To establish a new analytical method using gas chromatography/mass spectrometry (GC/MS) for evaluating the lipids adsorbed on silicone hydrogel (SH) contact lenses: cholesterol, cholesterol ester, wax, and squalene.
A novel GC/MS method was developed and validated for the repeatability, specificity, linearity, detection and quantitation limits, and percentage recovery. The lipids in an artificial tear solution were adsorbed on 5 SH lenses (asmofilcon A, balafilcon A, galyfilcon A, lotrafilcon A, and lotrafilcon B) and 1 conventional hydrogel lens (etafilcon A) in vitro. The lipids adsorbed were then extracted and analyzed by the GC/MS method.
Repeatability of this analytical method was less than 2.2% deviation for all test lipids; however, the analytes were completely discriminated with sharp peak shapes, and identified specifically. The correlation coefficient showing linearity was at least 0.991 under 50 μg/mL of lipid concentration. Detection and quantitation limits were statistically 0.5 to 0.8 μg/mL and 1.4 to 2.5 μg/mL, respectively, for all analytes. Percentage recovery was estimated as approximately 80% for 3 μg/lens, 90% for 5 μg/lens, and almost 100% for larger amounts of lipids. Quantitatively, the lipids absorbed on contact lenses were lotrafilcon A = (near equal) lotrafilcon B = (near equal) etafilcon A < asmofilcon A < galyfilcon A = (near equal) balafilcon A with the value of 0.4 to 7.6 μg/lens. Lipid adsorption on SH lenses varied depending on the lipid components and lens surface properties.
The GC/MS method established in this study is excellent for the repeatability, specificity, linearity, detection and quantitation limits, and percentage recovery, and provides a novel highly sensitive and useful tool for evaluating lipids adsorbed on SH lenses.