4.4.1 Stock dilutions (1 x 10^6 pg/μl)
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.
4.4.1 Stock dilutions (1 x 106 pg/μl)
For each amine:
1. Weigh out the specified amount (these values are adjusted for the weight of associated HCl and HBr molecules) into separate, labelled 12 ml glass vials.
2. Dissolve the standards in:
2.1. 9.975 ml chilled 0.2M perchloric acid (PCA; 29.6 ml 70 % perchloric acid in 1l polished water) and
2.2. 25µl 0.1M EDTA solution (3.722 g EDTA in 100 ml polished water)
3. Cover the vials in foil to exclude light.
4. Refrigerate (4°C).