Improvements of conductivity measurements of electrolyte solutions using a new conductometric cell design.
A new conductometric cell design, for precise conductance measurements, has been developed and tested using aqueous lidocaine hydrochloride as a model system. A small portion of a stock solution in the conductivity cell is diluted stepwise by pure solvent. The resistance of the cell is measured by means of a precision conductance bridge. Contrary to conventional technique in precision conductometry, the temperature is allowed to change during the measurements and corrected to the desired standard temperature. The temperature is determined using a thermistor immersed in the cell solution, which is agitated during the entire experiment. Using this new approach, significant improvements over conventional conductivity technique were observed. The time required for the measurements was considerably reduced, by a factor of at least ten. The amounts, especially of costly drugs, required in the measurements are also reduced. The pK(a) value obtained, 7.28, is close to the previously reported conductometrically determined average, 7.18. The precision of the single conductivity value is equally high, if not higher, as that obtained using conventional conductivity technique.
Merclin
Nadia
N
Department of Pharmacy, Physical Pharmaceutical Chemistry, Uppsala Biomedical Center, Uppsala University, P.O. Box 580, 751 23 Uppsala, Sweden. nadia.merclin@farmaci.uu.se
Beronius
Per
P
D000779:Anesthetics, Local; D003217:Conductometry / Q000295:instrumentation / Q000379:methods*; D007478:Iontophoresis / Q000379:methods*; D008012:Lidocaine; D012996:Solutions
D000779:Anesthetics, Local; D012996:Solutions; D008012:Lidocaine