The stereomicroscope is usually the first instrument employed since it requires no sample preparation and provides an upright image with a long working distance. These last two features make it a powerful tool for isolating small contaminants in a pure form for further analysis. The polarizing microscope (PLM) permits the crystalline solids such as minerals, chemicals, fibers, etc. by determination of their inherent optical properties such as refractive indices, birefringence, optic sign and interference figures. The fluorescence microscope permits the detection of minute quantities of contaminants by means of their auto-fluorescence or through the use of fluorescently tagged reagents. The interference microscope permits us to study the original surfaces of glass particles to determine if they are curved, spherical, tubular or exhibit mold marks from even the most minute splinters. The comparison microscope is used in the comparison of hairs and fibers when suspect sources of these contaminants are located.
The scanning electron microscope (SEM) permits specimens to magnified to more than 60,000X and the energy dispersive x-ray spectrometer (EDS) attached to it allows us to determine their elemental composition both qualitatively and quantitatively. The transmission electron microscope (TEM) makes it possible to magnify specimens more than 100,000X and study their crystallography and determine the elemental compostion of particles than cannot be seen in the light microscope.
The Fourier Transform infrared microspectrophotometer (micro-FTIR) makes it possible to identify the chemical composition of the most minute specks of unknown organic substances. Over 250,000 reference spectra in our searchable FTIR libraries make it possible to identify most pure organic compounds using this technique. Raman microscopy/spectroscopy is complimentary to FTIR spectroscopy in many ways and can often identify substances that are infrared inactive. Its spatial resolution is remarkable and particles less than one micrometer in size can often be chemically analyzed. Gas chromatography/mass spectroscopy (GC/MS) is a powerful combination for separating and identifying small amounts of unknown mixtures. The ability to separate complex mixtures and then identify the components is essential for accurate and timely analysis of many types of complex real life samples.
Many identifications are most conveniently and convincingly performed using the techniques and apparatus of microchemical analysis. Microchemical tests are often the best way to identify some substances such as gluten, lignin, saliva and blood, for example. Microchemical techniques can often supplement instrumental data and make ambiguous spectral assignments certain.
Crystalline compounds, even when they occur in mixtures, are most readily and certainly identified by X-ray diffraction (XRD). Using special techniques it is possible to obtain X-ray diffraction patterns from very small quantities of material. The diffraction pattern than then be searched against the entire JCPDS X-ray diffraction powder library to identify the specific crystalline phases that are present.