Spectrophotometric determination of ruthenium with 8-quinolinol

A spectrophotometric method is described for the determination of 2–80 μg of ruthenium. The method involves oxidation of ruthenium to ruthenate, addition of 8-quinolinol, adjustment of the pH to 4–6.5, digestion of the complex formed at 85° for 30 min, extraction with chloroform, and measurement of absorbance at 430 nm. Almost all other metals and excess of reagent are removed by washing the extract. About 98 % of ¹⁰⁶Ru tracer was recovered.     

Spectrophotometric determination of nitrite with p-nitroaniline and 2-methyl-8-quinolinol in hexadecyl-trimethylammonium bromide solution

Nitrite ion at low concentrations is determined spectrophotometrically by diazotization of p-nitroaniline and coupling of the diazonium salt with 2-methyl-8-quinolinol. The resulting dye is solubilized in hexadecyltrimethylammonium bromide micelles. The molar absorptivity is 4.72 × 10⁴ l mol^-1 cm^-1, and the Sandell sensitivity is 9.7 × 10^-4 μg cm^-2. Some interferences are reported, and preconcentration by evaporation is evaluated. The solubility of hexadecyltrimethylammonium bromide in water was determined as a function of temperature; the Krafft point is 19.6°C. Salting-in of the surfactant by potassium nitrate is described.     

A novel method for the spectrophotometric determination of nitrite in water

A rapid, simple, selective and sensitive method for the spectrophotometric determination of nitrite in water has been developed and optimum reaction conditions along with other analytical parameters have been evaluated. Nitrite reacts with barbituric acid in acidic solution to give the nitroso derivative, violuric acid. At analytical wavelength of 310 nm, Beer's law is obeyed over the concentration range 0.00–3.22 ppm of nitrite. The molar absorptivity is 15330 ± 259.7 (95%) with pooled standard deviation of 355.57 and R.S.D. of 2.32%. As well as the method is sensitive (2.99 × 10⁻³ μg NO₂ cm⁻²) and selective, it tolerates most of the potential interferents. It has been successfully applied to nitrite determination in natural waters by use of a calibration graph with determination limit of 1.66 μg NO₂ in 100 mL working solution corresponding to minimum 9.5 ppb NO₂–N in water samples. Lower concentrations of nitrite (3.0 μg NO₂/L sample) is precisely analyzed by using the method of dilution with sample, with R.S.D. of lower than 0.5%. The results were compared with standard N-(1-naphtyl)ethylenediamine dihydrochloride method and very good agreement between the data was observed. The method can easily be applied in the field.     

A rapid extractive spectrophotometric method for the determination of tin in canned foods with 5,7-dichloro-8-quinolinol

A rapid method for the spectrophotometric determination of tin in canned foods, based on formation of the binary Sn(IV)-5,7-dichloro-8-quinolinol complex and extraction into chloroform has been developed. The absorption maximum at 390nm ( = 1.26 x 10(4) l.mole(-1).cm(-1)) is used for the determination. Beer's law is obeyed up to 6mug of tin per ml. Organic matter is destroyed by digestion with acid. Potential interferences have been studied. The detection limit for tin is 2.5mg kg .     

Flow injection spectrophotometric determination of nitrite

4-Nitroaniline, which gives intensely yellow solution on dissolution in dilute hydrochloric acid, has been found to react with nitrite almost instantaneously in acidic medium yielding a colourless product that has been identified as 4-nitrophenyl diazo cation. The measurement of decrease in colour intensity suggested a new, simple and one-step reaction procedure that has been used for the reversed flow injection determination of 5microg-5 mg/l. NO(2)-N. The limit of detection has been found to be 2 microg/l. NO(2)-N. A number of species such as copper(II) and lead(II), which interfere in other spectrophotometric procedures, do not affect the results. The method has been applied to determine nitrite in natural waters when the %RSD was in the range 1.8-3.5%.     

Extractive spectrophotometric determination of nitrite in polluted waters

Nitrite is diazotised with p-nitroaniline in hydrochloric acid and coupled with 8-quinolinol in alkaline medium to give a purple azo dye (λ_max = 550 nm, ? = 3.88 × 10⁴ l mol^-1 cm^-1). Extraction of the dye into 3-methyl-1-butanol shifts the absorption maximum to 570 nm and improves the apparent molar absorptivity to 5.852 × 10⁴ l mol^-1 cm^-1. Beer's law is obeyed for 0.01–0.06 ppm nitrite. The Sandell sensitivity is 0.00078 μg cm^-2. The method is applicable to polluted waters.     

A spectrophotometric method for the determination of nitrite

Nitrite reacts with dichromate quantitatively under suitable conditions of temperature and acid concentration. A linear relationship was found to exist between nitrite concentration and the absorbance at 580 nm of the chromium (III) species produced. This was used to determine the nitrite. The influence of a number of ions on the determination of nitrite was investigated; up to 100-fold excess nitrate has no influence on the determination of nitrite.     

The spectrophotometric determination of chromium in sea water

The coprecipitation of chromium from sea water by several precipitates was examined. With hydrous iron(III) oxide a recovery of chromium of >99% was obtained within the pH range 7.0–9.0 at a chromium level of ca. 0.4 μg/l. Chromium was separated from iron by anion exchange and determined spectrophotometrically using diphenylcarbazide. The method showed a precision of ±0.02 μg Cr/1. Chromium occurs in sea water in the 3+ oxidation state.     

The solubilities of zinc complexes of 8-quinolinol and some derivatives of 8-quinolinol

The solubilities of bis-8-quinolinolo-zinc^II, bis-2-methyl-8-quinolinolo-zinc^II and bis-5 : 7-dibromo-S-quinolinolo-zinc^II have been measured over the pH range of 4.5 to 9 at ionic strengths of 0.114 and 0.230 and at 25° and 40°. A mathematical treatment of the results gave nearly constant solubility products only when a dissolved but undissociated molecule, in addition to all of the dissociated and partly dissociated species, was considered. The relative abundance of each species of molecule in solution has been calculated.     

Dapsone a new diazotizing reagent for the spectrophotometric determination of nitrite in waste and natural water samples

A new diazotizing reagent for the spectrophotometric determination of nitrite is described. The method is based on diazotization-coupling reaction between dapsone and phloroglucinol in hydrochloric acid medium. The reactions were conducted at room temperature, the molor absorptivity at 425 nm is 4.28 x 10(4) l mol-1cm-1 and was stable for 50 h. Beer's law was obeyed in the nitrite range of 0.008-1.0 microgram ml-1. Tolerance limits were tested for 33 species. The method has been found to be applicable for the determination of nitrite in natural and wastewater.     

Novel reactions for simple and sensitive spectrophotometric determination of nitrite

Nine spectrophotometric methods based on new reactions for the determination of tracer amounts of nitrite in environmental samples were developed. Replacement of toxic reagents was explored to attain the standards of clean chemistry. These methods utilize two classes of compounds namely; phenoxazines and sulphonamides, the well established drugs in the presence of limited amounts of hydrochloric acid. The methods were based on the oxidation of sulfanilamide (SAA), sulfadoxine (SDX) or sulfamethoxazole (SMX) by nitrite in hydrochloric acid medium and coupling with phenoxazine (PNZ), 2-chlorophenoxazine (CPN) or 2-trifluoromethylphenoxazine (TPN) which yielded red colored derivatives having an absorbance maximum in the range 530-540 nm and were stable for about 4 h. Beer's law was obeyed for nitrite in the concentration range 0.13-1.60 μg mL⁻¹. The reaction conditions and other important analytical parameters were optimized to enhance the sensitivity of the methods. Interference if any, by non-target ions was also investigated. The methods were applied determining nitrite in environmental samples. The performance of these methods were evaluated in terms of Student's t-test and variance ratio F-test to find out the significance of proposed methods over the reference spectrophotometric method.     

Simultaneous spectrophotometric determination of nitrite and nitrate by flow-injection analysis

An automatic direct spectrophotometric method for the simultaneous determination of nitrite and nitrate by flow-injection analysis has been developed. Nitrite reacts with 3-nitroaniline in the presence of hydrochloric acid (0.96-1.8 M HCl or pH 0.5-0.7) to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)-ethylenediamine dihydrochloride to form a stable purple azo dye, the absorbance of which is measured at 535 nm. Nitrate is reduced on-line to nitrite in a copper-coated cadmium column which is then treated with azo dye reagent and the absorbance due to the sum of nitrite and nitrate is measured; nitrate is determined from the difference in absorbance values. A copper column incorporated into the reaction manifold before the copperised cadmium column not only improves the long-term accuracy, but also extends the life time of the copperised cadmium column. Various analytical parameters, such as effect of acidity (pH), flow rate, sample size, dispersion coefficient, time, temperature, reagent concentration and interfering species, were studied. The calibration graphs were rectilinear for 0.1-3.5 mug ml(-1) of NO(3) and 10 ng ml(-1)-2.2mug ml(-1) of NO(2). The method is successfully applied to some food samples (meat, flour and cheese), environmental waters (inland and surface), beer and soil samples. Up to 30 samples can be analysed per hour with a relative precision of approximately 0.1-2%.     

Flow injection catalytic spectrophotometric simultaneous determination of nitrite and nitrate

A new flow injection catalytic spectrophotometric method is proposed for the simultaneous determination of nitrite and nitrate based on the catalytic effect of nitrite on the redox reaction between crystal violet and potassium bromate in phosphoric acid medium and nitrate being on-line reduced to nitrite with a cadmium-coated zinc reduction column. The redox reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of crystal violet at the maximum absorption wavelength of 610 nm. A technique of inserting a reduction column into sampling loop is adopted and the flow injection system produces a signal with a shoulder. The height of shoulder in the ascending part of the peak corresponds to the nitrite concentration and the maximum of the peak corresponds to nitrate plus nitrite. The detection limits are 0.3 ng ml⁻¹ for nitrite and 1.0 ng ml⁻¹ for the nitrate. Up to 32 samples can be analyzed per hour with a relative standard deviation of less than 2%. The method has been successfully applied for the simultaneous determination of nitrite and nitrate in natural waters.     

Sensitive spectrophotometric determination of nitrite in human saliva and rain water and of nitrogen dioxide in the atmosphere

A new simple, sensitive, and selective spectrophotometric method was developed for the determination of nitrite. The method is based on the reaction of nitrite with sulfathiazole in acidic medium to form a diazonium cation, which is subsequently coupled with N-(1-naphthyl)ethylenediamine dihydrochloride to form a highly stable, violet azo dye. The reaction product has an absorption maximum at 546 nm and obeys Beer's law over a nitrite range of 0.054-0.816 microg/mL. The molar absorptivity of the colored compound is 4.61 x 10(4) L/mol x cm). The detection limit is 12.1 microg/L. The relative standard deviation is 0.85% for 5 determinations of nitrite at 0.27 microg/mL. The reproducibility and validity of the proposed method are discussed in the present paper. The simplicity of the method is demonstrated by the high stability of the azo-dye product as well as the short time required for its complete formation in a reaction at room temperature without pH control or extra extraction. The sensitivity of the method is shown by the successful determination of nitrite in human saliva and rain water, and of nitrogen dioxide in the atmosphere. The results compare favorably with those obtained by the reference method. The selectivity of the method is indicated by its freedom from most interferences, even at high concentrations of nitrate (500 microg/mL).     

Extractive photometric determination of gallium with 8-quinolinol in layered crystals of bismuth telluride-estimation of the determination limit

A method for determining microgram amounts of gallium in milligram samples of layered monocrystals of the type A(V)(2)B(VI)(3) is described. For the separation of 1-5 mug of gallium(III) from a large excess of bismuth in a single extraction the recommended conditions are pH 3.6-4.2 (acetate buffer, V(aq) 40 ml), an adequate excess of 8-quinolinol for complete extraction and of thiosulphate for masking bismuth. The absorbance of a chloroform extract (V(org) = 10 ml) is measured at 392.5 nm in a 50-mm cell against a blank extract concurrently obtained with a solution of pure Bi(2)Te(3). Reference polycrystalline materials are used to check the precision and accuracy of the method. In routine analysis of layered monocrystals a relative standard deviation of 4-8% is to be expected for about 1 mug of gallium in the extraction system. Estimation of the limit of determination, based on two statistical models, is discussed with respect to the error of the method and the fluctuation of the blank.     

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.     

Extraction of ammonia and nitrite using modified magnetite iron oxide nanoparticles before spectrophotometric determination in different water samples

A new analytical approach was developed for the extraction and determination of ammonia and nitrite in environmental water samples involving magnetic solid-phase extraction (MSPE) with magnetite nanoparticles (MNPs) as the adsorbent. The procedure is based on the derivatisation of ammonia based on Berthelot reaction. The obtained indophenol dye was extracted using MSPE and determined spectrophotometrically at 655 ± 3 nm. Nitrite ion is determined after its reduction to ammonia in the presence of Zn/HCl. The main factors that affected the extraction efficiency were studied and optimised. The method gave calibration curves for ammonia with good linearity in the range 10–550 µg L^?1, and correlation coefficients (r) higher than 0.99. The detection and quantification limit was found to be 3.1 and 10.2 µg L^?1, respectively. The method showed good precision and accuracy, with intra- and inter-assay precisions of less than 6.6% at all concentrations. The recoveries ranged 89–105% and 88–105%, for ammonia and nitrite determination, respectively. The method was applied to the determination of the target analytes in real samples.