Quantitative Analysis Using Calibration Graph Method

2 Quantitative Analysis Using Calibration Graph Method 

In all measurements used to generate calibration curves the following mathematical relationship is followed  

The equation follows a linear straight line if response y increases with increasing concentration of the analyte x. The value a is the intercept or blank and b is the proportionality function. The normal method for plotting curves using this equation is to plot the v values (response) on the vertical axis and the x values (concentration) on the horizontal axis. The intercept a is on the vertical axis and may be zero, or as near it as possible. It is included in signal response for standard/sample analysis and must be subtracted from each measurement. 

Not all calibration curves generate a perfect straight line due to indeterminate or random errors. Most scattered points can be corrected using linear regression analysis to 

Wavelength drift during analysis can also occur after prolonged use and must be corrected. If a straight line exhibits a correlation coefficient of r = 0.999 then the line is deemed acceptable. The following formula is generally used to calculate the r value of the calibration line  

---

Nie et al. used a flow injection chemiluminescence method for the determination of dipyridamole in Persantin tablets [51]. A flow injection analysis system equipped with a chemiluminescence detector was used. Sodium hypochlorite was used as a chemiluminescent substance, and Triton X-100 was used as an enhancer of the chemiluminescence reaction. Sample solutions (pH 4-6) was injected into 0.2% Triton X-100 and treated with 0.5% sodium hypochlorite, and the chemiluminescence intensity then measured. The calibration graph was linear from 0.04 to 10 pg/mL of Persantin tablets (as its active ingredient dipyridamole), with a detection limit of 11 ng/mL. Recoveries were quantitative and the relative standard deviation ( = 3) was 2.7%. The method has been used to determine Persantin in injection and tablets, and the results obtained using this method agreed with those obtained by the Chinese Pharmacopoeial method. 

---