The Ultramicro Determination of Salicylates in Biologic Fluids

A method for determining salicylates in ultramicro volumes of blood, spinal fluid, and urine has been investigated. This method combines the simplicity of one reagent for color development and deproteinization with a high degree of accuracy and precision. Apparent salicylate values in blood and spinal fluid of normal individ-uals are of the order of 0.7 mg./100 ml. The application of this method to analysis of capillary samples of blood would be of value in the treatment of salicylate poisoning in children and in the maintenance of therapeutic salicylate levels in pediatric practice. I N PEDIATRIC PRACTICE, a rapid and accurate method for determining blood salicylate levels from small blood samples can be very useful. Several methods for determining salicylates in blood and other biologic fluids have been described (1-4). These, however, require either elaborate, time-consuming techniques or rather large volumes of sample. A search of the literature revealed two methods (.5, 6) that might be adapted to an ultramicro scale and yet be simple, rapid and ac-curate. Natelson (5) has described a method that is ultramicro as well as simple and rapid. A modification of this method has been used for some time in this laboratory for semi-micro aliquots of sample. The main objection to this method lay in the high blanks (4-7 mg./100 ml.) encountered, which result in apparent blood salicy-late levels in untreated patients close to the therapeutic range (10-1