Characterisation of a cigarette smoking machine designed for air-liquid interface exposures: an inter-laboratory study
The Borgwaldt RM20S smoking machine generates, dilutes and delivers whole cigarette smoke for in vitro testing at the air-liquid interface (ALI). The RM20S, in combination with BAT's exposure chamber (patent publication no. WO 03/100417 A1), enables direct exposure of in vitro cell/tissue cultures to whole cigarette smoke at the ALI, from 30 minutes to 3 hours duration. The machine smokes up to eight cigarettes simultaneously into eight independent syringes and dilutes this smoke consistently, in a dynamic range.
A rigorous evaluation of two RM20S machines from two independent locations was conducted, the laboratories being in Montréal and Southampton. Smoke dilution and precision were compared and characterised as an essential step to validating these machines. A methane gas standard was used to assess syringe dilution precision. Dilutions of 1:1000, 1:500 and 1:193 (gas:air, volume:volume) were tested and measurements were compared between labs and syringes. Quantification of methane for each syringe was made using the heated flame ionization detector (FID) total hydrocarbon analyzer. No statistically significant differences (P >0.05) were observed in the lower dilution ranges of 1:1000 and 1:500 between labs. For all three dilutions, combined residual standard deviation was between 6.3% and 17.3%, R2 >0.98 and error between 4.3% and 13.1%.
Values obtained from these experiments were within acceptable limits (RSD <10% and R2 >0.95) indicating that the equipment can reliably dilute accurate doses of whole smoke for ALI exposure and dosimetry studies. Despite some noticeable variability, all syringes were still consistent across locations. Furthermore, having assessed the precision of the smoking machine in two different laboratories and with different operators provides us with even greater confidence in the reliability of equipment and of smoke dose. These results suggest the Borgwaldt RM20S system provides a reliable and repeatable method for generating and delivering whole smoke to in vitro ALI exposure systems.