Internal std

[Liza]

Hi:


I'm new to lab - could someone please explain internal std (e.g. when do we need to incorporate internal std in method, how to choose the right internal std, does it get included in calculation, etc.)


Thanks in advance.

[apc]

Hello,

Internal standards are also known as "spiked samples". This means that prior to doing anything with your sample, you add a known amount of standard to your sample. Then you compare the the solution of the two samples: one with the spike and one without the spike. This basically allows you to check whether your detector is working correctly, but also for reporducibility purposes. Your internal std should obviously be known so that you can verify the accuracy of your data. You can purchase stds. from many chemical companies today. But depending on what you are doing, you or your prof may already have a specific std. in mind.

As for choosing an ideal internal std, there are some rules of thumb I was taught. (flash backs to good ol' analytical chemistry labs...*sigh*)

-the std.'s data should be easily reproduced and ideally not interfere with your sample, so that you get an sample peak and a spiked-sample peak (good resolution)
.
-You should prep your sample and spiked-sample the same obviously prior to running the experiment, but you want to make sure you don't lose your spike in the process.

-you shouldn't need to flood your detector with the spiked sample, it should relatively be similar concentrations to the sample, so you can tell relatively whether sample concentration is in fact similar.

-BUT most important of all...choose one that doesn't take forever to elute because, you'll just end up sitting there waiting for the last thing to elute (It'd be like watching grass grow.)

I think these are the things I usually look out for. Good luck at your new lab!

Hope to see your posts more often on this board. I too am a newbie to this forum.

Best Regards,
Alice

[tom jupille]

apc's description is a good one.

There is also a description of how internal standards work in the FAQ section. Click on the FAQ link near the upper left of the page and drill down through Liquid Chromatography Questions to the Terminology section.

You might also try doing a search of the Forum on the keywords "internal standard". These are only two of the 72 matches:
http://www.sepsci.com/chromforum/viewtopic.php?t=1581
http://www.sepsci.com/chromforum/viewtopic.php?t=1600

[HW Mueller]

Except that the word spiking might better be reserved for adding a known amount of analyte on "top of" the unknown amount present in the sample.