Catalytic Spectrophotometric Determination of Vanadium in Seawaters Based on the Bromate Oxidative Coupling Reaction of Metol and 2,3,4-Trihydroxybenzoic Acid

Abstract

Vanadium in the hydrosphere was believed to be a conservative element due to its almost uniform distribution in both oceanic and limnetic areas. [1][2][3] However, slight seasonal variations with the depth of water might be encountered due to biological processes and/or the geochemical cycles of particulate vanadium and phosphorus. 4,5 Yet few methods have been reported for vanadium determination in seawaters, probably due to the complex matrices involved and/or the high salinity of such samples. Namely, 6,8,9 NAA, 10,11 AAS 12,13 and HPLC 14,15 methods were reported with typical detection limits of 0. 01 -0.04, 0.02 -0.30, 0.03 -0.80, 0.32 -0.51 and 0.03 -0.2 ng ml -1 , respectively. However, the relatively high instrumental costs [6][7][8][9][10][11] and the need for preconcentration, 6,7,14 chromatographic separation, 6,7,9 extraction 8,10,13,14 or coprecipitation 11 are common disadvantages. On the other hand, catalytic methods of analysis [16][17][18][19][20][21][22][23][24][25][26][27][28] that require simple and low-cost instrumentation usually offer enhanced sensitivities with typical detection limits of 0.1 -1.0 ng ml -1 . Of these methods, the gallic acid-persulfate standard method 19,20 and its modifications [21][22][23] can detect as low as 1 ng ml -1 of V V . However, due to its limited tolerability of chloride ions, the modified method 23 was applied to seawaters only after evaporating the sample in the presence of concentrated H2SO4/HClO4 mixture to remove the interfering chlorides. Therefore, the need for a simple, sensitive and selective method for application to seawaters is desirable.The present work describes, for the first time, the determination of V V and/or V IV down to 0.008 ng ml -1 based on its catalytic effect on the bromate-oxidative coupling reaction of metol with THBA. The simplicity, selectivity and enhanced sensitivity of the developed method allowed the analysis of natural and seawaters without any separation or preconcentration processes. Experimental ApparatusAbsorbance measurements were made on a pre-calibrated Shimadzu-1601 (Kyoto, Japan) double beam UV-Visible spectrophotometer equipped with a multi λ-photometric program pack and 10 mm matched cells. The cell compartment of the spectrophotometer was thermostatically controlled by circulating water from a PolyScience thermostated water bath (IL, USA) with a temperature stability of ±0.1˚C. Eppendorf vary-pipettes 10 -100 and 100 -1000 µl (Westbury, NY, USA) were used to deliver accurate volumes. A calibrated EDT Model GP 353, pH-mV meter equipped with an EDT combined glass electrode (EDT Instrument Ltd., Dover Kent, UK) was used for pH measurements with an accuracy of ±0.01. All glassware and storage bottles were soaked in 10% nitric acid overnight and thoroughly washed with fresh distilled, deionized water prior to use. ReagentsAll reagents were of analytical grade and were used as received. Fresh distilled, deionized water was used throughout.A stock standard solution of 1000 mg l -1 of V V was prepared 20 from NH4VO3 (Al...

Simultaneous Determination of Trace Iron and Aluminum by Catalytic Spectrophotometry Based on a Novel Oxidation Reaction of Xylene Cyanol FF

“…Various oxidants including periodate and hydrogen peroxide are widely used in catalytic spectrophotometry. 17,[20][21][22][23][24] To the best of our knowledge, however, most of the catalytic spectrophotometric methods reported so far used one oxidant only. Few methods in the presence of two oxidants have been reported.…”

A novel indicator reaction for the catalytic determination of V(V) at ppb levels by the kinetic spectrophotometric method

“…In comparison with most instrumental techniques that can usually be coupled with prior separation and preconcentration process, the present kinetic method is a new, simple, sensitive, selective and precise method for the vanadium determination in especially natural water samples down to 0.46 ng mL -1 using a simple spectrophotometer. On the other hand, among the numerous catalytic methods for vanadium determination only eleven methods [36][37][38][39][40][41][42][43][44][45][46] dealt with real samples, probably due to the limited sensitivity and/or selectivity of such methods. Table.4 shows the advantages and disadvantages of the present kinetic method.…”

Determination of iron and aluminum based on the catalytic effect on the reaction of xylene cyanol FF with hydrogen peroxide and potassium periodate

“…The catalytic spectrophotometric methods for determination of species are usually based on the reactions of a dye by various oxidants. 20,[23][24][25][26][27] However, in those catalytic spectrophotometric methods reported thus far, the oxidation reaction of dye was usually proceeded by one oxidant only. In this work, a catalytic spectrophotometric method based on the oxidation of xylene cyanol FF by double oxidants is presented.…”