FAQs

Very broadly, there are two types of quartz fiber quality that we use for spectroscopy: high OH and low OH types. In order to deliver a maximum amount of UV light for certain applications, the high OH fibers are chosen, as this mitigates the creation of color centers due to damage from the high energy photons and allows transmission even down to 200 nm. Although this type of fiber is optimized for UV throughput, there is natural attenuation of light from ~300 nm and lower. Therefore, we recommend a total optical path of no longer then approx. 10 m for UV applications. On the other hand, for Vis/NIR and Raman (785 nm excitation), there is very little attenuation within low OH type fibers. These spectral ranges can transmit the light up to 100 m or more, depending on the details of the application.

When it comes to measurement of multiple locations, there are several options available. One option, which will produce the most reproducible results is cloning the spectrometer system for each measurement point, although this is the most costly one. Alternatively, we have options for either electronic or optical multiplexing. In electronic multiplexing, we control up to 8 of our spectrometers using a single set of operating electronics, thus saving in the cost of the electronics. In this configuration, there is no noise introduced to the measured signal as there are no moving optical parts. Alternatively, a single high end spectrometer can be paired with a fiber optical switch, operating on the principle of moving a light path through precise positioning of piezo bending elements, for up to 32 measurement points. Since there are optical elements that are moving, this introduces a very small amount of noise to the measurements. This option can dramatically lower the cost per measurement point if a high number of channels need to be realized.

Two different instruments responses are not identical. Therefore, a calibration model which is developed on one instrument will be mathematically corrected when transferring to a secondary instrument.    

Model calibration is required to correlate spectral features to a process result. Although a full recalibration is likely not required for an existing chemometric prediction, model maintenance/upkeep may be required if there is a change in sample matrix or desire for model improvement. Due to the design of tec5USA’s diode array spectrometers, our analyzer equipment maintains a permanent wavelength calibration. tec5USA offers an annual validation of the wavelength calibration and corrects any deviation which may have occurred.

Chemometrics is the term used for the process of building a method or mathematical algorithm to be deployed to predict properties of an unknown, but similar sample. It is done by analyzing known samples via a laboratory method for certain characteristics such as component levels, physical properties such as morphology, etc. These samples are then used as a training set to teach the analyzer of interest how spectra change with the change in property. Various algorithms are used and checked for robustness in their predictive properties. The mathematical equations that come out of this analysis are then used to examination unknown samples and predict these features. The data can then be used to adjust processes or make quality control decisions.

As with many analyzer solutions, spectroscopy requires an initial calibration specific to the specific target parameters. Our solutions are tailored to meet the needs of the end user, including spectrometer configuration, immersion probe & application support for model calibration. tec5USA offers fully packaged analyzer equipment which can be located directly into your hazardous process environment, without the need for a control room or external cabinet.

The limit of detection of any material depends on a number of factors. These factors include – the molar absorptivity of the compound of interest, the pathlength of the sampling apparatus, the signal-to-noise and dynamic range of the sensor, the stability of the measurement system including the optical path from the light source to the detector, and the stability of the light source itself. In some cases where there is excellent discrimination of a compound within a matrix, it could be possible to measure down to the parts per billion (ppb) range – but the specific application needs to be investigated to properly define the limit of detection.

Spectroscopy is the study of the interaction of light with matter. Light covers a broad range of the electromagnetic spectrum from high energy ultra violet (UV) photons to the near infrared (NIR), with the visible spectrum that we can see being in between. These different portions of the spectrum are important because they interact with matter in different ways. In the UV, these photons have high energy and therefore can induce electronic transitions, while the NIR photons can cause molecules to vibrate at unique frequencies. The way that we measure where compounds absorb light is by taking a spectrum, which is a graph showing the transmission of light as a function of the wavelength. All compounds have a unique absorption spectrum which can be used to identify the chemical composition of samples.

The spectroscopic methodology is determined by which parameters are important to monitor during a process. For example, if you want to monitor protein concentration in a bioreactor, in which the biosynthesis takes place in an aqueous medium, then you likely would want to use Raman spectroscopy for the application, as water does not contribute to the Raman signal. Alternatively, if moisture content is important, water has very strong absorption in the NIR due to several vibrational and combination modes that can be monitored; water is transparent in the UV and visible spectral region. Understanding which chemical is important as there could be various factors that influence the choice of methodology.