Chromatography Forum

I have a question in regards to figuring out the final concentration of an analyte after GC analysis.

I started with 1g of sample it went into 5ml reagent water after 30 minutes of shaking 5ml of MeCN was added. Mixture was shaken and then centrifuged. 50ul of the super went into 950ul of MeCN.

GC result is in ng/ml my calculation is result * dilution 1 * dilution 2 / sx weight

I haven been using 5 ml as my multiplier. Although the total volume is 10ml, I am taking my sample from the top layer so I would think that using 5 as my multiplier would make the most sense. When I use 10 as the multiplier my results are double than the expected value which would also support using the 5ml dilution as the multiplier.

I just want to make sure that i'm not missing a step, or not properly accounting for the dilutions.

You have it correct.

Great thanks.

ntward,

I am curious about something. You put a gram of your sample in 5 mL water, then later added 5 mL of acetonitrile?
And you got a phase separation that allowed you to pull out only the supernate?

Best regards,

AICMM

After the 1g of sample(baked good) is added to the water, the MeCN is added, along with MgSO4 and NaOAc. The sample is shaken and centrifuged. After centrifuging the MeCN is the top layer followed by a layer of fat and solids, below that the water layer. The analyte should be in the MeCN layer, but im having a hard time telling if I am fully recovering it.

Now you take the trouble to tell us what you are really doing, instead of the simplistic version that you first presented, a potential source of error becomes apparent. Your original calculation assumes that the top layer from which you take 50 ul has a volume of 5 ml. I would bet cash money that it hasn't.

Peter

the simpelest way to solve that is to use an internal standard.

BMU