Copper analytical losses

Analytical electron microscopy permits structural and chemical analyses of catalyst areas nearly 1000 times smaller than those studied by conventional bulk analysis techniques. Quantitative x-ray analyses of bismuth molybdates are shown from lOnm diameter regions to better than 5% relative accuracy for the elements 61 and Mo. Digital x-ray images show qualitative 2-dimensional distributions of elements with a lateral spatial resolution of lOnm in supported Pd catalysts and ZSM-5 zeolites. Fine structure in CuLj 2 edges from electron energy loss spectroscopy indicate d>ether the copper is in the form of Cu metal or Cu oxide. These techniques should prove to be of great utility for the analysis of active phases, promoters, and poisons. 

For the recyclability of catalyst 1, after completion of the oxidation of 4-methoxybenzyl alcohol, the reaction mixmre was treated with water (3 mL), and the organic layer, after drying (Na2S04) and GC analysis, was passed through a short pad of silica gel using ethyl acetate and hexane as eluent to afford analytically pure 4-methoxybenzaldehyde in quantitative yield. Evaporation of the aqueous layer afforded the copper complex 1 that was subsequently reused for the oxidation of 4-methoxybenzyl alcohol up to three times using fresh TEMPO whereupon no loss of activity was observed. 

Losses from volatilization of the analyte can be minimized by restricting the temperature at which ashing takes place. For determination of lead, copper, zinc, cadmium, and iron in foodstuffs, for example, good recoveries of the analytes were obtained by heating the samples slowly to 450°C and holding this temperature for 1 hour. A collaborative study showed no significant losses of the analytes under these ashing conditions [94],... 

Type IB sorbents are chiral ligand exchangers. Several columns are commercially available with either proline, hydroxyproline, or valine and Cu(II) bonded to silica [256]. The binding is via a 3-glycidoxpropyl spacer Cu(II) needs to be added to the mobile phase to minimize the loss of copper from the sorbent. Silica modified by L-( + )-tartaric acid has also been synthesized. These columns generally have poor efficiency and analytes are limited to bidentate solutes [256]. 

The first requirement can be easily fulfilled by the preconcentration of the analyte before the analysis. Preconcentration has been applied to sample preparation for flame atomic absorption (25) and, more recently, for ICP (79,80) spectroscopy. However, preconcentration is not completely satisfactory, because of the increased analysis time (which may be critical in clinical analysis) and the increased chance of contamination or sample loss. Most important, however, a larger initial sample size is necessary. The apparent solution is a more sensitive technique. Table 2 lists concentrations of various metals in whole blood or serum (81,82) in comparison to limits of detection for the various atomic spectroscopy techniques. In many cases, especially for the toxic heavy metals, only flameless atomic absorption using a graphite furnace can provide the necessary sensitivity and accommodate a sample of only a few microliters (Table 1). The determination of therapeutic gold in urine and serum (83,84), chromium in serum (85), skin (86) and liver (87), copper in semen (88), arsenic in urine (89), manganese in animal tissues (90), and lead in blood (91) are but a few examples in analyses which have utilized the flameless atomic absorption technique. 

Guss et al (1988) measured data at four wavelengths about the copper K edge, i.e. 1.2359 A, 1.3771 A, 1.3790 A and 1.5416 A. Of particular note in the data reduction was the need for an empirical method for coincidence losses to be used, as the analytical dead time correction for the area detector was unreliable at the upper end of the range of counting rates. As a result, merging f -factors within the data set at each wavelength were reduced by 20-60%, for the empirical versus the analytical coincidence method of data correction. 

Several metal oxides (platinum, gold," nickel, copper, ) and cobalt phtalo-cyanine have been employed as surface bound mediators for carbohydrate detection. In a dc amperometric mode of operation detectors based on these mediators exhibit a significant loss of response with time and/or exposure to analyte. Various potential pulse programs have circumvented this stability problem, but at the expense of sensitivity and complexity of the instrumentation. Silver electrodes coated with electrogenerated silver oxide exhibit electrocatalytic activity with respect to carbohydrate oxidation. This paper describes our efforts to utilize an electrode as a carbohydrate detector in a dc amperometric mode. 

The analytical measurement of iron or other soluble metal content in the corrodent stream is another method directly related to metal loss. This technique can give poor results if the corrosion products are insoluble or adherent to the metal surface. If the method is used in a two-phase system, either both phases must be analyzed for metal ions, or particular care must be taken to put the dissolved metal into the aqueous phase. Quantitative measurements of dissolved metals are used frequently in acidic systems or in special cases where the corrosion products are known to be soluble. There are inexpensive colorimetric tests available for measuring iron, copper, and other metals in solution. 

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