An evaluation of nitric oxide and nitrogen dioxide absorbers and filters.

The absorbance of NO (5-90 ppm) and NO 2 (0.5-4 ppm) by a number of absorbers and filters was assessed via bench testing. All absorbers (Sodasorb, Purafil CP, Purafil Select, Sofnolime, Sofnofil and 50/50 mix of Sofnolime/Sofnofil) except Sodasorb absorbed NO almost completely. Only Sofnolime absorbed NO 2 completely while Sodasorb and the Sofnolime/Sofnofil 50/50 mix had absorbances between 47% and 90%. The absorbance of four filters (ILF100, ILF150, ILF200 and HgCONO) as well as Sofnolime and the Sofnolime/Sofnofil 50/50 mix was tested in the expiratory port of a Servo 900C ventilator. All absorbers and filters produced a change in ventilator pressures. The HgCONO filter, Sofnolime and the Sofnolime/Sofnofil 50/50 mix all absorbed NO. At 80 ppm NO, the HgCONO filter had 100% absorbance for four hours while Sofnolime's absorbance was significantly reduced after one hour. All filters and absorbers tested on the ventilator except the Sofnolime/Sofnofil 50/50 mix and the ILF150 filter absorbed NO 2 completely for a period ranging from 90 minutes to four hours. We recommend the HgCONO filter and Sofnolime to absorb both NO and NO2. If absorption of NO 2 only is required we recommend the HgCONO, ILF100 or ILF200 filters or the Sofnolime absorber.