A sensitive spectrophotometric method for the determination of dithiocarbamate fungicide and its application in environmental samples

doi:10.1016/S0039-9140(97)00208-7

Talanta

Volume 45, Issue 6, April 1998, Pages 1097-1102

https://doi.org/10.1016/S0039-9140(97)00208-7 Get rights and content

Abstract

A sensitive spectrophotometric method based on the evolution of CS₂ and colour development by leuco crystal violet is described for the determination of dithiocarbamate fungicides, e.g. thiram, ziram and zineb. Dithiocarbamate fungicides release CS₂ on acid hydrolysis. This CS₂ is absorbed in ethanolic sodium hydroxide and forms xanthate. The xanthate formed is subsequently treated with potassium iodate and N-chlorosuccinimide, during which free iodine is liberated. Crystal violet dye was formed through selective oxidation of leuco crystal violet by liberated iodine, which has an absorbance maxima at 595 nm. The colour systems obey Beer's law in the range of 0.02–0.20, 0.02–0.24 and 0.04–0.32 ppm for thiram, ziram and zineb respectively. The molar absorptivity of the colour system were found to be 9.6×10⁵, 1.1×10⁶ and 6.8×10⁵±100 l mol⁻¹ cm⁻¹ for thiram, ziram and zineb respectively. The method has been successfully applied to the determination of these dithiocarbamate fungicides in various environmental samples.

Introduction

Thiram (bis-dimethyl thiocarbanoyl disulphide), ziram (zinc-dimethyl dithiocarbamate) and zineb (Zinc ethylene-1,2-bis-dithiocarbamate) are important and widely used fungicides. These are protective fungicides for use on seeds foliages, fruits and vegetable crops. These fungicides have chronic toxicity causing allergic infections to skin and asthmatic phenomena. Exposure to zineb can also cause functional changes in the cardiovascular system. The acute oral LD₅₀ value of thiram, ziram and zineb are 375, 1400 and 5200 mg kg⁻¹ respectively for rats 1, 2, 3.

Various instrumental methods have been reported for the determination of dithiocarbamate fungicides such as TLC [4], HPLC [5], GC [6], Polarography [7] etc. A few spectrophotometric methods are based on Clark's method [8] where dithiocarbamates are decomposed under acidic conditions to give carbon disulphide which is trapped in methyl potassium hydroxide to give potassium methyl xanthate, which is then titrated iodometrically. Petrascu 9, 10 and Rosenthal et al. [11] have modified Clark's method. Other methods 12, 13, 14, use toxic benzylmercaptan and metallic compounds and are less sensitive.

In the present communication a simple and sensitive method is proposed for the determination of thiram, ziram and zineb. The methodology involves the evolution of CS₂ from the above fungicides on acid hydrolysis. This CS₂ was absorbed in ethanolic NaOH and formed a pale yellow coloured xanthate. This xanthate is subsequently treated with potassium iodate and the iodine liberated is reacted with leuco crystal violet in the presence of N-chlorosuccinimide. The crystal violet dye formed showed maximum absorbance at 595 nm. This method has been applied to different environmental samples and its analytical parameters have been optimised. The method has been found to be more sensitive than other reported methods and is fairly reproducible.

Section snippets

Apparatus

A Systronics UV-vis spectrophotometer 108 with 2 cm matched silica cells was used for all spectral measurements. Systronics pH meter model 331 was used for pH measurements. The digestion–absorption apparatus is the same as described by Lowen and Pease [15].

Reagents

All reagents were of analytical reagent grade and double distilled deionised water was used throughout the experiment.

Stock solution of zineb (Indofil), ziram (Hindustan CIBA–Geigy) and thiram (Swarup)

1 mg ml⁻¹ solution of zineb in EDTA (0.1 mol l⁻¹), ziram in chloroform and of thiram in acetone were prepared. The required

Effect of temperature

Under the optimum conditions 30–35°C was the most suitable temperature for colour development.

Effect of time

It was found that 25 min. were necessary for complete colour development which was stable for several days.

Effect of pH

The pH of 4.0±0.1 was found to be the best for the formation of CV from LCV under optimum conditions. It was observed that pH above 5 severely affected the stability and sensitivity of the dye. Colour did not develop below pH 3.2. The pH was maintained at 4.0±0.1 by using phosphate buffer solution.

Conclusion

The present method for the determination of dithiocarbamates via CS₂ evaluation is simple, sensitive and fairly reproducible. The method is compared with the method reported by Verma et al. [14] using tetra-acetonitrilocopper(I) perchlorate and found to be more sensitive and selective and avoids the use of hazardous chemicals. This method is successfully applied to the determination of dithiocarbamate fungicides in the environmental and biological samples.

Acknowledgements

The authors are grateful to the Head, Department of Chemistry, Pt. Ravishankar Shukla University, Raipur for providing facilities. One of them (R.K.) is thankful to Pt. Ravishankar Shukla University for providing research scholarship.

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A sensitive spectrophotometric method for the determination of dithiocarbamate fungicide and its application in environmental samples

Abstract

Introduction

Section snippets

Apparatus

Reagents

Stock solution of zineb (Indofil), ziram (Hindustan CIBA–Geigy) and thiram (Swarup)

Effect of temperature

Effect of time

Effect of pH

Conclusion

Acknowledgements

J. Chromatogr.

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