Spectrophotometric Determination of Some Rare Earths and Yttrium with Alizarin Red S ROBERT W. RINEHART U. S.
Radiological Defense Laboratory, San Francisco 24, Calif.
Chemical and Dye Corp., were dissolved in water and made u p to 100 ml. Buffer. An aqueous solution iras made 2 5 in both acetic acid and ammonium acetate. Phenol Red Indicator. TWOhundred and twenty-five niilligrams of phenolsulfonphthalein were dissolved in water and made up to 1000 ml. Solut,ions for Adjusting Initial pH. Sodium hydroxide, 0.2&V, and hydrochloric acid, 0.03AY. Concentrated hydrochloric acid, C.P. Sodium hydroxide pellets, C.P. Water, distilled from alkaline permanganate in an all-glass still. Rare Earths and Yttrium
.4 method for determining microgram amounts of yttrium, lanthanum, praseodymium, neodymium, samarium, gadolinium, europium, and terbium prei iously separated from each other and from other interfering ions was developed to meet analytical requirements of certain field operations. Alizarin Red S in aqueous solution is added to an acetic acid-ammonium acetate buffered solution of the rare earth or j-ttrium and the absorbance at 550 mp is measured with a Beckman Model DU quartz spectrophotometer. The working range was found to be 10 to 120 y for the rare earths and 8 to 80 y for yttrium. iibsorption spectra for the Alizarin Red S-rare earth complexes were determined. The method represents a 100-fold increase in sensitivity over existing methods for determining rare earth and yttrium concentrations. Although nonspecific, it was particularly useful in conjunction with ion exchange techniques for separating the elements listed.
Purity',
a
A
TACK ( I ) first reported the analytical use of Alizarin Red S in the determination of aluminum. Many publications ( 2 , 4, 9, 11, 14, 17, 19, 20, 21, 2 3 ) on the use of Alizarin Red S as an analytical reagent have since agpeared and for the most part have dealt with aluminum and certain elements in Group IV. Kolthoff and Elmquist (20) reported the use of Alizarin Red S for determining small amounts of lanthanum, and Sandell (18) suggested that it might be used for determination of the raie earth elements. Spectrophotometric methods for praseodymium, neodymium, samarium, europium, and gadolinium utilizing their ionic absorbance require milligram amounts of the metals to attain precision (15, %'). Cerium can be determined spectrophotometrically in microgram quantities (,5, 13) and was not included in thi> work. Moeller and Jackson (16) separated neodymium by estracting the 5,7-dichloro-8-quinolinol chelate with chloroforn~ and determined the neodymium by measuring the absorbance of the chelate in chloroform a t 581.8 mp. Although this method was more sensitive than the methods involving the ionic absorbance, it was still too insensitive for the operations in question. Gravimetric methods are not suitable for the determination of microgram amounts of rare earths. Spectrographic techniques are specific and sensitive enough, but are of limited precision (3). A quantitative spectrophotometric procedure was desired for the determination of microgram amounts of lanthanum, praseodymium, neodymium, samarium, gadolinium, europium, terbium, and yttrium. These elements had been separated from each other on an ion exchange column and were free from interferingions (6-8,1.3). The work presented here makes use of the color produced when .4lizarin Red S in aqueous solution is added t o an acetate-buffered solution of a rare earth or yttrium. An attempt has been made to set up a general procedure for the rare earths mentioned. Because of the nonspecific nature of Alizarin Red S, the method is limited to the determination of essentially pure rare earths and yttrium.
Source YaOa Research Chemicals LanOs Research Chemicals' Research Chemicals: Prr011 NdaOs E. C . Botti SmaOs E. C. Botti Research Chemicals, EuiOa GdnOa Research Chemicals, TbaO? A . I
