Analysis of tear glucose concentration with electrospray ionization mass spectrometry

We have developed a mass spectrometry-based method that allows one to accurately determine the glucose concentration of tear fluid. We used a 1 mu L micro-capillary to collect tear fluid from the tear meniscus with minimal irritation of the eye. We analyzed the 1 mu L volume of collected tear fluid with liquid-chromatography electrospray ionization mass spectrometry with the use of D-glucose-6,6-d(2) as an internal standard. Repeated measurements and a recovery experiment on pooled, onion-induced tears showed that the analysis of the glucose in tears was precise (4% relative standard deviation) and provided 100% recovery. We found the tear glucose concentration of one fasting nondiabetic subject to be 13 to 51 mu M while the onion-induced tear glucose concentration of a different nondiabetic subject to be 211 to 256 mu M.