Kwong W T, Ho S L, Coates A L
Divisions of Respiratory Medicine and Lung Biology Research, Research Institute, Hospital for Sick Children and the University of Toronto, Toronto, Ontario, Canada.
J Aerosol Med. 2000 Winter;13(4):303-14. doi: 10.1089/jam.2000.13.303.
Particle size of nebulized aerosols can be measured directly using laser diffraction or by evaluating aerodynamic properties by cascade impaction. As of today, there are no generally accepted standards for measuring particle size distribution from nebulizers. Laser diffraction has been questioned because of potential evaporative losses of the small particles at the edge of the plume, causing an apparent shift in the particle size distribution and thus a larger mass median diameter (MMD). When particle-sizing wet aerosols, cascade impaction may give rise to an apparent shift in the distribution, resulting in a smaller mass median aerodynamic diameter (MMAD) due to evaporative losses of aerosol droplets as they enter the impactor at ambient temperature. The modified low-flow Marple 296 Personal Cascade Impactor (MPCI) is currently being proposed as the European standard for wet aerosol analysis to minimize evaporative losses during sampling. The present study compared the particle size distribution of salbutamol and sodium cromoglycate aerosols nebulized by the Pari LC Star, using laser diffraction (Malvern Mastersizer X; MMX) and cascade impaction (Andersen Cascade Impactor [ACI] and the commercially available MPCI), which was either at ambient temperature or cooled to the nebulized aerosol temperature (10 degrees C). MMDs obtained with the MMX were virtually identical to the MMADs measured with both impactors when cooled with no significant differences in geometric standard deviation (sigma(g)). When the impactors were operated at ambient temperature, MMADs were smaller (18 to 30%) with a significantly larger sigma(g) (p < 0.05) compared to the MMX. These findings suggest that droplet distribution data for wet aerosol where evaporation process has not been minimized must be viewed with caution. There was no evidence suggesting a significant evaporative loss of small droplets from the edge of the plume during laser particle sizing. The MPCI does not minimize evaporative losses of aerosol particles during sampling.
雾化气溶胶的粒径可直接使用激光衍射法测量，或通过串联冲击法评估空气动力学特性来测量。截至目前，尚无用于测量雾化器产生的粒径分布的普遍接受的标准。激光衍射法受到质疑，因为羽流边缘的小颗粒可能存在潜在的蒸发损失，导致粒径分布出现明显偏移，从而使质量中值直径（MMD）变大。对湿气溶胶进行粒径测定时，串联冲击法可能会导致分布出现明显偏移，由于气溶胶液滴在环境温度下进入冲击器时发生蒸发损失，导致质量中值空气动力学直径（MMAD）变小。目前正在提议将改进的低流量马普尔296型个人串联冲击器（MPCI）作为湿气溶胶分析的欧洲标准，以尽量减少采样过程中的蒸发损失。本研究比较了使用帕里LC之星雾化的沙丁胺醇和色甘酸钠气溶胶的粒径分布，采用激光衍射法（马尔文大师Sizer X；MMX）和串联冲击法（安德森串联冲击器[ACI]和市售MPCI），冲击器要么处于环境温度，要么冷却至雾化气溶胶温度（10摄氏度）。当冷却时，用MMX获得的MMD与用两种冲击器测量的MMAD几乎相同，几何标准偏差（σg）无显著差异。当冲击器在环境温度下运行时,与MMX相比，MMAD较小（18%至30%），σg显著更大（p<0.05）。这些发现表明，对于蒸发过程未得到最小化的湿气溶胶的液滴分布数据，必须谨慎看待。没有证据表明在激光粒径测定过程中，羽流边缘的小液滴存在显著的蒸发损失。MPCI在采样过程中并未将气溶胶颗粒的蒸发损失降至最低。
