Monitoring Moisture Content of Powders in a Fluid Bed Drier Using an FT-NIR Spectrometer

The FDA is encouraging the use of modern process analytical technologies (PATs) in pharmaceutical production and quality control. This is pushing the industry to move away from empirical to science-based standards for manufacturing control. As a results, new technologies are entering the manufacturing sector of the pharmaceutical industry.

Process Analytical Technologies enable the analysis and control of manufacturing processes to assure acceptable quality at the completion of the process. This is based on measuring critical quality parameters and performance attributes of raw and in-process materials and processes.

Monitoring the moisture/solvent content of drying powders is critical to guarantee that the correct powder characteristics are achieved. Fluid bed driers are commonly used in pharmaceutical manufacturing to dry powdered product prior to blending and tableting. The standard operating method involves either thieving a sample for primary analysis, e.g. Karl-Fischer titration or loss on drying, or drying the product for a specific period of time. Both these approaches do not ensure a constant control over the drying process and therefore do not guarantee the tight control necessary to repeatedly provide a product with the specified moisture. Near infrared spectroscopy combined with either an in-line diffuse reflectance measurement or a non-contact measurement through a viewing port is a valid alternative offering a means of continuously monitoring the drying process.

Near Infrared Analysis of Powder Moisture in a Fluid Bed Drier

Fluid bed drier bowls very often have a convenient window through which a non-contact, near-infrared diffuse reflection measurement can be made. The Bruker Optics MATRIX-F duplex near infrared spectrometer and emission head is an ideal way of measuring through a window. The emission head has four sources, which can be controlled individually based on the sample reflectivity. A single 600-mm fiber links each emission head to the spectrometer.

Application

A MATRIX-F duplex system was utilized to monitor the moisture content of a powder in a fluid bed drier using a viewing port in the fluid bed drier bowl. An essential consideration for the non-contact measurement is that the powdered material is constantly exchanged on the viewing window so that the NIR spectra are representative of the changing moisture content in the bulk powder. Near infrared spectra as shown in Figure 1 were continuously measured (16 scans, of roughly 8 s, at 8 cm-1 resolution) during the drying process in addition to time stamped samples for primary analysis.

FT-NIR absorption spectra of the sample collected throughout the drying steps. Significant differences are clearly observed which correlate to the drying process and changing moisture.

Figure 1. FT-NIR absorption spectra of the sample collected throughout the drying steps. Significant differences are clearly observed which correlate to the drying process and changing moisture.

The pulled samples were correlated to the near infrared spectra measured at the same time and a calibration model was developed (Fig. 2).

Cross validation results of a PLS based model for prediction of the water content, which show a very high correlation coefficient (98.61) and a low error (0.4%).

Figure 2. Cross validation results of a PLS based model for prediction of the water content, which show a very high correlation coefficient (98.61) and a low error (0.4%).

A profile of the drying process is shown in Figure 3. Near-infrared spectra results from a combination and overtone bands of C-H, N-H, O-H, etc. vibrations. Since most reaction mixtures and solvents contain some organic components with these bonds, they are suitable for near-infrared analysis.

The fluid bed drier moisture profile as measured by non-contact near infrared analysis.

Figure 3. The fluid bed drier moisture profile as measured by non-contact near infrared analysis.

The OPUS/QUANT quantitative analysis software package uses partial lease squares (PLS) to develop quantitative models. Generally, the development of a model needs measuring samples that contain a range of concentrations of the components of interest. The unique Quant self-optimization routine is then applied to develop the calibration model. Figure 1 comprises some spectra of the sample collected at various stages during the drying process. These spectra are correlated with samples thieved from the drier at the same time and analyzed using a standard method, such as loss-on drying or Karl-Fischer titration.

Measurement Options

Bruker Optics offers a wide variety of instrumentation to meet every specific needs. For process applications, MATRIX-F FT-NIR spectrometer is recommended due to its multiplexing capability, ruggedness and easy serviceability. A wide variety of process measurement accessories are offered for in-line and on-line measurements of liquids, solids and slurries. Near-infrared sample spectra can be collected from driers using either a contact measurement (diffuse reflectance probes which require a port) or a non-contact mode (diffuse reflectance through a window). Both methods utilize a diffuse reflectance measurement and depend on the product exchange on the probe tip/window in order to sample the changing product. The non-contact measurement has the advantages that no modifications are needed to the equipment and a larger sample area can be measured.

Implementation

The use of fiber optics helps locating the instrument in either an enclosure in a hazardous location next to the measurement sites or in a control room. High quality spectra can generally be collected in less than a minute and the quantitative analysis of multiple components easily performed. In a process environment the MATRIX-F duplex can be used along with the process software ADIO to perform the measurement and analysis of the sample and also output the results via a variety of I/O options such as 4-20 mA, Modbus, Profibus, Industrial Ethernet, etc.

This information has been sourced, reviewed and adapted from materials provided by Bruker Optics.

For more information on this source, please visit Bruker Optics.

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