Figure 3. Correspondence of results obtained with the column RIA procedure and the dextran-coated charcoal method patients on digitoxin therapy is immunologically indistinguishable from the digitoxin in the standards. In other words, the antibody recognizes the digitoxin in clinical specimens and standards as identical. As shown in Table II, acceptable results were obtained in a parallelism study over a sixfold range of dilution. These data indicate that various components in the serum, including potentially cross reacting materials, do not interfere in the test.

Clinical research (1-5) has established that neoplastic sarcomas and certain categories of carcinoma (lung, breast, colon, etc.) (6) exhibit a pronounced tendency to sequester serum gallium citrate and other gallium salts. The metal's therapeutic effectiveness in regressing or arresting malignant growth-either as absorbed nonradiogallium ( 6 ) or as (principally) the 67 isotope used for in situ radiotherapy (2)-has prompted exploration of new benchtop analytical procedures ( 7 ) for the measurement of trace Ga which might speed up tissue assay efforts and aid in the eventual identification of the responsible biochemical mechanism.Were it not for the classically severe kinetic complications which are associated with the aqueous gallium electrode reaction (GER) (8)(9)(10)(11)(12), the electroanalysis of Ga(II1) a t trace and ultratrace concentration levels could be readily accomplished using a variety of acidified supporting electrolyte media. As described (10-14) in several earlier studies, the chemical composition of the electrolyte can play a catalytic role in moderating the actual charge transfer rate. For example, it has been found (IO) that a kinetically fast (Le., Nernstian) gallium electrode process is attainable a t the dropping mercury electrode (DME) if the supporting electrolyte is adjusted to satisfy two criteria simultaneously: 1) the presence of an inert salt at a very high ionic strength ( J ) ; and 2) the incorporation of >0.1 M SCN-(12) or NB-(13) (halides are also marginally effective a t extremely high J values of 1 1 3 M ( I d ) ] . A supporting electrolyte comprised of acidified NaSCN/G.OM NaC104 was successfully employed in three recent investigations in which trace levels of gallium, including gallium in ashed tissue, were measured by ac phase-selective anodic stripping (PSAS) procedures (15-177, and Demerie et al. employed essentially the same media as the basis for their pulse polarographic analysis of gallium in samples of gallium arsenide semiconductors (18). However, binary electrolytes of the above types-which to our knowledge are the only ones known so far to produce room temperature GER reversibility-can pose a variety of practical analytical difficulties ( 1 9 ) , due to the densely concentrated salts required, problems that could be substantially alleviated by discovery of milder electrolyte conditions. We wish to report in this note evidence that the degree of kinetic reversibility of the gallium electrode process exhibits a pronounced reciprocal dependence on ionic strength and temperature. Results obtained from single sweep alternating current phase-selective polarograms (PSP) show that a simple 30-OC increment in reaction temperature removes the historical necessity for densely concentrated inert salts and enables one to obtain a Nernstian voltammetric current readout from acidified NaSCN alone a t the 1.0-molar level (J = l), and an analytically useful peak in 0.1M NaSCN. EXPERIMENTALApparatus and Reagents. The apparatus and reagents used to obtain the phase-selective polarogr...

The room temperature thiocyanate-catalyzed phase-selective anodic stripping (PSAS) analysis of ultra trace amounts of gallium is not readily extendible to solutions containing organic fragments (e.g., samples of biological origin), and it is further compromised by the unavoidable electrolyte-induced injection of unwanted trace metal contaminants. To circumvent this, a revised approach to gallium PSAS analysis was evaluated which utilizes the recent polarographic discovery that a modest increase in reaction temperature eliminates the conventional need for a corequisite auxiliary salt. The high temperature PSAS peak current response to NaSCN vs. the more preferable NH4SCN electrolyte is discussed, and NH4SCN-based voltammetric results are reported for the effects of temperature, NH4SCN concentration, pH, frequency ( ) and amplitude ( ) of the applied ac signal, and deposition time ( ). The results of PSAS peak current vs. bulk Ga(lll) concentration, peak current reproducibility for 67.8 ppb Ga(lll), and standard addition experiments are tabulated, with the first two compared to accompanying differential pulse anodic stripping (DPAS) measurements on the same solutions. While our 1.0 M NH4SCN PSAS results at 60 °C indicated that Ga can be measured rapidly with fair precision down to 20 ppb, it is necessary to conclude from a comparative evaluation of the influences of , , , and pH for the room temperature vs. high temperature cases that the 60 °C procedure is experimentally somewhat less flexible and, at the present time, probably more suitable to specialized applications.Electroanalytical and electrochemical studies of the catalyzed reversible gallium electrode reaction (GER) have achieved the stage (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) where rapid and inexpensive anodic stripping methods [e.g., phase-selective anodic stripping (PSAS), or differential pulse anodic stripping (DPAS)] can be applied under special conditions for the analysis of samples containing trivalent gallium in the 1 to 10 parts-per-billion (ppb, or ng/g) range. Potentially useful areas for clinical application of these methods for rapid tissue

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