 ppm standard sodium dodecylsulfate (SDS) solutions was 1.1%. And also, new phase separator with a convenient connector was designed. This Fl method was applied to the determination of anionic surfactants in river water.     

Spectrophotometric determination of copper by flow injection analysis with an on-line reduction column

A silver reductor minicolumn is used ina flow-injection system for reduction of copper(II) to copper(I), which is detected spectrophotometrically using bathocuproine disulphonic acid. The reductor functions very well at flow rates up to 4 ml min^?1; this allows sample injection ar rates up to 120 h^?1. Linear calibration is achieved for 5 × 10^?7– 1 × 10^?4 M copper. The detection limit is 3.4 ng and the midrange precision is 1%.     

Spectrophotometric determination of nitrite in foodstuffs by flow injection analysis

A simple method for the determination of nitrite in foodstuffs by flow injection analysis is described. Nitrite samples are prepared in a microwave oven, treated with a 1 mol/lNH₄Cl solution at a pH of 9 (all under nitrogen atmosphere) and are immediately analysed. Nitrite is diazotised in the FIA system with N-(1-naphthyl) ethylenediammonium dichloride to form the highly coloured azo dye, which is measured at 540 nm. The detection limit is 0.036 mg/kg for sample injections of 400 l. The sampling rate is about 50 samples per hour and the relative standard deviation is 0.67%.     

Spectrophotometric determination of pH by flow injection

Flow injection is used for the determination of pH over a wide range. Using an appropriate combination of pH-indicating dyes, plots of absorbance vs. pH are linear in the range pH < 1–8 for static measurements and pH 3.6–6.8 in the flow-injection experiment. In the current configuration, the flow-injection method has the capability of measuring approximately 100 samples h^?1 with a precision and accuracy of ±0.2 pH. The reasons for the linear calibration graphs, effects of ionic strength and day to day reproducibility are presented together with results for lake-water samples.     

Spectrophotometric determination of total phenolics by solvent extraction and sorbent extraction optosensing using flow injection methodology

Flow injection analysis (FIA) procedures for the Spectrophotometric determination of phenol involving in-line concentration by solvent and sorbent extraction have been developed. The imine product formed in the reaction between phenol and 4-aminoantipyrine (4-AAP) is either extracted into chloroform (solvent extraction) or is temporarily retained on C₁₈-modified silica material contained in a microcolumn (sorbent extraction). In the latter case two variants of detection have been used namely the Spectrophotometric measurement of the methanolic eluent containing the concentrated dye and at-column optosensing of the retained reaction product followed by methanol elution to maintain reversibility of the process. In the solvent extraction procedure a 10-fold increase of sensitivity compared to the common FIA method without extraction is achieved but no corresponding improvement in detectability is observed. Under optimized conditions the detection limit amounts to 8 μg l⁻¹. Using sorbent extraction methodology, high concentration factors can be obtained when large sample volumes are used. The only limitation in getting correspondingly lower detection limits are an increasingly high and variable blank value with sampling volume. The detection limits obtained for measurement of the absorbance in the eluent and on-column optosensing are 11 μg l⁻¹ and 0.4 μg l⁻¹, respectively. A study of the extractability of various phenol derivates using both solvent and sorbent extraction revealed lower relative response rates compared to the FIA method without extraction. Phenolics that possess an additional acidic group are present in ionized form at the high pH of the assay and are not extractable at all.     

Spectrophotometric determination of acidity-constants of unstable compounds by flow injection analysis

Spectrophotometric methods of determining acidity constants of ligands in solution can be used satisfactorily for the determination of such constants of unstable ligands by flow injection analysis. The technique can also be used in the stopped-flow mode, to allow the extent of the reaction causing the instability to be established. The procedures are applied to glyoxal bis(2-hydroxyanil), 6-methylpicolinaldehyde azine, 2-hydroxy-benzaldehyde hydrazone and benzoylpyridine oxime.     

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.     

Spectrophotometric determination of copper as a dithiocarbamate by flow injection analysis

Copper(II) ions (1–20 mg l^?1) are determined at 385 nm by injection into an aqueous carrier solution containing EDTA (0.05 M), carbon disulphide (0.03%) and diethanolamine (0.1%) in aqueous ammonia solution (0.5%) adjusted to pH 8.0. Chromium(VI) and, to a minor extent, iron(III) interfere. In the absence of EDTA, cobalt, iron(II), nickel, and manganese ions interfere but the sensitivity to copper is higher.     

Design and application of a new phase separator for flow injection liquid-liquid extraction

A new versatile phase separator for flow injection solvent extraction has been designed and its analytical performance investigated. Manifolds for various instrumentation and the corresponding operating procedures have been established. Experimental results show that the newly designed phase separator possesses several advantages over the existing ones, such as long term stability, robustness, sufficient phase separation and integral in situ collection of the solvent extracts at different phase flow rate ratios. The detection limits for cobalt, gold, iodide, iron, lead, nickel, nitrate and tungsten were 1.4, 0.45, 70, 1.9, 160, 0.9, 137 and 23 ng ml⁻¹, and the relative standard deviations 2.5, 1.3, 2.2, 2.9, 4.8, 3.6, 1.4 and 3.3%, respectively.     

Spectrophotometric determination of aromatic primary amines and nitrite by flow injection analysis

Aromatic primary amines are determined by injection into dilute hydrochloric acid carrier which merges sequentially with 4-N-methylaminophenol and dichromate. The purple-red color formed by oxidative coupling of amines with 4-N-methylaminophenol is measured at 530 nm. In contrast to the manual procedure, the flow-injection procedure avoided errors arising from the instability of the coupling intermediate, oxidation of the amine, and too great an excess of the oxidant. The method improves the selectivity for certain amines in the presence of those which are sterically hindered or have an electron-deficient aromatic nucleus. Nitrite is determined by diazotization of sulfanilamide and quantifying the residual sulfanilamide by oxidative coupling. The sample thourghout for the assay of amines (0.05–20 μg ml^?1 NH₂-N) and nitrite (1–10 μg ml^?1 NO₂^--N) was 120 h^?1. A system for the consecutive determination of aromatic primary amines and nitrite is decribed.     

Spectrophotometric determination of iodate,iodide and acids by flow injection analysis

The production of iodine by reaction of iodate and iodide in acidic solution is used for the spectrophotometric determination of 1–6 × 10^?5 M iodate, 2–8 × 10^?3 M iodide, and ca. 10^?3 M acids. The sample is injected into a carrier stream containing the other two ions. The injection rate is ca. 100 h^?1.     

Spectrophotometric determination of dopamine and methyldopa with metaperiodate by flow injection analysis

A flow-injection spectrophotometric method for determining dopamine and methyldopa is described. It is based on the oxidation reaction with metaperiodate. Calibration graphs were linear up to 2 × 10^–4 mol/l catecholamines. The method allows the measurement of 130 samples per hour and was successfully applied to the analyis of pharmaceuticals.     

Spectrophotometric determination of dopamine and methyldopa with metaperiodate by flow injection analysis

A flow-injection spectrophotometric method for determining dopamine and methyldopa is described. It is based on the oxidation reaction with metaperiodate. Calibration graphs were linear up to 2 x 10(-4) mol/l catecholamines. The method allows the measurement of 130 samples per hour and was successfully applied to the analyis of pharmaceuticals.     

Two-step solvent extraction flow injection system for the determination of anionic surfactants by spectrophotometry

 An automated flow injection procedure for the determination of anionic surfactants with two-step extraction was developed, based on the official methylene blue method. A washing step was used for on-line treatment of the extracted products with methylene blue to eliminate interferences. An improved gravitational phase separator was used to overcome the limitations of the membrane separator, and an effective separation of the two phases was performed by gravity separation in a conical cavity constructed of PTFE and stainless steel. Use of PTFE pump tubing allowed reliable and reproducible withdrawal and propulsion of organic extractant at low flow-rates. The calibration graphs were linear up to 6.0 mg/l of sodium dodecyl sulfonate in aqueous solution when 100 μl of sample was injected, a relative standard deviation of 4.6% (n=7) was achieved. The recoveries of the procedure were in the range of 89–107%. The results obtained for anionic surfactants in waste water samples agreed well with those obtained by the standard methylene blue batch method. Received: 1 December 1995/Revised: 1 April 1996/Accepted: 9 April 1996     

Spectrophotometric determination of periodate or iodate ions by liquid-liquid extraction as an ion-pair using tetramethylammonium iodide

A simple and accurate extractive Spectrophotometric procedure was developed for the microdetermination of periodate and iodate in aqueous media. The determination of periodate was based upon the extraction of the ion-pair formed between the periodate and tetramethylammonium iodide at pH 4 in chloroform followed by direct Spectrophotometric measurements at 509, 358 and 288 nm. The optimum concentration range evaluated by Ringbom's plot, the molar absorptivity, the Sandell's sensitivity and the stoichiometry of the formed ion-pair were critically determined. Iodate could be determined quantitively by the proposed procedure after oxidation to periodate with potassium persulphate. The effect of the diverse ions on the determination of the periodate and/or iodate by the proposed procedures was also investigated. The application of the method for the analysis of iodate or periodate in the artificial fresh water was successfully carried out.     

Spectrophotometric determination of sodium by ion-pair extraction with crown ether complexes and monoanionic dyes

A highly selective photometric procedure for the determination of sodium in blood serum is proposed, based on the ion-pair extraction of a sodium—cryptand complex. A comparative study of cryptands with various cavity sizes, different pairing anions and extraction solvents is described. The use of cryptand 211, picrate and toluene, as ligand, pairing anion and extraction solvent, respectively, allows sodium to be determined at the μg ml^?1 level. A 350-fold amount of potassium (by weight) does not interfere, nor do other alkali metals. Possible interferences by multivalent cations are masked by EDTA.     

Spectrophotometric determination of palladium with sulfochlorophenolazorhodanine by flow injection

Sulfochlorophenolazorhodanine (as its sodium salt) has been used in the automated development of a sensitive flow-injection procedure for the spectrophotometric determination of palladium. The resulting method has high sample throughput, good precision, and low consumption of both sample and reagents. The optimum pH for the reaction is 5.0 and the response is constant at pH between 4.7 and 5.3. The sensitivity (calibration slope) of the procedure is 4.4 x 10(3) l./mole. The linear dynamic range is 0.045-30.0 mug/ml. The sample throughput is at least 120/hr. An automated procedure for optimization of analytical variables is described and a two-variable response surface for the system is given. Interference studies on 19 metal ions show that the method has good selectivity.     

Spectrophotometric determination of thallium after its extraction as an ion-pair of the chloro-complex and pyronine G

A sensitive and selective procedure for the spectrophotometric determination of thallium is described. The method is based on the formation of an ion-pair between [TlCl(4)](-) and the pyronine G cation in chloride-containing acid media. The ion-pair is extracted into benzene and permits the determination of as low as 0.3 mug of thallium in a final volume of 25 ml at 530 nm. The system obeys Beer's law in the concentration range 1-14 mug of thallium in a final volume of 25 ml. Potassium iodate was found to be highly effective for the oxidation of Tl(I) to Tl(III) and the presence of excess oxidant does not interfere. The method can be used for the determination of thallium in high purity cadmium, cadmium sponge and rock samples.     

Spectrophotometric determination of fluoxetine by batch and flow injection methods

A rapid, simple, and accurate spectrophotometric method is presented for the determination of fluoxetine by batch and flow injection analysis methods. The method is based on fluoxetine competitive complexation reaction with phenolphthalein-beta-cyclodextrin (PHP-beta-CD) inclusion complex. The increase in the absorbance of the solution at 554 nm by the addition of fluoxetine was measured. The formation constant for fluoxetin-beta-CD was calculated by non-linear least squares fitting. Fluoxetine can be determined in the range 7.0 x 10(-6)-2.4 x 10(-4) mol l(-1) and 5.0 x 10(-5)-1.0 x 10(-2) mol l(-1) by batch and flow methods, respectively. The limit of detection and limit of quantification were respectively 4.13 x 10(-6) mol l(-1) and 1.38 x 10(-5) mol l(-1) for batch and 2.46 x 10(-5) mol l(-1) and 8.22 x 10(-5) mol l(-1) for flow method. The sampling rate in flow injection analysis method was 80+/-5 samples h(-1). The method was applied to the determination of fluoxetine in pharmaceutical formulations and after addition to human urine samples.