An inexpensive flow-through laser nephelometer for the detection of natural colloids and manufactured nanoparticles

The transport and fate of colloidal particles is coming under increasing scrutiny, largely because of the expected rapid expansion in the production of manufactured nanoparticles and because of possible interactions of natural and manufactured nanoparticles with pollutants. Risk assessments of engineered nanoparticles may only be carried out if means exist to quantify the processes that control the fate of the particles as they interact with materials in the environment. For aqueous systems, there are several analytical methods available that may be utilised to classify and quantify a colloidal suspension but where the particles are of a generally uniform nature, and in sufficient number, the turbidity of the fluid provides an accurate measurement of concentration. In order to investigate the transport of manufactured nanoparticles through small saturated rock columns, a simple and inexpensive laser nephelometer was developed which incorporates a low volume flow-through cell in order to provide a continuous record of the elution of particles from the column. The design, construction and evaluation of the device are presented together with example data. Although designed specifically for the laboratory study of colloid transport through columns, the device may be readily adapted for other purposes in the field or laboratory wherever an inexpensive and robust continuous means of turbidity measurement is required.