ASTM E2490-09(R2021) pdf free download

ASTM E2490-09(R2021) pdf free download.Standard Guide for Measurement of Particle Size Distribution of Nanomaterials in Suspension by Photon Correlation Spectroscopy (PCS)
5. Significance and Use
5.1 PCS is one of the very few techniques that are able to deal with the measurement of particle size distribution in the nano-size region. This guide highlights this light scattering technique, generally applicable in the particle size range from the sub-nm region until the onset of sedimentation in the sample. The PCS technique is usually applied to slurries or suspensions of solid material in a liquid carrier. It is a first principles method (that is, calibration in the standard under- standing of this word, is not involved). The measurement is hydrodynamically based and therefore provides size informa- tion in the suspending medium (typically water). Thus the hydrodynamic diameter will almost certainly differ from other size diameters isolated by other techniques and users of the PCS technique need to be aware of the distinction of the various descriptors of particle diameter before making com- parisons between techniques. Notwithstanding the preceding sentence, the technique is widely applied in industry and academia as both a research and development tool and as a QC method for the characterization of submicron systems.
6. Reagents
6.1 In general, no reagents specific to the technique are necessary. However, dispersing and stabilizing agents often are required for a specific test sample in order to preserve colloidal stability during the measurement. A suitable diluent is used to achieve a particle concentration appropriate for the measure- ment. Particle size is likely to undergo change on dilution, as the ionic environment, within which the particles are dispersed, changes in nature or concentration. This is particularly notice- able when diluting a monodisperse latex. A latex that is measured as 60 nm in 1 × 10 -3 M NaCl can have a hydrody- namic diameter of over 70 nm in 1 × 10 -6 M NaCl (close to deionized water). In order to minimize any changes in the system on dilution, it is common to use what is commonly called the “mother liquor”. This is the liquid in which the particles exist in stable form and is usually obtained by centrifuging of the suspension or making up the same ionic nature of the dispersant liquid if knowledge of this material is available. Many biological materials are measured in a buffer (often phosphate), which confers the correct (range of) condi- tions of pH and ionic strength to assure stability of the system. Instability (usually through inadequate zeta potential (2) can promote agglomeration leading to settling or sedimentation in a solid-liquid system or creaming in a liquid-liquid system (emulsion). Such fundamental changes interfere with the sta- bility ofthe suspension and need to be minimized as they affect the quality (accuracy and repeatability) of the reported mea- surements. These are likely to be investigated in any robustness experiment.
7. Procedure
7.1 Verification: 7.1.1 The instrument to be used in the determination should be verified for correct performance, within pre-defined quality control limits, by following protocols issued by the instrument manufacturer. These confirmation tests normally involve the use of one or more NIST-traceable particle size standards. In the sub-micron (< 1 × 10 -6 m) region, then these standards (for example, NIST, Duke Scientific- now part of Thermo Fisher Scientific) tend to be nearly monodisperse (that is, narrow, single mode distribution, PI < 0.1) and, while confirming the x (size) axis, do not verify the y (or quantity axis). Further, there is a lack of available standards for the sub-20 nm region and therefore biological materials (for example, bovine serum albumin–BSA, cholesterol, haem, size controlled dendrimers, Au sols) of known size (often by molecular modeling) can be utilized. Note that PCS is a first principles measurement and thus calibration in the formal sense (adjustment of the instru- ment to read a true and known value) cannot be undertaken. In the event of a “failure” at the verification stage, then the issues to check involve quality of the dilution water, state of disper- sion and stability of the standard under dilution plus instru- mental issues such as thermal stability, cleanliness and align- ment of optical components. The raw correlogram data can be examined during and after acquisition.