# Performance Comparison among KN95-Certified Face Masks by Classical Techniques and Innovative Test
## 2 Materials and Methods
### Novel Methylene Blue Test Method  
As reported in our previous work [31], the experimental setup of the new method developed for the evaluation of droplets and aerosol inhaled fraction can be described as follows: the emitter was simulated using a Hudson Micromist (Teleflex, Morrisville, NC, USA) small volume jet nebulizer operating at 7 L/m as driving flow. The nebulizer generates a distribution of nebulized drops with a median size of 5 \(\upmu\)m and an asymmetric distribution [32], thus covering the range of both airborne and droplet transmission models. To identify the degree of filtering efficacy, an aqueous solution (deionized water by system ARIOSO Water Purification System, Human Corporation, Seoul, Korea) of 3.44 g/L of methylene blue (Merck, Darmstadt, Germany, 95%) was employed to be nebulized. The receiver was simulated using a pneumatic lung simulator (Dimar, Mirandola, Italy) connected to a Styrofoam head mannequin (acting the part of an exposed individual) protected with the different investigated masks. We simulated a normal breathing pattern with 550 mL tidal volume per breath and a respiratory rate of 14 breaths per min. The emitter was placed in front of the receiver at a 40 cm distance; between the receiver and the lung simulator, a custom-made filter with disposable cotton pads [33], was placed to intercept the nebulized methylene blue. The nebulizer was operated for 30 min loaded with 12 mL of methylene blue solution. Thanks to this arrangement, it is intrinsically possible to take into consideration how each mask fits the head mannequin according to its shape. Measurements were replicated on three different samples for each mask type. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Name** & **Certification** \\ \hline
0 & GOLDEN STANDARD 3M & FFP2 1 \\
1 & KN 95 WN GUANGZHOU WEIN TECHNOLOGY & KN95 2 \\
2 & DYD KN95 PARTICULATE RESPIRATOR & KN95 2 \\
3 & KN95 POWECOM CINA & KN95 2 \\
4 & KN 95 1981 IVASIAN CINA & KN95 2 \\
5 & KN 95 (no brand) & KN95 2 \\
6 & KN95 BYD ELECTRONICS GB2626-2006 & KN95 2 \\
7 & TEDA TECLANDA KN 95 & KN95 2 \\
8 & MEDICAL MASK EN 146832014 KN95 SINILIAISI CINA & KN95 2 \\
9 & KN95 GB2626-2006 QINGHAI ZHONG DAO CINA & KN95 2 \\ \hline \hline \end{tabular} \({}^{\dagger}\)FFP stands for Filtering Factor Protection of types 12 and 3, according to Europe EN 149/2001 regulations standards, as depicted in the Introduction paragraph. \({}^{2}\)KN95 stands for the performance standard GB2626-2006 of China.  
\end{table} 
Table 1: Name, sequential sample number, and certification type of each tested device. Figure 1: Tested KN95 devices plus FFP2 golden standard mask (0); the sequential numbers are related to Table 1.  
The amount of methylene blue deposited on each cotton pad behind the facial mask was analyzed through UV-Vis spectrophotometry (Lambda 35, Perkin Elmer, Waltham, MA, USA), with the aid of an integrating sphere. The analysis was operated at a wavelength of 664 nm, corresponding to the maximum absorbance of MB [34], collecting diffuse reflectance values (R%). The development of the method started with the calibration of the instrument: a blank cotton pad (no MB nebulization) was considered as a 100 R% reference, equivalent to a 0% inhaled fraction. A saturated cotton pad (MB nebulization performed at 0 cm without a face mask) was instead considered as 0 R% reference, also corresponding to 100% inhaled fraction. The resulting filtering efficiency of all investigated masks was expressed as a percentage inhaled fraction: this was evaluated considering the different R% values obtained with the different samples and compared with the gold standard's R% value. We assessed the minimum amount of detectable inhaled fraction (i.e., sensitivity) in a calibration experiment in which nebulization time was decreased in 1 s steps: the minimum nebulization time required to detect an R% signal was 22 s, which corresponds to 1.22% of the total nebulization time used in our current experimental runs (1800 s).