How do you spike a sample for analysis?

Question

Does anyone know exactly how to perform spiking? I have a basic idea of what it is.... you add a portion of your standard to the sample. But how much of your standard should you add? Does it matter? eg suppose I want to spike 100 mls of a sample... what do I do?

Answer 1

Spiking a sample is not an exact science.

It refers to giving you a reference point for whatever anaysis you are doing.

Say you are running HPLC and you "spike" the sample with X.

How much X do you add - is your question - right? The answer is just enough to be able to detect it in the chromatogram, and not enough to interfer with your sample.

If your sample is 15 g in 100 ml of soln, adding a spatula tip sample if X (whatever it's weight is (probably about 25 mg)) is sufficient.

If your doing NMR you spike with CDCl3 (with trimethy silane)

TMS gives a BIG peak at 0.0 in the proton NMR so if you are looking for protons in the 1-2 range be careful how much you add - because the base line may become to broad to integrate reliably to get a proton count.

Usually, you are luckly CDCl3 is sold with TMS already added to it (I think 0.1% quantity).

Answer 2

You spike to the concentration you expect to see in your unknown sample or, more broadly, in the range you're looking to test.

For instance, you may be looking to create a concentration curve for an analytical method, or you want to test how the presence of varying amounts of an impurity affects a reaction. The amount you spike is based on what range you want to study.

Answer 3

you shouldnt do it.