Solubility of Benzodiazepines in Polyethylene Glycol 200 + Water Mixtures at 303.2 K Page: 521

                                
Journal of Chemical & Engineering Data, Vol. 55, No. 1, 2010 521

0.10
0.08
0.06

0.04

0.02
0.00

0.10
0.08
0.06
0.04
0.02
0.00

0.0    0.1    0.2     0.3    0.4    0.5     0.6    0.7    0.8    0.9    1.0
Figure 2. Experimental mole fraction solubility (xsa) of A, chlordiazepoxide; *, diazepam; and 0, and lorazepam at various volume fractions of polyethylene
glycol 200 (cqi) in binary solvent mixtures and the corresponding computed solubilities using - - -, method I; and -, method II.

K. Our measured value for the solubility of diazepam in water
(0.194 mmolL-1 at 303.2 K) is larger than the published
solubility data of Loftsson and Hreinsdottir (0.14817
mmolL-1 at (295.15 to 297.15) K)12 and of Shyanfar et al.
(0.15 mmol*L-1 at 298.15 K)13 as expected. Published studies
were performed at slightly lower temperatures, and the sol-
ubility of crystalline materials increases with temperature as is
evident from this work. The solubility of the benzodiazepines
was predicted using numerical methods I and II. The experi-
mental and predicted solubilities of the drugs versus the volume
fraction of PEG 200 in the binary mixtures were plotted in
Figure 2. As shown in the figure, the Jouyban-Acree model
provides a very good mathematical description of the experi-
mental solubility data of drugs at all composition ranges of PEG
200. The predicted data by using the previously trained eq 2
agree reasonably well with the corresponding experimental
solubilities for chlordiazepoxide and diazepam and deviated
slightly for lorazepam in the PEG 200 rich area. This finding is
also supported by small MRD values between the back-
calculated and experimental solubility data.
The main limitation of eq 1 is that it should be trained for
each drug employing a minimum number of experimental data
in binary solvents. The predictive version of the model, i.e., eq
2, predicts the solubility values with reasonable MRD values.
To the best of our knowledge, there is no accurate model to
predict the solubility of drugs in monosolvents at various
temperatures; therefore, the experimental values of xT and xTY
should be used as input data to predict the solubilities in mixed
solvents. The predicted solubilities were compared with the
corresponding experimental data, and MRD values were com-
puted and listed in Table 3. Generally, the overall MRDs of
the Jouyban-Acree model reveal that its trained version for
PEG 400 + water mixtures is a robust model to predict the

Table 3. Numerical Values of Adjusted Parameters of Equation 1
for Each Drug and the Mean Relative Deviation (MRD) for the
Predicted Solubilities Using Various Numerical Methods and Their
Overall Values

drug
chlordiazepoxide
diazepam
lorazepam

Jo
320.53
209.22
227.17

J1      J2
-428.60 792.36
-257.60 604.27
106.96  760.30
overall:

method I
5.5
3.6
1.9
3.7

method II
8.7
19.1
27.1
18.3

solubility of drugs in PEG + water mixtures and could be used
for prediction purposes with a relative uncertainty of less than
19 %.
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