By Redzilla on Monday, June 9, 2003 - 11:45 am:
Hi...I'm developing an HPLC method for the sunscreen active octinoxate. Everything is performing very well except for the most important part...I can't get my percent recovery any higher than 85%. I'm using a USP reference standard and my samples are raw materials that have been previously assayed by an outsourcing lab and are confirmed to be within the acceptable range. Any recommendations on what kind of adjustments to make to help with better sample recovery? New column and brand new Shimadzu HPLC.I have already validated this method on a previous sunscreen active...Any help would be greatly appreciated!
By Anonymous on Monday, June 9, 2003 - 01:04 pm:
It must be in your sample preparation step, could you give us some more details about your sample preparation? I guess your extraction is not good enough. Maybe you can search for a better solvent, wich dissolves all your active.
By Redzilla on Monday, June 9, 2003 - 01:58 pm:
The sample prep is very simple. It is just diluted in methanol. This material is soluble in alcohol. Also, this method has been used by another well known company...but I have been informed that with this particular active, that other people have had difficulty as well. Perhaps a different alcohol?
By KM on Monday, June 9, 2003 - 02:33 pm:
We dissolve our sunscreen samples (and standards) in N,N-dimethylformamide (DMF) and use HPLC on RP-18 column with detection at 313nm and have never had any issues with octyl methoxycinnamate (octinoxate). Our recovery data for this was 100.37 % recovery with a standard deviation of 1.07. Make sure that your absorbance isn't over 1000 mAU because sunscreens have big absorptivities and are present at relatively high concentrations.
By Redzilla on Tuesday, June 10, 2003 - 08:01 am:
To KM...
What mobile phase are you using? Right now I have a 90:10 MeOH/0.1% TFA...and I've tried moving to water instead of the TFA and I'm getting similar results. Just curious. Thanks! I am also using a C-18 column...
By KM on Tuesday, June 10, 2003 - 08:41 am:
Using 13 cm x 2.1 mm i.d. RP-18 (old type A silica, 10 cm column plus 3 cm column as guard column, same i.d. and stationary phase), we routinely use Solvent A = 45% (0.4% acetic acid in H2O), 55% THF, Flow = 0.25 ml/min. Wavelength = 313 nm
Column temperature = 27 *C if oxybenzone is also present. Samples that contain octyl methoxycinnamate but no oxybenzone can use the following mobile phase: 15% HPLC H2O, 85% either ACN or methanol, Flow = 0.25 ml/min. This is not proprietary, all comes from J. DiNunzio and R. Gadde, Journal of Chromatography 519 (1990), pp. 117-124.