A procedure for the purification of ferritin from human liver by heating a methanol-treated homogenate

A simple, rapid technique for purification of ferritin from human liver tissue is described. Methanol, at a final concentration of 40% (v/v) in liver homogenate, precipitates the majority of proteins but does not affect ferritin. Subsequent heating of this homogenate at 75 degrees C for 10 min results in a purified ferritin preparation as judged by immunoelectrophoresis and polyacrylamide gel electrophoresis. The resultant purified ferritin contained the same amount of iron as the original endogenous ferritin. There were no significant differences (paired t tests) in the amount of protein in the purified ferritin preparation when measured by rocket immunoelectrophoresis and by the Lowry procedure, suggesting that the antigenecity of ferritin was unaffected by the methanol and heat treatment. Both endogenous liver ferritin and radiolabeled human liver ferritin added to liver homogenates were recovered after methanol and heat treatment with similar yields (77 +/- 7% and 70 +/- 2%, respectively) when compared with the standard treatment of heating a homogenate at 75 degrees C. The overall ferritin yield with this rapid procedure was 40%.

An evaluation of the properties of enteric coating polymers: measurement of glass transition temperature

When submitted to X-ray crystallography, two enteric coating polymers, cellulose acetate phthalate and polyvinyl acetate phthalate, were found to be essentially amorphous in structure. Values for the glass transition temperature, Tg, of each polymer have been obtained using both a surface microindentation technique and differential scanning calorimetry. The effect on this parameter of an increasing concentration of a plasticizer, diethyl phthalate, has also been determined. Measured values for Tg have been compared with predicted values obtained using a suitable mixture-rule model: the surface microindentation technique values were closer to the predicted.

The permeability of enteric coatings and the dissolution rates of coated tablets

The effect of an increasing concentration of plasticizer and pigment on the permeability to both water vapour and simulated gastric juice of cellulose acetate phthalate and polyvinyl acetate phthalate has been evaluated. There were significant differences between the permeability coefficients of each polymer, particularly with regard to water vapour. The presence of additives within the film coatings had a greater effect on the properties of cellulose acetate phthalate than those of polyvinyl acetate phthalate. Suitable formulations of each polymer were used to enteric coat 325 mg aspirin tablets, which were subsequently subjected to both the Disintegration Test for Enteric Coated Tablets B.P. and a dissolution procedure to monitor the release of drug in simulated gastric juice and simulated intestinal fluid. Both polymers demonstrated their suitability for producing enteric coatings. However, polyvinyl acetate phthalate yielded a faster release of aspirin in simulated intestinal fluid than did cellulose acetate phthalate.

Solute migration during granule drying

Spherical granules of magnesium carbonate, incorporating polyvinylpyrrolidone (PVP) as granulating agent, have been dried at various temperatures under controlled conditions in a drying tunnel. At each drying temperature the rate of loss of moisture was continuously recorded. The PVP distribution, modulus of elasticity, Brinell hardness and friability of the granules were measured as a function both of moisture content and of depth from the granule surface. The radial distribution of PVP at different stages of the drying process and at three drying temperatures, and its effect on the physical properties of the granules, were thus found. This gave a picture of binder distribution within the granule and its effect on local strength as drying occurred and also of the overall change caused by alteration in drying temperature.

An infrared spectrophotometric study of the compaction mechanism of potassium bromide

Potassium bromide has been compacted in a vacuum die at pressures up to 1000 MN m−2, and the infrared transmittance of the resulting flat discs measured. Four mean particle sizes were used: 71, 110, 388 and 550 μm. Over the whole range of pressure, the 110 μm material had a higher transmittance. At any one particle size, the transmittance increased with increasing compaction pressure up to 400 MN m−2, then fell slightly and was followed by a less pronounced increase in the region of 1000 MN m−2. The following mechanical properties of the compacts were also investigated: tensile strength, relative density, surface hardness and dissolution time. The transmittance changes have been related to the probable compaction mechanism.

The properties of tablets manufactured on an automatically-controlled rotary machine

Four direct-compression bases: Celutab in the hydrous and the anhydrous form, Emcompress Special, and spray-dried lactose, have been compared with a traditional lactose granulation with respect to initial physical properties of the powder, tabletting performance and the characteristics of the tablets produced. The tablets were made on an instrumented rotary machine with feedback weight control operating to minimize time-dependent change within a batch, compression force being continuously monitored. Tensile strength by diametral crushing, porosity, disintegration time and surface indentation hardness were assessed and correlated with changes in compaction force, machine speed and tablet thickness. All materials gave wellformed tablets with no evidence of capping between 90 and 350 MN m−2, and weight variation was small except for Emcompress Special at the highest machine speed, when die filling became erratic.

Automatic weight-control in a rotary tabletting machine

A Manesty “Betapress” 16-station high speed rotary tabletting machine has been fitted with pressure rolls containing piezoelectric transducers in the axles. The compaction force exerted at each tablet compression event produces an electrical pulse which can be fed to an integrated-circuit pulse-discriminating unit. If, for any reason, the quantity of powder in any die is such that an over- or under-pressure occurs on compaction, the resultant incorrect-magnitude pulse is used to operate a stepping motor which adjusts the feed screw of the rotary machine in the correct direction to restore the desired operating conditions and maintain weight constancy. The degree of over- or under-pressure needed to cause corrective action is readily adjustable. An electromagnetically-operated solenoid valve is also controlled by the pulse-discriminator, so that tablets of incorrect weight are deflected by an air jet as they leave the die table. The ejection force can also be monitored and the signal used to operate an alarm if the force should become too large due to punch-sticking.

Solute migration during granule drying

Spherical granules of magnesium carbonate, 12 mm diameter, have been dried under controlled conditions in a drying tunnel at 44°, the rate of moisture loss being continuously recorded. The granulating agent was polyvinylpyrrolidone (PVP). Granules were removed at various times for analysis. By controlled attrition, successive layers of powder were removed from the granules. The powder was analysed for PVP by infrared spectroscopy, and the friability, modulus of elasticity and Brinell hardness of the granules were measured as a function of depth from the granule surface. The radial distribution of the PVP and its physical effect on the granule properties were thus found.

The application of photoelastic techniques to a rotary tabletting machine

Powders have been compacted on a rotary tabletting machine, using a Perspex die mounted above the die table, with an extended lower punch and a shortened upper punch. By high speed cine photography in polarized light, the fringes due to the radial stress in the die wall were recorded during compaction. At the same time, the upper and lower punch forces were monitored by instrumented pressure rollers coupled to a recording oscilloscope. The total information thus obtained was sufficient to enable compression cycles to be determined for the first time on a rotary machine.

The dissolution times of spherical particles

The differential equation governing the rate of change of radius of a spherical particle dissolving or growing in a fluid has been numerically integrated by computer. The particle radius, as a function of time, can thus be calculated, and the dependence of the overall particle lifetime upon physical parameters obtained. The effects of high mass flux, change of solubility with particle size, and progressive saturation due to dissolution into a finite volume of liquid can all be taken into account during the integration process. Results are presented for salicylic, boric and citric acids dissolving in and crystallizing from water; these represent the behaviour of sparingly soluble, moderately soluble and very soluble compounds respectively.

Computer analysis of the relation between tablet strength and compaction pressure

The load necessary to fracture lactose monohydrate tablets under diametral compression has been determined using an Instron physical testing instrument, so that true tensile failure was obtained in all cases, leading to improved reproducibility. Four ranges of tablet thickness were examined at 12·7 mm diameter. All tablets gave a linear increase of breaking load with compaction pressure up to 310 MN/m2. Expressing the tablet strength as the breaking load gave a separate regression line for each range of tablet thickness, whereas the use of tensile strength provided a common regression line, within given statistical limits, for all but the lowest range of tablet thickness. The fact that such a correlation is possible shows that the tensile strength is a property of the “as compacted” material and provides a new and useful parameter to maintain constancy of properties when tablet size is changed.

The kinetics of crystallization of potassium bromide from aqueous solution

The densities of aqueous solutions of potassium bromide have been determined as a function of concentration and temperature up to saturation at temperatures between 10 and 50°. The saturation line and nucleation were studied, over the same temperature range, in a circulatory crystallizer with continuous concentration monitoring. Small quantities of seed crystals were grown under different degrees of supersaturation and at different temperatures, so that the mass transfer coefficients and the activation energy for deposition from solution could be measured. The activation energy of the crystallization process was 100·9 kJ mol−1, indicating that the rate-determining step was the incorporation of KBr on to the crystal lattice. Rapidly-grown crystals might thus be expected to be softer, and this proved to be so.

The quantitative analysis of polyvinylpyrrolidone by infrared spectrophotometry

The quantitative assay of the binding agent polyvinylpyrrolidone (PVP) in granules of magnesium carbonate has been shown to be possible. The method is to determine the infrared absorption spectrum of a chloroform extract. Quantities of PVP down to 0·1 mg can be successfully assayed to ±1 % in solution as dilute as 0·1 % w/v.