Flow-injection spectrophotometric determination of calcium using murexide as a color agent

FI spectrophotometric determination of calcium using murexide has been developed. The problem of the color of the dye fading and/or its complex in an alkaline medium in the batch method can be overcome by taking advantage of FIA. A calcium solution is injected into an ethylenediamine–ethylenediamine hydrochloride buffer (1 M, pH 11) which also serves as a masking agent, and is then merged with the aqueous murexide (0.005%, w/v) and continuously monitored. Simple FIA manifolds, including an LED colorimeter detector hooked up to a PC-based data acquisition and evaluation system are described. Optimization of FIA systems has been made. The proposed procedures have been validated by using reference materials and comparing the results with the standard methods, and then applied to ores and drug samples.     

Flow-injection spectrophotometric determination of salbutamol with 4-aminoantipyrine

A flow-injection method is proposed for the determination of salbutamol. The method involves the condensation of salbutamol with 4-aminoantipyrine in the presence of hexacyanoferrate (III) in alkaline medium, producing a coloured quinoneimide that was detected absorptiometrically at 500 nm.

The values of four variables (two reactor lengths and two reagent concentrations) were optimised by means of the sequential simplex method and their influence studied in univariant way.

The method was validated and compared with the HPLC method established in the United States Pharmacopeia (USP). Linearity was demonstrated in the range 0–74.1 mg/L of salbutamol sulfate (r² = 0.9999). Commercial samples of pharmaceuticals containing salbutamol sulfate (tablets and oral solutions) were analysed and the results obtained with the proposed method agreed with the USP method in less than 1.6%, with precision similar to the HPLC method (1%–2% R.S.D.). The sampling frequency was 75 samples/hour.     

The determination of thiols with diphenylpicrylhydrazyl as a spectrophotometric reagent

Diphenylpicrylhydrazyl (DPPH), a stable, intensely purple free radical, is used as a reagent in the quantitative determination of various aromatic and aliphatic thiols by indirect spectrophotometric analysis. Plots of degree of reaction vs. time show that thiophenol and its derivatives react more quickly than aliphatic thiols with DPPH. Calibration plots are linear over the concentration range 0.05-3.00 x 10(-5)M thiol. The average relative error is in the range 1-2% and the absolute standard deviations range up to 0.50 x 10(-6)M.     

Flow-injection spectrophotometric determination of enalapril in pharmaceuticals with bromothymol blue

Enalapril (1.5–60 μ gl^?1) in aqueous solution is extracted into dichloromethane as its ion-pair with bromothymol blue in an unsegmented flow system and quantified spectrophotometrically. Up to 80 samples h^?1 can be processed, with r.s.d. of 1.0–3.4%. The degradation products of enalapril and excipients in the pharmaceutical dosage form do not interfere.     

Flow-injection spectrophotometric determination of acetyl-coenzyme A with immobilized phosphotransacetylase

Phosphotransacetylase (PTA) is immobilized on AF-Tresyl TOYOPEARL 650 gel and used on-line in a stainless-steel column (10 × 4 mm i.d.). CoA-SH liberated enzymatically from acetyl-CoA is reacted with Ellman's reagent [5,5′-dithiobis(2-nitrobenzoic acid)] in the carrier stream. The calibration graph for acetyl-CoA is linear from 4 × 10^?6 to 4 × 10^?4 M and the detection limits is 8 × 10^?7 M. The immobilized enzyme can be employed for over 4 months without any significant decrease in activity. The enzyme retains its activity in methanol even though the initial rate of reaction is decreased.     

Flow-injection spectrophotometric determination of aluminium in water with pyrocatechol violet

Optimum conditions for the adaptation of the spectrophotometric pyrocatechol violet method for aluminium to a flow-injection system are described. The detection limit is 3 μg Al l^?1 and calibration graphs are linear up to 3 or 10 mg l^?1 (with 200-μl or 10-μl injection loops, respectively). The relative standard deviation is 〈 2% at 0.1 mg Al l^?1. Potential interferences of 40 common inorganic ions and of 20 organic substances, including fulvic acid, are reported. With the use of conventional masking agents and predigestion of samples with high organic content, the method is suitable for determining total aluminium in natural waters.     

Flow-injection spectrophotometric determination of methyldopa in pharmaceutical formulations

A flow-injection spectrophotometric procedure is proposed for methyldopa determination in pharmaceutical preparations. The determination is based on formation of a yellow product (measured at 410 nm) after complexation of methyldopa with molybdate. Under optimal conditions, Beer's law is obeyed in a concentration range of 50-200 mg l⁻¹ methyldopa. Typical correlation between absorbance and analyte concentration was 0.9999. Usual excipients used as additives in pharmaceuticals do not interfere with the proposed method. The analytical frequency was 210 h⁻¹ and the relative standard deviation (R.S.D.) was ≤2% for sample solution containing 150 mg l⁻¹ methyldopa (n = 11). The analytical results obtained in commercial formulations by applying the proposed FIA method were in good agreement with labeled values and those obtained by the Brazilian Pharmacopoeia procedure at 95% confidence level.     

Malachite green as a reagent for detection and spectrophotometric determination of chromium(VI)

A sensitive and inexpensive method of spectrophotometric determination of chromium(VI), based on the absorbance of its complex with malachite green and acetic acid at pH 2.5 is reported. The complex shows a molar absorptivity of 8 x 10(4) l.mole(-1) cm(-1) at 560 nm, using malachite green and acetic acid as reference solution. The effect of time, temperature, pH and reagent concentration is studied and optimum operating conditions are established. Beer's law is applicable in the concentration range 2.0-22.8 mug/ml chromium(VI). The resin beads act as a catalyst and as little as 1.6 mug of chromium(VI) is detected in the resin phase as compared to 4.1 mug in the solution phase. The standard deviation in the determinations is +/-0.40 mug/ml for a 10.35 mug/ml solution.     

Automatic spectrophotometric determination of amyloglucosidase activity in fermentation samples with a glucose dehydrogenase reagent

An AutoAnalyzer procedure is described in which glucose, produced by the amyloglucosidase-catalyzed hydrolysis of maltose, is determined by using glucose dehydrogenase and NAD⁺. The method is selective, precise (1.1% r.s.d. from day-to-day) and rapid (60 samples h^-1).     

The spectrophotometric and titrimetric determination of gold with ferroin as reagent

A spectrophotometric and a photometric titration method in a two-phase system for the determination of gold with ferroin is reported. Both methods are rapid and reproducible with an accuracy of ±1%. In the spectrophotometric determination Co²⁺, Cu²⁺, Ni²⁺ , Fe³⁺, Zn²⁺, Mn²⁺ and Cr³⁺ do not interfere with the determination of gold and Pt⁴⁺, Pd²⁺, Hg²⁺, Ir⁴⁺ and Os⁴⁺ can be tolerated up to a ratio of 1:1. The titrations can also be carried out in the presence of a number of diverse ions, e.g. Ni²⁺, Cu²⁺, Co²⁺, Fe³⁺, Zn²⁺, Cr³⁺, Mn²⁺, without interference; the platinum metals and Hg²⁺ cause interference but, by the use of the spectrophotometric procedure, this can be reduced.     

Flow-injection extraction-spectrophotometric determination of perchlorate with brilliant green

Perchlorate (0-2.5 μg ml^?1) is determined spectrophotometrically at 640 nm after extraction into benzene of its ion-associate with Brilliant Green in a flow-injection manifold with a membrane separator. The injection rate is 20 h^?1. The detection limit is 36 ng ml^?1, based on 250-μl injections. The system is applied to the determination of perchlorate in potassium chlorate after prior selective destruction of chlorate.     

Indirect spectrophotometric determination of perchlorate using nitron as reagent

An indirect method is outlined for the spectrophotometric determination of small amounts of perchlorate. Perchlorate is quantitatively precipitated as nitron perchlorate in the presence of excess nitron. After separating off the precipitate, the excess reagent is determined in the supernatant liquid as nitron cobaltothiocyanate. The latter compound is extracted in 30% cyclohexanone in carbon tetrachloride and the absorbance of the extract measured at 625 nm. The method is simple, reproducible, and accurate to ±1%. The interferences of other anions were also investigated.     

Indirect spectrophotometric determination of borate using nitron as reagent

An indirect method is outlined for the spectrophotometric determination of small amounts of borate. Borate is quantitatively precipitated as nitron tetrafluoborate in the presence of excess nitron. After separating off the precipitate, the excess of reagent is determined in the supernatant liquid as nitron cobaltothiocyanate.     

Flow-injection ultraviolet spectrophotometric determination of sulphate in natural waters

The proposed method is based on measurement of the absorbance of the FeSO₄⁺ complex cation at 355 nm. Sample-injection and reagent-injection procedures are described. Calibration graphs are linear in the ranges 25–600 and 10–150 mg l^?1 sulphate, respectively. The main interference is from ultraviolet-absorbing organic compounds in the waters. Methods of eliminating the interference are discussed. Results for sulphate in river waters compare satisfactorily with those obtained by the gravimetric method. Depending on the pretreatment used, 10–30 samples can be analyzed per hour.     

Flow-injection spectrophotometric multidetermination of metallic ions with a single reagent exploiting multicommutation and multidetection

A flow system designed by computer-controlled discrete commutation devices is proposed for the multidetermination of metallic ions with a single chromogenic reagent. Intermittent addition of masking agents and changes of the reaction pH were exploited to implement selective determination of four species. Multidetection with an optical-fiber CCD-array spectrophotometer enabled simultaneous measurements at different wavelengths for multidetermination. The proposed system was applied to the determination of iron, copper, nickel and zinc in alloys and pharmaceutical preparations, yielding results in agreement with those obtained by flame atomic absorption spectrophotometry at the 95% confidence level. The sampling rate was estimated to be 80 determinations per hour. Coefficients of variation lower than 2% (n = 20) were achieved for all species.     

2-Oximinodimedone monoguanylhydrazone as spectrophotometric reagent for determination of iron

The synthesis, properties and analytical possibilities of 2-oximinodimedone monoguanylhydrazone as spectrophotometric reagent have been examined. A new method for the determination of iron has been developed in a concentration range varying from 0·2–5·0 ppm of iron; the molar absorptivity is 1·1×10⁴ litres mol⁻¹ cm⁻¹ at 600 nm and the relative error is ±0·3%. The method has been applied satisfactorily to the determination of iron in different inorganic samples.     

Flow-injection spectrophotometric multidetermination of metallic ions with a single reagent exploiting multicommutation and multidetection

A flow system designed by computer-controlled discrete commutation devices is proposed for the multidetermination of metallic ions with a single chromogenic reagent. Intermittent addition of masking agents and changes of the reaction pH were exploited to implement selective determination of four species. Multidetection with an optical-fiber CCD-array spectrophotometer enabled simultaneous measurements at different wavelengths for multidetermination. The proposed system was applied to the determination of iron, copper, nickel and zinc in alloys and pharmaceutical preparations, yielding results in agreement with those obtained by flame atomic absorption spectrophotometry at the 95% confidence level. The sampling rate was estimated to be 80 determinations per hour. Coefficients of variation lower than 2% (n = 20) were achieved for all species. Received: 25 October 2000 / Revised: 19 December 2000 / Accepted: 31 December 2000     

Arsenazo III as a spectrophotometric reagent for determination of lead

Arsenazo III is proposed as a spectrophotometric reagent for the determination of lead. The complex formation begins at pH > 2 and is greatest at pH 4-6. The molar absorptivity of the complex has a mean value of 2.8 x 10(4) 1.mole(-1).cm(-1) at 600 nm and remains nearly constant in the pH range 4-8. The ionic species taking part in the reaction are studied and the equilibrium constants for the different possible reactions are calculated. According to the values obtained, the reaction of PbOH(+) with H(5)L(3-) is predominant. The reaction studied is applied for the determination of micro amounts of lead in technical aluminium.     

Indirect spectrophotometric determination of palladium using 1,10-phenanthroline as reagent

Summary The spectrophotometric method for the determination of palladium is based upon the addition of a standard 1,10-phenanthroline solution to precipitate Pd(phen)Cl₂ and the determination of 1,10-phenanthroline concentration of the supernatant solution. The absorbancy readings were made in the absorption maximum at about 271 nm, in the concentration range of 10^–6 to 10^–5M 1,10-phenanthroline in 0.1 M hydrochloric acid and 0.1% hydroxylamine hydrochloride. For the phenanthroline system Beer's law is valid. Ions which either form with phenanthroline very strong complexes or interfere with the spectrophotometric determination of 1,10-phenanthroline must be absent. The method is simple, rapid, accurate and applicable to the macro and micro-determination of palladium in different systems. Standard deviation was found to be 0.085 ppm (in pure Pd solutions).

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Indirekte spektrophotometrische Bestimmung von Palladium mit 1,10-Phenanthrolin

Zusammenfassung Das Verfahren beruht auf der Fällung von Pd(phen)Cl₂ durch Zusatz einer bestimmten Menge Standard-1,10-Phenanthrolinlösung und spektrophotometrischer Bestimmung des Überschusses.Die Messungen werden bei dem Absorptionsmaximum bei etwa 271 nm und einer Konzentration von 10^–6M bis 10^–5M 1,10-Phenanthrolin in 0,1 M HCl und 0,1% Hydroxylaminhydrochlorid enthaltender Lösung durchgeführt. Das 1,10-Phenanthrolinsystem folgt dem Beerschen Gesetz. Ionen, die entweder mit 1,10-Phenanthrolin starke Komplexe bilden oder die spektrophotometrische Bestimmung von 1,10-Phenanthrolin beeinflussen, müssen abwesend sein. Die Methode ist einfach, rasch und genau und kann für Mikro- und Makrobestimmungen in verschiedenen Systemen angewendet werden. Die Standardabweichung beträgt 0,085 ppm (in reinen Pd-Lösungen).

     

Potassium ferrocyanide as a spectrophotometric reagent for the determination of uranium

Potassium ferrocyanide gives a colour reaction with U(VI), which is suitable for its determination. The complex absorbs in the wavelength range of 390–397 nm. The optimum pH range for colour development was 1.5–3.5. The molar absorptivity was found to be 4.65·10³ 1·mol^–1·cm^–1. Most of the anions up to 1000 g did not interfere. The method was made selective by extracting U(VI) first with DOSO from the mixture of interfering cations from 1–2M HNO₃ medium and then determining uranium in the back-extracted solution by developing the colour with ferrocyanide. 20 g/10 ml of U(VI) in the final solution could be satisfactorily determined within an RSD of ±2%.