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Internal Standard for GC quantification
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https://www.ionsource.com/tutorial/msquan/is.htm
hypervalent_iodine:
--- Quote from: coolman50544 on July 05, 2019, 09:40:23 AM ---
--- Quote from: hypervalent_iodine on July 04, 2019, 12:37:08 AM ---
--- Quote from: coolman50544 on July 03, 2019, 11:14:01 PM ---
--- Quote from: hypervalent_iodine on July 03, 2019, 08:15:20 PM ---Is there a reason why you want to use both external calibration and an internal standard? I don't believe this is usual practice, i.e. you would typically use one or the other.
--- End quote ---
I would imagine that it is assumed that the efficiency of liquid-liquid extraction of ethyl indole-3-acetate and benzedioxole are constant or change proportionally to each other. Extrapolating yields from the ratio of area of the product to area of the internal standard would account for any loss in extraction if the prior assumption is true. Our calibration curve is also based on the ratio of product of known concentration to area of the internal standard (extracted from a water/ethanol solution to DCM). Internal standard amount for known standards and reactions to be quantified are constant, of course.
I am worried that the prior assumption isn't true, however, since 1,3-benzedioxole is structurally quite different to the indole derivative.
--- End quote ---
In cases where you might use an internal standard in conjunction with an external calibration curve, the point is generally to account for random errors and fluctuations in the detector response. It allows you to measure the response factor so you can adjust the response of your samples and get more precise readings, although I think it is easier to do as you describe and plot the ratios (works out the same). It isn't to account for loss during prior purification steps, and the method I think you are describing would not be able to do that since I assume that you add the standard during sample prep and not during your purification. As for what you use for the standard, you are looking for something that behaves similarly in GC, but produces a clear and distinct response. They don't have to be chemically similar.
--- End quote ---
Could you provide any further readings/sources of the use of internal and external standards, especially in conjunction?
--- End quote ---
What sort of detector are you using?
coolman50544:
--- Quote from: hypervalent_iodine on July 05, 2019, 11:41:44 AM ---
--- Quote from: coolman50544 on July 05, 2019, 09:40:23 AM ---
--- Quote from: hypervalent_iodine on July 04, 2019, 12:37:08 AM ---
--- Quote from: coolman50544 on July 03, 2019, 11:14:01 PM ---
--- Quote from: hypervalent_iodine on July 03, 2019, 08:15:20 PM ---Is there a reason why you want to use both external calibration and an internal standard? I don't believe this is usual practice, i.e. you would typically use one or the other.
--- End quote ---
I would imagine that it is assumed that the efficiency of liquid-liquid extraction of ethyl indole-3-acetate and benzedioxole are constant or change proportionally to each other. Extrapolating yields from the ratio of area of the product to area of the internal standard would account for any loss in extraction if the prior assumption is true. Our calibration curve is also based on the ratio of product of known concentration to area of the internal standard (extracted from a water/ethanol solution to DCM). Internal standard amount for known standards and reactions to be quantified are constant, of course.
I am worried that the prior assumption isn't true, however, since 1,3-benzedioxole is structurally quite different to the indole derivative.
--- End quote ---
In cases where you might use an internal standard in conjunction with an external calibration curve, the point is generally to account for random errors and fluctuations in the detector response. It allows you to measure the response factor so you can adjust the response of your samples and get more precise readings, although I think it is easier to do as you describe and plot the ratios (works out the same). It isn't to account for loss during prior purification steps, and the method I think you are describing would not be able to do that since I assume that you add the standard during sample prep and not during your purification. As for what you use for the standard, you are looking for something that behaves similarly in GC, but produces a clear and distinct response. They don't have to be chemically similar.
--- End quote ---
Could you provide any further readings/sources of the use of internal and external standards, especially in conjunction?
--- End quote ---
What sort of detector are you using?
--- End quote ---
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