2.6. Determination of the in vitro sun protection factor
The in vitro method measures the reduction of the irradiation
by measuring transmittance after passing through a film of
product. As in the operative conditions of the transmission
measurement are correct, this to be a very precise and single
value, always reproducible for the same product and
expressed as a single UV curve, in the percent transmittance
or absorbance scale (Fig. 1). The crude R. kordesii petal extract,
the gel formulation (1.5% carbomer 937) containing R. kordesii
petal extract were analyzed for the in vitro SPF. The crude R.
kordesii petal extract gel formulation was dissolved in methanol
UV solv:water (6:4). Scans of the samples in solution were
run from 320 to 290 nm using 1 cm quartz cuvettes in a Shimadzu
UV-1700 spectrophotometer.16 The commercial sunscreens,
Himalaya SPF 30, were used for the calculation of
the correction factor and a solution of 8% homosalate (v/v)
diluted to 0.2 mg/ml was used as standard. The SPF model used
in this study was based on the following equation proposed by
Mansur et al.17
Table 1 e Composition (%, w/w) of gel formulations used
for the chemical stability study and for the determination
of SPF.
Active ingredients QuantityCarbomer 973 1.5 mg
Propylene glycol 10 ml
Triethanolamine 0.5 ml
Methyl paraben 0.25 mg
R. kordesii petal extract 1.42 mg
Distilled water qs 100 ml
Table 2 e Physicochemical parameters