Polystyrene latex standards

Heller and Tabibian (13) noted that errors, due to laterally scattered light and the corona effect, as large as to cause a 30 reduction in measured turbidity, may result if instruments which are perfectly suitable for ordinary absorption measurements are used for turbidity measurements without proper modifications. To evaluate the performance of our turbidity detector, particle suspensions of various concentrations of several polystyrene latex standards were prepared. Their extinction coefficients were measured using both a bench-top UV spectrophotometer (Beckman, Model 25) and the online detector (Pharmacia). 

The polystyrene seed latex was monodispersed. Even after several grow-ups (polymerizations) the final 1650 A latex was monodispersed. Hydrodynamic chromatography on the 1650 A latex gave a mean diameter of 1660 a with a size variance as small as for normal polystyrene latex standards (typical standard of 1760 8 with a standard deviation of 23 a). The final latex particle size could be accurately predicted from the initial particle size and the total amounts of monomer and polymer used. 

The analysis method employed is the patented external gradient method described in detail elsewhere (1,4). The overall instrument performance was evaluated using monodisperse polystyrene latex standards, covering a range from 0.176 urn to 1.09 pm, obtained from Dow Diagnostics, Indianapolis, Indiana. 

The disc centrifuge used in this study has been described previously (4, 5). (A commercial verlson of the instrument is now available from Brookhaven Instruments Corporation, Ronkonkoma, NY, as the Brook-haven DCP-1000 Particle Size Analyzer.) The latexes used in this study are monodisperse Dow polystyrene latex standards covering a range of sizes and two commercial latexes designated as 2 and 4, both of which had a broader dispersity than the polystyrene latex standards. All of the latex sample preparations analyzed in the statistical study were prepared in a similar manner. All the fluids were held in a thermostatically controlled temperature bath at 25°C. The temperatures at the beginning and end of each run were recorded. 

Results obtained on two different samples containing the four latexes mentioned above plus an additional polystyrene latex standard, namely 0.357pm, are shown in Figure 5. Using the same procedure described previously, in four separate experiments and using disc speeds of 4004, 6015, 8057, and 10,160 rpm, a distinct separation of the standards is seen over this wide range of Analyzer disc speeds. 

Ki, the detector response factor, describes the signal generated when particles are present in the eluant as it transits the detector flow-through cell. Detector response arises primarily from scattering of light by the latex particles (15), although a small contribution from light absorption by the sample may occur (16). Polystyrene latex standards of known size and concentration were used to determine Ki factors for conversion of detector response into mass concentration information. 

Fig. 34.A Correction for zone broadening of a model fractogram. a represents the original curve and the corrected one whereas b is the uncorrected fractogram. Reproduced from [460] with kind permission of the American Chemical Society. B Comparison of differential particle size distributions of narrowly distributed polystyrene latex standards derived by MALLS and Fl-FFF without correction for zone broadening. Reproduced from [461] with kind permission of Academic Press...

In the first experimental work on FIA-FIFF [1], the system efficiency was studied by examining the effect of the ratio of injection flow rate to frit flow rate on hydro-dynamic relaxation the initial tests showed a possibility of using hydrodynamic relaxation in asymmetrical flow FFF with a number of polystyrene latex standards, in both normal and steric/hyperlayer modes of FFF Normally, relaxational band broadening under hydrodynamic relaxation arises from a broadened starting band. The length of an initial sample band during hydrodynamic relaxation is dependent on flow rates as... 

Figure 15. Fractograms of chromatographic silicas identified (by letter) in Table 11 obtained by using (a) sedimentation FFF system Sed 1 and (b) flow FFF system Flow II. The diameter scale at the top is obtained by using a calibration process based on equation 10 and the measured retention times of polystyrene latex standards. For sedimentation FFF, density compensation is carried out by adjusting the spin rate for each support material in accordance with its density (20). The corresponding spin rates utilized are A, 465 B, 479 C, 425 D, 500 ...

Figure 41.1 shows, for illustrative purposes, the fracto-grams for two different size ranges of polystyrene latex microspheres. (Polystyrene latex standards with narrow size distributions are ideal probes for testing the resolving power and accuracy of particle characterization methods. Those techniques unable to resolve close-lying latex... 

Figure 12. Normalized reflection spectra from several polystyrene latex standards. Taken with probe configuration 2. (1 collecting fiber next to the delivering fiber).

FIG. 1.8 Electron micrograph of cross-linked monodisperse polystyrene latex particles. The latex is a commercial product (d = 0.500 jun) sold as a calibration standard. (Photograph courtesy of R. S. Daniel and L. X. Oakford, California State Polytechnic University, Pomona, CA.)... 

Monodisperse spheres are not only uniquely easy to characterize, but also very rarely encountered. Polymerization under carefully controlled conditions allows the preparation of the polystyrene latex shown in Figure 1.8. Latexes of this sort are used as standards for the size calibration of optical and electron micrographs (also see Section 1.5a.3). However, in the majority of colloidal systems, the particles are neither spherical nor monodisperse, but it is often useful to define convenient effective linear dimensions that are representative of the sizes and shapes of the particles. There are many ways of doing this, and whether they are appropriate or not depends on the use of such dimensions in practice. There are excellent books devoted to this topic (see, for example, Allen 1990) and, therefore, we consider only a few examples here for the purpose of illustration. 

Single-particle optical analyzers are especially useful for continuous measurement of particles of uniform physical properties. However, as discussed earlier, uncertainties develop in the measurement of particle clouds that are heterogeneous in composition because the refractive index may vary from particle to particle. Thus, in making atmospheric aerosol measurements, workers have assumed an average refractive index characteristic of the mixture to estimate a calibration curve or have reported data in terms of the equivalent particle diameter for a standard aerosol, such as suspended polystyrene latex spheres. 

The polystyrene latex (PSL) spheres were obtained from Seragen Diagnostics. The nominal sizes of these standards were from electron microscopy measurements. The samples were prepared by diluting the 10% solids in filtered, doubly distilled water, adding a small amount of SDS to help disperse the samples and sonicating with Branson 60 watt bath sonicator for 30 seconds to disperse any aggregates. The relative volumes (weights) of the two sizes of PSL in the mixed sample were estimated to be accurate to about 5-10%. 

The mixture was sonicated to eliminate aggregates. A polystyrene latex with a broad distribution was obtained from Kodak. This distribution had been characterized previously by electron microscopy, ultra centrifuge and Coulter counter. A monodlsperse, surfactant free, sulfated, polystyrene standard and a mixture of 10 such monodlsperse standards were purchased from Interfaclal Dynamics Corporation. A polyvinyl chloride latex with a broad distribution was donated by B. F. Goodrich. This sample had been characterized by Joyce Loebl disc centrifuge. These samples were diluted to 0.01% solids and sonicated to eliminate aggregates. 

The raw data trace for a mixture of 6 standard polystyrene latex microspheres is shown in Figure 2. This separation was done in 20 minutes at 10,450 rpm. While particle size data in the first few minutes is difficult to quantitate accurately with the DCP, this separation demonstrates the resolution capability of the instrument. Figures 3-7 show typical raw data, and number, surface and weight differential and cumulative distribution plots produced by the data system along with the corresponding report. 

Many papers report the fractionation of polystyrene latexes or mixtures thereof, as such commonly available spherical latex standards are an ideal system to test FFF setups or evaluations (for an example, see [362,401]). Recent coupling of Fl-FFF to MALLS enables a very high precision in particle size determinations. One example is shown in Fig. 31, where two Duke standard latex batches of a nominal size of 100 nm were investigated by Fl-FFF/M ALLS, underlining both separation power and resolution. Using traditional techniques such as photon correlation spectroscopy (PCS) and classic Fl-FFF detection, these samples seem to be identical. However, with Fl-FFF/MALLS, the batches could be separated as two discrete size distributions with a peak size that differed by 3 nm. However, it is not stated if a precise temperature control was maintained so that, critically considered, the observed differences could also have their origin in slight temperature... 

Monodisperse polystyrene (latex) spheres having a radius value in the range 30-100 run with a standard deviation of 8% or less characterizing the size uniformity. Such samples can be obtained from Duke Scientific Corp. as 3000 Series Nanospheres (www. dukescientific.com), Polymer Laboratories as PL-Latex Plain White (www.polymerlabs. com), and Polysciences, Inc., as Nanobead Traceable Size Standards (www.polysciences. com). 

Polystyrene Latex (PSL) Bead Solution Filtration Experiments were conducted to obtain filter retention, flow rate, and Ap data for a DI water based PSL bead mix solution prepared using particles ranging from bead diameters of 0.772 to 20 pm. It is a common practice to use PSL bead challenge solutions (created by mixing different size PSL bead standards in specific volumetric ratio to simulate slurry-like particle size distribution for the bead mix solution) to obtain relative quantitative retention data for various filters. These solutions are expected to retain stable PSD and provide more consistent information compared to real CMP slurries, which may change particle characteristics over time. 

Narrowly classified latices are available from Dow Chemicals [134] but doubt has been expressed on the accuracy of their sizing. A 3.49 pm polystyrene latex was independently sized by electron microscopy and found to have a mean diameter of 3.40 pm [135]. This standard was used by Coulter Electronics as a standard to size other Dow latices [136] that are available from them as standard suspensions. 

Calibration of optical devices is most frequently performed using polystyrene latex spheres that can be generated from dilute aqueous suspensions and dried before measurement. The ASTM developed a standard for the use of reticles, or disks, that can be placed in the path of the beam of a laser diffraction device for the purpose of calibration. Some manufacturers maintain that their instmments... 

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