rb6banjo wrote:
Let's say your stock standard is in water (just for convenience).
0.005 mL x 1.0 g/mL = 0.005 g added
That means your sample size is really 0.025 g (a dilution by 20%, 0.020/0.025 = 0.80). Usually, you want the volume/mass of your overspike to not affect the overall volume/mass of your sample. In your case, it does affect it.
Here you go. So, 0.4 µL of 5,000 ppm standard to 0.020 g of oil matrix gives a total mass of 0.0204 g of sample analyzed.
5,000x0.0004/(0.020+0.0004) = 98 ppm (not the 100 you want but not too bad)
If you have to add 40 µL of the stock standard to 0.020 g of the blank matrix then:
5,000x0.04/(0.020+0.040) = 3,333 ppm (not the 10,000 ppm you want)
You really need to make your standards in your blank matrix but use a large mass of blank matrix relative to the amount of standard you add. This way, you don't dilute it dramatically when you add your standard.
Thanks, this makes a lot of sense.
My next question though, is how do I calculate the true result of my sample?
Lets say it lands in between the 98 ppm and 3,333 pm at 2000 ppm on the calibration curve.
Since I prepared the sample by adding 5 uL of sample to 0.020 g of blank matrix would it still be 2000 ppm? My result needs to be in ug/g