Online solute concentration measurement

With the advancement of online measurement techniques such as focused beam reflectance measurement (FBRM) and Fourier transform infrared (FTIR), it is now possible to obtain particle size distribution and solution concentration information rapidly through these in-situ probes. In one experiment, hundreds of data points can be generated. With proper experiment design, the model-based experimental design for crystallization is capable of obtaining high-quality crystallization kinetic data with a small number of experiments. This approach can thus save significant experimental effort and time in the development of crystallization processes. 

Many different trace/matrix separation procedures are also applied prior to the ICP-MS determination, or even on-line (e.g. Muller and Heumann 2000). ID finds increasing application in combination with ICP-MS, thereby reducing the problems of analyte losses in sample preparation, but not the problem of interferences in the ICP-MS measurements (e.g., Yi and Madusa 1996) and that of contamination during sample preparation. Schuster and Schwarzer (1998) have described a new very versatile online capable column t/m-separation and preconcentration procedure for the selective separation and preconcentration of Pd even from solutions containing high concentrations of the other PGM. Moldovan et al. (2003) recently published another method for on-line preconcentration and determination of Pd using ICP-MS. 

Moniero et al.[24] developed an indirect AAS method for the determination of local anaesthetics (lidocaine. tetracaine and procaine hydrochlorides) in pharmaceutical preparations using FI on-line precipitation-dissolution. A cobalt solution is injected into a carrier stream containing the sample, and the precipitate formed is retained on an online stainless steel filter. The determinations were made by measuring the residual cobalt concentration in a similar way as for the indirect determination of sulphonamides (cf. Sec. 9.4.2). A sampling frequency of 100 h was achieved with a precision of 0.6% r.s.d.. 

The opportunity to measure the dilute polymer solution viscosity in GPC came with the continuous capillary-type viscometers (single capillary or differential multicapillary detectors) coupled to the traditional chromatographic system before or after a concentration detector in series (see Viscometric Detection in GPC/SEC, p. 2411). Because liquid continuously flows through the capillary tube, the detected pressure drop across the capillary provides the measure for the fluid viscosity according to the Poiseuille s equation for laminar flow of incompressible liquids.Most commercial online viscometers provide either relative or specific viscosities measured continuously across the entire polymer peak. These measurements produce a viscometry elution profile (chromatogram). Combined with a concentration-detector chromatogram (the concentration versus retention volume elution curve), this profile allows one to calculate the instantaneous intrinsic viscosity [rj], of a polymer solution at each data point i (time slice) of a polymer distribution. Thus, if the differential refractometer is used as a concentration detector, then for each sample slice i. 

---