Colorimetric determination of osmium (VI) with 1-naphthylamine-3,5,7-trisulfonic acid

An investigation has been made of the organic compound, 1-naphthylamine-3,5,7-trisulfonic acid, for use as a colorimetric reagent for the determination of trace quantities of osniiun(Vl). When this compound is added to an osmium (OsO₄^-2) solution, a violet colored organo-osmium complex is formed which has highest sensitivity at wavelength 560 mμ. The complex reaches maximum color intensity after four hours. The solution should be brought to pH 1.5 and maintained at tins pH with a buffer, after maximum color development. The colored complex conforms to Beer's law over an osmium concentration range of 0 to 6 p.p.m. Its absorbance is not affected by either excess reagent (up to a 7 : 1 ratio) or by temperature variation over the range 15° to 35° C. Many metallic ions interfere with the color reaction and hence require a separation, of osmium from these ions.The nature of the complex in solution was studied by the following three methods: (1) mole ratio, (2) continuous variations and (3) slope ratio. All three methods indicate a ratio of reagent to osmium of 2 to 1.A procedure for the colorimetric determination of osmium(VI) has been developed; it has a sensitivity of 1 part osmium in 15,000,000 parts of solution, with good precision.     

A new colorimetric reagent for molybdenum

Disodium-1,2-dihydroxybenzene-3,5-disulfonate (“Tiron”) gives a bright yellow color with molybdenum(VI). Under optimum conditions (wavelength 390 mμ and pH 6.6-7.5) the sensitivity of this reaction is about 1 part of molybdenum in 10,000,000 parts of solution, when measurements are made on a Beckman Model DU Spectrophotometer using a 1-cm cell.An extensive study on the use of Tiron for the determination of molybdenum in a variety of materials is under way.     

The spectrophotometric determination of molybdenum and uranium with quinalizarin

Quinalizarin reacts very sensitively with molybdenum and uranium to form colored chelates having λ_max at 520 and 630 nm, respectively. The molar ratio for both the chelates is 1:1 (metal:reagent). Optimum conditions including the range for adherence to Beer's law, effect of pH on color intensity, effect of excess of the reagent, sensitvity, and interference of the foreign ions has been reported for the photometric determination of these metal ions using quinalizarin, in 50% ethanolic medium and at 30 °C.     

Isophthaldihydroxamic acid as a spectrophotometric reagent for the determination of molybdate ion

Isophthaldihydroxamic acid produces colored solutions with molybdate ions in basic medium. The resultant product is extracted into a toluenic solution of trioctylmethylammonium chloride (Adogen). The yellow color obtained in the organic solvent (molar absorptivity 6.050 liters · mol⁻¹ · cm⁻¹ at a wavelength of 350 nm) has been used for the spectrophotometric determination of molybdenum in the range of 1.3 to 6 ppm with a relative error of the mean value of 1.3%.     

钼-水杨基荧光酮-溴化十六烷基三甲基铵显色反应的研究

在0.2-0.8/Ⅳ的盐酸介质中,钼(Ⅵ)与水杨基荧光酮以及溴化十六烷基三甲基铵,可以形成一红色三元络合物。络合物的最大吸收峰位于530纳米,表观摩尔吸光系数ε₅₃₀=1.40×10⁵。钼的浓度为0-8微克/25毫升时,络合物溶液的吸光度遵守比尔定律。三元络合物的组成经测定Mo:SAF:CTMAB=1:2:2。常见金属离子中,除钛与钨(Ⅵ)以外,均不干扰钼的测定。利用本显色反应,曾对多种合金钢中的钼含量进行了测定,取得了较好的效果。     

2,3,5,6-Tetrakis-(2'-pyridyl)-pyrazine as a colorimetric reagent for iron

The reactivity of the tridentate organic ligand, 2,3,5,6-tetrakis-(2'-pyridyl)-pyrazine, toward hydrogen ion and transition metal ions was investigated. The purple color of the bis-2,3,5,6-tetra-(2'-pyridyl)-pyrazine-iron(II) complex can be used in a colorimetric method for iron(II). The complex in aqueous solution exhibits a wavelength of maximum absorption at 575 mμ and a molar absorptivity of 19,800 in the pH range of 3.0–7.0. Beer's law is obeyed over the concentration range 5.0–100· 10^-6M. The perchlorate salt of the complex is extractable into chloroform and nitrobenzene with absorption maxima of 570 mμ and 573 mμ and molar absorptivities of 19,200 and 17,400, respectively. The effects of diverse ions and the results of determinations on selected samples are discussed.     

Spectrophotometric determination of molybdenum with phenylfluorone

Spectrophotometric studies on the reaction between molybdenum as molybdate (MoO₄^2?) and phenylfluorone are presented. The reaction conditions are optimized to develop an intense color (molar absorptivity is 3.8 × 10³) selective and sensitive for the Spectrophotometric determination of molybdenum. The absorbance is measured at 560 nm, at a pH of 1.5–3. The colored complex is stable for up to 24 hr, Beer's law is obeyed, over the concentration range of 1 to 4 μg/25 ml. The relative standard deviation is 2% and the sensitivity of the method is 1.60 × 10^?4 mg/ml.     

Chelate formation of ammonium aurintricarboxylate with bivalent copper : Micro-determination of copper by the colorimetric method

The formation of a coloured copper II chelate by ammonium aurintricarboxylate with λmax at 540 mμ may be utilised in the colorimetric determination of cupric ions on a micro-scale. It has been found that, for satisfactory results, at least a twentyfold molar excess of the reagent should be added. The colour intensity can be measured by using a spectrophotometer or a photoelectric colorimeter with a suitable filter.The colour is stable at room temperature for sufficiently long periods, but the intensity decreases above 30°C. For the formation of a colour suitable for measurement, the pH should be within 5.3–6.7. The smallest amount of copper that can be detected by the reagent is 1.7 p.p m. Details have been worked out for the use of this reagent, and the interference by various foreign ions has been noted and tolerance limits determined spectrophotometrically.     

Spectrophotometric determination of molybdenum with 8-mercaptoquinoline

8-Mercaptoquinoline was found to be sensitive for the colorimetric determination of molybdenum. A procedure is outlined in which the complex formed, Mo(C₉H₆NS)₂, is extracted into chloroform and the extinction measured at 425 mμ. The effects and removal of interfering ions are discussed.     

Spectrophotometric determination of osmium with 1-naphthylamine-4,6,8-trisulfonic acid

This investigation was undertaken to determine if the naphthylamine sulfonic acid-osmate (OsVI) reaction is suitable for a spectrophotometric determination of osmium. The 1-naphthylamine- 4, 6,8-trisulfonic acid osmate complex is water-soluble and forms a stable violet-colored system at PH 1 to 1.5 that is independent of reagent concentration. At 555 mμ the colored complex obeys Beer's law over a concentration range of 0.1 to 6.5 p.p.m. osmium and remains stable with respect to time and temperature. The effects of pH, temperature, reagent concentration, and diverse ions were studied. The nature of the organo-osmate complex in solution was studied by three techniques and the effect of temperature and pH on the rate of complex formation was determined. A procedure for the removal of osmium from all interfering ions was developed based on well known distillation techniques.A convenient, sensitive, reproducible and accurate method for the spectrophotometric determination of osmium has been developed.     

Spectrophotometric determination of vanadium (V) with 2-naphthohydroxamic acid

2-Naphthohydroxamic acid in methanol gives an intense and stable red-orange color with vanadium (V), sensitive to 0.009 μg V/cm², for log I₀/I = 0.001 abs. unit at wavelength 450 mμ. The value for σ is ±0.006 a.u., equivalent to ±0.08 p.p.m. V. The colored complex obeys Beer's law over the range 1–10 p.p.m. vanadium. The absorbance (in 1-cm cell) at 10 p.p.m. was so great that no data were obtained at higher concentrations. Under the conditions of the reaction, the combining ratio of vanadium and 2-naphthohydroxamic acid appears to be 1 to 2. Optimum conditions for the use of 2-naphthohydroxamic acid as a spectrophotometric reagent for vanadium-(V) were established; the procedure was applied to the determination of vanadium in steels and non-ferrous alloys with good precision and accuracy.     

Spectrophotometric determination of trace molybdenum in plants and seeds with 3,5-dibromo-4-hydroxyphenylflurone

A novel spectrophotometric method based on a new reagent, 3,5-dibromo-4-hydroxyphenylflurone, was developed for the determination of molybdenum in plants and seeds. 3,5-Dibromo-4-hydroxyphenylflurone showed outstanding analytical characteristics for spectrophotometric determination of molybdenum. The reaction conditions are simple and stable. In 0.2 mol l(-1) phosphoric acid medium (which can combine with iron and other metal ions and greatly improves the selectivity of the color system), molybdenum(VI) reacts with 3,5-dibromo-4-hydroxyphenylflurone to form a 1:2 red complex with an absorption maximum at 530 nm, the color reaction can completed in 2 min and the absorbance of the molybdenum complex remains stable for at least 72 h at room temperature. Its stability constant is 1.21 x 10(28) at 25 degrees C. Beer's law is obeyed over the range 0-0.6 microg ml(-1) Mo(VI). The reagent has very high sensitivity and selectivity; the molar absorptivity of the complex is 1.35 x 10(5) 1 mol(-1) cm(-1) and the limit of quantification, the limit of detection and relative standard deviation (n = 10) were found to be 6.7 ng ml(-1), 2.2 ng ml(-1) and 1.01%, respectively. Cu (50000-fold), Fe (20000-fold), K (20000-fold), NH4+ (20000-fold), Mg (15000-fold), Zn (10000-fold), Na (10000-fold), Al (4000-fold), Ca (25000-fold), Mn (2000-fold), Ce (500-fold), Cr (400-fold) and Bi (200-fold) do not interfere with the determination of trace levels of molybdenum up to the excesses indicated. The selectivity is much superior to that of other published methods. The proposed method was applied to the direct determination of molybdenum in plants and seeds with satisfactory results. The synthesis of the reagent and conditions of color reaction were studied in detail.     

n-Pentyl-2-pyridyl ketoxime as a selective colorimetric reagent for copper

n-Pentyl-2-pyridyl ketoxime hydrochloride has been prepared and examined as a colorimetric reagent for copper. It is less sensitive than some reagents, but shows a remarkable selectivity toward copper. The copper(I) -oxime compound can be extracted into isoamyl alcohol or into chloroform. In isoamyl alcohol the colored compound conforms to Beer's law in concentrations up to 5.6 · 10^-4M and has a molar absorptivity of 2650 at 360 mμ. A procedure for the colorimetric determination of copper is given and its reliability is shown.     

A solvent extraction study of molybdenum chloride and molybdenum thiocyanate complexes

The effect of reducing agents on molybdenum(VI) solutions in hydrochloric acid was studied by a solvent extraction technique to elucidate the composition of the colored molybdenum thiocyanate complex. Neither copper(I) chloride nor ascorbic acid have any effect on the extraction of MoO₂Cl₂; it is inferred that tin(II) chloride reduces Mo(VI) stepwise to a polynuclear Mo(V)·Mo(VI) complex and then to Mo(V). The colored thiocyanate complex produced by copper(I) and by ascorbic acid differs only slightly in extraction characteristics from the uncolored Mo(VI) complex. It is suggested that the color may be produced by an isomerization reaction of MoO₂(SCN)₂, and thus that the colored species may be a hexavalent rather than pentavalent molybdenum complex.     

Spectrophotometric determination of microgram amounts of platinum

2-Ethyl-10-[3-(dimethylamino-2-methyl)propyl]phenothiazine hydrochloride (ethylisobutrazine hydrochloride) forms an orange-red complex with platinum(IV) at room temperature (26 ± 2 °C) in hydrochloric acid-sodium acetate buffer medium containing copper(II) ions. The complexation is complete within 10 min. The complex exhibits an absorption maximum at 529 nm with a molar absorptivity of 1.90 × 10⁴ liters mol^?1 cm^?1. Beer's law is obeyed over the concentration range 0.4–7.8 ppm of platinum. A 50-fold molar excess of the chromogenic reagent is necessary for the development of maximum color intensity. Job's method of continuous variation, the molar-ratio method, and the slope-ratio method indicate a 1:1 composition for the complex. The effects of pH, time, temperature, reagent concentration, order of addition of reagents, and interference of various ions are reported. The reagent has also been used successfully for the determination of platinum in minerals and alloys.     

Spectrophotometric determination of molybdenum with 9-methyl-2,3,7-trihydroxy-6-fluorone

9-Methyl-2,3,7-trihydroxy-6-fluorone is proposed as a highly sensitive reagent for molybdenum. Thc rose-red complex shows maximum absorption at 510 mμ and obeys Beer's law from 0.2 to 3 p.p.m. of molybdenum, the optimum range being 08 to 3 p p m. where the percent relative analysis error is only 28. In solution the complex contains molybdenum and the reagent in the ratio 1:1. The instability constant of the complex is about 2.09·10^-6.     

Use of some new chelating agents for the colorimetric determination of iron: Ethylenediamine-bis-sulphosalicylaldehyde

Ethylenediamine-bis-sulphosalicylaldehyde, which gives strong violet-red coloration with. ferric salts owing to the formation of a stable metal chelate complex, Fe(C₈H₉O₄NS)Cl.H₂O, has been utilized for the colorimetric determination of ferric iron, using a Hilger-Spekker photoelectric absorptiomcter. The maximum intensity of absorption occurs at pH 2.8–5.5 in the green region (510–520 mμ) of the visible spectrum.The colour complex has been found to obey Beer's law between 0.25 and 10 p.p.m. The influences of several foreign, ions on the reaction have been carefully studied. The metal chelate complex has been isolated and its properties studied.     

Silver nanoparticles plasmon resonance-based method for the determination of uric acid in human plasma and urine samples

We have developed a simple and sensitive colorimetric procedure for the quantification of trace amounts of uric acid. It is based on the finding that uric acid in a medium containing ammonia and sodium hydroxide at 65?°C can reduce silver ions to form yellow silver nanoparticles (Ag NPs). These are stabilized in solution by using poly(vinyl alcohol) as a capping agent. The yellow color of the solution that results from the localized surface plasmon resonance of Ag NPs can be observed by the bare eye. The absorbance at 415?nm is proportional to the concentration of uric acid which therefore can be determined quantitatively. The calibration curve is linear in the concentration range from 10 to 200?nM, with a limit of detection of 3.3?nM. The method was successfully applied to the determination of uric acid in human plasma and urine samples.

Spectrophotometric determination of nitrite and nitrate using phosphomolybdenum blue complex

A method for spectrophotometric determination of nitrite and nitrate is described. This method is based on the reduction of phosphomolybdic acid to phosphomolybdenum blue complex by sodium sulfide. The obtained phosphomolybdenum blue complex is oxidized by the addition of nitrite and this causes a reduction in intensity of the blue color. The absolute decrease in the absorbance of the blue color or the rate of its decrease is found to be directly proportional to the amount of nitrite added. The absorbance of the phosphomolybdenum blue complex is monitored spectrophotometrically at 814 nm and related to the concentration of nitrite present. The effect of different factors such as acidity, stability of the complex, time, temperature, phosphate concentration, molybdenum concentration, sodium sulfide concentration and the tolerance amount of other ions have been reported. Maximum absorbance is at 814 nm. The range of linearity using the conventional method is 0.5-2.0 ppm with molar absorptivity of 1.1 x 10(4) l mol(-1) cm(-1). and a relative standard deviation of 2.6% for five measurements. The range of linearity using the reaction rate method is 0.2-3.6 ppm with a relative standard deviation of 2.4% for five measurements. The method is applied for determination of nitrite and nitrate in water, meat products and vegetables.     

The rapid colorimetric determination of molybdenum with dithiol in biological, geochemical and steel samples.

A rapid method for the determination of molybdenum in botanical, biological, geochemical and steel samples with dithiol, is described. Botanical and biological samples are ashed at 550 °C before leaching with 4 M hydrochloric acid, while geochemical samples are fused with potassium hydrogensulphate, and steels are decomposed with nitric and hydrochloric acids. The dithiol complex of molybdenum is formed by the addition of an alkaline solution of dithiol to the sample solution, and then extracted into isoamyl acetate. Ascorbic acid and citric acid are used to eliminate interferences from iron and tungsten, and the addition of potassium iodide gives the procedure very high tolerance to copper. Up to 150 geochemical samples or ashed botanical or biological samples can be analysed per man-day. Sensitivity of the method is 0.05, 0.5 and 10 p.p.m. for biological, geochemical and steel samples, respectively. The relative standard deviation is better than ±7% over the standard range used, and recovery of added molybdenum is complete.