Ascorbic acid reduction

Phosphorus and Silicon in Waters, Effluents and Sludges [e.g. Phosphorus in Waters, Effluents and Sludges by Spectrophotometry-phosphomolybdenum blue method. Phosphorus in Waters and Acidic Digests by Spectrophotometry-phosphovanadomolybdate method. Ion Chromatographic Methods for the Determination of Phosphorus Compound, Pretreatment Methods for Phosphorus Determinations, Determination of silicon by Spectrophotometric Determination of Molybdate Reactive Silicon-1 -amino-2-naphthol-4, sulphonic acid (ANSA) or Metol reduction methods or ascorbic acid reduction method. Pretreatment Methods to Convert Other Eorms of Silicon to Soluble Molybdate Reactive Silicon, Determination of Phosphorus and Silicon Emission Spectrophotometry], 1992... 

In the Murphy and Riley [85] method 10ml of demineralized water and 2ml of concentrated nitric acid were added to 0.15-0.2g of dry sediment (predried at 103°C) or plant material in a 100ml Erlenmeyer Flask. After a preliminary oxidation by evaporation of water and nitric acid on a hot plate, 2ml of concentrated perchloric acid were added, and the sample was boiled until clear. After cooling, the sample was diluted to 100 ml and an aliquot was withdrawn for orthophosphate determination by the ascorbic acid reduction method of Murphy and Riley [85]. Blanks and standards were treated as samples. 

An unusual reaction pattern has been found for the electrochemical and chemical (by ascorbic acid) reduction of the rhenium(II) thioether complex [Re(9S3)2] " (9S3 = 1,4,7-trithiacyclono-nane). Instead of the formation of the corresponding rhenium(I) complex, C bond cleavage and the release of ethene was observed and the brown rhenium(III) species [Re(9S3)(SC2H4SC2H4S)]" (250) was isolated as a BF4 salt. Lfpon electrochemical reduction of [Re(9S3)(SC2H4SC2H4S)]" further loss of ethene was observed while the analogous technetium complex can be reversibly reduced to [Tc(9S3)(SC2H4SC2H4S)]. 

The aquatic samples in 8 M HN03 are evaporated and the dry residue is dissolved in 20 mL 0.5 M HC1. After the addition of approximately 50 mg of ascorbic acid (reduction of Fe3+ to Fe2+), the solution is transferred to PTFE vessels equipped with a silver sheet bottom. Polonium is electrodepos-ited at 90°C for 4 h.34-36... 

FIG. 11 Ascorbic acid reduction in orange juice treated with various Echinacea extracts (1%) E. purpurea herb (EPH) and root (EPR), and E. angustifolia herb (EAH) and root (EAR). 

Monomers not commercially available were prepared by known methods 4,4 -bis(p-aminophenyl)-2,2 -bithiazole (22), 2,5-bis(p-aminophenyl )oxadiazole (22), N,NMbis( p-aminophenyl )isophthalamide (27), 2V,N -m-phenylenebis(m-aminobenzamide) (23), and 1,4-bis(p-amino-phenyl) butadiene (16). Cuprous chloride was obtained by ascorbic acid reduction of CuCl2 according to Stathis (26). 

Redox systems which have been the subject of recent examlnC atlon include potassiian permanganate - tartaric acid ( ), and potassium persulfate — ascorbic acid.( ) Whilst experiments were with the water soluble acrylamid they should be adaptable to emulsion conditions. The ascorbic acid reductant is of inters est as it is not interfered with by air or monomer stabilisers. 

The ascorbic acid reduction method of Murphy and Riley (18) can also be used for orthophosphate analyses in estuarine waters since hydrolysis of polyphosphates and salt effects are absent in this technique. 

Ascorbic acid reductant 1% m/v solution for cadmium and 2% m/v for lead, prepared by dissolving 0.5 or 1.0 g ascorbic acid in 50 ml 0.2 M aqueous potassium chloride solution containing 4 ml of 0.2 M hydrochloric acid. 

Figure 9.8. Decrease of the ESR signal intensity with time of different lipid nanoparticles during the ascorbic acid reduction assay. The lipid nanoparticles were stabilized with poloxamer 188 and labeled with tem-pol benzoate. With kind permission form Springer of Sciencefic Business Media Pharm. Res., Physicochemical Investigations on Solid Lipid Nanoparticles and on Oil-Loaded Solid Lipid Nanoparticles A Nuclear Magnetic Resonance and Electron Spin Resonance Study, 20, 1274-1283, (2003), K. Jores, W. Mehnert and K. Mader.

Negative interferences in the tin(II) chloride reduction method may also be caused by the presence of higher concentrations of iron(III), aluminum, calcium, and chloride [100]. The Fe, Al, and Ca interferences are presumably due to competitive complexation of the phosphate, while that for chloride is probably due to inhibition of the phosphomolybdate reduction. The chloride interference in this method is particularly problematic, especially for the determination of phosphate in marine and estuarine waters, and for this reason, the ascorbic acid reduction method of Murphy and Riley [83] is often favored. 

This is not problematic if the sample is digested in an open vessel, where the chlorine is boiled off. If digestion is performed in a closed vessel in a microwave oven or autoclave, the chlorine is trapped, and subsequently interferes in the detection process involving the ascorbic acid reduction step. This problem is readily avoided by introducing sodium sulfite into the reaction vessel [167]. 

Edward, T.U. David, M.F. and Rubio, F.J. Ascorbic acid reduction of residual active chlorine in potable water prior to halocarboxylate determination. Journal of Environmental Monitoring 2000, 2 (3), 253-256. 

Table 3.1. Rate Constants and Thermodynamic Parameters for Ascorbic Acid Reduction at 25°C... 

XiaohuiJi, Y.Q. Jing, J. Liu, H. Wu, H. Yang, W. Size Control Over Spherical Silver Nanoparticles by Ascorbic Acid Reduction. Colloid. Surf. A Physicochem. Eng. Aspects 2010,372,172. 

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