Continuous Measurement of Individual Formaldehyde Exposure with a DIY Photometer

Formaldehyde is widely used in pathology for the preservation of tissue specimens. Due to a lack of alternatives, it continues to be used despite its toxic properties. Currently existing sensors are not suitable for daily use in pathology due to their long reaction times in the range of minutes (electrochemical) or the size of their volume of more than 5 liters (optical). In order to accurately record the individual exposure of employees and thus enable targeted protective measures, a mobile formaldehyde sensor based on a 340 nm UV-LED is presented. To enhance the absorption in a compact design, a multi-pass cell is developed that extends the light-gas interaction by mirroring the light. With the developed photometer, it is possible to measure formaldehyde concentrations down to a minimum of 2 ppm at an averaging period of 1 s. The limiting factor to further decrease the lowest measurement limit of the photometer is the light loss in the multi-pass cell due to beam expansion and absorption by the mirrors. Possibilities to reduce the light loss are shown in order to monitor the permissible individual exposure at work of 0.3 ppm.