Calculating freezing point of NaH2PO4-K2HPO4 mixed electrolyte solution with semi-empirical hydration model / 药学学报

The methods for determination of freezing point include cooling curve cryoscopy and air humidity cryoscopy. These methods are usually influenced by many factors, such as instrumentation, environment and operators. Despite the numerous experimental methods, precise freezing point values are challenging to obtain due to time-consuming procedures, limited sample size and extensive manual work. In this study, a semi-empirical hydration model (SEHM) was developed to calculate freezing point of NaH2PO4-K2HPO4 mixed electrolyte solution. According to SEHM, the water activity of mixed electrolyte solution was calculated by molality of solutes. Then the freezing point of solution was calculated. The calculated results were compared with those obtained by cooling curve cryoscopy and air humidity cryoscopy. The results indicate that the SEHM calculations are comparable to the measurements of cooling curve cryoscopy and air humidity cryoscopy.

Air humidity solubility assay / 药学学报

Measurement of drug solubility is one of the key elements of compound characterization during the drug discovery and development process. A broad variety of solubility assay methods have been developed, including equilibrium method which requires analysis of the equilibrium composition and kinetic method which monitors the concentration of a compound dynamically at the time when a precipitate first appears or disappears in the solution. Despite the numerous experimental methods, precise drug solubility values are hard to obtain for time-consuming, sample size and manual work. In this article, we reported a new method, namely air humidity solubility assay, which measures the relative humidity of the air in equilibrium with the solution at a given temperature, and then calculates solubility from the relative humidity according to extended-non random two liquid (NRTL) model. NaCl was used as a model drug, and the solubility was measured at the temperature of 20-50℃. The results indicate that the solubility of NaCl determined with the new method is generally comparable to that determined by gravimetry that is reported in literature. The new method has a relative error of less than 2%. Although the accuracy is lower than that of gravimetry, air humidity solubility assay is more convenient, practical, operational and universal. This method provides a supplement to the existing methods.

Cross-validation of the osmotic pressure based on Pitzer model with air humidity osmometry at high concentration of ammonium sulfate solutions / 药学学报

The osmotic pressure of ammonium sulfate solutions has been measured by the well-established freezing point osmometry in dilute solutions and we recently reported air humidity osmometry in a much wider range of concentration. Air humidity osmometry cross-validated the theoretical calculations of osmotic pressure based on the Pitzer model at high concentrations by two one-sided test (TOST) of equivalence with multiple testing corrections, where no other experimental method could serve as a reference for comparison. Although more strict equivalence criteria were established between the measurements of freezing point osmometry and the calculations based on the Pitzer model at low concentration, air humidity osmometry is the only currently available osmometry applicable to high concentration, serves as an economic addition to standard osmometry.

Using extended Wilson model to study the relationship between critical relative humidity and solubility of electrolytes / 药学学报

Based on thermodynamic principle, the critical relative humidity of electrolytes is closely related to their solubility. The authors explored the relationship theoretically and calculated critical relative humidity of 21 electrolytes from their solubility in the light of Raoult's law and extended Wilson model. The results indicate that the critical relative humidity values calculated by Raoult's law can not accord with the reported ones and there is a systematic error in the high concentration range; while these calculated by extended Wilson model are comparable to the reported ones.

Stability of penicillin potassium with linear degradation programmed humidifying experiments / 药学学报

A linear degradation humidifying model for drug stability experiment is introduced. This new humidifying model is presented as: H(r) = -M1-ln {exp(- MH(r,0)) - [exp(-MH(r,0)) -exp(-MH(r-m)) t(m)-t}. Where H(r) is the relative humidity; t is the time; H(r,m) and t(m) are the final relative humidity and time of the experiment, respectively. M is humidifying constant used in the humidifying program. In the new programmed humidifying model, a linear relationship between the content function of drugs and the relative humidity is obtained, the degradation of drugs can be more uniform within different humidity ranges and the experimental results are more accurate than those in the reported linear humidifying model. The stability of penicillin potassium, as a solid state model, was investigated by the linear degradation programmed humidifying and the exponential heating experiments. The results indicated that the kinetic parameters obtained by the linear degradation programmed humidifying and the exponential heating models were significantly more precise than those obtained by the linear programmed humidifying and the reciprocal heating models.

Application of highly accurate nephelometric titration in the assaying of phenytoin sodium / 药学学报

<p><b>AIM</b>To determine phenytoin sodium by a highly accurate nephelometric titration.</p><p><b>METHODS</b>The titration operating conditions were optimized and the solubility product constant of phenytoin silver precipitation was determined.</p><p><b>RESULTS</b>The result of the titration is comparable to those of control experiments.</p><p><b>CONCLUSION</b>The proposed method has been found to be accurate, precise, specific, reproducible, and linear.</p>

Influence of light and temperature on the stability of procaine hydrochloride injection / 药学学报

<p><b>AIM</b>To study the influence of light and heat on the stability of procaine hydrochloride injection.</p><p><b>METHODS</b>Accelerated tests upon exposure to light at high temperatures were employed.</p><p><b>RESULTS</b>In experiments with either isothermal heating or exposure to light at high temperatures, the drug degradation rate obeys first-order kinetics. The total rate constant, ktotal, caused by both light and heat can be divided into two parts: ktotal = kdark + klight, where kdark and klight are the rate constants caused by heat and light, respectively. The klight can be expressed as klight = Alight x E x exp(-Ea,light/RT). Where E is the illuminance of light, Alight is an experimental constant related to light sources, and Ea,light is an experimental constant.</p><p><b>CONCLUSION</b>Because the form of klight is similar to the Arrhenius equation, it is suggested that Ea,light might be the observed activation energy of the rate-determining step of the subsequent processes of the photochemical reaction. This viewpoint is supported by the fact that the Ea,light is independent of light sources.</p>

Effect of programmed humidification and temperature on drug stability / 药学学报

<p><b>AIM</b>To simplify the study on the effect of relative humidity and temperature on drug stability.</p><p><b>METHODS</b>The stability of penicillin potassium as a model was studied with programmed humidifying and heating.</p><p><b>RESULTS</b>Results of our programmed humidifying and heating experiments are comparable to those of traditional experiment at constant humidity and temperature.</p><p><b>CONCLUSION</b>Programmed humidifying and heating experiments are applicable to drug stability study.</p>

Highly-accurate nephelometric titrimetry / 药学学报

<p><b>AIM</b>To indicate the titration end-point of precipitation reaction by measuring the relative intensity of the scattered light in the titrate for use in pharmaceutical analysis.</p><p><b>METHODS</b>A visible light-emitting diode (LED) was used as a light source and a photodiode was used as the optical detector. Light on the detector creates an electric current through the diode. With the addition of the titrant, the titrate became turbid and the intensity of the scattered light in the solution increased gradually. If the precipitation reaction proceeded the completion and the solubility of the precipitate was small enough, the intensity of the scattered light will reach maximum at the stoichiometric point; thus, the titration end-point can be indicated. The accuracy of nephelometric titrimetry was discussed theoretically and the titration of NaCl with AgNO3 was used as a model. To demonstrate the applicability of the new titrimetry in pharmaceutical analysis, phenytoin sodium and procaine hydrochloride were titrated with AgNO3 and NaOH solutions, respectively.</p><p><b>RESULTS</b>With our new titrator and nephelometric sensor, the accuracy and precision of our new titrimetry can be better than 0.2% under suitable conditions.</p><p><b>CONCLUSION</b>This new titrimetry can be used for pharmaceutical analysis.</p>

Effect of light and heat on the stability of furacilin aqueous solution / 药学学报

<p><b>AIM</b>To study the effect of both light and heat on the stability of furacilin aqueous solution and the probability of substituting for isothermal accelerated tests by nonisothermal accelerated tests upon exposure to light at high temperatures.</p><p><b>METHODS</b>The isothermal and nonisothermal accelerated tests were employed. The accelerated tests were proceeded in the dark and exposed to light at high temperature. Tungsten, ultraviolet and fluorescent lamps were employed in exposure tests.</p><p><b>RESULTS</b>The degradation of furacilin aqueous solution in isothermal heating experiments or the exposure experiments to light at high temperatures obeys zero-order kinetics. The total degradation rate constant k caused by both light and heat can be divided into two parts: k = kdark + klight, where kdark and klight are the degradation rate constant caused by heat and light, respectively. The klight can be expressed as klight = Alight.exp(-Ea,light/RT).E, where E is the illuminance of light; Alight and Ea,light are both experimental constants. The parameters obtained in nonisothermal accelerated tests were comparable to those obtained in classic isothermal accelerated tests.</p><p><b>CONCLUSION</b>Nonisothermal accelerated tests may substitute for isothermal accelerated tests during the study of the effects of both light and heat on the stability of drugs, in order to save time, labor and drugs.</p>