Searching for the perfect surface area normalizing term - a comparison of BET surface area-, geometric surface area- and mass-normalized dissolution rates of anorthite and biotite

Dissolution rates were calculated for a range of grain sizes of anorthite and biotite dissolved under far from equilibrium conditions at pH 3, T = 20 degrees C. Dissolution rates were normalized to initial and final BET surface area, geometric surface area, mass and (for biotite only) geometric edge surface area. Constant (within error) dissolution rates were only obtained by normalizing to initial BET surface area for biotite. The normalizing term that gave the smallest variation about the mean for anorthite was initial BET surface area. In field studies, only current (final) surface area is measurable. In this study, final geometric surface area gave the smallest variation for anorthite dissolution rates and final geometric edge surface area for biotite dissolution rates. (c) 2005 Published by Elsevier B.V.

Dissolution rates of earthworm-secreted calcium carbonate

The dissolution of CaCO3 granules secreted by earthworms in soil leaching columns was governed by soil pH and exchange sites available for Ca. Results indicate that granules could last for significant periods of time in soils and that, therefore, granules could be an important source of soil calcite.

Production and dissolution rates of earthworm-secreted calcium carbonate

Earthworms secrete granules of calcium carbonate. These are potentially important in soil biogeochemical cycles and are routinely recorded in archaeological studies of Quaternary soils. Production rates of calcium carbonate granules by the earthworm Lumbricus terrestris L. were determined over 27 days in a range of soils with differing chemical properties (pH, organic matter content, water holding capacity, bulk composition, cation exchange capacity and exchangeable cations). Production rate varied between soils, lay in the range 0–0.043 mmolCaCO3 (0–4.3 mg) earthworm−1 d−1 with an average rate of 8 × 10−3 mmolCaCO3 (0.8 mg) earthworm−1 d−1 and was significantly correlated (r = 0.68, P ≤ 0.01) with soil pH. In a second experiment lasting 315 days earthworms repeatedly (over periods of 39–57 days) produced comparable masses of granules. Converting individual earthworm granule production rates into fluxes expressed on per hectare of land per year basis depends heavily on estimates of earthworm numbers. Using values of 10–20 L. terrestris m−2 suggests a rate of 18– 3139 molCaCO3 ha−1 yr−1. Data obtained from flow-through dissolution experiments suggest that at near neutral pH, granule geometric surface areanormalised dissolution rates are similar to those for other biogenic and inorganic calcium carbonate. Fits of the data to the dissolution relationship r = k(1 − ˝)n where r = dissolution rate, k = a rate constant, ˝ = relative saturation and n = the reaction order gave values of k = 1.72 × 10−10 mol cm−2 s−1 and n = 1.8 for the geometric surface area-normalised rates and k = 3.51 × 10−13 mol cm−2 s−1 and n = 1.8 for the BET surface area-normalised rates. In 196 day leaching column experiments trends in granule dissolution rate referenced to soil chemistry corresponded to predictions made by the SLIM model for dissolution of limestone in soil. If soil solution approaches saturation with respect to calcium carbonate granule dissolution will slow or even stop and granules be preserved indefinitely. Granules have the potential to be a small but significant component of the biogeochemical cycling of C and Ca in soil.

Nanoparticle preparation process using novel microjet reactor technology for enhancing dissolution rates of poorly water soluble drugs

In this study a novel method MicroJet reactor technology was developed to enable the custom preparation of nanoparticles. rnDanazol/HPMCP HP50 and Gliclazide/Eudragit S100 nanoparticles were used as model systems for the investigation of effects of process parameters and microjet reactor setup on the nanoparticle properties during the microjet reactor construction. rnFollowing the feasibility study of the microjet reactor system, three different nanoparticle formulations were prepared using fenofibrate as model drug. Fenofibrate nanoparticles stabilized with poloxamer 407 (FN), fenofibrate nanoparticles in hydroxypropyl methyl cellulose phthalate (HPMCP) matrix (FHN) and fenofibrate nanoparticles in HPMCP and chitosan matrix (FHCN) were prepared under controlled precipitation using MicroJet reactor technology. Particle sizes of all the nanoparticle formulations were adjusted to 200-250 nm. rnThe changes in the experimental parameters altered the system thermodynamics resulting in the production of nanoparticles between 20-1000 nm (PDI<0.2) with high drug loading efficiencies (96.5% in 20:1 polymer:drug ratio).rnDrug releases from all nanoparticle formulations were fast and complete after 15 minutes both in FaSSIF and FeSSIF medium whereas in mucodhesiveness tests, only FHCN formulation was found to be mucoadhesive. Results of the Caco-2 studies revealed that % dose absorbed values were significantly higher (p<0.01) for FHCN in both cases where FaSSIF and FeSSIF were used as transport buffer.rn