Variable | Level | ||
−1 | 0 | +1 | |
Concentration of sodium fluoride, %w/v | 1% w/v | 2% w/v | 3% w/v |
Concentration of PVP, %w/v | 0 | 1 | 2 |
Volume of sample solution, mL | 10 mL | 20 mL | 30 mL |
Drying surface area, cm2 | 38 cm2 | 79 cm2 | 143 cm2 |