Spectrophotometric determination of phenylephrine hydrochloride in pharmaceuticals by flow injection analysis exploiting the reaction with potassium ferricyanide and 4-aminoantipyrine

This paper presents a method for the determination of phenylephrine hydrochloride in pharmaceuticals by spectrophotometric flow injection analysis exploiting the reaction with potassium ferricyanide and 4-aminoantipyrine, which leads to the formation of a condensation product with strong absorptivity at 500 nm. The linear dynamic range was between 0.95 and 9 mg/L, with a limit of detection of 0.2 mg/L and a sampling throughput of 120 samples per hour. The method was applied to eyewashes and nasal decongestant liquid medicines.     

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 flow injection determination of chloride in ethanol

A flow injection procedure is described for the spectrophotometric determination of chloride in ethanol, based on the mercury(II) thiocyanate—iron(III) reaction. Effects of reagent composition and ethanol content of the sample are investigated in detail. The proposed system can analyse 120 samples of ethanol (94–100% v/v) per hour, with a relative standard deviation lower than 1%, when the chloride content ranges from 0.1–6.0 ppm. Recoveries of ca. 96% are found.     

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 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.     

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.     

Spectrophotometric determination of acid volatile sulfide in river sediments by sequential injection analysis exploiting the methylene blue reaction

This paper demonstrates the application of sequential injection analysis to perform sulfide determination using the methylene blue chemistry, based on two reagents: 3.63 mmol l(-1)N,N dimethyl-p-phenylene diamine hydrochloride in 1.1 mol l(-1) HCl solution and 19 mmol l(-1) FeCl(3), also in 1.1 mol l(-1) HCl. These solutions are aspirated inside the holding coil of the sequential injection system as two reagent zones sandwiching the sample zone. Under optimized conditions, the detection limit was calculated at 40 mug l(-1) S(2-), with a linear dynamic range from 0.05 to 2 mg l(-1) S(2-). This linear range can be extended up to 32 mg l(-1) using in-line dilution for sulfide concentrations greater than 2 mg l(-1). The robust characteristic of the SI system with syringe pump leads to very stable analytical curves (precision of 4%), minimizing the laborious preparation of sulfide standards. The method was applied in the determination of acid volatile sulfide in river sediments.     

Multicommutation in flow analysis. Part 3. Spectrophotometric kinetic determination of creatinine in urine exploiting a novel zone sampling approach

Zone sampling performed on a single analytical channel and associated with the stopped-flow approach was proposed and applied to the spectrophotometric kinetic determination of creatinine in urine based on Jaffé's reaction. The flow network comprised microcomputer controlled three-way solenoid valves. With multicommutation, the potentialities of zone sampling and stopped-flow were expanded, and the design of the flow set up was simplified. Influence of the main related parameters such as system configuration, reagent concentrations, temperature and timing were studied. The proposed system handled about 24 samples per hour. Baseline drift was not observed during extended operation periods (8 h). Sample pretreatment was not required. Results were reproducible (R.S.D. < 3%) and in agreement with those obtained in a batch procedure.     

The rapid determination of chemical oxygen demand in waste waters and effluents by flow injection analysis

Chemical oxygen demand (COD) and the limitations of the standard method of determination are discussed. A fully automated method based on a commercial     

Spectrophotometric flow injection methods for zinc determination in pharmaceutical and biological samples.

Zinc ions form a yellow complex with di-2-pyridyl ketone salicyloylhydrazone (DPKSH). This complex showed maximum absorption at 376 nm, and it was used to develop spectrophotometric flow injection methods for Zn(II) determination in different samples. Two types of flow systems were proposed. In the first system, a linear analytical curve was obtained in a concentration range from 0.217 to 4.60 mg L(-1) Zn(II), with a detection limit of 48.8 microg L(-1). In the second system, a minicolumn packed with an anion exchanger resin was used to concentrate Zn(II) as a chlorocomplex, and a linear analytical curve within a concentration range from 0.0824 to 2.06 mg L(-1) Zn(II) was obtained, having a detection limit of 13.9 microg L(-1). The developed methods were applied to biological and pharmaceutical samples, and a great compliance was observed by comparing the results with ones obtained by an atomic absorption technique.     

Spectrophotometric determination of micro amounts of cationic polymeric flocculants by flow injection analysis

Cationic polymeric flocculants in water are determined spectrophotometrically with the anionic compound 3-(2-hydroxy-3-carboxyanilide-1-azonaphthalene)-4-hydroxybenzenesulfonic acid at pH 10 by flow injection analysis. The calibration graph at 680 nm is rectilinear from 0 to 20 mg l^?1 under optimal conditions. The relative standard deviation for 20 injections of Cat-Floc (10 mg l^?1) was 1.2%; the sample throughput was 60 h^?1.     

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.     

Spectrophotometric determination of calcium with a flow injection system

The indirect spectrophotometric determination of 0.8–7.2 ppm calcium in the presence of magnesium, phosphate and sulphate by flow injection analysis (f.i.a.) is described. The method is based on the exchange reaction between the calcium and the zinc complex of ethylene glycol-bis(2-aminoethylether)tetraacetic acid (EGTA) in the presence of 4-(2-pyridylazo)resorcinol (PAR): Ca + Zn(EGTA) + 2 PAR ? Zn(PAR)₂ + Ca(EGTA). A home-made and a commercial flow injection system with a sampling rate of 80 h^?1, are compared. Results for water samples are in good agreement with those obtained by atomic absorption spectrometry.     

Spectrophotometric simultaneous determination of nitrite, nitrate and ammonium in soils by flow injection analysis

A new rapid flow injection procedure for the simultaneous determination of nitrate, nitrite and ammonium in single flow injection analysis system is proposed. The procedure combines on-line reduction of nitrate to nitrite and oxidation of ammonium to nitrite with spectrophotometric detection of nitrite by using the Griess-llosvay reaction. The formed azo dye was measured at 543 nm. The influence of reagent concentration and manifold parameters were studied. Nitrite, nitrate and ammonium can be determined within the range of 0.02–1.60 μg mL⁻¹, 0.02–1.60 μg mL⁻¹ and 0.05–1.40 μg mL⁻¹, respectively. R.S.D. values (n = 10) were 2.66; 1.41 and 3.58 for nitrate, nitrite and ammonium, respectively. This procedure allows the determination and speciation of inorganic nitrogen species in soils with a single injection in a simple way, and high sampling rate (18 h⁻¹). Detection limits of 0.013, 0.046 and 0.047 μg mL⁻¹were achieved for nitrate, nitrite and ammonium, respectively. In comparison with others methods, the proposed one is more simple, it uses as single chromogenic reagent less injection volume (250 mL in stead of 350 mL) and it has a higher sampling rate.     

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.