**1. Introduction**

Metals possess higher density, atomic numbers are considered as heavy metals. They are part of the ecosystem present in the form of minerals and also in the elemental form. Heavy metal ions [HMIs] are proved to be toxic to humans, animals and even to plants as they accumulate to form stable compounds. Over a period of exposure or accumulation to HMIs lead to serious health issues with respect to [w.r.t.] skin, neurological system, kidney etc. [1]. HMIs toxicity and its adverse effects are magnified due to the human activities such as mining, rigorous industrial activities adding HMIs to the various ecological system. Once it happens then animals and humans are prone to HMIs that is really disaster. Considering these facts seriously world health organization and environmental protection agency set the permissible levels for the HMIs in various samples [2]. Above that level that particular sample is not fit for usage or consumption. In this scenario there is a pressing need for the analytical methods through which the exact quantity of the HMI[s]

can be measured. There is a scope for the analysis of HMIs in the wide variety of samples such as water, air, food, and biological samples etc.

It is well known fact that, there exist efficient methods either individual or coupled with detection techniques for the quantification of HMIs. Atomic absorption spectroscopy, inductively coupled mass spectroscopy, inductively coupled atomic emission spectroscopy, Ion selective high-performance liquid chromatography etc. All the mentioned methods possess good linear range, sensitive down to ppb level concentration and accurate. At the same time, they are expensive, needs to be operated by skilled person, cannot be carried to field, and may require greater volume of sample. Hence, even today researchers are putting their efforts to develop analytical methods to overcome the mentioned shortcomings. There exist few techniques such as electrochemical, optical, methods based on electrical conductivity, refractive index etc. Compared to the earlier mentioned methods latter are less expensive, easy to handle and smaller in size. But there are few challenges with the latter mentioned methods such as sensitivity and selectivity. Thrust to achieve these goals is still alive, hence, one can witness lot of publications on the same topic. But, it does not mean that electrochemical, spectroscopic methods are failure. Researchers are striving to match the sensitivity and selectivity of the electrochemical and spectroscopic methods with that of earlier mentioned methods. Another improved aspect is the size. True size of both i.e. instrument and sample [volume] required for the analysis are significantly minimized. Naked eye sensing of heavy metal ions is made possible. Just addition of sample containing HMI to the reagent system in a culture tube results the color [change] that can be recognized with naked eyes. Moving a step ahead electrochemical and spectroscopic methods are miniaturized down to small paper strip. Paper based electrochemical and colorimetric methods are trending now. Important Analytical parameters for all the above discussed methods have been summarized with broader perspective in the **Table 1** for the comparison purpose [6, 7].


*\* EC-Electrochemical, SP -Spectrophotometric, SF-Spectrofluorimetric.*

*\*\*Classical Potentiostat and Spectrophotometers are miniaturized to portable and handy devises with customized facilities especially for the spot analysis [3–5].*

#### **Table 1.**

*Generalized comparison of the parameters of analytical significance of widely followed methods for HMIs quantification.*

*Electrochemical and Optical Methods for the Quantification of Lead and Other Heavy Metal… DOI: http://dx.doi.org/10.5772/intechopen.95085*

Because of this solid background HMIs quantification by electrochemical and optical methods will be a topic of interest for large group of readers. Keeping the beginners in mind discussion is focused on the fundamentals of electrochemical approaches, types of materials and strategies used for the quantification of HMIs by both electrochemical and optical methods. It must be noted that exhaustive literature citation is avoided because of the page limits and also to avoid the monotony.
