Topics
1. Development of sampling and preconcentration devices
Sampling is the preliminary step in all analyses. When an instrument operates in real-time and continuously, this sampling phase must be automated. To achieve sufficient sensitivity for the detection of pollutants in the environment, a pre-concentration phase is often necessary and is an integral part of sampling.
There are two general cases. In the first case, the pre-concentration is not selective, and many molecules of interest are trapped. The following steps must then include a separation and detection capable of discriminating between each of the target molecules. In a second case, this sampling and preconcentration step is selective to one or more compounds, for example, from the same family. This makes it possible to use shorter separation steps or dispense with them, and potentially less efficient detectors.
Selective preconcentration is therefore of great interest and can be obtained with functionalised and/or hierarchical materials.
2. Development of analyte separation systems
To analyse a multi-pollutant mixture (particularly VOCs, OVOCs, PAHs and aldehydes), the molecules need to be separated after the sampling/pre-concentration stage and before the detection. For example, in gas chromatography, a column is used to separate the analytes before detection.
Miniaturised devices incorporating a chromatographic column will be tested which may make it possible to reduce the size of the instrument.
In some cases, involving a single molecule to be detected, this separation phase is not essential. Indeed, if the detector is selective for the targeted compound or if the sampling step (incorporating a derivatisation reaction) is specific for this same molecule, the separation is useless.
3. Detector development
If the analytical instrument incorporates a sample pre-concentrator, it is possible to use less sensitive, less expensive, and more compact detectors such as electrochemical or photoionisation detectors. Compared with other detectors like Flame Ionisation Detector (FID), these detectors don’t require gases to operate (hydrogen and air), which limits the portability of the instrument.
4. Development of calibration devices
For a reliable and accurate measurement of target molecule concentrations, it is necessary to calibrate the instruments beforehand. Therefore, a calibration source, either internal or external to the instrument, is needed. For liquid-phase analysis, dilute solutions of compounds can be obtained from certified standard commercial solutions by simple dilution in the appropriate solvent. For gas-phase analyses, gas mixtures exist for certain species, particularly the most volatile. However, these gas cylinders are rarely easy to transport as they are cumbersome. The aim here is to develop more compact and less gas-consuming devices for the generation of VOCs and SVOCs mixtures at perfectly controlled and reproducible concentrations.
For example, a compound can be generated in the gaseous phase by a permeation placed in a controlled-temperature enclosure supplied by a constant flow of nitrogen. . After a certain stabilisation time, the concentration obtained is stable over time. This concentration depends mostly on the emission rate of the permeation tube used, which is expressed in ng h-1. Several permeation tubes should be used to generate a gaseous mixture of several compounds.
Studies and developments are being carried out here to :
- Reduce the time required to stabilise the concentration of the compound(s) in the gas phase;
- Predict the concentration generated based on abacuses and the experimental conditions used;
- Improve the stability of the concentrations generated;
- Improve the reproducibility of the concentrations generated;
- Improve the portability of the device by reducing its size and weight;
- Reduce manufacturing costs.
Other alternatives to the permeation tube may also be considered.
5. Development of analyte derivation methods
Sometimes, the target molecules have either low response factors with certain detectors or inadequate properties, such as polarity, to be well separated by a chromatographic column. In such cases, it is of great interest to transform the target molecule into one that can be more easily analysed and detected.
The derivatisation reaction must be rapid and complete to determine the concentration of the target species from the concentration of the reaction product and the stoichiometry of the derivatisation reaction. This is the case, for example, for the measurement of aldehydes in air using the standard reference method.
6. Validation under laboratory conditions
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7. Validation in real-life conditions
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