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A N A L Y T I C A L CHEMISTRY, VOL. 50, NO. 1, JANUARY 1978
Comparison between Neutron Activation Analysis and Graphite Furnace Atomic Absorption Spectrometry for Trace Aluminum Determination in Biological Materials Kayhan Garmestani, Alan J. Blotcky," and Edward P. Rack General Medical Research, Veterans Administration Hospital, Omaha, Nebraska 68 105 and Department of Chemistry, University of Nebraska, Lincoln, Nebraska 68588
A simple and rapid method for the determination of trace aluminurhiin urine and bone using atomic absorption with graphite furnace atomization is described. Direct atomization of raw urine and nitric acid dissolved bone resulted in aluminum values that were systematically higher for bone and variable lor urine, as compared to a neutron activation analysis procedure. This was the result of calcium and phosphate interference of the aluminum signal. The optimum procedure involves digestion of bone or urine at 60 OC with concentrated nitric acid and a solution containing CaCI, and K2HP0, to negate the effects of varying calcium and phosphate contents in the samples. The residue was brought up to volume and injected into the graphite furnace. Detection limits (2a)of 20 ppb are reported. The precision of the method is 3 % RSD when measured at the 600-pg analytical level.
There has been increasing evidence in recent years indicating that aluminum is involved in human metabolism and disease ( 1 , 2). Currently in the literature there are several reported techniques involving destructive neutron activation analysis (3-6) and atomic absorption involving both direct injection of sample or preinjection wet chemistry (7-10) for t h e determination of aluminum in biological matrices. However, because of aluminum's ubiquity both in the environment and in reagents as well as its intractable chemical nature, there exists discrepancies among various reported values employing different techniques. For example, in the International Atomic Energy Agency 1976 intercomparison of trace elements in animal muscle ( I I ) , aluminum analyses were done by six laboratories, two of which used atomic absorption and the remaining four employed nondestructive neutron activation analysis. Values for these determinations ranged from 5-37.5 ppm. Currently there is no biological aluminum assayed Standard Reference Material available, such as bovine liver or orchard leaves, which can be used to test the validity of an analysis. As a result it was felt that an intercomparative study of two different techniques for determining trace aluminum in bone and urine must be carried out before definitive studies on the role of aluminum in metabolism and disease can be initiated. A need exists for the rapid determination of aluminum in biological specimens. Neutron activation analysis ( N U ) gives excellent results ( 3 ) ,but few people have access to a reactor. We have developed a method based on furnace atomic absorption (AA) which is in much more general use throughout t h e world. We compared an AA method, where nondigested raw urine and bone dissolved in nitric acid were introduced into the graphite furnace of the atomic absorption spectrometer, to our previously reported NAA procedure. From this study it was apparent that interfering ions affected the AA results. A study of the influence of these interfering ions on the aluminum absorbance led to a simple procedure for the rapid 0003-2700/78/0350-0144$01 0010
determination of aluminum in urine and in bone.
EXPERIMENTAL Acid Digestion Procedure. All glassware was thoroughly cleaned to remove traces of aluminum prior to analysis. Glassware was initially scrubbed with distilled water 10.02 pg Al/mL), then placed in Mallinckrodt 0.1 M hydrofluoric acid for at least 1 h, and then rinsed thoroughly with water (Fontenelle Springs Electrified Water, 0.01 pg Al/mL). A wet-ashing procedure was employed in digesting the urine specimens prior to analysis by neutron activation and destructive atomic absorption. No digestion procedure was employed in the nondestructive atomic absorption experiments. For the neutron activation analysis experiments, 10 mL of urine was placed in Vycor crucibles containing 10 mL of concentrated HN03 (Baker Ultrex 50.01 pg Al/mL). The crucibles were then placed on a sand bath and heated to
