ELECTROCHEMICAL ASSAY OF VARIOUS POLYMERIC PRODUCTS FOR PHTHALATE CONTENTS

Abstract

Phthalates are widely used as plasticizer in polymeric products, deodorants, nail polish, printer inks, insecticides, toys, PVC shower curtains, lubricants, food wraps, blood-bags, catheters, etc. They can disrupt endocrine functions and induce reproductive and developmental problems. Because of the ubiquity of phthalates and their potential role in increasing risk for cancer and reproductive dysfunction, there is an ever increasing demand for analytical methods suitable for their monitoring in various environmental and biological matrices. The present work addresses the development of four new polarographic and voltammetric methods for the determination of the mentioned toxic organic compound in polymeric products. In the first part of the study a faster, simpler and sensitive method was developed for determination of aliphatic phthalates using differential pulse polarography (DPP) as standard technique. The choice and concentration of base electrolyte, solvent, initial potential, effect of water addition and interference by other phthalates were the main parameters to optimize for enhancement of peak current and to obtain well-defined polarogram with lower background current using 1.3 x 10-4 mol L-1 dibutyl phthalate (DBP) solution. Best results were obtained in the presence of tetra methyl ammonium bromide (TMAB) as electrolyte in methanol solvent with initial potential, -1.4 V. A linear calibration plot was observed in the range of 3 x 10-7 – 1.6 x 10-4 mol L-1 DBP solution as model for aliphatic phthalates with lower detection limit of 5.9 x 10-8 mol L-1 and linear regression coefficient of 0.9987. The developed polarographic method was successfully applied for analysis of aliphatic phthalates in various samples of locally available polymer products such as baby toys, nipples, teethers, infusion blood bags and shopping bags. The results of the current method were compared with those obtained by a reported method and good agreement was found between them. A fast, simple and highly sensitive Square Wave Voltammetric (SWV) method was developed for determination of total water soluble phthalates using 95% dibutyl phthalate (DBP) as an example at glassy carbon electrode (GCE). The study showed that 100 μmol L-1 aqueous solution of DBP gives best response with 0.05 mol L-1 Tetra butyl ammonium bromide (TBAB), at stirring rate of 1400 rpm, deposition time, 20 s and pH value, 4.0±0.1. The optimum frequency and scan rate was 100 Hz and 0.9 V/s respectively. Voltammetric response was linear in 3 ranges, 70–110 μmol L-1, 20–60 μmol L-1 and 2–10 μmol L-1 with correlation coefficient of 0.9873, 0.9978 and 0.9935 respectively and limit of detection (LOD), 0.47 μmol L-1 for total water soluble phthalates in aqueous medium. The developed method was successfully applied for total phthalates determination in various samples of water stored in PVC coolers and plastic bottles. A new simple, fast and sensitive differential pulse voltammetric method was developed for the determination of different aliphatic phthalates. Dibutyl phthalate (DBP), diethyl phthalate (DEP), didecyl phthalate (DDP), and diallyl phthalate(DAP) can be determined in 0.1 mol L-1 TMAB methanol using a hanging mercury drop minielectrode and a meniscus modified silver solid amalgam electrode. Optimum conditions were found including concentration and composition of supporting electrolyte and solvent, scan rate, pulse amplitude, pulse width, etc.. Both peak potentials and peak heights of DEB, DBP, and DDP are similar suggesting the possibility to determine their mixture by measuring the total peak height of the mixture of these three substances and the DPV peak of DAP is shifted to less negative potential because of electron withdrawing effect of allyl substituent which, is in agreement with negative value of Hammett constant for allyl (σp = –0.14). The results showed that the peak potential of model mixture of these phthalates do not differ by more than ± 15 mV from peak potentials of individual phthalates and experimentally found peak heights corresponding to different model mixtures do not differ by more than 10 % (HMDmE) or 20 % (m-AgSAE) from the calculated sum corresponding to individual compounds present in the model mixtures. It was verified using model mixture containing different concentrations of DEP, DBP, and DDP (the total concentration being in the range 2–10x10-6 mol L-1 that an approximate estimation of the sum of above mentioned substances can be carried out with relative error around ± 20 % for HMDmE and ± 30 % for m-AgSAE, respectively. Due to the risk associated with mercury toxicity, there is an increasing trend among analytical chemists to replace mercury with some non toxic electrode materials. For this purposed new voltammetric method have been developed for the determination of aliphatic phthalate such as DBP, DEP, DDP, and DAP esters at newly synthesized silver amalgam paste electrode ( AgA–PE) Another simple, faster, and sensitive differential pulse voltammetric method was developed for the determination of different aliphatic phthalates such as DBP, DEP, DDP, and DAP in 0.1 mol L-1 TMAB in methanol solvent. Optimum conditions were found included concentration and composition of supporting electrolyte, methanol as solvent, scan rate, pulse amplitude, pulse width, etc. Linear calibration curves were obtained from 1 x 10-5 to 1 x 10-6 mol L-1 concentration range for different aliphatic phthalate esters. These newly investigated methods are more efficient, economical and sensitive for the analysis of the phthalic acid or phthalate esters in different media. Electroanalytical equipments are very economical and these newly developed methods can be adopted at domestic and industrial scale for continuous monitoring of these phthalates at trace levels in various polymeric products, plastic bottled waters, and cooler waters etc as for recommendations by WHO, EPA and other health / environmental organizations.