Evaluation of the Radiometer Ion Scanning System 820 for the analysis of lead in urine.

We have evaluated the application and performance characteristics of a system that utilizes potentiometric stripping analysis (PSA); an electrochemical technique recently proposed for use in the routine determination of lead in urine. Its advantages over current methods for urinary lead are its low cost and minimal requirements for sample pretreatment. We adapted the published procedure to enable the use of a single protocol over a wide lead concentration range (10-500 /~g/L), Using spiked urine pools, we found the precision and recovery to be acceptable for clinical usage over this range. A comparative study using Individual spiked patient urines demonstrated good correlation with a bismuth hydroxide coprecipitation/ atomic absorption (AA) procedure [Y (pg/L, PSA) = -11 Fg/L + 1.10X (ku3/L, AA); Sy.x = 32/~g/L; S a = 15 /~g/L; S b = 0.08, N = 22]. Approximately 10% of the randomly chosen urines in this study exhibit negative interferences with the PSA method. However, these interferences were readily recognizable when using a standard addition technique to obtain concentrations from analytical signals, and were resolvable following either dilution with dilute acid or addition of Triton X-100. While we consider the system's performance characteristics acceptable, the length of time required for each urine lead determination (approximately 40 minutes) is a notable limitation to the routine clinical adoption of the instrument in its current configuration. amalgamated on a mercury-coated glassy carbon electrode during a potentiostatic deposition step. The stripping step differs from that used in ASV in that the reduced metal is reoxidized chemically with mercuric ions, and not by a potential ramp. The stripping step is monitored potentiometrically and the stripping time is converted to metal concentration using a standard addition technique. It has recently been proposed that this highly sensitive and specific method could be used in the routine analysis for lead in urine (4). The two advantages of PSA over current clinical laboratory methods for urinary lead [spectrophotometry (dithizone), atomic absorption spectrophotometry and ASV] are the relatively inexpensive instrumentation, and the minimum requirements for sample pretreatment. With regard to the latter advantage, lead determinations by PSA can be made directly on acidified urine, even in the presence of ethylenediaminetetraacetic acid (EDTA) (4). Thus, extraction, acid digestion, or treatment with a metal exchange reagent appears to be unnecessary in PSA. With these potential advantages in mind, we have evaluated the application and performance characteristics of the Radiometer Ion Scanning System (ISS) 820 (London Company, Cleveland, Ohio) for the clinical determination of lead in urine. Using a modified protocol with urine pools containing added lead nitrate, we determined the precision and accuracy to be acceptable for medical usage. However, the cost advantage of the relatively inexpensive instrument is offset in the current design by the length of technologist time required for the analysis of each sample.