3.2. Effect of pH and buffer solutions
The effect of pH on the GSK 1349572 of the products was studied using different pH values of HCl or NaOH that ranged from 2 to 12. As shown in Fig. 3, it was found that the products formed with maximum absorption when the final pH of the solutions was 8.40 for 1,6-diaminohexane and 6.02 for benzidine as examples from the studied amines after the addition of NaOH, and a decrease in absorbances was observed through the addition of HCl, which may be attributed to the liberation of hydrogen fluoride. Therefore, different buffers with the above optimum pH were prepared to examine the sensitivity. It was found that they have no effect on the colour intensity.
Figure 3. Effect of pH on the absorbance of DNFB product with (a) 10 μg/ml benzidine, (b) 2 μg/ml 1,6-diaminohexane.Figure optionsDownload full-size imageDownload as PowerPoint slide
3.3. Effect of base
Various bases, such as NaOH, KOH, Na2CO3, NaHCO3, NH4OH and CH3CO2Na were examined in order to obtain high sensitivity. It was found that these bases reduced the intensity of the aliphatic amine-DNFB products except of 1,6-diaminohexane which shows increasing colour intensity in the presence of NaOH. For the aromatic amines, it was found that NaHCO3 gave high intensity with benzidine and p-phenylenediamine and CH3CO2Na for m-aminophenol. The optimum amounts of these bases are cited in Table 4.