MACO Calculation

I am trying to calculate the MACO for a mouthwash so the acceptable daily intake is not applicable. Would the following calculation be acceptable?

MACO = mg analyte product A divided by kg batch size of product A x weight in kg of the smalles batch size (product B) divided by a safety factor of 1000 x product contact surface area of shared equipment.

For example:6.63 kg of sodium fluoride per 600 kg batch = 6, 630,000 mg/600 kg =11,050 mg NaF/kg batch
11,050 mg NaF/kg x 19 F- /42 NaF = 4999 mg Fluoride ion/kg batch
Shared equipment = 21,106 in2
Safety factor = 1000
Smallest batch size = 6000 kg


MACO = 4999 mg F- x 600 kg (smallest batch) =0.1421 mg Fluoride Ion/in2
Kg batch 1000 x 21,106 in2

Therefore, for a 9 in2 swab area, the maximum allowable fluoride residue is 1.28 mg F- .
Thus this make sense?