Spacer small volume

An alternative type of cell, which consists of two parts of optically flat windows, is suitable for CD and MCD measurements of small-volume samples. One of the window affords a trough for filling in the sample. Otherwise, a well-calibrated spacer is inserted to a conventional cell for adjusting its path length. The light path length is calibrated by using the absorbance of an appropriately diluted solution of benzene or toluene. 

Advances in technology have permitted the miniaturization of many electrochemical systems [2]. In particular, application of modern fabrication techniques permits the manufacture of electrochemical cells of extremely small volume, Fig. 16.2. The first step in this direction was probably the development of thin-layer electrochemical cells. These contain large (2-3 mm) electrodes in a rectangular cell of dimensions typically 2 cm x l cm but of small height produced by a spacer of thickness 2-100 xm, which corresponds to a cell volume of 4-200 p.L [3]. Cell volumes have been progressively reduced, so that now measurements often have to be made with microelectrodes. 

Wildhaber, J.H. Devadason, S.G. Eber, E. Hayden, M.J. Everard, M.L. Summers, Q.A. LeSouef, P.N. Effect of electrostatic charge, flow, delay and multiple actuations on the in vitro delivery of salbutamol from different small volume spacers for infants. Thorax 1996, 51, 985-988. 

Wildhaber JH, Devadason SG, Hayden Ml, Eber E, Summers QA, LeSouef PN. Aerosol delivery to wheezy infants a comparison between a nebulizer and two small volume spacers. Pediatr Puhnonol 1997, 23 212-216. 

Dolovich et al. reported that oropharyngeal deposition was reduced from 65% of the emitted dose to 6.5% in a group of patients with varying degrees of airflow obstruction who inhaled aerosol from an MDI alone and an MDI used in combination with the small volume Aerochamber spacer, respectively. Total and regional lung deposition fractions were unaltered by the addition of the spacer (76). 

Hardy J, Jasuja A, Frier M, Perkins A. A small volume spacer for use with a breath-operated pressurised metered dose inhaler. Int J Pharm 1996 142 129-133. 

Sedimentation of drug particles in the aerosol is another factor that reduces the available aerosol and shortens the time available for inhalation after actuation. The velocity of sedimentation is proportional to the aerodynamic diameter of the particles. In a narrow spacer, the sedimentation distance is short and therefore the loss of aerosol is faster in small-volume tube spacers than in large-volume spacers. This principle is taken to its extreme in a vertical spacer, compared with the traditional horizontal spacer. 

The single most important factor determining drug delivery is the size of the spacer large-volume spacers deUver more drug than small-volume spacers. The optimal size depends on the pMDI, and therefore dedicated spacers should... 

In adults, the lung dose achieved with intermediate- and large-volume spacers is about twice that obtained with the corresponding pMDI alone (i.e., 20-35% of the metered dose) (28,61,90-92). In one study, lung doses from pMDIs with and without a large-volume spacer were similar (93), which may be explained by a lack of priming of the plastic spacer. The small-volume spacer AeroChamber de-... 

The choice of spacer depends on the drug to be delivered. The requirements for delivery of bronchodilators and steroids differ, and different devices may be advisable. Simple containers or small-volume spacers may be used for bronchodilators, whereas optimized spacers are essential for delivery of inhaled steroids. Inexpensive but ineffective spacers may cause expensive loss of drug. 

Figure 7. Small-volume optically transparent thin layer electrochemical cell. (A) Quartz cover plate, (B) Teflon spacer, (C) gold minigrid optically transparent electrode, (D) quartz disc, (E) plastic body, (F) inlet syringe port, (G) Pt syringe needle for auxiliary electrode. Adapted from Reference (40) with permission.

A variety of commercial S-chambers are available for 10 X 10-, 10 X 20-, and 20 X 20-cm plates. One type is a sandwich plate cover with permanently fixed glass spacers on two sides. It is 2 cm shorter than a 20 X 20-cm plate and is positioned so that it does not dip into the solvent. Therefore, there is no need to scrape off the layer at the sides. The sandwich composed of the TLC plate and the cover plate, which is open at the top and held together by four stainless-steel clamps, can be developed in a regular N-tank. Other models consist of a cover plate plus a small-volume chamber for vertical development. 

SANDWICH CHAMBER (S-CHAMBER). A developing chamber formed from the plate itself, a spacer, and a layered or nonlayered cover plate that stands in a trough containing the mobile phase, or some other type of small-volume chamber in which vapor-phase saturation occurs quickly. 

In Fl-FFF, the channel is created by placing a mylar spacer with the channel cut out between two porous frits. A membrane hlter of a specihc molecular weight cutoff is placed on one of the frits and acts as the accumulation wall to permit flow, without loss of particles. The applied force is then a perpendicular flow of the carrier solution across the porous frits. Fl-FFF is a versatile technique capable of separating macromolecules as small as roughly 1000 Da, in which case it is comparable to gel permeation (size exclusion) chromatography. However, Fl-FFF can also be applied to the separation of colloidal particles. In this case the hydrodynamic diameter of the colloidal particle is related to the retention volume, V by the equation... 

Figure 2a shows the separation of DNP-amino acids using three spacer acids (i.e., acetic acid, propionic acid, and n-butyric acid) in the stationary phase [2]. Hydrophilic DNP-glutamic acid is eluted between acetic and propionic acids DNP-alanine between propionic and n-butyric acids, and hydrophobic DNP-leucine after n-hu-tyric acid. The method can be effectively applied for the separation and concentration of a small amount of organic ions present in a large volume of the sample solution. However, the most useful application has been... 

The molecular interpretation of thermodynamic data of temperature and pressure effects on proteins and their reactions is based on the data obtained from small molar mass model compounds in water. Weber and Drickamer [75] have pointed out the role of mechanical effects on the volume of association of molecular complexes by introducing molecular spacers that prevent molecules to get in close contact. As can be seen from Table 2, these mechanical effects can show up considerably in the volume changes, ft is clear that such effects should also influence hydrophobic interactions in proteins. 

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