Sequential spectrophotometric determination of water-soluble calcium and magnesium in soils using chlorophosphonazo I

Summary A new procedure has been developed for the sequential spectrophotometric determination of water-soluble calcium and magnesium in soils using CPA-I. Optimum conditions for the spectrophotometric determination, Beer's law range, sensitivity of the color reaction, precision and the interference of various foreign ions are reported. The composition of the complexes also has been determined.

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Spektrophotometrische Reihenbestimmung von wasserlöslichem Calcium und Magnesium in Bodenproben mit Chlorphosphonazo I

Zusammenfassung Ein neues Verfahren zur spektrophotometrischen Reihenbestimmung von wasserlöslichem Calcium und Magnesium in Bodenproben mit CPA-I wurde ausgearbeitet. Die optimalen Bedingungen für die spektrophotometrische Bestimmung, der Gültigkeitsbereich für das Beersche Gesetz, die Empfindlichkeit der Farbreaktion, die Genauigkeit und die Störung durch verschiedene Fremdionen wurden angegeben. Auch die Zusammensetzung des Komplexes wurde bestimmt.

     

A new reagent for the spectrophotometric determination of magnesium (II): Khimduchlorophosphonazo-I

Summary The colour reaction of magnesium(II) with Khimduchlorophosphonazo-I (KCPA-I) has been studied spectrophotometrically with a view to develop a procedure for the determination of exchangeable magnesium in acidic soils.The optimum acidities are pH 8.78–9.90. The absorption maximum and molar absorptivity of the coloured complex are 580 nm and 1.85 · 10⁴ l · mol^–1 · cm^–1, respectively. The colour intensity is stable for 4 h and is found to obey Beer's law within the concentration range of 0–20 g per 25 ml. The method is simple and reliable (standard deviation 0.8–1.2%). It has been applied to the determination of exchangeable magnesium.

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Neues Reagens für die spektralphotometrische Bestimmung von Magnesium (II): Khimduchlorophosphonazo-I

Zusammenfassung Die Farbreaktion von Magnesium mit Khimduchlorophosphonazo-I wurde im Hinblick auf die Entwicklung eines entsprechenden Analysenverfahrens untersucht. Der optimale pH-Wert liegt im Bereich von 8,78–9,90. Das Absorptionsmaximum liegt bei 580 nm, der molare Extinktionskoeffizient beträgt 1,85 · 10⁴l · mol^–1 · cm^–1. Die Färbung bleibt 4 h lang stabil und befolgt das Beersche Gesetz von 0 bis 20 g/25 ml. Das Verfahren ist einfach und zuverlässig (Standardabweichung 0,8–1,2%) und wurde zur Bestimmung von austauschbarem Magnesium in sauren Böden angewendet.

     

The determination of magnesium in the presence of large amounts of zinc: A spectrophotometric method

The spectrophotometric determination of magnesium in the presence of large amounts of zinc is described. Zinc as well as some other interfering metals are removed by mercury cathode electrolysis and aluminium is removed by a chloroform extraction with 8-hydroxyquinoline.     

Simultaneous spectrophotometric determination of calcium and magnesium with chlorphosphonazo-III by flow injection analysis

In this flow-injection method, the total concentration of calcium and magnesium is determined by using triethanolamine/hydrochloric acid buffer (pH 7.0) and chlorphosphonazo-III (CPA-III) in the flow streams, and the concentration of calcium alone is determined by using 1.6×10^?3 M hydrochloric acid and CPA-III in the flow treams. At pH 7.0, medium, the linear calibration ranges were 0–2.00 mg l^?1 for both calcium and magnesium and the detection limits were each 0.02 mg l^?1; at pH 2.2, the linear calibration range for calcium and the detection limit were 0.20–2.00 mg l^?1 and 0.1 mg l^?1, respectively. Injection rates are 200 h. The method is suitable for analyzing natural waters.     

A sequential injection system for the spectrophotometric determination of calcium, magnesium and alkalinity in water samples.

A sequential injection methodology for the spectrophotometric determination of calcium, magnesium and alkalinity in water samples is proposed. A single manifold is used for the determination of the three analytes, and the same protocol sequence allows the sequential determination of calcium and magnesium (the sum corresponds to the water hardness). The determination of both metals is based on their reaction with cresolphtalein complexone; mutual interference is minimized by using 8-hydroxyquinoline for the determination of calcium and ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) for the determination of magnesium. Alkalinity determination is based on a reaction with acetic acid, and corresponding color change of Bromcresol Green. Working ranges of 0.5 - 5 mg dm(-3) for Ca, 0.5 - 10 mg dm(-3) for Mg, and 10 - 100 mg HCO3- dm(-3), for alkalinity have been achieved. The results for water samples were comparable to those of the reference methods and to a certified reference water sample. RSDs lower than 5% were obtained, a low reagent consumption and a reduced volume of effluent have been accomplished. The determination rate for calcium and magnesium is 80 h(-1), corresponding to 40 h(-1) per element, while 65 determinations of alkalinity per hour could be carried out.     

An insight into the solution equilibria of magnesium(II) with purpurin and spectrophotometric determination of magnesium

The complexation equilibria of magnesium(II) with purpurin (PURP) are studied spectrophotometrically as a function of pH in 50% (v/v) ethanol-water medium at 20 degrees C. The uncharged complex formed at pH 9.5 allows precise and accurate determination of magnesium over the concentration range 0.8-4.3 mug ml(-1). The molar absorptivity of the Mg-PURP complex at 540 nm and detection limit for Mg are 9.2x10(3) l mol(-1) cm(-1) and 75 ng ml(-1), respectively. The proposed method is rapid and possesses reasonable selectivity. Under the optimum conditions, the use of first-derivative spectrophotometry has the advantage of high sensitivity than normal spectrophotometry and allows the determination of 0.2 mug ml(-1) of magnesium. The validity of the method is examined by analysing several SRM Portland cement samples and a variety of cement materials of variable magnesia content.     

A precise spectrophotometric determination of a major constituent in pure materials: Application to pure magnesium metal

A spectrophotometric method is proposed for the direct assay of pure materials. The bulk of the metal to be determined is reacted with an accurately measured amount of a chelating agent, and the small excess of metal ion is determined spectrophotometrically with a chromogenic reagent. The optimal conditions can be predicted by drawing the theoretical spectrophotometric titration curves near the equivalent point of a supposed titration with the chelating agent as titrant and the chromogenic reagent as indicator. The method was applied to pure magnesium metal with EDTA as the chelating agent and calmagite as the chromogenic reagent, and the relative standard deviation was found to be 0.014%. The accuracy and precision appear to be much better than those attainable by titrimetry or differential spectrophotometry.     

Semimicro spectrophotometric determination of nitroglycerine in propellants by use of 2,4-xylenol

A semimicro spectrophotometric method using 2,4-xylenol is proposed for the determination of nitroglycerine in propellants. The propellant is extracted with methylene chloride, the extract is diluted, and a 10-ml aliquot is evaporated just to dryness. Then 2,4-xylenol reagent and 63% v/v sulphuric acid are added to hydrolyse the nitroglycerine to nitrate and form 6-nitro-2,4-xylenol which is steam-distilled in a Parnas-Wagner Kjeldahl distillation apparatus into a water-ammonia-isopropyl alcohol mixture. The absorbance of the yellow solution of the anion of the 6-nitro-2,4-xylenol is measured. The calibration curve is prepared from potassium nitrate and an empirical factor (5.50) is used to convert from nitrogen content to nitroglycerine (the theoretical factor is 5.40). The 2,4-xylenol should be added before the sulphuric acid in order to prevent interference from diphenylamine and ethyl centralite. The method is designed for the usual nitrocellulose double-base propellants containing 8-50% of nitroglycerine.     

Seventeen new 14- and 15-crown-formazans: their synthesis and evaluation in spectrophotometric determination of lithium

A number of new crown-formazans with 14 and 15 membered rings have been synthesized, characterized and investigated as selective spectrophotometric chelating agents for lithium. The effect of sodium ion concentration on the background lithium signal was studied. A comparative study for the sensitivity of these new crown-formazans in spectrophotometric determinations was studied and compared with those reported previously. The three new 14- and 15-crown-formazans 4a-c containing the pyridyl N-oxide at the formazyl carbon showed the highest selectivity to lithium determination in the presence of sodium ion.     

The use of chloranil for spectrophotometric determination of some tranquillizers and antidepressants

Chlorpromazine hydrochloride, promethazine hydrochloride, promazine hydrochloride, perphenazine, thioridazine hydrochloride, chlorprothexine, opipramol hydrochloride, amitriptyline hydrochloride, imipramine hydrochloride and hydroxyzine hydrochloride are estimated in their pure state and in pharmaceutical formulations by means of the reaction of the free bases with chloranil in dioxan-ethanol medium to give a coloured product with maximal absorbance at 550 nm. The method is precise, accurate and specific and recommended for routine analysis for the drugs mentioned.     

Indirect kinetic spectrophotometric determination of hydroxylamine based on its reaction with iodate.

A simple, precise and accurate method is proposed for rapid determination of trace amounts of hydroxylamine based on the reaction of hydroxylamine with iodate in acidic media. The reaction of neutral red by the produced nitrite ion was used to monitor the reaction spectrophotometrically at 525 nm by a fixed time method. Hydroxylamine in the range of 0.0400-1.200 microg mL(-1) could be determined. The relative standard deviation for 10 determinations of 0.500 microg mL(-1) hydroxylamine was 1.81% and the limit of detection was 0.010 microg mL(-1). The proposed method was applied to the determination of hydroxylamine in water samples with satisfactory results.     

Use of diode-array detectors for the simultaneous spectrophotometric determination of calcium and magnesium by flow injection

A method for the simultaneous flow injection spectrophotometric determination of calcium and magnesium with Arsenazo III based on the use of diode-array detector and merging zones is described. The method is applicable to the resolution of mixtures in which the chromogenic reagent has a high absorbance and its spectrum strongly overlaps those of its complexes. In resolving the mixtures, the excess reagent is considered as another component. Quantitation is based on the normal absorbance and first-derivative absorbance spectra. The method is applied to 0.2–1.5 μg ml^?1 Ca and 0.1–1.0 μg ml^?1 Mg. The analysis rate is 50 h^?1.     

1,2,4,6-Tetraphenylpyridinium perchlorate as a reagent for ion-association complex formation and its use for the spectrophotometric determination of gold

The synthesis, characteristics, and applications of 1,2,4,6-tetraphenylpyridinium perchlorate (TPPP) as an agent that forms ion-association complexes is described. This new spectrophotometric analytical reagent forms with AuCl₄^?1 a 1:1 complex which is slightly soluble in water and can be extracted with isopentyl acetate, with maximum absorbance 313 nm, molar absorptivity 3.44 × 10⁴ liters mol^?1 cm^?1. The variables involved in the formation and extraction of the complex in the mentioned organic solvent are studied. In the selected conditions, 1 M hydrochloric acid medium, the extraction efficiency was 95.3%. The apparent stability constant of the complex is log K = 5.9 ± 0.1 at 20 °C. The extracted complex is useful for the spectrophotometric determination of gold in the range of 0.05 to 0.5 ppm. Standard deviation at 0.2 ppm (10 determinations) was 0.0022 and the relative error was ±0.78%.The interferences of many foreign ions are studied, concluding that the procedure proposed shows a high selectivity.The method has been applied satisfactorily to the determination of gold in ores, leads and other materials.     

Flow-injection spectrophotometric determination of paraoxon by its inhibitory effect on the enzyme acetylcholinesterase.

A spectrophotometric enzymatic flow injection (FI) system for the determination of diethyl-p-nitrophenylphosphate (paraoxon) is proposed. The method was based on the determination of the acetic acid formed by the enzymatic reaction of the acetylcholinesterase, immobilized on glass beads, with the substrate acetylcholine. The acetic acid formed permeates through a PTFE membrane and is received by a solution (pH 7.0) containing the acid-base indicator Bromocresol Purple (B.C.P.), leading to a pH change and therefore to a color change. The variation of the absorbance of the solution is detected spectrophotometrically at 400 nm. The determination of paraoxon is related to its inhibitory action on the enzyme. Therefore the analytical signal is the difference between the signal that corresponds to the free and the one that corresponds to the inhibited enzyme, considering a fixed acetylcholine concentration. The correlation between the peak height and paraoxon concentration at a given acetylcholine concentration is linear in the range from 5.0 x 10(-7) mol L-1 to 5.0 x 10(-5) mol L-1 (r = 0.998) of paraoxon, with a relative estimated standard deviation (R.S.D.) of +/- 1.7% (n = 10) considering a solution containing 5.0 x 10(-6) mol L-1 of paraoxon and a solution containing 5.0 x 10(-3) mol L-1 of acetylcholine. Therefore, the quantitative limit detection is about 2.5 x 10(-7) of paraoxon (3 sigma). A 1,1'-trimethylene-bis(4-formylpyridinium bromide)dioxime (TMB-4) solution was used to reactivate the enzyme.     

A spectrophotometric determination of europium in lanthanide and other mixtures by use of Methylene Blue

A spectrophotometric determination of 0.1-1 mg of europium in a lanthanide(III) mixture is described. Europium(III) is selectively reduced in a Jones reductor and the europium(II) allowed to react with a measured excess of Methylene Blue (MB) solution. The dye is reduced to the colourless leuco form according to the equation, MB + 2 Eu(II)-->leuco MB + 2 Eu(III) and the excess of MB is determined spectrophotometrically at 664 nm. Optimum conditions are discussed and various applications presented.     

Adsorbed resin phase spectrophotometric determination of vanillin or/and its derivatives

The reactive mechanism, stability and interrelating properties, and thermodynamic constants of β-cyclodextrin polymer (β-CDP) including vanillin, 4-hydroxybenzaldehyde and piperonal were investigated. The effects of pH, temperature, time and solvent concentration on the inclusion reaction were determined. The optimum conditions were determined (pH, 3.0; temperature, normal atmospheric temperature; time, 90 min; ethanol concentration, <1%). The method was applied for the direct ultraviolet solid phase spectrophotometric determination of vanillin in peanut toffee and toffee, and the other aromatic aldehydes using β-CDP adsorbed resin with satisfactory results. The β-CDP resin has less background absorbance in ultraviolet region compared to other ion-exchanger resins.     

Flow-injection spectrophotometric determination of cyanate in bioremediation processes by use of immobilised inducible cyanase

A new flow injection (FI) method for photometric monitoring of cyanate in bioremediation processes using immobilised native cyanase is described. The method is based on the catalytic reaction between cyanate and bicarbonate to produce ammonia and carbon dioxide in the presence of an inducible native cyanase, immobilised in a reactor packed with glass beads. Two degrees of purification of the biocatalyst were used-heated cell-free extract and purified extract of cyanase from Pseudomonas pseudoalcaligenes CECT 5344. The ammonia produced by the enzymatic reaction is finally monitored photometrically at 700 nm using a modification of the conventional Berthelot method. The method furnishes different calibration curves depending on the degree of purification of the cyanase, with linear ranges between 1.23 and 616.50 micromol L(-1) ( r(2)=0.9979, n=7) and between 1.07 and 308.25 micro mol L(-1) ( r(2)= 0.9992, n=7) for the heated cell-free extract and the purified cyanase extract, respectively. No statistically significant differences between the samples were found in the precision study evaluated at two cyanate concentration levels using one-way analysis of variance. A sampling frequency of 15 h(-1) was achieved. The method was used to monitor cyanate consumption in a cyanate bioremediation tank inoculated with Pseudomonas pseudoalcaligenes CECT 5344 strain. The correlation between cyanate degradation and ammonia production was tested using a conventional method. Finally, the method was applied to different samples collected from the bioremediation tank using the standard addition method; recoveries between 85.9 and 97.4% were obtained.     

Flow-injection spectrophotometric determination of sulfadiazine and sulfamethoxazole in pharmaceuticals and urine.

A rapid and sensitive flow-injection spectrophotometric method is proposed for the determination of sulfadiazine and sulfamethoxazole. This method is based on the diazotization of sulfonamide with sodium nitrite, and a coupling reaction of the diazo-compound with alpha-naphthylamine. The optimum experimental conditions are obtained by using the controlled and weighted centroid simplex method. The linear ranges for the determination of sulfadiazine and sulfamethoxazole are 0.2-20 microg ml(-1) and 0.1-20 microg ml(-1), and their detection limits are 0.06 microg ml(-1) and 0.05 microg ml(-1), respectively, and the sampling frequency is 130 samples per hour. The method has been used to determine sulfadiazine and sulfamethoxazole in pharmaceuticals and urine without separation. The results are in agreement with those obtained by a high-performance liquid chromatograph technique at the 95% confidence level.