Flow-injection catalytic spectrophotometic determination of molybdenum(VI) in plants using bromate oxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine.

A novel flow-injection spectrophotometry has been developed for the determination of molybdenum(VI) at nanograms per milliliter levels. The method is based on the catalytic effect of molybdenum(VI) on the bromate oxidative coupling of p-hydrazinobenzenesulfonic acid with N-(1-naphthyl)ethylenediamine to form an azo dye (lambda(max)=530nm). Chromotropic acid (4,5-dihydroxy-2,7-naphthalenedisulfonic acid) acted as an effective activator for the molybdenum(VI)-catalyzed reaction and increased the sensitivity of the method. The reaction was monitored by measuring the change in absorbance of the dye produced. The proposed method allowed the determination of molybdenum(VI) in the range 1.0-20ngmL(-1) with sample throughput of 15h(-1). The limit of detection was 0.5ngmL(-1) and a relative standard deviation for 10ngmL(-1) molybdenum(VI) (n=10) was 2.5%. The interfering ions were eliminated by using the combination of a masking agent and on-line minicolumn packed with cation exchanger. The present method was successfully applied to the determination of molybdenum(VI) in plant foodstuffs.

Automatic microdistillation flow-injection system for the spectrophotometric determination of fluoride.

An automatic flow-injection (FI) system including on-line separation by microdistillation and spectrophotometric detection has been developed for the determination of trace amounts of fluoride. This ion was separated from sample matrix by distillation in the presence of sulfuric and phosphoric acids, and was subsequently determined with spectrophotometry based on the mixed-ligand complex of lanthanum(III)-fluoride-alizarin complexone. The proposed FI system has high sampling frequency (20 samplesh(-1)), small sample size (600 microl) and the dynamic range of 0.05-15 mgl(-1) with relative standard deviations of below 1.2%. Interfering ions such as aluminum(III) and iron(III) was effectively eliminated. The method was successfully applied to the determination of fluoride in industrial drainage after water treatment.

Flow-injection photometric determination of manganese(II) based on its catalysis of the periodate oxidation of N,N'-bis(2-hydroxy-3-sulfopropyl)tolidine.

A novel flow-injection spectrophotometric method has been developed for the determination of manganese(II) at sub-nanogram/ml levels. The method is based on its catalytic effect on the oxidation of N,N'-bis(2-hydroxy-3-sulfopropyl)tolidine (HSPT) by periodate. The catalytic effect of manganese(II) was enhanced by the presence of 2,2'-bipyridine as an activator. By monitoring the change in absorbance of the oxidation product of HSPT at 670nm, manganese(II) ranging 0.02-3.0ngml(-1) could be determined with the relative standard deviations of less than 2%. The interfering ions were effectively suppressed by the addition of 2,2'-iminodiethanol and citric acid. The proposed method is directly applicable to the determination of manganese in lake and river water samples.

Flow-injection simultaneous determination of selenium(IV) and selenium(IV + VI) using photooxidative coupling of p-hydrazinobensenesulfonic acid with N-(1-naphthyl)ethylenediamine.

A flow-injection spectrophotometric method has been developed for the simultaneous determination of selenium(IV) and (IV + VI) at nanogram per milliliter levels. It is based on the catalytic effect of selenium(IV) on the photooxidative coupling of p-hydrazinobenzenesulfonic acid (HBS) with N-(1-naphthyl)ethylenediamine (NED) to form an azo dye (lambda(max) = 538nm). In this reaction, bromide acted as an activator for the catalysis of selenium(IV) and an reducer for selenium(VI) to selenium(IV) in an acidic medium which allowed the determination of selenium(IV + VI). A sample solution, being split by Y-piece into two portions, passed through the low-temperature coil (4m, 25 degrees C) and the high-temperature coil (20m, 100 degrees C). By monitoring the absorbance of the dye produced in the two portions, selenium(IV) and (IV + VI) in the range of 0.2-6ngml(-1) were determined simultaneously. The relative standard deviations for 3ngml(-1) selenium(IV) and (VI) (n = 10) were 1.2 and 1.3%, respectively. There were few interfering ions in the selenium determination. The proposed method was applied to the determination of selenium(IV) and (VI) in natural water samples.

Flow-injection spectrophotometry of vanadium by catalysis of the bromate oxidation of N,N'-bis(2-hydroxyl-3-sulfopropyl)-tolidine.

A highly sensitive flow-injection method is proposed for the catalytic determination of vanadium(V) at sub-nanogram per milliliter levels using a new indicator reaction. The method is based on the catalytic effect of vanadium(V) on the bromate oxidation of N,N'-bis(2-hydroxyl-3-sulfopropyl)-tolidine. 1,2-Dihydroxybenzene-3,5-disulfonate was used as an activator in the vanadium(V)-catalyzed reaction and significantly enhanced the sensitivity of the method. Vanadium(V) in the range 0.01-3.0 ng ml(-1) was easily determined with sampling rate of about 30 h(-1). Vanadium(IV) could be also determined. The limit of detection (S/N=3) was 0.008 ng ml(-1) and the relative standard deviations were 1.4 and 1.6% for ten determinations of 0.2 ng ml(-1) vanadium(IV) and vanadium(V), respectively. Interferences from metal ions could be suppressed by the addition of ethylenediamine-N,N,N',N'-tetrakis(methylenephosphonic acid) as a masking agent. The proposed method was successfully applied to the determination of vanadium in water samples.

Flow-injection chemiluminescent determination of vanadium(IV) and total vanadium by means of catalysis on the periodate oxidation of purpurogallin.

A flow-injection chemiluminescent (CL) method is proposed for the successive determination of nanogram levels of vanadium(IV) and total vanadium. The method is based on the catalytic effect of vanadium(IV) on the oxidation of purpurogallin by periodate to produce light emission at 4 degrees C. The presence of hydrogen carbonate enhanced the light emission arising from the vanadium(IV)-catalyzed reaction. Since vanadium(V) did not catalyze the CL reaction of purpurogallin, vanadium(V) was determined after being reduced to vanadium(IV) by using an on-line silver-reducing column. Calibration curves for vanadium(IV) and (V) were linear in the range 0.1-10 ng ml(-1) with sampling rate of about 50 h(-1). The limit of detection for signal-to-noise ratio of 2 was 0.05 ng ml(-1) and the relative standard deviations were 1.4 and 1.6% for ten determinations of 2.0 ng ml(-1) vanadium(IV) and (V), respectively. Interferences from metal ions could be eliminated by the use of O,O'-bis(2-aminoethyl)ethyleneglycol- N,N,N',N'-tetraacetic acid and diphosphate as masking agents. The proposed method was successfully applied to the determination of vanadium(IV) and total vanadium in fresh water samples.