PubMed · 14125121
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L R DRAPER, C R MENCKEN. 1964. AN AUTOMATIC PIPETTING MACHINE.. https://pubmed.ncbi.nlm.nih.gov/14125121/
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The technique of DGT (Diffusive Gradients in Thin Films) was further developed to allow simultaneous measurement of sulfide and trace metals at the same location in sediment. The new combined DGT probe consisted of a layer of gel impregnated with AgI, overlain by (1) a layer of gel containing Chelex, (2) a layer of gel and (3) a filter membrane. Diffusion of sulfide was controlled by layers (1) to (3), while diffusion of metals was controlled by layers (2) and (3). The Chelex gel trapped metals that were measured after elution with acid. The AgI gel trapped sulfide through the formation of Ag2S. This was then measured densitometrically as the colour changed from pale yellow to grey. Experiments demonstrated that concentrations of metal or sulfide measured by the combined device were no different to the concentrations measured by more conventional devices. The presence of Chelex in the gel did not impede the diffusion of sulfide. Deployment of a combined probe in marine sediment revealed simultaneous remobilisation of metals and sulfide at the same location. Solubility calculations indicated that some precipitation of amorphous FeS was probably occurring at the maxima in sulfide concentrations. There was general undersaturation with respect to NiS, but ZnS was supersaturated at all locations. There appeared to be localised active zones of organic matter decomposition, where reduction of manganese oxides, iron oxides and sulfate occurred simultaneously. Mass balance calculations indicated that Ni could not be supplied by release from decomposing organic matter. Manganese oxides were the most likely source, but supply from reductive dissolution of iron oxides could not be entirely discounted. Supply from either Fe or Mn oxides could account for the Zn maxima. Application of the newly developed combined probe provides new information that helps understanding of the complex nature of trace metal and sulfur chemistry in sediments.
In this work we report a sequential-injection (SI) analysis method for the direct determination of phosphate in urine with on-line dilution and photometric detection. The developed SI manifold incorporated an additional dilution coil (DC) connected to one of the ports of the selection valve. On-line dilution was performed by aspirating a zone of sample with volume V(S) from the sample line into the holding coil (HC), transferring volume V(T) of that zone into the DC, and, finally, aspirating a portion of V(T) with volume V(A) back into the HC. This dilution introduces an additional dispersion of the initial sample zone represented by the effective dispersion coefficient D(eff) which can be tailored to the desired value by appropriate selection of the volumes V(S), V(T), and V(A). Actual detection of phosphates was performed by the molybdenum blue method with detection at 690 nm. By employing an on-line dilution step with a D(eff)= 100, the calibration curve for phosphate was linear in the range 0.05 x 10(-2) to 3 x 10(-2) mol L(-1) which covers the actual phosphate concentration in urine samples. The regression coefficient was r2 = 0.996, the relative standard deviation was sr = 3.9% at the 1 x 10(-2) mol L(-1) level (n = 10), and the injection frequency was 30 injections h(-1). The method was applied to urine samples with recoveries > 97%.
A method for the direct determination of kinetic constants for phosphoglucomutase and its phosphorylated products is described. Fourier transform ion cyclotron resonance gas-phase ion/molecule reactions between trimethyl borate and glucose phosphate, phosphorylated at either the 1 or the 6 position, generate mass spectra distinguishable with regard to product ion distribution. A multicomponent quantification method is utilized to determine the composition of a binary mixture of the two positional isomers. Using this method, the conversion between glucose-1-phosphate and glucose-6-phosphate can be directly monitored without the use of coupling enzymes. The values of K(m) for glucose-1-phosphate and glucose-6-phosphate were determined using the substrate-velocity plot and the Haldane relationship, respectively. Values of V(max) for both the forward and the reverse directions were measured, and the equilibrium constant for the reversible reaction was determined using this methodology. Kinetic parameters measured correlate well with those obtained using traditional methods. The assay was demonstrated to be accurate and particularly convenient to determine kinetic constants for enzymatic systems that involve the interconversion of phosphorylated positional isomers.