Chromatography Forum

Hi,

What is difference between surrogate, internal and injection standard.

Jason

Greetings Jason,
A surrogate is a compound or mixture of compounds that are added to a sample in order to monitor how well your extraction process went (or whatever process your running your sample thru). For example, I run EPA 8270/625 for BNA's (base/neutral/acids) and we currently extract for ~90 compounds. We add a separate mixture of 3 acids and 3 bases as surrogates into each sample and based on the recovery we obtain we can determine a good or bad extraction thru control limits made from control charts.
An internal standard (which I'm pretty sure is the same as an injection standard) is another mixture added to each sample to help determine the concentration of a differing compounds based on a formula using response factors generated from an initial calibration curve. Hope this helps.

Internal standards:

1) added before extraction - surrogate
checking the extraction process
2) added after extraction (to vials) - ISTD (injection)
checking injection and detector fluctuations



p.s.
my english is bad..sorry

terminology obviously differs between groups and disciplines! Beware, one person's surrogate is another's internal standard. Provided you understand what you (and others) are doing, and why, it doesn't matter too much what you call it.