Using Paradigm Workflows to Determine Concentrations

Extracting valuable information about how much of a particular component is found within a sample is a vital application of FTIR spectroscopy. Part of the Thermo Scientific™ OMNIC™ Paradigm Software, TQ Analyst EZ offers a key method of creating ways to gather quantitative measurements from a spectrum.

This process may be as complicated as a CLS multivariate quantitative analysis application, which determines the concentrations of several components, or as easy as a baseline-corrected peak area.

A simple peak height analysis was created in order to reveal the advantages of incorporating TQ Analyst EZ methods into a workflow, which was based upon the N-H stretching band near 3300 cm-1 measured on the Thermo Scientific™ Nicolet™ Summit FTIR Spectrometer. The spectrometer was configured by using the Thermo Scientific™ Everest Diamond ATR Accessory.

A fast and accurate method of measuring the additive value in a plastic formulation was facilitated by the Everest ATR Accessory with rugged single bounce diamond crystal, which can perform this analysis even with rigid, irregular shaped samples.

Using the Nicolet Summit FTIR Spectrometer and Everest ATR Accessory to acquire high-quality infrared spectra from plastic parts.

Figure 1. Using the Nicolet Summit FTIR Spectrometer and Everest ATR Accessory to acquire high-quality infrared spectra from plastic parts.

Using TQ Analyst EZ to measure the peak height has multiple benefits when creating a workflow, despite the fact that OMNIC Paradigm can be used to make the same measurement (as is demonstrated below). The first such advantage that TQ Analyst EZ has performed this calculation is that, once the method is created, it can subsequently be used with future workflows as well as being compatible with legacy OMNIC systems.

Indeed, the risk of varying results created by different instruments is greatly reduced with this compatibility. In addition to this, many TQ methods that were developed for older systems are able to be used directly in conjunction with the instruments running OMNIC Paradigm Software.

Measuring the N-H stretch peak height in an ATR spectrum.

Figure 2. Measuring the N-H stretch peak height in an ATR spectrum. Image Credit:

The figure below shows the TQ Analyst interface for creating a new method. This example depicts the use of the N-H stretch peak at 3300 cm-1. If it can be assumed that Beer’s law applies (Abs = A*B*C) and that the path length and the Absorptivity of this peak are both known, it is possible to divide the measured peak height by the value, in order to find the concentration. In this example, a Maximum Peak Height in Region with a two-point baseline is used to calculate the intensity of the peak.

Creating a TQ Analyst EZ method to calculate the concentration from the peak heigth.

Figure 3. Creating a TQ Analyst EZ method to calculate the concentration from the peak height.

A further advantage that TQ Analyst EZ has is its capacity to generate composite variables that can merge the values from several component measurements. The Composite calculation is simple, assuming the concentration is a linear function of absorbance. A zero correction may be added or even second-order Algebraic Formula used in some cases.

Using the Composite feature to scale the peak height by the absorptivity.

Figure 4. Using the Composite feature to scale the peak height by the absorptivity.

The OMNIC Paradigm software then automatically generates the resulting workflow. The method and spectrum that are to be analyzed can be selected by the user simply clicking on the TQ Analyst tile. Indeed, the automatic display of the component names and other information is activated when this method is selected. The first component, in this example, is the measured peak height, whereas the second is the composite, as calculated above.

Adding the TQ method to a simple OMNIC Paradigm workflow.

Figure 5. Adding the TQ method to a simple OMNIC Paradigm workflow.

This information has been sourced, reviewed and adapted from materials provided by Thermo Fisher Scientific – Materials & Structural Analysis.

For more information on this source, please visit Thermo Fisher Scientific – Materials & Structural Analysis.

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