Flow cells, fast HPLC analysis

FTIR instrumentation is mature. A typical routine mid-IR spectrometer has KBr optics, best resolution of around 1cm-1, and a room temperature DTGS detector. Noise levels below 0.1 % T peak-to-peak can be achieved in a few seconds. The sample compartment will accommodate a variety of sampling accessories such as those for ATR (attenuated total reflection) and diffuse reflection. At present, IR spectra can be obtained with fast and very fast FTIR interferometers with microscopes, in reflection and microreflection, in diffusion, at very low or very high temperatures, in dilute solutions, etc. Hyphenated IR techniques such as PyFTIR, TG-FTIR, GC-FTIR, HPLC-FTIR and SEC-FTIR (Chapter 7) can simplify many problems and streamline the selection process by doing multiple analyses with one sampling. Solvent absorbance limits flow-through IR spectroscopy cells so as to make them impractical for polymer analysis. Advanced FTIR... 

The main disadvantage of smaller particles is the increased back-pressure during the operation of HPLC systems. The pressure can be calculated according to Darcy s law and is inversely proportional to the square of the particle size. For example, a 33 X 4.5mm column packed with 1.5pm nonporous silica particles needed a pressure of approximately 500 bar (the Umit for most commercial pumps in HPLC units) at a flow rate of 2ml min with acetonitrile and water. A general relation between particle size, pressure drop, plate number, and analysis time is provided in Fig. 7. The assumed specific conditions for viscosity, analyte diffusivity, retention factor, and other parameters are given in the legend. Fast analysis times combined with a limited flow rate also necessitates the need for fast detector systems, small volume detection cells (small volume injection loops, yet, all these challenges have been successfully resolved. 

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