There should be no problem in measuring the starch in plasterboard.It is suggested that you grind about 100 g in a kitchen blender and then fine mill to pass 0.5 mm screen.  Run a standard assay, but adjust volume to 10 mL after alpha-amylase treatment.  Keep a close check on the pH. Plasterboard may push the pH value up (pH up to about 8 should be fine). You may be advised to run a DMSO format concurrently just to be sure. When you treat with amyloglucosidase, It is recommended that you take 0.2 and 0.4 mL aliquots of digest (to get the colour up), also, be careful about checking the pH.

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