Spot applicator for quantitative thin-layer and paper chromatography, suitable for clinical analysis.

fluoride tubes, the absolute insulin values would be incorrect. The fact that blood collected in an oxalatefluoride tube is more severely hemolyzed is emphasized by the data in Figure 1 and Table 2. In the comparison of insulin and hemoglobin levels in two different plasma tubes, it is obvious that samples collected in tubes containing EDTA are more suitable for accurate insulin analysis than when oxalate-fluoride is used. The difference in measurable insulin concentration in these studies probably results from enzymatic degradation of the insulin molecule rather than an interference of hemoglobin in the assay. Brodal (1) has shown that the degradation of insulin solutions by red blood cell hemolysates is temperature -and pH-dependent, suggesting the involvement of the glutathione-dependent insulin-degrading enzyme known to be present in red cells. The conditions used with the Phadebas Insulin Test Kit (overnight incubation at room temperature) might afford an opportunity for enzymic insulin degradation if the necessary components were present. In summary, samples with clearly visible hemolysis should not be used for insulin determinations. Because use of the oxalate-fluoride Vacutainer tube (“graystoppered blood sugar tube”) almost always leads to a hemolyzed specimen, this kind of tube is unacceptable for insulin assay.