If I look at any tables or calculators, I find that negative ion formate adduct has a monoisotopic mass of
+44.9982 units. If I try to calculate myself, I get slightly different result:
H + C + O + O = 1.007825 + 12.0107 + 15.9994 + 15.9994 = 45.017325
The difference is
0.019, what is already not indifferent, as usually I calculate with a tolerance of
+- 0.02 units, which means this can cause me miss many hits. I could not find out what may cause this difference.
Later had similar experiences with the acetate, as in tables
+59.013851 can be found, but if I calculate:
3 x H + 2 x C + 2 X O = 3 x 1.007825 + 2 x 12.0107 + 2 x 15.9994 = 59.043748
Which means even more,
My question is what causes the difference, and what is the correct wat to calculate these masses?