Question about ISTD calibrations and chemstation
Posted: Fri May 13, 2016 8:30 pm
Im hoping someone can look over my process and let me know if Im making any errors.
I have set up a 6 point curve for three analytes, the curve ranges from from from 10 ppm to 250 ppm. Each std contains an internal std at 100 ppm.
Using chemstation I added each level of the curve as normal, I selected the istd peak and labelled it as the istd and entered in the amount 100 ppm.
When I prep samples I have been spiking each sample with 100 ppm of the istd.
My first question I have is inragrd to my dilutions. Due to the concentration of the three analytes I have to run two dilutions for each sample.
The sample is first mixed with 20ml of solvent. this mixture is injected for the first run.
For the second run I make a 1:20 dilution from the 20mls. (950 ul of solvent, 50ul sample)
When spiking either the first dilution or second what is the most straight forward way to account for any additional dilution caused by adding the istd?
For instance if I were add 100ul of istd to my 1:20 dilution how is that extra volume accounted for? What I have been doing is adding 900ul solvent, 50 ul of istd, and 50ul of sample, this way my sample is still a 1:20 dilution as the total volume is the same as it would be if I used 50ul of sample into 950ul of solvent.
For the sample that is not further diluted though I still have to "spike" it with 50ul the istd, am I correct that the addition of the istd would technically be a dilution, albeit a small one?
Second Question
Would it be ok to dissolve my istd in the extraction solvent, rather than spiking each sample? If I were to do that and used the same spiked solution to make my 1:20 dilution should still be at the same 100ppm concentration.
third question
When using chemstation and quantifying based on an istd what happens if the technician prepping the sample is slightly off with either the spiking, or if in the original solvent slightly over or under the desired volume? On the chromatogram that prints out the ISTD always says 100 ppm as that is the quantity entered in the curve, but what would happen if a syringe was off and only 50ppm of teh istd was actually put in the sample?
Thank you in advance for your help, it is very important that I use best practices and fully understand the rationale and any possible errors that may occur.
I have set up a 6 point curve for three analytes, the curve ranges from from from 10 ppm to 250 ppm. Each std contains an internal std at 100 ppm.
Using chemstation I added each level of the curve as normal, I selected the istd peak and labelled it as the istd and entered in the amount 100 ppm.
When I prep samples I have been spiking each sample with 100 ppm of the istd.
My first question I have is inragrd to my dilutions. Due to the concentration of the three analytes I have to run two dilutions for each sample.
The sample is first mixed with 20ml of solvent. this mixture is injected for the first run.
For the second run I make a 1:20 dilution from the 20mls. (950 ul of solvent, 50ul sample)
When spiking either the first dilution or second what is the most straight forward way to account for any additional dilution caused by adding the istd?
For instance if I were add 100ul of istd to my 1:20 dilution how is that extra volume accounted for? What I have been doing is adding 900ul solvent, 50 ul of istd, and 50ul of sample, this way my sample is still a 1:20 dilution as the total volume is the same as it would be if I used 50ul of sample into 950ul of solvent.
For the sample that is not further diluted though I still have to "spike" it with 50ul the istd, am I correct that the addition of the istd would technically be a dilution, albeit a small one?
Second Question
Would it be ok to dissolve my istd in the extraction solvent, rather than spiking each sample? If I were to do that and used the same spiked solution to make my 1:20 dilution should still be at the same 100ppm concentration.
third question
When using chemstation and quantifying based on an istd what happens if the technician prepping the sample is slightly off with either the spiking, or if in the original solvent slightly over or under the desired volume? On the chromatogram that prints out the ISTD always says 100 ppm as that is the quantity entered in the curve, but what would happen if a syringe was off and only 50ppm of teh istd was actually put in the sample?
Thank you in advance for your help, it is very important that I use best practices and fully understand the rationale and any possible errors that may occur.
