Aspirin calibration curve

Assay of paracetamol and aspirin in tablets using a narrow range calibration curve... 

Analysis is carried out on tablets containing naproxen 100 mg and aspirin 250 mg per tablet. A narrow range calibration curve is constructed within 20% of the expected concentration of the diluted tablet extract. UV monitoring of the column effluent is carried out at 278 nm. Suggest a column and mobile phase for this analysis both aspirin and naproxen are discussed earlier in this chapter. Suggest a suitable column and mobile phase for this analysis. The following data were obtained for the analysis ... 

The vital importance of size and shape as compared with absolute molecular weight is emphasized by another pair of exceptions on the calibration curve in Figure 5-37—aspirin and propylparaben. These two compounds have essentially identical molecular weights (180.2 and 180.1, respectively), but are easily separated by SMGPC. From the structures, it can be deduced that propylparaben acts as a larger molecule in solution than does aspirin. This is probably due to a solvent effect where the THF hydrogen-bonds to the polar groups in propylparaben. Thus, propylparaben should elute before aspirin, and as shown on the calibration curve, it does. 

A. Figure 13-1 shows an example chromatogram for the separation of aspirin, phenacetin, and caffeine on a low-efficiency column. Figure 13-2 shows the example chromatograms used in the construction of the phenacetin calibration curve (Fig. 13-3). 

Measure the retention times. For the aspirin chromatograms, also measure the areas. The peak areas may be obtained from the height times the width at half-height for each. Alternatively, the peaks may be cut out and weighed. Or the instrument may print out the integrated areas. Using a spreadsheet, plot a calibration curve of peak area against concentration. 

From a comparison of retention times, identify the components of each analgesic. Measure the areas of the aspirin peaks, and from the calibration curve determine and report the concentrations in the various tablets. If there is any overlap of the aspirin peak with another, extrapolate to the baseline and measure the area from the baseline. If two chromatograms were run, report the average concentration. 

Fig.6. Calibration curves of chloride electrode in KCl solutions without aspirin - 1, in KCl solutions containing respectively hydrolyzed aspirin (o) or salicytale ions (-+ ) in concentrations 0.5 mM - 2, 1.0 mM - 3,... 

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