by
JGK » Tue Oct 08, 2013 10:20 pm
faris wrote:
Hi Guys. I need help with my calcualtion. Let me first explain my procedure;
1-Three grams of meat mixed with 9 mL of water and homoogenized and centrifuged.
2- One mL dried and redissolved in 125 uL and injected into the GC. Also, 125 uL as standareds is injected directly into the GC for comparison and aslo to generate a standard curve.
how can I calculate my analyte?. Thanks
Also, can I use this equation:
Internal STD nanogram added*analyte peak area)/(GC reponse factor*3 gram of meat* internal STD peak area)
and hoe I can calculate my internal STD recovery.
At no point in this description do you say you actually add an "internal STD" into the mix. What you are describing is an "external standard" method.
For an Internal STD method you should be adding a known quantity of the IS to the samples and standards immediately prior to analysis.
Internal STDs added prior to extraction are now often referred to as "surrogates). Their recovery would be determined against unextrcted spikes. For example in the above extraction, if you spiked a sample with 100 ng of the surrogate, you should compare the spiked extract with a 10ng/125µL solution to estimate the recovery.