internal standard concentration

[organicchem]

Hello,
in USEPA 8260 & 8270 it is mentioned that the area count of internal standard should be between 50-200% of the area of the target anlytes in the mid pont calibration analysis. So i my calibration range is 600 800 1000 4000 6000ppb whether i should opt 1000 as my internal standard or else 3000ppb.

for you valuable comments.

thanks

[JonKlar]

If your average sample has concentrations this high you are going to have to maintain your instrument constantly. You should drop your calibration range to something like 5ppb to 150 ppb and dilute your samples accordingly. As for your internal standard concentration, I find it easiest to just use the same concentration as the calibration midpoint

[Alexandre]

I found that for 8270 analytes up to 10 ppm is a bit high, but still OK. It depends. Dont need to go higher.
ISTD area is ~75% of your max analytes’ responses (mean of several,if you use one ISTD for a group of analytes). You can go lower ~50, if want to same money on isotope ISTDs.