Flow-through methods

Looney TJ. USP apparatus 4 [flow through method] primer. Dissolution Technol 1996 3(4) 10—12. 

Acute toxicity (semistatic method) Acute toxicity (flow-through method)... 

An Organization for Economic Co-operation and Development (OECD) monograph (OECD, 1981) describes static, semistatic, and flow-through methods Gobas and Zhang (1995) have developed a method suitable for very hydrophobic chemicals. 

A first distinction must be made between the methods which use one sample for each point on the adsorption isotherm (i.e. immersion methods) and those using a single sample through which the solution of increasing concentration is allowed to flow (i.e. flow-through methods). A critical outline of most of these methods is given by Everett (1986). 

Flow-through methods. In these methods, only one sample is used and is successively brought into equilibrium with solutions of increasing concentration. Most frequently, the sample is initially equilibrated with the pure solvent. Each increase in concentration produces an adsorption of solute by displacement of solvent from the solid surface. The changes in concentration produced by adsorption are usually monitored by the same techniques as those used in the immersion methods, except that they are now located on-line. A general requirement of these methods is that the sample can form a permeable bed and does not block the filter this usually requires a grain size over, say, 2 pm and prevents any tendency to gel formation. 

The amount adsorbed can be determined on-line by simply installing the appropriate detector at the outlet of the microcalorimeter (cf. the flow-through method for determining the adsorption isotherm). 

Apparatus IV flow-through method 4-16mL/min Apparatus V paddle over disc Apparatus VI cylinder method Apparatus VII reciprocating holder method... 

Kristensen P, Nyholm N (1987) Ringtest Programme 1984-1985. Bioaccumulation of Chemical Substances in Fish, Flow-Through Method. Commission of the European Commimity. Degradation Accumulation Subgroup. March 1987 (Final Report)... 

Further advantages of the flow through method include (i) selection of laminar or turbulent solvent flow conditions (ii) simple manipulation of medium pH to match physiological conditions and (iii) application to a wide range of dosage forms e.g., tablets, hard and soft gelatin capsules, powders, granules, implants, and suppositories. 

Looney, T.J. USP Apparatus 4 (Flow-through method) primer. Dissolution Technologies 1996, 3 (4), 10-12. 

International Organization for Standardization (ISO) (1996d) Water Quality-Determination of the Acute Lethal Toxicity of Substances to a Freshwater Fish (Brachydanio rerio Hamilton-Buchanan (Teleostei, Cyprinidae) - Part 3 Flow-through Method, ISO 7346-3. ISO, Paris. 

The majority of sorption kinetic stndies have ntilized either batch or flow-through methods coupled with aqueous measurements for determination of the concentrations of species of interest. More recent work has focused on molecular-scale approaches, including spectroscopic and microscopic techniques that allow for observations at increased spatial and temporal resolution to be made, often in situ and in real time. Complementary to both macroscopic and molecular-scale observations has been the utilization of theoretical techniques, such as molecular mechanics and quantum mechanics, to model surface complexes computationally. It has been through the integration of macroscopic, molecular-scale, and theoretical approaches that some of the most profound observations of sorption-desorption phenomena over the past decades have been made. 

Macroscopic techniques for assessing kinetically controlled reactions have typically been burdened by relatively slow data collection rates. Typically, these data collection rates range from tens of seconds to minutes. The two main types of macroscopic experiments use either batch or flow-through methods (Amacher, 1991 Sparks et al., 1996). 

Flow-through methods with off-line detection 503... 

Flow-through methods with online detection 508... 

Jimoh, M., Frenzel, W.. and Muller, V. (2005). Microanalytical flow-through method for assessment of the hioavailability of toxic metals ui enviromnental samples. Anal. Bioanal. Chem. 381, 438-444. 

For sparingly soluble substances, the volume in standard vessel methods may not be sufficient to dissolve the dose. In this case, the USP IV flow-through method is beneficial, since it provides a continuous renewal of the dissolution fluid. However, the maximum flow rate will limit the apparent solubility in this procedure. Sufficient solubility will not be obtained for a rapidly releasing formulation of a drug with very low solubility in relation to the dose. 

Two field experiments investigating the mobility of pesticides leached by sprinkler irrigation are discussed. The first experiment applied a pulse of chloride and napropamide, a moderately adsorbed herbicide, to a 0.6 ha field which was subsequently leached with 25 cm water low in chloride over a two-week period. Soil core samples were taken at 36 locations to 300 cm and were analyzed in 10 cm increments for chloride and pesticide. Oistribution coefficient measurements were made at each sampling location by hatch equilibrium and column flow through methods. 

Vessels of large volume aud limited surface area to be cleaned are not adapted to fill-and-empty or flow-through methods. Qeaning reagents have been applied in the form of a gel. Also, the interior surface may be cleaned by using automated spray devices that do not require personnel to remain inside the vessel. In some instances, reactants, both alkalis and acids, have been put into the hollow space by means of steam and allowed to condense on the interior walls. Cleaning tank exteriors chemically has not met with great success. 

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