Raman immersion probe

One of the basic unit operations is dry mixing that is used in most manufacturing schemes. In Fig. 10.6, an example of the use of Raman monitoring for blend control is shown. In this case the blending procedure is very fast and the mixture is well blended within the 5 min used. De Beer et al. used an in situ Raman immersion probe setup to study an ibuprofen-xanthan gum... 

Fig. 9.2.1 Sketch of (A) a Raman immersion probe and (B) an immersion probe tip and spherical lens.

Figure 5.3 (a) Sketch ofthe Raman immersion probe, (b) Sketch of the immersion probe tip and spherical lens. 

For application where the probe optic is actually immersed into the sample stream [255], the vast majority of installations can be served by a probe optic that is specified to operate up to SOO C and 2000 psi. In Fig. 37, a schematic of a commercial inmiersion probe is shown. This type of immersion probe is constructed with either a stainless-steel or a Hastelloy C 276 body, which allows the probe to be fixed in place using a standard 0.5-in. compression fitting. Many thermocouple and pressure sensor ports found in the process industry are 0.5-in. compression type and these openings into the process are readily useable by Raman immersion probes. 

Raman spectroscopy has been shown to be useful in the study of the kinetics associated with the solution-mediated aqueous transformation of anhydrous carbamazepine to its dihydrate phase. Using a Raman immersion probe to establish the phase composition, the thermodynamics associated with the system were studied in ethanol-water mixtures through measurements of the solubility of both forms over the temperature range of 0-60 Raman spectroscopy was also... 

There have been substantial changes in Raman sample interfaces recently. The approaches now can be divided broadly into two categories based on the sampling volume. The probes intended to sample small volnmes include the more traditional noncontact or standoff probes, immersion probes, and optical microscopes. Large volume sampling approaches are newer and include WAl and SORS probes and transmission confignrations. 

Figure 7.4 Collection of commercial Raman probes designed for different installations (a) laboratory scale probe with interchangeable immersion or noncontact optics, shown with immersion option (b) probe shown in (a) installed in laboratory fermentation reactor (c) production scale immersion probe (d) probe shown in (c) installed in a glass reactor (e) gas phase probe with flow through cell (f) probe shown in (e) installed in process piping (g) wide area illumination (WAI) noncontact probe after completion of a pharmaceutical tablet coating operation. Adapted, with permission. Copyright 2004 Kaiser Optical Systems, Inc.

The ability to separate the fiber-optic tip and sample by as much space as required makes Raman sampling extremely flexible. For example, 15-foot immersion probes to insert in the top of chemical reactors have been made. The laser beam travels down the 15-foot probe shaft, finally coming to a focus just outside of the optical window at the probe s tip. A photo of such a probe is shown in Figure 5.4(a). Non-contact probes could also be made to come to a focus at similar distances, but then the beam must be enclosed to address safety concerns. 

The ability to monitor the chemical composition of a reaction mixture in situ in real time allows both sensing and control of the process variables in order to provide more consistent product, improved efficiency and reduced costs. In situ monitoring also allows analysis of processes not amenable to sampling such as extremes of temperature and/or pressure, and toxic or air-sensitive reagents. Instmments designed for in situ measurement of IR and Raman spectra are available commercially. IR instruments typically use an ATR element at the end of a metal immersion probe (usually stainless steel or hastelloy to give good chemical compatibility). The probe is linked to the spectrometer... 

As we have seen along this paper, RS is well suitable for liquid analysis, especially aqueous solutions. The development of different kinds of Raman probes allows various measurement setup. Thus, a measurement can be done remotely at a distance of a few centimetres by lenses or in contact with special probes for liquid or powder analysis. So when it is possible, an immersion probe is recommended for liquid analysis in order to get a more... 

In the initial pilot-plant experiments, an immersion probe was used as the interface to the sampling stream [32]. The analyzer itself was a dispersive CCD-Raman spectrometer using a 532-nm diode laser as the excitation source fitted in nitrogen-purged National Electrical Manufacuters Associate (NEMA)-rated enclosure (Class 1, Div. II [33]. In Figs. 15 and 16, characteristic spectra of several of the individual components in the process steam are shown. 

Fig. 4.8. Schematic of SERS experiment on pollen cellular fraction. Freeze-dried pollen was incubated with water, the supernatant was probed by SERS by adding a small amount to a solution of gold nanoparticles. The Raman experiments were carried out using a water immersion objective...

Near-field Raman imaging with a scanned probe has been reported [18, 19]. However, the technique is painfully slow (5-10 h, even for strong scatterers) and it has found very little use. Acquisition time can be decreased by using a polystyrene bead as a very high numerical aperture immersion lens. Working at 532 nm, Kasim et al. used a 60x/1.2 immersion aperture as an optical tweezer to simultaneously position the bead and operate it as a high NA lens [20]. They obtained a spatial resolution of about 80 nm on doped silicon with a few minutes scan time (Fig. 5.1). However, because of the need for a relatively smooth surface and a very intense scatterer, this technique is not likely to find much application in biomedical or pharmaceutical applications [21, 22],... 

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