基于ICP-MS的二氧化硅亚微米粒子特征参数分析

将电感耦合等离子体质谱仪（ICP-MS）配合外部质谱信号采集存储装置，用于研究表征亚微米颗粒粒径和浓度参数。在模拟采集模式下，以300~2 000 nm粒径的SiO₂粒子为例，通过优化进样系统及仪器的工作参数，分析了样品提取速率和雾化气流速对单颗粒质谱信号强度的影响。在优化的实验条件下，SiO₂颗粒粒径部分检测限为233 nm，对300~900 nm粒径粒子测量的线性相关系数大于0.99，但对1 500、2 000 nm粒径粒子的检测结果出现明显偏差。论证了利用样品传输效率测量悬浮液粒子浓度的可行性，并将ICP-MS的粒径测量结果与扫描电镜法（SEM）、光子相关光谱法（PCS）的测量结果进行比较，3种方法对于粒径小于900 nm粒子的测定结果基本一致，且具有相似的测量精度。该方法分析速度快、结果准确，可用于SiO₂亚微米粒子粒径、浓度参数的测量。

Analysis of Characteristic Parameters of Sub-micron Silicon Dioxide Particles by ICP-MS

Nanoparticles and sub-mciro particles were increasingly adopted in the field of catalyzer, semiconductor, magnetic material, biomedical additives, consumer goods and food. Inductively coupled plasma-mass spectrometer (ICP-MS) is an alternative way to determine characteristic parameters of particle. However, the transient signals duration in a range of 300-800 μs from individual particles is shorter than that offered by the most of ICP-MS instruments. In this work, a method of ICP-MS combined with extra data acquisition and storage devices for measuring the diameter and concentration of sub micrometer particles was established. An Elan 6000 ICP-MS was used with the analog output pin connecting to a current amplifier. The amplified signal was recorded by an oscilloscope. The data acquisition rate of 40 kHz was used to obtain an individual peak for each particle. A data processing algorithm including filtering noise and subtracting the threshold was developed in this work to process the raw data. The silicon dioxide particles in the range of 300-2000 nm were used for the optimization of sample system and instrument conditions, the effect of sample uptake rate and sample gas flow rate on the signal intensity from single particle were discussed as well. The signal intensity increased initially with the gas flow rate which may be due to the increasing of nebulization efficiency and approaching to the optimum ionization position, and then decreased after reaching the maximum because of the ion diffusion. The optimum sample gas flow rate was 0.90-0.95 L/min for sample uptake rate of 100 μL/min. Under the conditions of optimization, the diameter detection limit of SiO₂ particle was 233 nm, which depended on the background interference, instrument sensitivity and electronic noise. The correlation coefficient of linear calibration curves of particle mass for 300-900 nm particles was over 0.99. While, there were significant deviations for 1 500 nm and 2 000 nm particles measurements. The transport efficiency calculated using particle concentration method was in good agreement with the filter trap method. With the increasing of sample uptake rate, the transport efficiency reduced from 33% to 2.2%. The diameter results given by ICP-MS, photon correlation spectroscopy (PCS) and scanning electron microscope (SEM) showed the consistence under 900 nm. In comparison, a slight worse diameter resolution based on ICP-MS was observed. The broadening effects were considered to be caused by variations in droplets size and ionization positions in plasma. The goals will be focused on improving the transport efficiency of sample introduction system in the future.