Kinetic investigation and the Arrhenius plot
The degradation of SAC in acidic, basic and oxidative mediums at different HCl (0.01, 0.05 and 0.1 M, keeping temperature 90 ºC), NaOH (0.005, 0.01 and 0.05 M, keeping temperature 40 ºC) and H2O2 (5%, 10% and 15%, keeping temperature 90 ºC) strengths was studied. Also SAC degradation was studied as a function of temperature in acidic (30, 60, 70, 90ºC and room temperature, keeping HCl strength 0.1M), basic (40, 65, 90ºC and room temperature, keeping NaOH strength 0.01M) and oxidative (50, 70, 90ºC and room temperature, keeping peroxide strength 15 %) mediums. The degradation processes were induced and observed using the proposed HPLC method by monitoring the decrease in drug concentration with increasing …show more content…
It is obvious that the change in the buffer pH changed the retention times of the drugs slightly (Fig. 2e), Furthermore, the pKa values for VAL are 3.9 for the carboxylic group, and 4.7 for the tetrazole-NH group while for SAC, 4.6 is its pKa [17], so the chosen pH should be away from the pKa values of the compounds of concern. At higher pH than 7, broad peak of VAL was obtained. So pH 3 is the optimum pH to be used during the study as reported in other literature for VAL[8-11] …show more content…
No difference was observed in retention time and symmetry of peaks by using different buffer concentration. Thus 25mM was chosen during our study.
Detection wavelength
With the aim of finding the best wavelength in order to quantify both VAL and SAC with high sensitivity and selectivity, the photo diode array detector (DAD) was set at 225 and 250 nm which represents the λmax of each of VAL and SAC respectively. Both VAL and SAC possess relatively higher response at wavelength 250 when compared to wavelength 225. At 225 nm only VAL has high response but SAC shows low response with low peak area recorded. So, 250 nm was chosen as the best wavelength for our study.
System suitability
The system suitability parameters were tested as an integral part of method development. According to FDA different parameters were calculated[18]. The values of capacity factor and theoretical plates were 1.50, 2.11 and 12667, 13649, for VAL and SAC, respectively. While asymmetry factor value was 0.82 for each drug. The selectivity and resolution were 1.24 and 5.97, respectively. Figure 3 shows the separation of VAL (at 4.5 min) and SAC (at 5.6 min) with suitable sharpness, resolution and peak
The degradation of SAC in acidic, basic and oxidative mediums at different HCl (0.01, 0.05 and 0.1 M, keeping temperature 90 ºC), NaOH (0.005, 0.01 and 0.05 M, keeping temperature 40 ºC) and H2O2 (5%, 10% and 15%, keeping temperature 90 ºC) strengths was studied. Also SAC degradation was studied as a function of temperature in acidic (30, 60, 70, 90ºC and room temperature, keeping HCl strength 0.1M), basic (40, 65, 90ºC and room temperature, keeping NaOH strength 0.01M) and oxidative (50, 70, 90ºC and room temperature, keeping peroxide strength 15 %) mediums. The degradation processes were induced and observed using the proposed HPLC method by monitoring the decrease in drug concentration with increasing …show more content…
It is obvious that the change in the buffer pH changed the retention times of the drugs slightly (Fig. 2e), Furthermore, the pKa values for VAL are 3.9 for the carboxylic group, and 4.7 for the tetrazole-NH group while for SAC, 4.6 is its pKa [17], so the chosen pH should be away from the pKa values of the compounds of concern. At higher pH than 7, broad peak of VAL was obtained. So pH 3 is the optimum pH to be used during the study as reported in other literature for VAL[8-11] …show more content…
No difference was observed in retention time and symmetry of peaks by using different buffer concentration. Thus 25mM was chosen during our study.
Detection wavelength
With the aim of finding the best wavelength in order to quantify both VAL and SAC with high sensitivity and selectivity, the photo diode array detector (DAD) was set at 225 and 250 nm which represents the λmax of each of VAL and SAC respectively. Both VAL and SAC possess relatively higher response at wavelength 250 when compared to wavelength 225. At 225 nm only VAL has high response but SAC shows low response with low peak area recorded. So, 250 nm was chosen as the best wavelength for our study.
System suitability
The system suitability parameters were tested as an integral part of method development. According to FDA different parameters were calculated[18]. The values of capacity factor and theoretical plates were 1.50, 2.11 and 12667, 13649, for VAL and SAC, respectively. While asymmetry factor value was 0.82 for each drug. The selectivity and resolution were 1.24 and 5.97, respectively. Figure 3 shows the separation of VAL (at 4.5 min) and SAC (at 5.6 min) with suitable sharpness, resolution and peak