Al Analysis by Atomic Absorption

Introduction

Al is the third most abundant element found on the earth’s crust following O and Si, and is found in feldspar, cryolite, mica, and other mineral ores. Industrially speaking, Al is precipitated on cathode during the process of separating alumina (Al2O3) from bauxites (ores comprised of Al₂O₃, or Al(OH)3 and impurities) using carbon electrodes inside molten cryolite (Na3AlF6). Al has a silvery-white color and is lightweight. Its malleability makes it easy to process and thus is used in a variety of industries. Oxide-coated aluminum has superior anti-erosion and insulating properties, and often is used in capacitors. Because staining may be used to apply carbon coating, this aluminum is also used in decoration and construction. Because they are lightweight and strong, duralumin (Cu 4%, Mg 0.5%, Mn 0.5%) and other aluminum alloys are used in buildings, vehicles, airplanes, and machine parts. Like Zn, Al is an amphoteric metal, thus reactions with acids produce trivalent salts such as AlCl₃ and Al(NO₃)₃. Both Al₂O₃, an amphoteric oxide, and Al(OH)₃, an amphoteric hydrate, are insoluble in water but both are soluble in either hydrochloric acid or sodium hydrate solution. As Al(OH)₃ becomes a colloid that attaches ions or pollution to its surface at neutral region and then sinks, it often is used as a water purification agent. Al(OH)₃ is also used in antacids to neutralize stomach acid as well as in other pharmaceuticals. Not only does the ulcer drug Sucralfate (complex of Al and sucrose) work by binding with proteins in the stomach and intestinal membrane to protect affected areas, it also binds with pepsins to help control their effect on organs. Corundum, a natural hard alumina crystal is used as an abrasive on metals and glass. Blue corundum (including Fe and Ti oxides) and red corundum (including Cr oxides) are processed into sapphires and rubies respectively. Al salts include alum, which is used in chemical fertilizers and dyes. Alum is a MAl (SO₄)₂ ⋅12H₂O-type double salt that is formulated by mixing sulfuric aluminum with ammonia or alkali metal sulfates. Normally, alum means potassium aluminum alum, and K replaces M. With characteristics resembling those seen in trivalent metal ions, aluminum ions easily bind with transferrin, an iron-transporting protein, and it is believed that excessive amounts of aluminum in the body absorbs into the bones and muscles, resulting in brittle bones and muscular atrophy, or accumulate in the brain resulting in Alzheimer’s disease. In this issue, we explain the relation of the sensitivity between the graphite tube types and the addition of interference inhibitors and points of the tube selection through the example of furnace measurement of Al.

April 27, 2006 GMT