surrogate concentration in the calibration standards

[hplc.chem]

Dear All,
I am quantifying PAHs in soil using an HPLC/UV. The procedure I am using is based on ultrasonic extraction then a silica column clean up. I am planning to use Decafluorobiphenyl as a surrogate standard to check for any losses during the procedure.

Is there any rule or common practice to decide what concentration should be added to the samples and to the calibration standards?

I found some methods use a fixed concentration in both samples and calibrators but others generate a calibration curve for the surrogate.

Any ideas or experiences are appreciated.
Many thanks in advance.

[Steve Reimer]

Surrogate added to the samples should be such that the final concentration in your extract is somewhere in the middle of your calibration.
Generally for extracted samples the surrogate concentration in the calibration standards span the acceptance range or more. These are not hard and fast. I use a fixed surrogate concentration in my volatiles calibration because the autosampler adds a fixed amount. In my semivolatiles, the calibration surrogate concentrations span a similar range to the target analytes.

[mckrause]

You want to span a range of concentrations from low (<10% of what you're adding) to high (200% of what you're adding) so that you can adequately calculate the concentration you recovered. You should have relatively good sensitivity for DFBP, so I'd work with a nominal spiking concentration more or less equivalent to the internal standard.

[hplc.chem]

Many thanks for all of you.