Abstract: An improved kinetic assay is provided for spectrophotometrically determining the dissolved carbon dioxide (CO.sub.2) content of a body fluid (e.g., blood, plasma or serum), wherein at about pH 8.0 the CO.sub.2 is present substantially as bicarbonate ion (HCO.sub.3.sup.-). The assay sample is first subjected to a coupled reaction mixture containing phosphoenolpyruvate (PEP) and phospho-enolpyruvate carboxylase (PEPC) which enzymatically catalyzes conversion of HCO.sub.3.sup.- to oxaloacetate (OA). The OA produced is subjected to a second coupled reaction mixture containing nicotinamide adenine dinucleotide (NADH) and malate dehydrogenase (MDH) which thereby reduces the OA to malate and oxidizes the NADH to AND.sup.+. The CO.sub.2 level in the body fluid sample may indirectly be determined by spectrophotometrically measuring the change in NADH concentration.

Abstract: An improved kinetic assay is provided for spectrophotometrically determining the dissolved carbon dioxide (CO.sub.2) content of a body fluid (e.g., blood, plasma or serum), wherein at about pH 8.0 the CO.sub.2 is present substantially as bicarbonate ion (HCO.sub.3.sup.-). The assay sample is first subjected to a coupled reaction mixture containing phosphoenolpyruvate (PEP) and phosphoenolpyruvate carboxylase (PEPC) which enzymatically catalyzes conversion of HCO.sub.3.sup.- to oxaloacetate (OA). The OA produced is subjected to a second coupled reaction mixture containing nicotinamide adenine dinucleotide (NADH) and malate dehydrogenase (MDH) which thereby reduces the OA to malate and oxidizes the NADH to NAD.sup.+. The CO.sub.2 level in the body fluid sample may indirectly be determined by spectrophotometrically measuring the change in NADH concentration.

Abstract: An improved method of Kohlrausch-regulated electrophoresis (isotachophoresis) is disclosed for the preparative separation of respective macromolecular components such as proteins in a crude sample. The preferred method involves use of a substantially linear, polyethylene glycol derivatized trailing ion having a relatively high mass to charge ratio and a low mobility which is substantially independent of pH changes over a relatively broad pH range. The most preferred trailing ion is a polyethylene glycol dicarboxylic acid having a molecular weight of about 6,000-7,500, a pKa value of about 3.7, and a fully ionized mobility of about -1.3.times.10.sup.-5 cm..sup.2 /volt/sec. The method hereof permits large scale protein separations and subsequent collection of purified protein fractions over a wide range of pH conditions and without interfering reactions between the proteins and trailing ion.