Rapid quantification of free cholesterol in tears using direct insertion/electron ionization-mass spectrometry.

Purpose: To establish a simple and rapid analytical method, based on direct insertion/electron ionization-mass spectrometry (DI/EI-MS), for measuring free cholesterol in tears from humans and rabbits.

Methods: A stable-isotope dilution protocol employing DI/EI-MS in selected ion monitoring mode was developed and validated. It was used to quantify the free cholesterol content in human and rabbit tear extracts.

Alkaloids from the roots of Stemona aphylla.

Three known compounds, stemofoline (1), (2'S)-hydroxystemofoline (2), and (11Z)-1',2'-didehydrostemofoline (3), along with two new alkaloids, stemaphylline (4) and stemaphylline-N-oxide (5), have been isolated from a root extract of Stemona aphylla. The structures of these alkaloids were determined on the basis of their spectroscopic data. The analysis of the crude dichloromethane extract by GC-MS in the EIMS mode showed the presence of alkaloids 1-4, the alkaloid 11, and stilbostemin R (12).

Care regimen and lens material influence on silicone hydrogel contact lens deposition.

Purpose: To quantitatively detect proteins and cholesterol extracted from worn silicone hydrogel contact lenses and determine the effect of various lens care solutions on deposit accumulation.

Methods: Contact lenses, made from different polymers and worn on a daily wear schedule with different lens care solutions, were collected. Lipid and protein deposits were extracted by methanol:chloroform (1:1, v/v) and protein extraction solution (containing urea and surfactant), respectively.

Human lens lipids differ markedly from those of commonly used experimental animals.

Electrospray ionisation tandem mass spectrometry has allowed the unambiguous identification and quantification of individual lens phospholipids in human and six animal models. Using this approach ca. 100 unique phospholipids have been characterised.