Crystal size determination

Insulin suspensions. When the hormone is injected as a suspension of insulin-containing particles, its dissolution and release in subcutaneous tissue are retarded (rapid, intermediate, and slow insulins). Suitable particles can be obtained by precipitation of apolar, poorly water-soluble complexes consisting of anionic insulin and cationic partners, e.g the polycationic protein protamine or the compound aminoqui-nuride (Surfen). In the presence of zinc and acetate ions, insulin crystallizes crystal size determines the rate of dissolution. Intermediate insulin preparations (NPH or isophane, lente or zinc insulin) act for 18 to 26 h, slow preparations (protamine zinc insulin, ultralente or extended zinc insulin) for up to 36 h. 

The particle sizes relevant for inorganic pigments stretch between several tens of nanometers for transparent pigment types to approximately two micrometers. For practical applications it is very desirable to determine not only the mean particle size but also the whole distribution. These parameters must not be confused with the crystal size determined by X-ray diffraction, as pigment particles usually are not monocrystals. 

SZl sample, reference materials of this work, is constituted by pure tetragonal ZrOz, with an average crystal size (determined with the classical Scherrer equation) of 85 A (Table 1). The stabilisation of the tetragonal ZrOz depends on the presence of TPAOH in the reaction mixture. In fact, variable amounts of monoclinic phase are detected in the products synthesised in the absence of organic base (SZ2 sample. Table 1). This is probably related to the pH of the sol, but this hypothesis should be confirmed. Basic medium usually enhances the condensation reactions [15], but at the same time the ability of sulphates to form complexes with Zr precursors up to pH = 11 [16] and the low water content in the sol prevent the growth of zirconia particles. 

Ice Crystal Size Determination. Frozen green beans were taken from storage at times which corresponded to the biochemical assay points and put into the Isothermal freeze fixative, Asquith and Reid (1). 

The synthesized materials posses large pore volume and a good thermal and hydrothermal stability. Table 1 shows textural properties of the calcined materials the use of a surfactant leads to higher surface areas and pore volume than those observed for reference C-0 and C-4 samples. On the other hand, the increase in surface area correlates well with the intensity of the carbonate bands observed by DRIFT. Examination of the N2-physisorption isotherms let us assume a non-ordered mesoporous structure. This was confirmed by the lack of a small angle X-ray difliraction peak. By XRD the Ce02 cerianite phase was identified and crystal size determined by the Rietveld method showed that samples C-1 through C-3 are nanometric particles with crystal size of about 4-7 nm while reference samples C-0 and C-4 were much larger (w30 and 19 nm, respectively). 

A usual requirement is control over the concentration of crystals in the discharge slurry. In many cases, however, crystal size is important as well. Crystal concentration is customarily measured as density, if the crystals are uniformly dispersed across the sensitive span of the detector. Crystal size determination unfortunately does not lend itself to on line analysis. 

Crystal size determinations from fractured surfaces are problematic since it is not clear how the fracture propagates with regard to the grains or crystals. Sometimes evaluation is impossible (Fig. 6). 

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