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NIR Spectroscopy in Bioprocessing

Real–Time Data on Manufacturing Bio–Processes with NIR spectroscopy

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Frewitt fabrique de machines SA
Sartorius AG

A Spectroscopic Process View

Near-infrared spectroscopy (NIR) uses light excitation ranging between 900 and 2,500 nm. In this region of the spectrum, overtones and combination vibrations absorb most functional groups (OH, CH, NH, etc.). During this process, the absorption of the functional groups is dependent upon their chemical environment. Due to the multitude and the similar excitation energies of these combination vibrations and oscillations, there is overlapping of the absorption bands.

The resulting wide bands within a NIR spectrum therefore include the information of several bond types, meaning that direct band assignment is not always straightforward. For this reason, mathematical-statistical processes are required in order to evaluate the spectra (chemometrics).

NIR –Quantitative or Qualitative?

The assessment of the NIR spectra can be carried out in a qualitative or quantitative manner as the process does not involve calibrations and no reference measurements are required for a qualitative assessment. As in the case of pattern detection, the spectrum is compared so that, for instance, both the identity of a material and the similar manner.

A requirement for each process device is that the sensor system demonstrates a high level of robustness under process conditions. Modern NIR process spectrometers are therefore, designed without any moving parts and work with redundant light sources in order to guarantee lasting use without maintenance over many years.

Similar Structure – Different Results

The structure of each spectroscopy method is essentially very similar: The main components are the radiation source and the detector, which registers the light after interaction with the sample. State-of-the-art NIR spectrometers (Figure 1)

Figure 1: Principle of a diode array spectrometer
Figure 1: Principle of a diode array spectrometer
(Picture: Sartorius Stedim Biotech)
used in the process, separate the light according to wave lengths; here the grating acts as the dispersive element. A photodiode array is often used as a detector.

The advantage of this type of assembly is that the overall spectral range is recorded simultaneously. Thus, this ensures that the entire spectrum of the measurement comes from the same sample, even during standard sample currents.

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