Na Analysis by Atomic Absorption

Introduction

The sodium’s crustal abundance is the 6th largest following the elements oxygen, silicon, aluminum, iron and calcium, and it exists mainly in such forms as rock salt (NaCl), Chile saltpeter (NaNO₃) and natural soda (Na₂CO₃). Furthermore, the salt content in seawater is about 34g/L, and after the chlorine ion, the sodium ion is present in the next highest quantity at about 11g/L. Metallic sodium is obtained from electrolysis of a salt solution mixture of sodium chloride (NaCl) and calcium chloride. Sodium is an extremely soft metal having a silver color, and after silver, copper and gold, has great electrical conductivity. In addition, sodium is highly reactive, reacting violently with water to generate heat and hydrogen gas, and produce sodium hydroxide (NaOH). When heated in air above its melting point, it ignites and is converted to the light- yellow colored sodium peroxide (Na2O₂). Under high temperature and high pressure, it further reacts to form white colored superoxide (NaO₂). Sodium possesses a strong reducing characteristic, and this is utilized to produce margarine by adding hydrogen to the carbon double bond in vegetable oil. Further, it has a low melting point allowing its easy conversion to the liquid state, and with its high heat conductivity and other characteristics, it is used as a coolant for removing heat from nuclear reactor. Various useful salts can be made from sodium. For example, sodium hydroxide is used in such chemical industrial fields as paper and pulp, soap, etc. In the case of sodium hydroxide, since it is deliquescent, allowing it easily absorb moisture, it must be handled with care. Sodium bicarbonate (NaHCO₃) is used for such products as neutralizing agents and stomach antacids as well as baking soda and baking powder, etc. Sodium chloride, beyond its use as a seasoning, is used as a raw material for producing sodium hydroxide, sodium carbonate as well as metallic sodium. Concerning sodium in living organisms, potassium is present in greater quantities in plants than sodium, however, in animals, sodium exists in greater quantities. In humans, sodium is present at about the rate of 1.5g/kg, and of that, 0.9g/100mL is present in blood, in which it plays roles in maintaining the shape of red blood cells and maintaining intracellular ion balance. Analysis of sodium is conducted for environmental applications as well as nutrition- related applications for the food industry. Further, because sodium is so prevalent in the environment, it is widely analyzed as an index of environmental pollution in the semiconductor and electronic materials fields.

October 19, 2004 GMT