Evaluating A Laser Diffraction Instrument For Accuracy

Before selecting a particle size analyzer, or any other measurement device, several questions must be answered. Is the instrument accurate? Are the measurements it makes reproducible? What is the precision of the device? How will the company selling the instrument support the product? And of course, is it easy to use? Other issues may be more or less important depending on the specific requirements, such as: will it be possible to make a meaningful correlation between measurements made with this instrument and those in a company's historical database? In this article, the accuracy of a Beckman Coulter® LS™ Series analyzer, LS 13 320 is determined. This instrument has a range from 0.04 micron to 2000 microns and can measure across the entire range in a single analysis.

Before directly addressing the question of accuracy, it is worth spending a little time discussing the laser light scattering technique and how it works. The laser light scattering method, generally referred to as laser diffraction (LD), is the fastest growing technique for sizing particles from submicron sizes to a few millimeters. The reasons include its huge dynamic range of measurement, excellent reproducibility and ease of use. Many applications that were formerly the domains of sedimentation, sieving and microscopy are now routinely handled using light scattering, including ceramics, clays, cement, foodstuffs and others. Its flexibility in handling samples dry or wet, in any transparent fluid including organic solvents, make it the perfect choice for laboratories characterizing a wide range of materials.