Abstract: An optical detector circuit for a photometric instrument for providing a high precision, low cost A/D conversion of a detected optical signal. A sampled signal is integrated in a sample signal integrator while a reference signal integrator is integrated in a reference signal integrator. Using dual slope techniques, the integrated reference signal is provided as an input signal to the sample signal integrator during a de-integration cycle to provide a ratio of the detected signal to the reference signal, useful in nephelometers. An inverted blanking signal may also be integrated in the sample integrator prior to an integration of the sample signal to improve the accuracy of the dual slope integration. The period of integration is selected as a multiple of the primary sources of interfering noise such as power line and flourescent light frequencies.

Abstract: A method for detecting the presence of cystic fibrosis ciliostatic factor in mammalian body fluid comprisescontacting an enzyme whose activity is inhibited by the factor with a substrate for the enzyme in the presence of the body fluid, the substrate being substantially resistant to reactions catalyzed by enzymes in the body fluid, whereby the substrate is converted by the enzyme at a measurable rate, andcomparing the rate of substrate conversion with the rate of substrate conversion by the enzyme in the absence of cystic fibrosis ciliostatic factor.

Abstract: A method for assaying circulating immune complexes comprisescontacting the circulating immune complexes in solution in serum with a staphylococcal protein-A linked to a detectable label, whereby a CIC-protein-A-label complex is formed,selectively precipitating the CIC-SPA-label complex by contacting the complex with polyethylene glycol,separating the precipitated CIC-SPA-label complex from the serum,measuring the quantity of the label in the precipitated CIC-protein-A-label complexcomparing the measured quantity of label with at least one standard prepared by subjecting a solution containing a known amount of CIC or functional equivalent material to the same assay. The method requires only a single precipitation step and in a preferred embodiment the formation of the CIC-SPA-label complex may be formed in a single step.

Abstract: A maltodextrin phosphorylase limit dextrin in the presence of maltodextrin phosphorylase and inorganic phosphate, is used as a substrate for alpha-amylase, which initiates a series of enzymatic reactions resulting in a chromogen response which can be used to measure the concentration of alpha-amylase in a body fluid. A novel limit dextrin and its preparation also are described.