Improvements in the N,N-diethyl-p-phenylenediamine method for the determination of free and combined residual chlorine through the use of FIA

In the determination of free and combined chlorine, the reaction of permanganate standards with N,N-diethyl-p-phenylenediamine (DPD) exhibits nonlinearity presumably because both the colored semiquinoid product and the colorless quinoid product are both formed. The titrimetric DPD method titrates both of the products while the colorimetric method monitors only the colored semiquinoid products. This results in a nonlinear response for the colorimetric method above 1.0 mg/l. as Cl(2). Under FIA conditions, the nonlinearity of the DPD colorimetric method is eliminated in the 0.1-5.0 mg/l. (as Cl(2)) range and the linear range is expanded to 0.1-8.0 mg/l. as Cl(2). Also, relative standard deviations are improved by 0.5-11% relative to the colorimetric method and 1.5-4.0% relative to the titrimetric method. The FIA method was developed further to sequentially determine both free and combined chlorine, since chloramine was found to have a negligible interference in the free chlorine determination.     

A fluorimetric method for the determination of chlorine and tetrachloroethene by bleaching of rhodamine B

A new fluorimetric method for the determination of tetrachloroethene and chlorine is based on the irreversible bleaching of Rhodamine B, which is either immobilized in a silicone polymer, or collected on a filter from an aerosol. Tetrachloroethene is decomposed to produce small amounts of chlorine, which reduces the fluorescence of Rhodamine B. With the immobilized Rhodamine B the detection limits were 2.1 mg/m(1) for chlorine in air, and for C(2)Cl(4) 3.5 mg/m(3) and 2.3 mg/l. in the gas and liquid phase respectively. A Rhodamine B aerosol was used as a trace catcher. This aerosol was mixed with the trace gas, irradiated, and collected on a membrane filter and its fluorescence intensity was measured. The detection limits by this approach were estimated to be 6 mug/m(3) for Cl(2) and 55 mug/m(3) for C(2)Cl(4).     

Aquatic degradation of triclosan and formation of toxic chlorophenols in presence of low concentrations of free chlorine

The degradation of 2-(2,4-dichlorophenoxy)-5-chlorophenol (triclosan) in chlorinated water samples was investigated. Sensitive determination of the parent compound and its transformation products was achieved by gas chromatography with mass spectrometry detection after sample concentration, using a solid-phase extraction sorbent and silylation of the target compounds. Experiments were accomplished using ultrapure water spiked with chlorine and triclosan concentrations in the low mg/l and ng/ml ranges respectively. Chlorination of the phenolic ring and cleavage of the ether bond were identified as the main triclosan degradation pathways. Both processes led to the production of two tetra- and a penta-chlorinated hydroxylated diphenyl ether, as well as 2,4-dichlorophenol. The formation of 2,3,4-trichlorophenol was not detected in any experiment; however, significant amounts of 2,4,6-trichlorophenol were noticed. All of these five compounds were also identified when triclosan was added to tap-water samples with free chlorine concentrations below 1 mg/l. Minor amounts of three di-hydroxylated phenols, containing from one to three atoms of chlorine in their structures, were also identified as unstable triclosan chlorination by-products. The analysis of several raw wastewater samples showed the co-existence of important concentrations of triclosan and its most stable by-products (2,4-dichlorophenol and 2,4,6-trichlorophenol), reinforcing the potential occurrence of the described transformations when products containing triclosan are mixed with chlorinated tap water.     

The use of chlorophenol red for the selective determination of chlorine dioxide in drinking water

In recent years, the use of chlorine dioxide as an alternative disinfectant for drinking water has become increasingly attractive. As a result, an accurate method for the determination of mg l(-1) concentrations of chlorine dioxide is needed. Improvements to chlorophenol red (CPR) spectrophotometry result in a selective method for ClO(2) with few interferences. CPR selectively reacts with 0.1-1.9 mg l(-1) ClO(2) at pH 7, yielding a linear response (0.9994) with a limit of detection of 0.12 mg l(-1) ClO(2). Several species, ClO(2)(-), ClO(3)(-), NH(2)Cl, and free available chlorine (FAC), were studied as potential interferents using this method. There was found to be less than 2% interference due to 1.38 mg l(-1) ClO(2)(-), 9.87 mg l(-1) ClO(3)(-1), and 5.31 mg l(-1) NH(2)Cl. The interference from up to 1.19 mg l(-1) FAC was 3.7% and could be further reduced by the addition of oxalic acid, sodium cyclamate or thioacetamide.     

Spectrophotometric determination of nitrate using chromotropic acid

A spectrophotometric method is described for the determination of nitrate in the 0.5 to 50μg range using chromotropic acid as the reagent and masking agents for the elimination of possible critical interferences due to chloride, chlorine, iron(III) and oxidants. The method can be applied directly for the determination of 0.2–20 mg of nitrate/l in 2.5-ml samples of water. Over 4000 mg of chloride/l can be tolerated. The method is simple, rapid and reliable. At the 1 mg/l level for nitrate the coefficient of variation at the 95% confidence limit is 4% There are no interferences.     

Determination of 2,4-D in aqueous solution by neutron activation analysis

A method based on neutron activation analysis was developed for the determination of fractions of milligrams of 2,4-D (2,4-dichlorophenoxy acetic acid) in aqueous solution in laboratory tests. The indirect determination of 2,4-D was based on the quantification of chlorine,³⁸Cl, produced by neutron activation. The range of application was 0.01–100 mg l⁻¹. No loss of³⁸Cl by chemical effects of the nuclear reaction was found. The advantages of the proposed method include high precision and sensitivity of determination. Results were compared with those obtained by UV-Vis spectrophotometry, where concentrations less than 1 mg·l⁻¹ were not detected.     

Immobilization of reagents by polymeric materials. Determination of metamizol

A method for immobilization of inorganic reagents, based on the dispersion of the reagent into an unsaturated polyester solution is applied to immobilization of lead dioxide. The obtained solid is of application in a flow-injection manifold for indirect atomic absorption determination of metamizol in pharmaceutical formulations. The procedure gives a linear calibration graph up to 6 ppm of metamizol with a relative standard deviation of 1.6% (3.0 mg/l) and a sample throughput of 72 hr(-1).     

Automated flow-injection procedures for glycerol and triglycerides

An automated flow-injection manifold with stopped flow and merging zones is reported for the determination of triglycerides (50–250 mg dl^?1) and glycerol (5.0 × 10^?6?1.0 × 10^?2 M). In each case, a single reagent cocktain (20 μl) is synchronously merged with sample (20 μl) and the rate of formation of NADH monitored spectrophotometrically at 340 nm. For glycerol, the reagent contains glycerol dehydrogenase and NAD in Tris buffer, pH 8.0; for triglycerides, lipase in also included. The correlation coefficient for triglycerides over the range 50–250 mg dl^?1 was 0.971.     

o-Dianisidine: a new reagent for selective spectrophotometric, flow injection determination of chlorine.

A flow injection analysis (FIA) procedure for the determination of free chlorine in industrial formulations and water samples is proposed. The manifold is provided with a gas-diffusion unit which permits the removal of interfering species and also the preconcentration of chlorine. The determination of chlorine is performed on the basis of the oxidation by o-dianisidine as a chromogenic reagent to a coloured product which can be monitored at 445 nm. The method (for a preconcentration step of 60 s) is linear over the range 0.04-1.00 mg l(-1) of chlorine, the limit of detection is 0.04 mg l(-1), the reproducibility of the procedure (as RSD of the slope) is 3.7% for a series of four independent calibrations, the precision (as RSD of a series of 30 continuous FIA peaks of 0.56 mg l(-1) of chlorine) is 1.4% and the sample throughput is 40 h(-1). A detailed comparative study of the analytical characteristics of a single mono-channel reverse FIA assembly and the same system but provided with a Fluoropore membrane filter of 0.5 microm pore size was performed to check the advantages of the new approach in terms of sensitivity, selectivity and limit of detection.     

Flow-injection photometric determination of mercaptans in light oil products with chromatomembrane extraction

A procedure was developed for the flow-injection photometric determination of mercaptans in light oil products. The use of sodium nitroferricyanide as the photometric reagent at 540 nm provides a detection limit of mercaptan sulfur of 0.3 mg/L at a volume of the sample of 3 mL; the analytical range is from 1 to 50 mg/L.     

Selective flow-injection determination of residual chlorine at low levels by amperometric detection with two polarized platinum electrodes

Flow-injection amperometry with two polarized platinum electrodes is used for the determination of residual chlorine based on the oxidation of iodide. Interferences of iron(III), copper(II), nitrite and atmospheric oxygen are eliminated in the proposed procedure. The detection limit for residual chlorine is 2 μg l^?1 at a sampling rate of 120 h^?1; linear calibration graphs are obtained up to 0.8 mg 1^?1. A method for the simultaneous flow-injection determination of residual chlorine and copper(II) is also proposed.     

Electrochemiluminescent determination of L-cysteine with a flow-injection analysis system.

A flow-injection electrochemiluminescent method for L-cysteine determination has been developed based on its enhancement of the electrochemiluminecence of luminol at a glassy carbon electrode. This method is simple and sensitive for cysteine determination. Under the selected experimental parameters, the linear range for cysteine concentration was 1.0 x 10(-6) - 5.0 x 10(-5) mol/l, and the detection limit was 0.67 micromol/l (S/N = 3). The relative standard deviation for 11 measurements of 1.0 x 10(-5) mol/l cysteine was 4.5%. The proposed method has been applied to the detection of cysteine in pharmaceutical injections with satisfactory results.     

Flow-injection extraction spectrophotometric determination of dichromate with the tetramethylenebis(triphenylphosphonium)cation

Chromium(VI) (0–5 μg) can be determined spectrophotometrically at 365 nm after flow-injection extraction into chloroform of the ion-associate, tetramethylenebis(triphenylphosphonium) dichromate. The carrier stream is distilled water and the reagent stream contains 1 M sulphuric acid and 0.5% (w/v) tetramethylenebis(triphenylphosphonium) bromide. The sampling rate is 24 h^?1. The calibration graph is linear up to 20 μg ml^?1 and the detection limit is 0.44 μg ml?1 chromium, based on injection volumes of 250 μl. The system has been applied to the determination of chromium in a range of steels.     

Reverse flow-injection manifold for spectrofluorimetric determination of aluminum in drinking water

A simple reverse flow-injection (rFIA) manifold for the direct determination of aluminum in drinking water is proposed. This rapid and sensitive method is based on the formation of an Al(3+) complex with salicylaldehyde picolinoylhydrazone (SAPH), which shows a maximum blue-green fluorescence (lambda(ex)=384 nm, lambda(em)= 468 nm) at pH 5.4. Operative conditions both for batch and rFIA procedures were investigated including reagent concentration, buffer solutions, injection loop, reacting coil and wavelengths used for the fluorimetric detection. The tolerance limits of foreign ions have been also evaluated, before and after the addition of masking agents. The reverse flow-injection procedure allows determination of Al(3+) at ppb level (LOD: 1.9 mug l(-1)) within a working range of 5-30 mug l(-1). The proposed method was successfully employed for the determination of Al(3+) in several commercial drinking, soft drinking (as certified reference material), and tap water samples.     

Application of the slotted quartz tube in flow-injection flame atomic-absorption spectrometry

The slotted quartz has been applied to flow-injection flame atomic-absorption spectrometry (FI-FAAS) showing several important advantages. The tube life was improved by a factor of 5-6 compared to conventional continuous aspiration. Flow impact systems were found not to be necessary in the applications so that larger enhancement factors may be achieved without sacrifice in precision. For 1.0 mg/l. copper, 1.0 mg/l. lead, 0.1 mg/l. cadmium and 1.0 mg/l. gold sensitivity enhancement factors of 3.1, 5.5, 5.3 and 4.0 were obtained with precisions of 1.3%, 1.1%, 1.6% and 1.7% RSD (n = 11) respectively. Application of the slotted quartz tube FI-FAAS method to the determination of heavy metals in urine has shown improved tolerance to interfering matrices. Recoveries obtained by spiking undiluted urine samples with 0.1 mg/l. copper and lead, and 0.01 mg/l. cadmium were in the range 100-102%.     

Flow injection analysis for residual chlorine using Pb(II) ion-selective electrode detector

A simple flow injection analysis (FIA) system for residual chlorine in tap water has been developed by using a Pb(II) ion-selective electrode (ISE) detector. The method is based on a specific response of the Pb(II)-ISE to residual chlorine. The FIA system consists of a millivolt meter, a peristaltic pump, a Pb(II)-ISE detector and a recorder. A linear working curve between peak height and concentration of residual chlorine was obtained from 0.1 to 1 mg l(-1) for the developed FIA system. The relative standard deviation for repeated injections of a 0.2 mg l(-1) residual chlorine sample was 2%. The regression line and its correlation factor between the conventional o-tolidine colorimetric method and the present method were Y=0.75X+0.17 and 0.967, respectively, for this determination.     

Differential Pulse Voltammetric Determination of Free Chlorine for Water Disinfection Process

The electrochemical detection of free chlorine based on the reduction at a gold electrode has been studied. The differential pulse voltammetric curves exhibited well‐defined cathodic peaks. Investigations with this system suggested that the active species in the cathodic reaction is HClO. Excellent reproducibility was demonstrated at pH 5. The peak height could be used for accurate and rapid determination of free chlorine in a sample water. A linear relationship (r²=0.99) was found for the concentration range of 1–5 mg Cl dm^?3 and the detection limit was estimated to be 0.04 mg Cl dm^?3.     

Flow-injection spectrophotometric determination of cobalt by extraction as tetrathiocyanatocobaltate(II) with the ethylenebis(triphenylphosphoniu) cation

Cobalt (0–10 μg) may be determined spectrophotometrically at 625 nm after flow-injection extraction into chloroform of the ion associate ethylenebis(triphenylphosphonium) tetrathiocyanatocobaltate(II). The carrier stream contained 10% (w/v) ammonium fluoride and the reagent stream contained 0.5% (w/v) ethylenebis (triphenylphosphonium) bromide and 5% (w/v) ammonium thiocyanate. The injection rate was 20 h^?1. The calibration graph is linear up to 20 μg ml^?1 and detection limit is 0.23 μg ml^?1 cobalt, based on injection volumes of 500 μl. The system has been applied to the determination of cobalt in a range of tool steels.     

A sensitive extracto-photometric method for determination of residual chlorine in greywater

A new photometric method for chlorine determination based on the oxidative transformation of iodide to iodine and subsequent extraction in ethyl acetate has been developed. The effects of several chemical variables (pH, ionic strength, and iodide concentration) have been studied. Characteristics of the method were linear range 0-0.6 mg C12/L, limit of detection 5 microg Cl2/L, and coefficient of variation 0.6%. The method has been applied to greywater without previous sample treatment.     

Simultaneous spectrophotometric determination of cyanide and thiocyanate after separation on a melamine-formaldehyde resin

A simple indirect spectrophotometric method for the determination of cyanide, based on the oxidation of the cyanide with chlorine (Cl(2)) is described. The residual chlorine is determined by the color reaction with o-tolidine (3,3'-dimethylbenzidine). The maximum absorbance for Cl(2) is at 437 nm. A linear calibration graph (0-4.0x10(-5) M CN(-)) is obtained under optimal reaction conditions at room temperature and pH 11-12. The stoichiometric mole ratio of chlorine to cyanide is 1:1. The effective molar absorptivity for cyanide is 5.87x10(4) l mol(-1) cm(-1) at pH 1.6. The limit of quantification (LOQ) is 3.6x10(-7) M or 9.4 ppb. Effects of pH, excess reagent, sensitivity, reaction time and tolerance limits of interferent ions are reported. The method was applied to the determination of cyanide in a real sample. The basic interferent usually accompanying CN(-), i.e. thiocyanate, is separated from cyanide by sorption on a melamine-formaldehyde resin at pH 9 while cyanide is not retained. Thiocyanate is eluted with 0.4 M NaOH from the column and determined spectrophotometrically using the acidic FeCl(3) reagent. The initial column effluent containing cyanide was analyzed by both the developed chlorine-o-tolidine method and the conventional barbituric acid-pyridine (Spectroquant 14800) procedure, and the results were statistically compared. The developed method is relatively inexpensive and less laborious than the standard (Spectroquant) procedure, and insensitive to the common interferent, cyanate (CNO(-)).