Rapid Photometric Determination of Copper in Ferrous Alloys. Use of Alpha-Benzoinoxime

Abstract

A direct colorimetric method for the determination of copper in plain and low-alloy steels and cast irons has been developed. A nitric acid solution of the steel is treated with Rochelle salt to complex iron and the pH is adjusted to 11.3 to 12.3 with sodium hydroxide. A solution of -benzoinoxime in sodium hydroxide is added and the green copper complex is extracted with chloroform.The color may be measured with a spectrophotometer or a filter photometer.The method is rapid and accurate.Three samples may be run in about 20 minutes, and the average error of a single determination is 0.005% copper.The only elements causing appreciable interference are nickel (above 2%) and cobalt (above 0.25%).AT THE present time, there is need for a simple rapid method for the determination of the small amounts of copper present in cast irons and steels. The reagent -benzoinoxime is relatively specific for copper and has been used as a gravimetric reagent. The present investigation has been directed towards determining the proper conditions for the use of a-benzoinoxime in the colorimetric determination of copper in iron and steel.Feigl (1) reported the use of -benzoinoxime as a reagent for copper in 1924. Kar (3) and Silverman (4) reported its use for the gravimetric determination of copper in steels. Although Feigl had stated previously that -benzoinoxime was specific for copper, Jennings (#) reported that nickel, cobalt, platinum, and palladium also formed complexes with the reagent. REAGENTS AND EQUIPMENTAlpha-benzoinoxime (Eastman Kodak), 0.5% solution in 0.25 N sodium hydroxide. Sodium hydroxide, 10% in water. Rochelle salt, 300 grams in 500 ml. of water. Chloroform, reagent gra.de. Beckman spectrophotometer, Model DU. Klett-Summerson filter photometer, with test-tube attachment. Beckman pH meter, Model M. found necessary to remove them by filtration. The above procedure may be used without change.If the sample does not dissolve readily in the 1 to 2 nitric acid, a few drops of hydrochloric acid may be used to complete solution.The calibration curve was obtained by adding known amounts of a standard copper solution to 0.5-gram samples of Bureau of Standards steel 22b. With the spectrophotometer, the curve was linear up to at least 0.21% copper, while with the filter photometer the curve tapered off above 0.15% copper.

Light Absorption Spectrometry

“…Examples of the application of absorptiometric methods to alloys are the green chromium-phosphate complex for chromium in 18-8steels (209), the green benzoin-a-oxime complex for copper in ferrous alloys (48), and the 1,10-phenanthroline complex for iron in high temperature alloys (148) and aluminum alloys (164). Various colorimetric methods are used for chromium, cobalt, molybdenum, tungsten, and vanadium in high-speed steel (116), and for molybdenum, nickel, silicon, and titanium in stainless steels (176).…”