Formaldehyde monitoring is difficult using traditional chromatographic techniques, but it is very simple to monitor in real-time using Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) due to a very fast proton transfer ionization by H3O+.
We recently spoke with a customer that wanted to verify the concentration of aqueous solution standards of formaldehyde. The fact that SIFT-MS is highly immune to humidity in the sample also makes it ideally suited to this type of analysis.
To test the effectiveness of this measurement we injected 10 uL of a 1 mg/mL solution of formaldehyde in water into a 1 L tedlar bag. Applying the ideal gas law gives an expected gas-phase concentration of 8.3 ppm.
The result of a SIFT-MS measurement on this sample is shown in Figure 1. Note that the Voice200Ultra was not calibrated for formaldehyde before performing this measurement. The measured concentration comes from the Syft Library, which contains the reaction kinetics of formaldehyde (and over 1,000 other compounds) enabling the concentration to be calculated with excellent accuracy without calibration.
Figure 1: Sample of Formaldehyde
Furthermore, there was no sample preparation of any sort required for this measurement. The gas sample is just directly presented to the inlet of the Syft instrument and the concentration of formaldehyde is instantly reported.
Figure 2 shows the results of doing a simple 100-fold dilution of this sample demonstrating the linearity of the SIFT-MS technique, which extends over 5 orders of magnitude.
Like all analytical techniques, the limit of detection of a SIFT measurement is governed by the noise distribution of a sample blank. However, because the sample is delivered and measured continuously with SIFT, the limit of detection is also time dependent.
Figure 2 below shows the result of formaldehyde measurement on a blank (clean air) sample. This measurement establishes the limit of detection of formaldehyde at 210 ppt for a 10 second measurement.
Figure 2: 100-fold dilution of Formaldehyde