Particle optical microscopy

FT-IR microspectroscopy has also been used for the identification of undispersed particles or for contaminants in plastics applications. This technique is particularly useful for resolving customer complaints, contamination issues, as well as for process development problems. As a general rule, particles 20 pm or larger can be analyzed by FT-IR spectroscopy. The approach requires focusing the IR beam onto the particle of interest using the optical microscope and then scan the FT-IR spectra several times (100 scans) either in transmission or reflectance mode. A reference spectrum of an area of the sample without a defect is also recorded under the same conditions. The reference spectrum is then subtracted from the sample spectrum. The difference spectrum is used to identify the unknown particle. Optical microscopy is often used together with FT-IR microspectroscopy to aid in selecting the area of interest to be analyzed. 

Microscopic identification models ate similar to the CMB methods except that additional information is used to distinguish the source of the aerosol. Such chemical or morphological data include particle size and individual particle composition and are often obtained by electron or optical microscopy. 

Ultrafiltration utilizes membrane filters with small pore sizes ranging from O.OlS t to in order to collect small particles, to separate small particle sizes, or to obtain particle-free solutions for a variety of applications. Membrane filters are characterized by a smallness and uniformity of pore size difficult to achieve with cellulosic filters. They are further characterized by thinness, strength, flexibility, low absorption and adsorption, and a flat surface texture. These properties are useful for a variety of analytical procedures. In the analytical laboratory, ultrafiltration is especially useful for gravimetric analysis, optical microscopy, and X-ray fluorescence studies. 

Particle Formation, Electron microscopy and optical microscopy are the diagnostic tools most often used to study particle formation and growth in precipitation polymerizations (7 8). However, in typical polymerizations of this type, the particle formation is normally completed in a few seconds or tens of seconds after the start of the reaction (9 ), and the physical processes which are involved are difficult to measure in a real time manner. As a result, the actual particle formation mechanism is open to a variety of interpretations and the results could fit more than one theoretical model. Barrett and Thomas (10) have presented an excellent review of the four physical processes involved in the particle formation oligomer growth in the diluent oligomer precipitation to form particle nuclei capture of oligomers by particle nuclei, and coalescence or agglomeration of primary particles. 

Morphology of the blends was studied by both optical microscopy and SEM. It was found that HDPE forms a continuous phase and rubber is dispersed as distinct domains. The 50 50 blend shows finer particle dispersion than other blends. In 25 75 blend both HDPE and rubber form the continuous layer. The morphology is independent of the method of preparation. 

Figure 5.14 The microstructure of the set cement is clearly revealed by Nomarski reflectance optical microscopy. Glass particles are distinguished from the matrix by the presence of etched circular areas at the site of the phase-separated droplets (Barry, Clinton Wilson, 1979).

Eischer, U. Ch. and Pohl, D. W. (1989) Observation of single-particle plasmons by near-field optical microscopy. Phys. Rev. Lett., 62, 458-461. 

Particle Size Measurement. The best way to evaluate an emulsion s stability is probably to measure its particle size distribution. A number of methods are available for droplet size determination (see Sec. VIII.A). Optical microscopy, although a time-consuming technique, is a direct way of measuring droplets larger than 1 pm. Nowadays, laser lightscattering, diffraction, and transmission methods are becoming popular for routine determination of particle size [151, 152],... 

R Evans. Determination of drug particle size and morphology using optical microscopy. Pharm Technol... 

Different methods are available for the determination of the particle-size distribution of powdered solids [30]. These are optical microscopy (usually combined with image analysis), sieve analysis, laser light scattering of suspended particles, and electrical zone sensing. 

The first linkage between a microscope and an IR spectrophotometer was reported in 1949 [15]. Today, every manufacturer of IR spectrophotometers offers an optical/IR microscope sampling accessory. The use of optical and IR microscopy is a natural course of action for any solid state investigation. Optical microscopy provides significant information about a sample, such as its crystalline or amorphous nature, particle morphology, and size. Interfacing the microscope to an IR spectrophotometer ultimately provides unequivocal identification of one particular crystallite. Hence, we have the tremendous benefit of IR microscopy for the identification of particulate contamination in bulk or formulated drug products. 

Particle morphology can be examined with optical microscopy and scanning electron microscopy. A discussion of both techniques is presented. 

Various methods are employed to size particles by optical microscopy. For spherical particles, the diameter suffices, but for nonspherical particles, altema-... 

Transmission electron microscopy (TEM) resembles optical microscopy, except that electromagnetic instead of optical lenses are used to focus an electron beam on the sample. Two modes are available in TEM, a bright-freld mode where the intensity of the transmitted beam provides a two-dimensional image of the density or thickness of the sample, and a dark-field mode where the electron diffraction pattern is recorded. A combination of topographic and crystallographic information, including particle size distributions, can be obtained in this way [32],... 

The melt mixed 80/20 PS/iPP blend displays a set of exotherms, where the amount of the iPP component that was heterogeneously nucleated is substantially reduced as indicated by the decrease of the crystallization enthalpy in the temperature region where the iPP crystallizes in bulk, i.e., at 109-111 °C (exotherm labeled A). This effect is due to the confinement of iPP into a large number of droplets. If the number of droplets of iPP as a dispersed phase is greater than the number of heterogeneities present in the system, fractionated crystallization occurs. The number of droplets for this composition is known (by scanning electron microscopy observations) to be of the order of 1011 particles cm-3 and polarized optical microscopy (POM) experiments have shown that this iPP contains approximately 9 x 106 heterogeneities cm-3. In fact, it can be seen in Fig. 1 that the fractionated crystallization of the iPP compon-... 

Figure 7.4. Optical microscopy image of permanently linked magnetic particles. Each streptavidin coated particle is linked to its neighbors by on average 3 dibiotin dsDNA of 151 base pairs. After the field has been switched off, the chains persist and spontaneonsly bend under thermal flnctnations. (From [27], with permission.)...

Solid lipid microparticles can also be analyzed by optical microscopy (e.g., with respect to particle size or presence of drug crystals within the particles [41,42,106]),... 

Figure 6. Particle size distributions of sorbitol samples obtained using optical microscopy and image analysis.

Electron and optical microscopies. Counting the particles and measuring their sizes can be done by optical or electron microscopy, the former for particles with diameters from 0.4 /im to several hundred microns,... 

Optical microscopy and scanning electron microscopy (SEM) were used to evaluate the drug incorporation and surface shape of the microspheres prepared under the various conditions. Particle size was determined using a Tiyoda microscope. Samples of microspheres (180-200) were dispersed on a slide and their diameter was then sized using suitable objectives. 

---