Standard latexes

A comparison is made of the detector signal in the absorption versus scattering mode. Particle sizes are calculated for the standard latex samples and their mixtures using recently reported analytical. methods which account for imperfect resolution. 

A certain proportion of fluoroelastomers is used in latex form. The compounding techniques used are similar to those used for standard latexes i.e., solid ingredients are first dispersed in water with the use of surface active agents and liquid ingredients are prepared as emulsions prior to their addition to the latex. The dispersions of solids are prepared in ball mills or high-speed mills (e.g., Kady). 

Figure 4 shows the results obtained on another sample containing four different standard latexes with particle sizes of 1.091, 0.822, 0.600 and 0.497pm, using a spin fluid of 11 ml of water topped with an external gradient of 9 ml of water and 1 ml of methanol and a disc speed of 3586 rpm. Peak appearance times of 3.6 minutes, 7.1 minutes, 12.5 minutes and 19 minutes correspond to calculated particle size values of 1.142, 0.813, 0.613 and 0.497 pm respectively, which are in excellent agreement with the nominal values of the standards. 

Figure 5. DCP separation of standard latexes at four different disc speeds by the EGM method.

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... 

Fig. 31. Fl-FFF-MALLS particle size distribution for two Duke standard latexes of nominal size 100 nm but from two different batches. Reproduced from [374] with kind permission of John Wiley and Sons...

Leynadier F, Herman D, Vervolet D, Andre C. Specific immunotherapy with a standardized latex extract versus placebo in allergic health care workers. J Allergy Clin Immunol 2000 106 585-590. 

At present the most sensitive indicators of effect arey aM-U and RBP-U, both belonging to the low molecular mass proteins (Herber et al.. 1988). Enhancement of started at a Cd-U concentration of 3-6 molecular mass proteins are used for the assessment of tubular damage, the determination of RBP-U is to be preferred over /SaM-U, as the latter protein already deteriorates in the bladder at pH 5.5. For the determination of / aM-U. RBP-U and also Alb-U a standardized latex immunoassay method is available (Herber et al., in press). Another possibility to assess tubular proteinuria and glomeruiar proteinuria is SDS-Page electrophoresis (Herber et al., 1988). 

Since the 1950s, batch emulsion polymerization has been used to prepare standard latexes which have specific particle sizes, narrow particle size distributions and well-defined particle surfaces, though most of the definitive research activity in this area occurred during the 1960s and 1970s [e.g. consult 35-37], The latexes can either be prepared as required or purchased from ranges which are commercially available. In either case, they invariably are polystyrene latexes which have been cleaned after preparation (by processes such as exhaustive dialysis and ion exchange [38]) and fully characterized. 

Standard latexes now are used routinely by colloid scientists as model colloids in experimental studies, a use which has facilitated a much deeper understanding of both practical and theoretical aspects of colloid science than would otherwise have been possible. Standard latexes also are widely used for calibration of instruments which measure particle size. 

Particle size range detectable depends on the aperture tube used. Each aperture tube is effective over a size range of about 2-40% of its nominal diameter. Apertures of sizes from 15 to 4000 pm are available. Before use, it is necessary to calibrate the equipment with a standard latex containing monosize spherical particles of mean size within 5-20% of the aperture diameter. 

Standard latex, Dow Chemical Co., polystyrene standard latex. Run No. LS-1044-E, particle diameter 0.109 ym, a 0.0027 ym, was used in electron microscopy. 

Standard latexes, and other reference materials, are available from various organizations [18—24]. One of the calibrations standards available to fineparticle scientists are latex spheres which were made on board the space shuttle in 1985. Because these spheres were formed in the absence of gravity they are perfectly spherical. The National Bureau of Standard makes available standard reference material in the form of ten micron microspheres mounted on glass slides. In the first type of slide a few thousand microspheres are deposited as a regular array on a glass microscope slide. In the other type, the fineparticles are randomly distributed [18]. A series of standard non-spheri-cal fineparticles have been prepared by the Community Bureau of Reference Commission of the European Community for use in comparing the performance of size methods. These reference powders are known as BCR standards and several publications are available describing the use of such reference materials [19]. 

Figure 5.21. Hydrodynamic chromatography results for a mixture of two types of standard latex spheres and a marker [54].

Figure 6.17. Typical data generated by the Amherst Process Instruments Inc. Aerosizer for aerosol systems, and powders aerosolized prior to characterization smdies. a) Calibration using aerosols of standard latex spheres of known size, b) Characterization of a mixture standard of polystyrene latex spheres, c) Characterization of a sample of 5 micron silica microspheres mixed with a small number of 10 micron microspheres. D) Glass spheres used in reflective paint (ballotini). E) Two oil mists diatacterized by direct injection into the Aerosizer .

Calibration was effected on 140 and 280 pm orifice tubes using standard latex suspensions (COULTER ELECTR. LTD., GB-Luton) of nominal sizes 18.3 and 46.5 pm, respectively, according to two different procedures recommended in the instruction manual the volume calibration which is performed without the PCA equipment by using an exactly weighed quantity of standard material (Method A) the number calibration which is performed with the PCA equipment (Method B). 

Sinn, C., NiehOser, R., Overbeck, E., Palberg, T., Particle Characterization Using Multiple Scattering Decorrelation Methods, Part 1, Standard Latex Particles, Part. Part. Syst. Charact, 1999, 16, 95-101. 

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