Sample Handling Devices:

Raman spectrometer has a distinct advantage over IR spectrometery since it allows the use of glass for holding aqueous solutions. The possibility of using aqueous samples is particularly significant as it permit ascertaining water pollutants besides biological and inorganic samples. More so, because the laser source provides a focused coherent radiation, the sample container could be extremely small which in turn requires exceedingly smaller sample volume. This is a highly desirous attribute. A number of sampling devices are in use we would take a few examples of the devices for handling solid, liquid and gaseous samples.

A solid sample is ground to a fine powder and packed within a small cavity to be kept in the path of incident radiation. The liquid samples instead are taken in a fine capillary that is about 5 cm long and has an outer diameter of about 1 mm. For analysing gaseous samples, a cuvette consists of a cylindrical glass tube along with mirrors on both the ends; one of the mirrors has a small window to let the incident radiation to pass by. While the cuvette containing the sample is placed in the radiation path the incident laser beam enters the sample by the window and undergoes multiple reflections in the sample. The scattered light at the right angles to the sample is then suitably collected and measured.

Fibre-optic probes are a recent advancement in sample handling. These probes exploit the fact in which the visible or near IR radiation could be transmitted to distances as huge as 500 m using optical fibre as the vehicle. This permit handling samples much farther from the instrument and without any physical manipulation of the sample. In a classical fibre-optic probe the laser beam from the source is focused onto a fine bundle of optical fibres known as input fibres that transport it to the sample. These input fibres are enclosed through a set of optical fibres known as collection fibres. These are meant to collect the scattered radiation from the sample and send it back to the instrument where it is directed to a appropriate monochromator.