Determination of Pentachlorophenol in Environmental Samples by Spectrophotometry

Prashant Mundeja^1*, Manish Kumar Rai¹, Deepak Kumar Sahu¹, Kalpana Wani¹, Mamta Nirmal¹ and Joyce Rai²

¹School of Studies in Chemistry Pt. Ravishankar Shukla University, Raipur (Chhattisgarh), 492010, India

²Chhattisgarh Council of Science and Technology, Raipur (Chhattisgarh), 492007

*Corresponding author: prashantmundeja@gmail.com

[Received: 07 September 2019; Revised: 05 April 2021; Accepted: 13 April 2021]

Abstract. Pentachlorophenol (PCP) (2,3,4,5,6- pentachlorophenol) is an organochlorine compound used as a pesticide and a disinfectant. PCP is used as a herbicide, insecticide, fungicide and disinfectant.  Some applications include agricultural seeds (for nonfood uses), leather, masonry, wood preservation, cooling tower water, rope, and paper mills. Determination of Pentachlorophenol was based on the reaction of PCP with concentrated nitric acid followed by potassium iodide for the liberation of iodine. Liberated iodine reacted with leuco malachite green for the formation of green colour dye which was measured at 610 nm against a reagent blank. Parameters affecting the reaction were studied. The interfering effect of various species was also investigated and the methods were applied on some vegetables and fruit samples.

Keywords: Environmental samples, Leuco malachite green, Organochlorine, Pentachlorophenol, Spectrophotometry.

Introduction

Pentachlorophenol belongs to organochlorines group of pesticides which are considered as persistent organic pollutants (POPs). PCP functions as insecticide, herbicide, bactericide etc. PCP is used in pulp and paper industry, treating of cable coverings, controlling moulds in petroleum production and drilling etc. Examples of PCP include DDT, lindaane, dieldrin etc. Insecticides kill insects by disrupting insect’s nervous system (Ali et al., 2018, Yadav and Devi, 2017). They are also used as pest control universally (Liu et al., 2020). Inhalation of PCP causes vomiting, intestinal inflammation, loss of appetite, respiratory difficulties and coma. Several advanced technologies are developed for estimation of pesticide residues in variety of environmental samples such as GC–MS (Kolberg et al., 2011), GC-ECD and gas chromatography (Shinger et al., 2012, Mahdavian et al., 2010). These sophisticated instruments require maintenance, care and expertise, besides these are costly. To overcome all these drawbacks, alternative methods that are based on easy availability of reagents and equipments are being developed. One such method is use of spectrophotometer in analysis of pesticide discussed below.

Experimental Procedure

Apparatus

For all spectral measurements, A UV-VIS spectrophotometer (Systronic) model 104 with 1 cm matched quartz cell was used and a digital pH meter (Systronic) model 335 was used.

Reagents

A stock solution of Pentachlorophenol was prepared by dissolving 1 mg / ml PCP in water. 0.05% solution of LMG was prepared where 25 mg of LMG was dissolved in 100 ml of water and 1.5 ml of 85 % phosphoric acid and  further diluted by addition of  500 ml distill water.   13.6 g sodium acetate trihydrate was dissolved in 80 ml of  
 water for preparation of buffer.

Procedure

An aliquot consisting of 0.5 to 5 µg of pcp, two drops of concentrated nitric acid were added and warmed for 2 minutes till the appearance of yellow colour. Later 1 ml of potassium iodide, 0.5 ml of sodium acetate buffer and 1 ml of leuco malachite green was added and left for 10 minutes for development of green colour dye. Made up the volume up to the mark with water and analyzed the absorbance at 610 nm taking blank solution as reference.

Determination of Pentachlorophenol in Soil, Fruits and Vegetables

To the 5 g of soil sample, 20 ml of 0.3% sulfuric acid, 10 ml of 6 % m/v hydrogen peroxide and  glycerin 0.5ml was added and boiled at 160 – 180 ^o C for 20 min  and 2 ml of hydrogen peroxide was  again added and boiled for  another 10 minutes. To the mixture, 50 ml of deionized water was added. For determination of pentachlorophenol in different fruits and vegetables. The samples were weighed and mashed along with acetone de-ionized water (1:1) and strained using a thin cotton cloth and centrifuged at 1800 rpm for 10 min. 5 ml of sample aliquot were treated with proposed method.

Results and Discussion

                                       Concentration of Pentachlorophenol used was 2 μg / ml

Table 3.  Effect of Interference on the Determination PCP

*Tolerance limit is the amount of foreign species that causes an error of ±2% in absorbance value.

  The green coloured dye obtained showed maximum absorption at 610 nm. Beer’s law was obeyed over the concentration range of 0.5 – 5 µg of pentachlorophenol per 25 ml of the final solution. The molar absorptivity  and  sandell’s sensitivity obtained was 0.62 × 10⁶  L mol^-1 cm^-1 and 0.0053 × 10^-4 µg cm^-2  respectively. Standard deviation and relative standard deviation obtained was 0.0012 and 0.40 %  respectively. Absorbance value was  found to be maximum for  pH value 4 which  gradually decreased with increasing pH and sodium acetate buffer solution was needed to stabilize the color. It was observed that  for complete  development of colour 15 minutes were required. Study of effect of foreign species and pesticides to assess the validity of method was done. 2 µg of pentachlorophenol and analyzed by the proposed method. The method was  found to be free from interference (table 6.5). Maximum colour intensity was obtained by adding 1 ml LMG and no effect on absorbance was observed with  increasing volume of LMG. Therefore, no effect on the reaction was observed by excess of LMG. The proposed method was applied on the environmental samples. The amount of PCP found to be 1.80 in soil, 1.96 µg in rice, 2.20 µg in beans, 2.51 µg in potato, 1.43 µg in sugarcane. Gupta et al (1998) used a method  based on the reaction of pentachlorophenol with concentrated nitric acid to form chloranil, which liberates iodine from potassium iodide. Beer's law is obeyed over the concentration range of 0.1-1.6 micrograms pentachlorophenol/25 mL (0.004-0.064 ppm) at 592 nm.

Table 4. Determination of PCP in Environmental samples

Conclusion

This proposed method is found to be simple, sensitive, and rapid spectrophotometric method for the analysis of Pentachlorophenol. Also, it used less toxic substance as reagents for the analysis. This method can be considered as one of the good alternative to most of the high costing, delicate apparatus which need much more in maintenance. It can be very efficiently applied for the determination of pentachlorophenol in fruits and vegetables samples.

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