Sweat Residue Lab Report

1. Introduction

Redox reaction between fingerprint sweat residue and the surface of metals is a major factor that causes corrosion on metals due to the presence of chlorides ions in fingerprint sweat. With exposure to sweat residue, chemical reaction happened between the interaction of sweat residue and the metal surface, which causes the metal surface to oxides and eventually degraded.

Besides sweat, various controllable and uncontrollable factors, such as oxygen, moisture and environmental conditions are other factors that have an impact on how fast a metal corrodes. So, the aim of this discussion is to analyse the effects of sweat on metallic surfaces.

2. General Composition of Sweat

Perspiration discharges through the sweat glands of our fingertips is mainly made up of water, amino acids (Table 1), sebum (Table 2) and various minerals (Table 3).

Amino Acid Value of Abundance

Serine 100

Ornithine-Lysine 45

Alanine 30

Threonine 15

Valine 10

Glutamic acid 8

Phenylalanine 6

Tyrosine 5

Table 1. Relative abundance of amino acids in sweat.

Lipid Percentage

Glycerides 33

Fatty acids 30

Wax esters 22

Cholesterol esters 2

Cholesterol 2

Squalene 10

Table 2. Percentage of lipids in sweat.

Mineral Amount

Sodium 0.9 gram/litre

Potassium 0.2 gram/litre

Calcium 0.015 gram/litre

Magnesium 0.0013 gram/litre

Zinc

Sodium chloride consists of two ions, that are sodium ion (Na+) and chlorine ion (Cl-). Like sodium chloride, water also consists of two ions, that are hydrogen ion (H+) and hydroxyl ion (OH-). Hence, if metal compounds which are more reactive than hydrogen such as sodium or potassium are electrolyzed in water, hydrogen ion will be transferred towards the negative electrode (i.e. hydrogen ions get one electron) and hydrogen gas is formed. Whereas, chlorine ion will be moved towards the positive electrode (i.e. chloride ion lose an electron) to produce chlorine