Limitations of a single-optical-fibre fluorimeter system due to background fluorescence

An optical-fibre fluorimeter system has been developed which is capable of measuring concentrations of an oxazine-based dye down to one part in 1010 by weight in water, using a dual-fibre system. When a single fibre was used for transmitting both the excitation wavelength and fluorescence, the sensitivity was reduced to one part in 106 due to the fluorescence of the fibre. The fluorescence was associated with a significant absorption peak around 630 nm found in `dry¿ silica fibres (i.e. ones with low O-H content). UV-grade silica fibres of high O-H content exhibited less fluorescence.