I prepare different concentration of ascorbic acid such as 80 migram per ml, 40,20,10,5,2.5,1.25,0.625 and absorbance measured by uv spectrophotometer at 517nm....
I think you're calibrating a common colorimetric assay for ascorbate, using the radical dye 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH). This assay is known to produce non-linear results that are difficult to interpret. Your assay conditions will dictate your actual observations. I suggest you make certain your standard curve always includes values to provide a full sigmoidal range (0-100% inhibition). And run your standard curve in triplicate or more to get some statistical power for your result.
It is theoretically possible for the IC50 value of standard ascorbic acid to be 0.2030 microgram per ml, but it would depend on the specific assay and experimental conditions used to determine the IC50 value.
To confirm whether the IC50 value of ascorbic acid is 0.2030 microgram per ml in your assay, you would need to perform a dose-response curve using a range of concentrations of ascorbic acid, such as the concentrations you have prepared (80 microgram per ml, 40 microgram per ml, etc.). From the dose-response curve, you would determine the concentration of ascorbic acid that produces a half-maximal response, which is defined as the IC50 value.
It's also worth noting that the UV spectrophotometer at 517nm is not typically used to determine the IC50 value of ascorbic acid. IC50 values are usually determined using assays that measure a specific biological response, such as enzyme inhibition or cell proliferation. If you are trying to determine the antioxidant activity of ascorbic acid, for example, you may want to use an assay such as the DPPH radical scavenging assay or the ORAC assay, which are commonly used to measure antioxidant activity.
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