Primary standard for the number concentration of liquid-borne particles in the 10 to 20 µm diameter range

Abstract

The national primary standard for the number concentration of liquid-borne particles in the 10 to 20 µm diameter range has been developed at the National Institute of Advanced Industrial Science and Technology (AIST), Japan. The standard consists of a total number counting type flow cytometer (T-FCM) and an electronic balance. The T-FCM is a commercial flow cytometer modified so that the total number of particles in an aqueous suspension sampled in a test tube can be counted, and the electronic balance is used to determine the mass of the suspension. This standard is intended to be used for calibrating commercial standard suspensions of monodisperse polystyrene latex (PSL) particles. The measurand in the calibration is the mass-based number concentration (the particle number in a unit mass of a suspension), and the calibration capability covers the concentration range from 5 × 102 to 2 × 106 particles g−1. When the concentration of the suspension is higher than 2 × 103 particles g−1, the suspension is first diluted to about 1 × 103 particles g−1 to suppress the coincidence loss in particle counting by the T-FCM. The validity of the calibration with the T-FCM was examined by comparison with an independent method in which a scanning electron microscope (SEM) was used to determine the number concentration of particles deposited on a silicon wafer. For a suspension of 10 µm PSL particles with a concentration of approximately 1 × 106 particles g−1, the concentration values determined by the T-FCM and SEM methods were 1.042 × 106 and 1.035 × 106 particles g−1, respectively: The difference was less than 0.7%. The relative expanded uncertainty of the measurement by the T-FCM method with the coverage factor k = 2 was 4.4%.

Primary standard for the number concentration of liquid-borne particles: extension of the diameter range from the micrometer to the sub-micrometer level and reduction of the measurement uncertainty

“…To validate the measurement results obtained using the M-OPC method, we conducted an independent microscopic analysis to evaluate the number concentration of the same 1M suspensions, namely, a scanning electron microscopy (SEM) method involving the use of a JSM-6060 SEM instrument (JEOL Ltd., Japan). As described in previous papers [17,19], droplets of approximately 1 μl of a 1M suspension were separately placed on a well-cleaned silicon substrate. The mass of each droplet, M SEM , was measured with an electronic microbalance with a scale interval of 0.1 μg (XP2U, Mettler Toledo, USA).…”

“…Meanwhile, the National Metrology Institute of Japan (NMIJ) of the National Institute of Advanced Industrial Science and Technology supplies calibration services for the particle number concentration of aqueous suspensions to standard suspension manufacturers working in the diameter range of 2 μm-10 μm and a number concentration range of 500 particles g −1 -2000 000 particles g −1 based on a specially modified optical flow cytometer [17,18], which enables the absolute measurement of particle number concentration through counting all the particles sampled in a test tube via a procedure involving several repetitions of rinsing. However, one issue here relates to how the measurement procedure using the flow cytometer requires a long measurement time due to the limited flow rate (∼180 μl min −1 ).…”

Reference measurement procedures for the accurate determination of cell concentrations: present status and future developments/Referenzmessverfahren für die genaue Bestimmung von Zellkonzentrationen: Status und zukünftige Entwicklungen

“…To meet the requirements of a primary measurement procedure, i.e., low uncertainties and traceability to SI units, the sample preparation and volume determination of the measurement suspension is based on gravimetrical methods. Following this idea would fi rstly allow quantifi cation of cell concentrations in terms of particles per mass [40] . However, this type of concentration is not common in haematology and haematopathology.…”

Primary Determination of Particle Number Concentration with Light Obscuration and Dynamic Imaging Particle Counters

“…Relative expanded uncertainties with this instrument are typically (1.5 to 4) % of number concentration. Sakaguchi and Ehara described a method to determine the number concentration of (10 to 20) µm microspheres with a relative expanded uncertainty of 4.4 %, using a slightly modified flow cytometer [10]. They also reported additional measurements by scanning electron microscopy (SEM) that have lower uncertainty (relative expanded uncertainty of 1.0 %), but that are arduous to perform.…”

“…There are similar approaches to address counting and volumetric errors in the literature. For example, Sakaguchi and Ehara [10] avoided transient effects by bracketing a volume of particle-laden solution with clean sheath fluid during the measurement process. Kammel et al [9] understood the exact timing of their instrument, since it was specially built for the purpose.…”