Abstract: A lithium ion-selective membrane that favors the bonding of lithium and depresses sodium interference is invented by a charge balance approach. A lithium ion-selective electrode (Li-ISE) having the membrane of this invention demonstrates a fast kinetic response, good precision and reproducibility, high sensitivity and the ability to retain the sensitivity after a long-term contact with biological samples. The sensor shows Nernst linearity with a slope of 55.4 mV for lithium ion concentrations between 0.5 &mgr;mol/L and 10 mmol/L. The membrane includes at least about 2% by weight of 6,6-dibenzyl-1,4,8,11 tetraoxacyclotetradecane ionophore; from about 0.025% to about 1% by weight of potassium tetrakis(4-chlorophenyl)borate additive; a plasticizer; and a polymeric material.

Abstract: An improved reagent combination of the type comprising a first solution comprising an aryl amine and an acid; and a second solution comprising a nitrite compound. The regent combination is characterized in that is further comprises a salt, wherein the salt is present in any preselected distribution in the solutions.Also, an improved method for colorimetrically determining bilirubin in a sample comprising mixing an aliquot of the above first solution with an aliquot of the above second solution to form a stable diazo reagent; contacting a sample to be assayed with a total bilirubin accelerator buffer system to form a prereaction medium; contacting the prereaction medium with the stable diazo reagent; and measuring the color of the azobilirubin formed form the coupling reaction of the stable diazo reagent with the bilirubin present in said sample.In addition, an improved method for producing a diazo reagent of the type comprising reacting an aryl amine with a nitrite compound in the presence of an acid.

Abstract: An albumin reagent of the type comprising bromcresol green, a buffering agent having a buffering capacity in the pH range of about 4 to about 4.2, and polyoxyethylene(23) lauryl ether. The albumin reagent is characterized in that it contains from about 0.18 to about 0.22 gm/l bromcresol green and has a polyoxyethylene(23) lauryl ether:bromcresol green weight ratio of from about 10:1 to about 12:1.