Simultaneous determination of sodium, potassium, chloride, urea nitrogen, and glucose from capillary blood.

I N RECENT REPORT5 (1-3) we have fully described a heat clot-extraction technic for the separation of low molecular weight, water-soluble constituemits of serum froni serum proteimis. The present communication outlines applicatiomi of thatmethod, to the simultaneous determination of sodium, potassium, chloride, glucose, and urea nitrogen from a single 0.1-ml. serum sample without the use of ultramicro technics. Established methods are employed for individual determinations with aliquots of a heat clot extract. To 0.10 ml. of serum in a 25by 1’OO-mni. test tube, add 1 drop of buffered urease suspension (2.0 ml. of M Tris-acetate buffer, pH 4.55 ± 0.05, and 0.10 ml. glycerol-urease extract [4]). Incubate for 10 mm. at 37#{176}, add 6 drops of absolute methanol, and place in a 60#{176} water bath for 4 mm. Gently overlay the resultant clot with 2.0 ml. of water, stopper, and place in a 37#{176} water bath for 60 miii. The extract represents a 1 :21 serum dilution. Glucose is measured with an acceptedl glucose oxidase method, using 0.20 ml. of extract (2). Chloride is measured by titration of 0.50 ml. of extract, after addition of 2 drops of 0.1SN i’iitric acid and 1 drop of 100 mg./100 ml. s-diphenylcarbazone, with a 0.30 gm./100 ml. mercuric nitrate solutiomi (5). Sodium and potassium are measured with a dilution of 0.50 ml. of extract to a volume suiting the flame photometer used. Urea nitrogen is measured by adding 0.30 ml. of extract to Nessler’s reagent (1) and immediately measuring the resultant color at 440 m. Table 1 shows that the averages of replicate determinations obtained