Measurement and Identification of Particles in Injectable Liquids by FTIR-Microscopy

Stefano Pera, Material characterization, Eng. Stefano Pera, MILANO , Italy
Maria Grazia, Material Characterization Product Specialist, Perkinelmer, Milan, Italy

An important problem in producing injectable liquids is to count, measure the dimensions and identify the origin of particles suspended: the scope of this presentation is describing the method to solve this problem.

Liquids must be filtered and particles are collected on filters: it is possible to use either white filters and grid filters. The following step is the acquisition of a visible image of the filter and in case of grid filters it is also necessary to instruct the software how to recognize the grid points from particles selecting the dimensions of the particles to search. The visible image must be converted to black&white  and it is also necessary to define the dimensions range to search particles: finally the software will give the particles distribution and their dimensions.

For identification we need using a microscope in infrared mode: using the motorized stage and the autofocus function we select a specific particle. The Microscope will suggest best aperture in order to take the IR spectrum of the particle without including the surrounding but in order to have the maximum energy. Normally spectra are acquired with 4 cm-1 resolution in order to be comparable with spectral libraries and for each particle we can enter the proper acquisition time necessary to have the best possible sensitivity. The final step is to compare the spectrum of the particle with the spectra library that can be a commercial one or preferably a customized library obtained analyzing all the possible objects that can go into the liquid: for example plastic from gloves, fibers from shirts, rubber form gaskets etc: the creation of this data bank is not a big job as it is enough to acquire spectra using the Universal ATR, each sample requires few second and even a single fiber can give a good spectrum.