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OCR Salters B Individual Investigation - Help needed with colorimetry

I am analysing and testing the purity of aspirin tablets, one of my methods is colorimetry and I really don't know if my current method is right. Any help and advice would be hugely appreciated. Here is my current method for preparing standard solutions:
1) weigh 0.4g of aspirin into a 100cm3 conical flask
2) add 10cm3 of 1 mol dm-3 NaOH to the conical flask
3) warm at 50C for 10 minutes
4) leave the solution to cool for a few minutes and then transfer to a 500cm3 volumetric flask
5) make up to the mark with distilled water, this is stock solution containing sodium 2-hydroxybenzoate from 0.80g dm-3 solution of aspirin
6) use a 50cm3 burette to measure 10cm3 of stock solution into a 100cm3 volumetric flask
7) make it up to volume with 0.02 mol dm-3 iron(III) chloride solution, this is standard solution A
8) in a similar way make standard solutions B-G using 8,6,4,2,1,0.5 cm3 of stock solution
9) measure the absorbance of each standard solution using the colorimeter
10) plot a calibration graph

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