Reference cell

A method for validating path length and optical characteristic of a fibre optic probe, the method comprising the steps of:

• (a) providing a fibre optic probe reference cell (8) comprising a base wall (11), first and second opposed upstanding walls (12) and further walls, which further walls are perpendicular to the opposed upstanding walls, each further wall having an optical window (13, 15), the cell further comprising a top wall (14), which top wall (14) is provided with a further optical window (16), which further optical window (16) is adapted to permit transmission of light to and from a fibre optic probe (1), which walls (11, 12, 14) define a chamber (10), wherein the chamber (10) is provided with a reference material and wherein the base wall (11) comprises a reflector (19) adapted to reflect incident light from a fibre optic probe (1) back to said fibre optic probe (1);
• (b) connecting the fibre optic probe reference cell (8) to the fibre optic probe (1) comprising a fibre optic cable (2) having a first input optical fibre (5) and a second output optical fibre (6), which first input and second output optical fibres (5, 6) extend to a sampling end (4), said fibre optic cable (2) being connected at an end to an analyzer adapted to process the first input optical fibre (5) and the second output optical fibre (6);
• (c) transmitting light through the first input optical fibre (5) into the chamber (10) to interact with the reference material;
• (d) transmitting incident light back to the fibre optic probe (1) to determine path length of the fibre optic probe reference cell (8) and absorption characteristics of the reference material;
• (e) calibrating the fibre optic probe (1) based on the path length of the fibre optic probe reference cell (8) and the absorption characteristics of the reference material;
• and
• (f) validating the calibration step by determining the path length of the fibre optic probe reference cell (8) and the absorption characteristics of the reference material in a spectrophotometer.