Estimation of Lead Content in Aqueous Solution Using pH-metric Method

Abstract

Lead estimation is widely used in environmental monitoring, industrial quality control, and public health protection. Conventional techniques for estimating lead concentrations, such as atomic absorption spectroscopy (AAS), inductively coupled plasma–optical emission spectroscopy (ICP–OES), inductively coupled plasma–mass spectrometry (ICP–MS), UV–visible spectrophotometry, and electrochemical methods, provide accuracy and sensitivity; however, these methods are relatively expensive. Furthermore, sample preparation for these methods requires the maintenance of high purity. Complexometric titration is another method for estimating lead content. However, its results may be less reliable because of parallax errors. The present work proposes a novel pH-metric technique for estimating lead content in a given lead sample solution. The method is based on the pH-metric titration of a lead nitrate solution using disodium hydrogen phosphate as the titrant. During titration, various chemical reactions occurring between plumbous ions (Pb²⁺) and hydrogen phosphate ions (HPO₄²⁻) are believed to be responsible for the continuous change in pH. The resulting pH curve shows four distinct regions. Initially, the pH decreases and then remains stable up to a certain volume of added titrant. This region is referred to as the stabilisation volume. The stabilisation volume is a characteristic parameter representing the volume of titrant over which the pH remains nearly constant. Experimental observations reveal that the stabilisation volume depends on the concentration of the titrant used. As the titrant concentration increases, the stabilisation volume decreases. Based on the observed pH profile during the titration process, possible chemical reaction mechanisms are proposed. A unique feature of this method is that the nature of the pH curve predicts the possible chemical reactions occurring during the titration process. This novel pH-metric approach does not require an external indicator and is believed to offer a promising alternative for lead estimation.