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Biomedical subjects

H A Dingjan

Publications and source records attributed to H A Dingjan.

5 recordsLinked to original sources
PubMed1987

Polarographic determination of extraction constants.

The extraction constant of three organic compounds containing nitrogen as a picrate ion pair in a water-chloroform system were determined by following polarographically the picrate concentration in the aqueous phase as a function of the added amount of reagent. The extraction constants were also determined spectrophotometrically (via batch extraction). The obtained results are in good agreement. The proposed method is applicable for extraction constants with values between 10(3) and 10(9).

Ions↗
PubMed1985

Generalized theory for two-phase ion-pair and complexometric titrations. I. Two-phase titrations without side reactions.

A systematic theoretical treatment of the two-phase titration based on ion-pair and metal-complex formation is presented. Equations for the titration curve, accuracy, equivalence point and choice of the indicator are derived. Much attention is paid to the parameters determining the 'titratability' viz. extraction constant, distribution constant, phase volume ratio and the concentration of the analyte. Special attention is given to the role of intermediate ion-pair and metal-complex formation in the aqueous phase. The ion-pair formation in aqueous solution is examined closer by means of the relationship between the association constant in water, the degree of dissociation of the ion pair (alpha) and the concentration of the counter ion. The merits of this theoretical treatment are illustrated with literature examples.

Chemical Phenomena↗
PubMed1985

Generalized theory for two-phase ion-pair and complexometric titrations. II. Two-phase titrations with side reactions.

For the two-phase titration based on ion-pair and metal-complex formation full attention is given to side reactions in both phases. Their significance for the applicability of this type of titration is evaluated. Side reactions in the aqueous phase diminish and in the organic phase promote the 'titratability'. Equations for the calculation of the side reaction coefficients, the titration curve and the selection of the optimal pH and minimal side reaction interference (in the aqueous phase) are presented. Finally a full description is given of the two-phase titration including all parameters determining the 'titratability'. The merits of the developed theory are illustrated by literature examples.

Chemical Phenomena↗
PubMed1983

Hydrolysis and determination of meprobamate.

Most pharmacopoeial methods for meprobamate are based on acid hydrolysis, followed by determination of the ammonia formed. In order to find optimum conditions the hydrolysis was studied with the aid of TLC. Various types and concentrations of acid were tested. Refluxing with 25% (wt/vol) HCl for two hours proved to be sufficient to achieve complete hydrolysis (99.4 +/- 1%). This method is less time-consuming than that of the European Pharmacopoeia and the hydrolysate does not turn brown as is the case with high concentrations of H2SO4.

Benzaldehydes↗