In-process aid or quality-monitoring tool

The pharmaceutical industry must be able to prove that blends of active and excipient (binding) ingredients are uniformly distributed in order to ensure delivery of the intended dosage. Traditional manual sampling and laboratory composition analysis is 

Blending also plays a role in the chemical industry. The use of Raman spectroscopy to control gasoline blending, particularly oxygenated species such as methanol, ethanol, propanols, and butanols, is discussed in US patent 5,596,196.64 The system can be operated in a feed-forward and/or feedback control scheme. In feed-forward, the composition of each of six remote feed tanks is measured sequentially. A control computer then 

Distillations are perfect candidates for Raman process monitoring since many potential fluorescent or interfering species are reduced or removed. The Institut Francais du Petrole holds two relevant patents discussing the use of Raman spectroscopy to control the separation of aromatics by adsorption on simulated moving beds and the separation of isomers, particularly aromatic hydrocarbons with 8-10 carbon atoms such as para-xylene and orffio-xylene.67 68 

Dow Corning has reported monitoring the concentration of a chlorosilane distillation stream with Raman spectroscopy. On-line GC was used, but the 20-60-minute response time proved too slow to detect important column dynamics. The on-line GCs also required extensive maintenance due to the hydrochloric acid in the stream. The Raman system is used to predict the concentration of nine species. Many could not be detected or distinguished by NIR.69 

In situ Raman spectroscopy is being used to investigate corrosion products from zinc in a humid atmosphere and sodium chloride70 and from Type 304L stainless steel in aerated water at elevated temperatures and pressures.71 The changes in detected species over time helped identify possible corrosion mechanisms and the effect of different variables on corrosion rates and mechanisms. 

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