Zn Analysis by Atomic Absorption

Introduction

Zinc is obtained mainly from mineral ores such as smithsonite (ZnCO₃), sphalerite, or wurtzite (ZnS). Zinc is refined by calcinating the ore to form zinc oxide, which is then reduced with carbon (dry reduction method) or dissolved in sulfuric acid and subjected to electrolytic reduction (wet reduction method). Zinc is used primarily as corrosion-resistant plating. Corrugated iron is steel sheet plated in zinc, which has a higher ionization tendency than steel. Zinc-plated corrugated iron, as well as tin-plated sheet iron, is a commonly used material. Zinc is also widely used in alloys, such as brass, which is a zinc-copper alloy. The oxidation number of zinc compounds is normally limited to +2. Zinc oxides and hydroxides are amphoteric compounds that dissolve in both acids and alkalis. The applications of zinc compounds include the use of zinc oxide (ZnO) as a dye, pigment, and ink; and zinc in pharmaceuticals, such as zinc ointments with bactericidal properties. Zinc sulfide (ZnS) is used with copper as a fluorescent material in cathode-ray tubes that fluoresces yellow/green when irradiated by the electron beam. Zinc is an essential element that participates in various functions in organisms, including immunological actions, alcohol metabolism, and stabilizing biomembranes. Many enzymes and proteins containing zinc have been discovered, and their roles include 1) maintaining the protein structure, 2) fixing enzymes to the matrix during enzyme reactions, and 3) catalytic actions. Whereas iron and copper often participate in reduction reactions in organisms, zinc is often related to hydrolysis. Of the transition metals, the zinc content in the human body is second only to the iron content. The zinc content in a 70kg person is approximately 2g. About 50% of the zinc in the body is contained in the blood, 25% to 30% in the skin and bones, and the remainder in the pancreas, eyes, and sperm. The required daily intake of zinc is approximately 15mg and zinc deficiency leads to loss of sense of taste (ageusia) and skin diseases. As zinc tends to be deficient in the body, supplements and natural foods are now available in more and more stores. While excessive zinc consumption rarely causes problems, poisoning by zinc eluted from food cans is known to cause abdominal pains and nausea and the inhalation of zinc vapor from overheated zinc metal is known to cause fever and trembling. The analysis of zinc was originally conducted in the environmental field, including mains water and sewage, and is now widely used in the electroplating and metals, food, and pharmaceutical industries. This Application News introduces AA flame analysis of zinc in copper and AA furnace analysis of zinc in river water.

July 21, 2004 GMT