Determination of reducing carbonyl groups in cellulose in the solvent system LiCl/N,N-dimethylacetamide

Abstract

 The 2,3,5-triphenyltetrazolium chloride (TTC) method for the determination of reducing carbonyl groups in cellulose in water suspensions has been thoroughly evaluated. By reduction of TTC in alkaline medium, triphenylformazane (formazane) is produced. It is thermally unstable and an unavoidable loss results in a relatively high detection limit for the determination of reducing carbonyl groups in most celluloses with a low content of such groups. Besides, oxidized cellulose is unstable in the alkaline media in which the reaction is performed. The determined content of reducing groups has also been shown to be affected by the amount of sample, indicating that absorption of triphenylformazane takes place. A new method for determination of reducing carbonyl groups in cellulose in homogeneous medium has been developed. Cellulose is dissolved in the solvent system LiCl/N,N-dimethylacetamide and reacts with TTC in the presence of tert-butylamine at 75 ^°C for 10 min and formazane is subsequently determined spectrophotometrically at 524 nm. None of the systematic errors inherent in the “aqueous” suspension method can be defined. The new procedure is also more reproducible and has a lower detection limit of 7 nmol reducing groups in a given mass of sample. The two procedures have been tested on five differently oxidised cellulose samples and the difference in the determinations are discussed.