Ripple Dean C, DeRose Paul C
National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
J Res Natl Inst Stand Technol. 2018 Jan 11;123:1-21. doi: 10.6028/jres.123.002. eCollection 2018.
Accurate number concentrations of particles in liquid media are needed to assess the quality of water, pharmaceuticals, and other liquids, yet there are limited reference materials or calibration services available with clear traceability to the International System of Units. We describe two methods, based on very simple modifications of commercial particle counter instruments, that can provide traceable number concentration measurements. One method used a light obscuration counter. Fitting a model to the data enabled correction for timing and coincidence errors, and gravimetric calibration of the syringe pump gave a traceable determination of measured volume. Other potential biases were diagnosed by analysis of the particle size distribution. The other method used a dynamic imaging particle counter (a flow imaging microscope). The instrument was intentionally configured so that each particle passing through the flow cell was imaged multiple times. Following the particle image acquisition runs, runs with a rinse solution released and counted microspheres adsorbed to tubing or flow-cell walls. Software assembled the redundant particle images into tracks, and the total number of tracks was assigned as the number of particles counted. Both light obscuration and dynamic imaging methods, when applied to polystyrene microspheres of approximately 4 μm diameter, achieved expanded uncertainties ( = 2) of approximately 2 % of number concentration and agreed to within a difference of 1.1 %.
为评估水、药品和其他液体的质量，需要准确测量液体介质中颗粒的数量浓度，但目前可溯源至国际单位制的参考物质或校准服务有限。我们描述了两种方法，它们基于对商用颗粒计数器仪器进行非常简单的改进，可提供可溯源的数量浓度测量。一种方法使用光散射计数器。对数据拟合模型可校正计时和重合误差，通过对注射泵进行重量校准可溯源测定测量体积。通过分析粒径分布诊断其他潜在偏差。另一种方法使用动态成像颗粒计数器（流动成像显微镜）。有意对仪器进行配置，使每个通过流动池的颗粒被多次成像。在进行颗粒图像采集运行后，用冲洗液释放并计数吸附在管道或流动池壁上的微球。软件将冗余的颗粒图像组合成轨迹，并将轨迹总数作为计数的颗粒数量。当将光散射和动态成像方法应用于直径约4μm的聚苯乙烯微球时，数量浓度的扩展不确定度（k = 2）约为2%，两者的测量结果相差在1.1%以内。
