When spiking blank (pre-extraction) samples at defined concentrations, they undergo the entire extraction process in which a dilution factor and fractional yields are inserted. For example, you spike the sample at a concentration of 10 ng/g, you add e.g. 6 mL of an organic solvent (to 1 g of sample) of which you only aspire 5 mL. Instantaneously, you know you have lost a pre-calculated portion of your analyte. However, spiking the final extract or preparing a solution in solvent is something totally different. You have no losses there. How do you account for this difference?
Hi. Thank you for this question. Indeed, calculations differ depending on the pre-extraction and post-extraction blank. However, you need to keep in mind that you are evaluating matrix effects. 1) So the first case is pre-extraction spike and what you need to do is the same as you would calculate concentration in your real sample. All the dilutions etc need to be taken into account, just like calculating concentration for your samples. And then you can compare the results with what you spiked. 2) If you are doing post-extraction spike you can forget everything that has been before. You need to spike the post-extraction extract in such a manner that you know the concentration in post-extraction spike. For example you know that you have 5 ml of this extract and you spike in a manner that you know the concentration of analyte in this extract. And then you do additional steps you might need (dilutions etc) and analyse the sample. And then you can calculate the analyte concentration in post-extraction extract. And then you compare this with what you spiked. No need to worry about steps that happened before the extraction. I hope this helps.
When spiking blank (pre-extraction) samples at defined concentrations, they undergo the entire extraction process in which a dilution factor and fractional yields are inserted. For example, you spike the sample at a concentration of 10 ng/g, you add e.g. 6 mL of an organic solvent (to 1 g of sample) of which you only aspire 5 mL. Instantaneously, you know you have lost a pre-calculated portion of your analyte. However, spiking the final extract or preparing a solution in solvent is something totally different. You have no losses there. How do you account for this difference?
Hi. Thank you for this question. Indeed, calculations differ depending on the pre-extraction and post-extraction blank. However, you need to keep in mind that you are evaluating matrix effects. 1) So the first case is pre-extraction spike and what you need to do is the same as you would calculate concentration in your real sample. All the dilutions etc need to be taken into account, just like calculating concentration for your samples. And then you can compare the results with what you spiked. 2) If you are doing post-extraction spike you can forget everything that has been before. You need to spike the post-extraction extract in such a manner that you know the concentration in post-extraction spike. For example you know that you have 5 ml of this extract and you spike in a manner that you know the concentration of analyte in this extract. And then you do additional steps you might need (dilutions etc) and analyse the sample. And then you can calculate the analyte concentration in post-extraction extract. And then you compare this with what you spiked. No need to worry about steps that happened before the extraction. I hope this helps.