Dissolution devices

Sanghvi PP, Nambiar JS, Shukla AJ, Collins CC. Comparison of three dissolution devices for evaluating drug release. Drug Dev Ind Pharm 1994 20(6) 961-980. 

In comparison to the approach of Ginski et al. [48], the Miyazaki s method appears to be more elaborate and complex and is thus coming closer to the in vivo situation. The device can simulate various effects of pH on dissolution and is, as an open system, closer to in vivo conditions compared to a closed one. However, it exhibits the drawback of not freely adjustable pH values acting on the drug. Low flow rate in the dissolution vessel may limit applications of complete dosage forms and allows predominantly only the use of granules, pellets, or grinded tablets. Furthermore, the application of compendial dissolution devices appears to be a more robust approach. 

The approach of Kataoka et al. [54] shows some desirable features, such as downsized, in vivo relevant volumes, and low complexity of the device and thus low error proneness. However, the device lacks the possibility to add complete dosage forms and the use of compendial dissolution devices would be a more robust approach. 

It is safe to assume that for a given dissolution device, the ultimate drug delivery rate will be a combination of hydrolysis (dissolution) and drug diffusion out of the polymer. Of the systems stuped to date, the release rates for biodegradable devices are essentially zero-order. 

Dissolution and Solubility - The search for apparatus which will afford reliable and reproducible information concerning the dissolution of pharmaceutical dosage forms continues. Swarbrick reviewed the various theoretical models that have been proposed to describe the dissolution process, as well as the devices used in its measurement. Wagner has also published a comprehensive review of this field. Others have tested dissolution devices of their own design. 

Figure 3.24. and C determination in irradiated nuclear fuel dissolution device and gas collection system (Neeb et al., 1980)... 

In this review, polarizers are classified according to common DNP implementations, as introduced above, specifically O-DNP for liquids, SS-DNP and D-DNP. This is, of course, artificial because the same microwave and radiofrequency sources can be used in liquids or in solution, except for the use of different cooling arrangements, MAS or a dissolution device. This classification is, however, useful to describe current experimental implementations. 

Mobile ions, such as sodium or potassium, tend to migrate to thep-n junction of the IC device where they acquire an electron, and deposit as the corresponding metal on the p-n junction this consequendy destroys the device. Furthermore, mobile ions also support leakage currents between biased device features, which degrade device performance and ultimately destroy the devices by electrochemical processes such as metal conductor dissolution. 

For example, chloride and duoride ions, even in trace amounts (ppm), could cause the dissolution of aluminum metallization of complimentary metal oxide semiconductor (CMOS) devices. CMOS is likely to be the trend of VLSI technology and sodium chloride is a common contaminant. The protection of these devices from the effects of these mobile ions is an absolute requirement. The use of an ultrahigh purity encapsulant to encapsulate the passivated IC is the answer to some mobile ion contaminant problems. 

After the ozone has been generated, it is mixed with the water stream being treated in a device called a contactor. The objective of this operation is to maximize the dissolution of ozone into the water at the lowest power expenditure. There is a variety of ozone contactor designs. Principal ones employed in wastewater treatment facilities include ... 

The determination of polarisation curves of metals by means of constant potential devices has contributed greatly to the knowledge of corrosion processes and passivity. In addition to the use of the potentiostat in studying a variety of mechanisms involved in corrosion and passivity, it has been applied to alloy development, since it is an important tool in the accelerated testing of corrosion resistance. Dissolution under controlled potentials can also be a precise method for metallographic etching or in studies of the selective corrosion of various phases. The technique can be used for establishing optimum conditions of anodic and cathodic protection. Two of the more recent papers have touched on limitations in its application and differences between potentiostatic tests and exposure to chemical solutions. ... 

Such approximation is valid when the thickness of the polymeric layer is small compared to die thickness of die crystal, and the measured frequency change is small with respect to the resonant frequency of the unloaded crystal. Mass changes up to 0.05% of die crystal mass commonly meet this approximation. In die absence of molecular specificity, EQCM cannot be used for molecular-level characterization of surfaces. Electrochemical quartz crystal microbalance devices also hold promise for the task of affinity-based chemical sensing, as they allow simultaneous measurements of both tile mass and die current. The principles and capabilities of EQCM have been reviewed (67,68). The combination of EQCM widi scanning electrochemical microscopy has also been reported recently for studying die dissolution and etching of various thin films (69). The recent development of a multichannel quartz crystal microbalance (70), based on arrays of resonators, should further enhance die scope and power of EQCM. 

From a reaction engineering viewpoint, semiconductor device fabrication is a sequence of semibatch reactions interspersed with mass transfer steps such as polymer dissolution and physical vapor deposition (e.g., vacuum metallizing and sputtering). Similar sequences are used to manufacture still experimental devices known as NEMS (for nanoelectromechanical systems). 

FIGURE 14 In vitro rate of release of testosterone from a PCL capsule (reservoir device), illustrating rate control by drug dissolution when the polymer membrane thickness is small. (From Ref. 68.)... 

Although it was possible to achieve constant in vitro release of levonorgestrel for up to 410 days at which point the experiment was discontinued, release of the drug was not controlled by surface erosion of the polymer but instead the device underwent bulk erosion and release of levonorgestrel was completely controlled by its rate of dissolution. Bulk erosion of the rod-shaped device was evident by scanning electron microscopy as shown in Fig. 17. 

Kuhn, A. T. Jones, M. P. (1982). A model for the dissolution and fluoride release from dental cements. Biomaterials, Medical Devices and Artificial Organs, 10, 281-93. 

Energy effects associated with the dissolution of a given substance (which in the following is distinguished with the index " ) can be determined experimentally. They depend on the system s initial and final state, but not on the path taken by the process. Hence, for calculations, the device of thermodynamic cycles is often used, where the true path of the process is replaced by another path (which may even be a path that actually cannot be realized) for which the energy effects of the individual intermediate steps can be determined. 

In mart, an overlooked feature is the occurrence of mucoid-like plugs in the foetal nostrils (Schaeffer, 1910). The presence of this blockage can be confirmed by endoscopic inspection in utero these plugs seem likely to affect free amniotic flow, since they appear to be reinforced by a folded membranous gathering at the nasal vestibule (PI. 4B). A degree of restriction of fluid access to the VN aperture, which is immediately caudal to the nostril aperture, and is patent in foetal life, may be a protective feature (Jordan, 1972). The timing of the dissolution of these sealant devices prior to parturition is regrettably not known. 

SPE is a useful device for working up of polymer additive dissolutions the apolar polymer is retained on the Cj 8 sorbent, while analytes may be eluted. In the fractionation of dissolutions it is advantageous to make use of the differences in polarity and affinity of the components with the sorbent. SPE of applied samples may be done with cartridges or disks, either off- or on-line. A flow-chart for the use of SPE has been published [3], Applications of SPE have been described in several monographs [511,512]. 

Application to solid polymer/additive formulations is restricted, for obvious reasons. SS-ETV-ICP-MS (cup-in-tube) has been used for the simultaneous determination of four elements (Co, Mn, P and Ti) with very different furnace characteristics in mg-size PET samples [413]. The results were compared to ICP-AES (after sample dissolution) and XRF. Table 8.66 shows the very good agreement between the various analytical approaches. The advantage of directly introducing the solid sample in an ETV device is also clearly shown by the fact that the detection limit is even better than that reported for ICP-HRMS. The technique also enables speciation of Sb in PET, and the determination of various sulfur species in aramide fibres. ETV offers some advantages over the well-established specific sulfur analysers very low sample consumption the possibility of using an aqueous standard for calibration and the flexibility to carry out the determination of other analytes. The method cannot be considered as very economic. 

Principles and Characteristics Of the chromatographic methods discussed in Chapter 4 essentially only SEC and HPLC are used to some extent for the analysis of dissolutions containing both macromolecular and additive components. SPE is a useful device for working... 

Fig. 2 Two types of dissolution-controlled, pulsed delivery systems (A) single bead-type device with alternating drug and rate-controlling layers (B) beads containing drug with differing thickness of dissolving coats.

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