Determination of pentosan

N. Durust and M.E. Meyerhoff, Determination of pentosan polysulfate and its binding to polycationic species using polyion-sensitive membrane electrodes. Arm Chim. Acta 432, 253-260 (2001). 

A number of reagents give, with furfural, colored compounds which are useful for quantitative colorimetry. The reaction with aniline has been studied by Stillings and Browning, who were able to determine furfural at low concentrations even in the presence of appreciable amounts of methylfurfural and hydroxymethylfurfural. For further details on the determination of pentosans, the reader should consult the recent re dew by Browning. ... 

When an acid solution of phloroglucinol (Pt. 11) is added to furfural a black precipitate, known as a phloroglucid, is formed. From the weight of this phloroglucid we. may calculate, by empirical methods, the amount of furfural and, from this, the amount of pentose sugar with which we started, or also, the amount of pentosan.. This is the basis of the analytical method for the determination of pentosan compounds in plant materials. As the pentosans possess considerable nutritive... 

Pentosan Reagent.—With furfural (p. 853) it forms an insoluble greenish black phloroglucid compound. As pentosans (p. 338) yield furfural on boiling with hydrochloric acid, phloroglucinol is used as a reagent for the determination of the furfural obtained and from this the amount of pentosan is calculated empirically. This is the official method for determination of pentosans in food stuffs. 

The well known method of Tollens for the determination of pentosans by distillation with dilute hydrochloric or sulphuric acid, and precipitation of the resulting furfur-... 

One source of error in the determination of pentosans the distillation method of Tollens is due to the pro-... 

Pentoses and pentosans can be determined ) after conversion to polarographically active furfural in acidic media. Xylose, for example, is heated vsrith hydrochloric acid d — 1-06) for 2-3 hr at 160°C and, after cooUng, the wave in 0 2 M KOH is recorded. This method was used for the determination of pentosans in cellidose. )... 

The determination of the structure of a plant gum involves the establishment of its homogeneity, its equivalent weight, and rotation and its uronic acid and pentosan content by the well-known methods. The nature of the constituent sugars and the uronic acid are then determined, after hydrolysis of the gums, by ciystallization or by conversion into characteristic crystalline derivatives. As an example the hexose mannose may be identified as the free sugar or in the form of its anilide, methyl glycoside or phenylhydrazone. Autohydrolysis of the acid... 

Pentosans. This determination is made by Tollens and Kriiger s method, which is based on the transformation of pentosans into furfural by distillation with hydrochloric acid and on subsequent precipitation of the furfural with phloroglucinoL The analysis comprises, therefore, two distinct operations ... 

Volumetric methods for determination of furfural from pentosans in-... 

Pentosan and methylpentosan determinations are described in standard works. When these determinations are made on polyuronides, they are inaccurate and of restricted use in calculating the relative number of pentosan and methyl pentosan units per uronic acid unit. This is especially true when pentoses, methylpentoses and hexoses occur together in a polyuronide. 

Tappi standard T 223 outlines the procedure for pentosan analysis. Briefly, wood meal is boiled in 3.85 N HCl with some NaCl added. Furfural is generated and distilled into a collection flask. The furfural is determined colorimetrically with orcinol-iron(III) chloride reagent. Another method also generates furfural, and the furfural is determined gravimetrically by precipitation with 1,3,5-benzenetriol. These and other methods of pentosan analysis are described and discussed in Browning s book (36). 

With the sealed ampoule process used for their kinetic studies, Root, Saeman, Harris, and Neill [20] achieved fiirfiiral yields well in excess of 70 % at temperatures above 220 °C, whereas industrial furfural processes, operating at lower temperatures and featuring a continuous removal of the furfural by steam stripping, have typical yields below 60 %. By contrast, in analytical chemistry, at a proven yield of 100 % [21], the formation of furfural from xylose or pentosan is routinely used for the quantitative determination of these substances. It is of great importance to elaborate the reasons for this yield paradox . 

Pentosans in wood cellulose, estimation of, >8 Perchlorate in potassium nitrate, determination of, 2... 

PURITY OF TECHNICAL PRODUCTS Relatively little attention has been paid to the possibilities of utilizing polarography for the analysis of organic technical products. It must be mentioned that the scarcity of the published data is added to by the relative reluctance of industrial chemists to publish. The analysis of mixtures of amines, determination of nitrilotriacetie acid and other amines in technical ethylenediami-netetraacetic acid, and of pentoses and pentosans in cellulose have already been described in Chapter VI. A few other examples are given here. 

Pentosan was determined by the method of Dische and Borenfreund (28) on grains grown at Swift Current, 1981... 

The only pentosans which have been studied to any great extent are the xylans. These can be obtained from all lignified cell membranes by extraction with 5% sodium hydroxide solution after lipids, pectic materials etc. have been removed. The conditions necessary to avoid degradation during isolation have been outlined.2 Early structural determinations indicated that arabinose was present as a non-reducing end-group in a branched molecule which had a chain-length of 18-20 D-xylo-furanose residues.27 It has been shown recently, however, that the xylan from esparto holocellulose can be purified free of arabinose after several re-precipitations of the copper-complex.28... 

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