I am doing an in vitro release profile of human amniotic membrane (HAM) impregnated with honey. HAM was soaked with honey for 24h. Then, transferred into 12 well plate containing 1mL of PBS and incubated at 37C. 100uL of PBS in the well was collected at predetermined time (hour 1, 3, 12, 24 & 72) into 96 well plate and read by using spectrophotometer at 300nm. The PBS in 12 well plate is replenished with the same amount.

Based on my spectrophotometer reading, I had problem where my blank (PBS) has reading and some blank reading is higher than sample reading. Giving the negative value when I make calculation (sample reading - blank reading).

Does my method is reliable? How can I do calculation for the cumulative honey released from HAM over time?