4.4. Preparation of internal and external standards

The internal standard for DA and 5-HT is 3,4-dihydroxybenzylamine (DHBA), while that for OA and TA is synephrine. Because of the instability of amines in solution, new standards should be made up daily to ensure accuracy. However, the stock dilutions may be relatively stable for a few days of use if they are kept properly chilled and shielded from light.