Determination of ascorbic acid in pharmaceutical dosage forms and urine by means of an oscillatory reaction system using the pulse perturbation technique
A simple and reliable method for the determination of ascorbic acid (AA) is proposed and validated. It is based on potentiometric monitoring of the concentration perturbations of an oscillatory reaction system in a stable nonequilibrium stationary state close to the bifurcation point. The response of the Bray–Liebhafsky (BL) oscillatory reaction as a matrix, to the perturbation by different concentrations of AA, is followed by a Pt electrode. The linear relationship between maximal potential shift and the logarithm of the amount of AA is obtained between 0.01 and 1.0 μmol. The sensitivity of the proposed method (as the limit of detection) is 0.009 μmol and the method has excellent sample throughput (30 samples per hour). The procedure was used for AA determination in pharmaceutical formulations and urine. The results are in agreement with those obtained using the official method. Some aspects of the possible mechanism of AA action on the BL oscillating chemical system are discussed.
Advances made by Belgrade's group in research of oscillatory reactions
Oscillatory dynamic states as one form of selforganization of nonlinear systems can be found in almost all sciences, like mechanics, physical chemistry or biomedicine. Although origin of these oscillations is different, computational challenges in modelling oscillatory phenomena remain similar in all fields. Since 1979 researchers from Belgrade’s group perform systematic examinations of oscillatory reactions. As stability of steady states is the central point in modelling oscillatory reactions, in last 10 years they have adapted and improved powerful tool of the Stoichiometric Network Analysis for this goal. Moreover, bifurcations of few types were identified in several models of oscillatory reactions. Even very complex chaotic motions in phase space were characterized and quantified by several numerical techniques. Multiple time scale behaviour is found within the core of the complex dynamic behaviour of mixed-mode oscillations. Analytical applications were developed, too.
STUDIES ON TERRESTRIAL CONTAMINANTS OF METEORITES
During t h e l a s t ha l f d e c a d e a n unpara l le led upsu rge h a s t aken p l ace in t h e s tudy of meteor i tes , e s p e c i a l l y t h e ca rbonaceous chondr i tes . S c i e n t i s t s from all ove r t h e world, employing t h e newes t a n d most s e n s i t i v e an a1 y t i c a l t ec hni q u e s , i n v e s t i g a t e t h e ch e m i c a l composition of t h e o rgan ic mate t ia l found in t h e s e meteor i tes . In t h i s way they a r e trying to de te rmine t h e phys ica l c o n s t a n t s of t h e meteor i tes and e s t a b l i s h , on t h e b a s i s of minera logica l and petrolog ica l s t u d i e s , t h e cha rac t e r i s t i c s of t h e environmental condi t ions f r o m which t h e s e s t o n e s or ig ina ted and to desc r ibe and ident i fy cer ta in mic ros t ruc tu res which abound in s o m e of t h e s e ca rbonaceous chondr i tes . A l l of t h e s e research i n t e r e s t s a r e d i rec ted towards o n e pa r t i cu la r problem, t h e def in i te so lu t ion of which may indeed have revolutionary e f f e c t s o n ou r c o n c e p t s of t he universe. T h e ques t ion is whether or not t h e s e meteor i tes conta in t r a c e s of ex t ra t e r r e s t r i a l l i fe , t hus proving tha t some kind of biota eve r e x i s t e d o ther t han on t h e ear th , o r if a l l of t h o s e f ea tu res tha t t end to subs t a n t i a t e t h e prev ious ly mentioned h y p o t h e s i s a r e only t h e r e s u l t of contaminat ion by te r res t r ia l matter. T h e impor tance of t h i s problem w a s emphas ized by Berna l (1961: 130) in t h e following way: “ T h e v i t a l ques t ion cou ld be s e t t l e d o n c e and for a l l if s p e c i f i c molecu le s s u c h a s porphyrins o r nuc leo t ides were found. A counter ind ica t ion a t t he moment is t h e extremely low phosphorous conten t of t h e meteorite.” S ince tha t s t a t emen t w a s made, porphyrins (Hodgson & Baker, 1964) a n d poss i b l y nuc leo t ides (Nagy et al., 1963a) have been ident i f ied f r o m t h e Orgueil meteor i te , but s t i l l t he q u e s t i o n of t h e e x i s t e n c e of extrat e r r e s t r i a l life is far from be ing proven. I t is clear from the a b o v e tha t o n e of t h e b a s i c problems tha t o n e faces in t h e s tudy of meteor i tes is tha t of contamination. In order t o e s t a b l i s h unques t ionably t h e e x i s t e n c e o r p a s t e x i s t e n c e of ex t ra te r res t r ia l l i f e through t h e s t u d i e s of meteor i tes , two primary q u e s t i o n s h a v e to b e dea l t with s imul taneous ly . O n e h a s to d e c i d e