in such embodiments the probe tip can be separated from the light delivery device though a variety of mechanisms in a preferred embodiment the probe tip is attached to the light delivery device though a touhey borst adapter such that after usage the probe tip can be removed and replaced with another probe tip the detachable probe tip is of a length sufficient to penetrate the sample and attach to the light delivery assembly in preferred embodiments of the detachable probe tip the length of the probe tip is at least about 20 mm in length depending on its usage the probe tip may simply be thrown away after removal disposable probe tips obviate problems associated with cleaning the probe tip and avoid the potential of contamination from one sample to another instruments of the present invention include multiple probe tips that can be associated with a single light delivery device alternatively multiple light delivery devices may be associated with each probe tip the path length is the distance between the end of the probe tip and inside surface of the sample vessel holding the liquid the inside surface being the surface of the vessel which is substantially perpendicular to the probe tip the end surface of the probe tip which both defines the path length and is in contact with the liquid is substantially parallel to the inside surface of the sample vessel which is adjacent to the detector in one embodiment the probe tip is positioned above the sample vessel holding the sample and aligned so that the light.