The factor Xa reagent says it is 71 nkat, but I need to know what that is in g/ml and mol/ml.

One katal (kat) is the amount of enzyme that converts one mole of substrate per second. Activated enzymes from Chromogenix such as FXa and thrombin are measured in nkat. 1 nkat = 1 x 10^-9 mol of product released per second. The conversion is as follows:

FXa has a MW approximately 44,000.

The specific activity for FXa is 1.9 nkat/mg, as determined with chromogenic substrate S-2222.

This gives that 71 nkat corresponds to 37.4 mg FXa (=37.4 x10^-6 g FXa)

This corresponds to 8.5 x 10^-10 mol = 0.85nmol.

The concentration in mol/l and g/l will depend on the dilution volume you choose.

Note: 1 IU corresponds to 20 nkats, which means 71 nkat_S-2222 = 3.55 IU.