School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
Analyst. 2011 Sep 7;136(17):3487-95. doi: 10.1039/c0an00843e. Epub 2011 Mar 4.
We have developed and studied methods to characterize the time-varying composition of liquid microdroplets, under controlled changes to environmental conditions, using Raman tweezers. This work has focussed on measurements of inorganic salts, such as nitrate and sulfate anions, which comprise a major fraction of the dissolved solutes in atmospheric aerosols. The experimental Raman intensities for the anions of inorganic salts in optically tweezed droplets were found to be in good agreement with theoretical estimates of photon scattering. The detection limit for sodium nitrate salt in a single particle was found to be ~4 pg. The mass of an inorganic salt in the droplet can be estimated from the Raman intensity of the anion bands using a calibration curve which is independent of droplet volume. The volume of the droplet, and concentration of solute, can be found directly from the spacing of morphology dependent resonances in the Raman band of water, or indirectly from the integrated-intensity of the Raman band for the solvent. The later strategy eliminates the uncertainty in the collection efficiency of Raman-scattered light related to varying particle sizes.
我们已经开发并研究了使用拉曼钳来描述在环境条件受控变化下，液体微滴时变组成的方法。这项工作集中于对硝酸盐和硫酸盐等无机盐的测量，它们是大气气溶胶中溶解溶质的主要成分。在光学钳制液滴中，无机盐阴离子的实验拉曼强度与光子散射的理论估计值吻合良好。在单个粒子中，对硝酸钠盐的检测限约为 4pg。可以使用与液滴体积无关的校准曲线，根据阴离子带的拉曼强度来估算液滴中无机盐的质量。可以直接从与形貌相关的水拉曼带的共振间距或从溶剂的拉曼带的积分强度间接确定液滴的体积和溶质的浓度。后一种策略消除了与粒径变化相关的拉曼散射光收集效率不确定性。
