Spiked sample

[123jayne]

I had a sample of 4 alkaloids in a mix of 30%methanol 70
% phosphoric acid
I spike this with 5ml of alkaloid mix
my extraction percentage was above 100% why is this?

[123jayne]

sorry I spiked the bark solution with the 4 alkaloids then made the solution up with methanol and phosphoric acid

[Arne]

Jayne,

whatever solvent the spike is delivered in may enhance the extraction efficiency of your alkaloids.

alternatively, the concentration of your spiking solution may be incorrect.

Here are two ways to do a good spike:

1.
Sample (unspiked) - take 0.5 parts sample and 0.5 parts solvent
Smaple (spiked) - take 0.5 parts sample and 0.5 parts solvent containing the analytes. This procedure corrects for any changes in the matrix. It does cut your sensitivity in half, however.

2.
Spike your sample with a small amount of concentrated analyte, so that the matrix isn't appreciably changed.