Centrifugal liquid membrane method

H. Nagatani and H. Watarai, Direct spectrophotometric measurement of demetallation kinetics of tetraphenylporphyrinato zinc(II) at the liquid-liquid interface by a centrifugal liquid membrane method. Anal. Chem., 70, 2860-2865 (1998). 

From the beginning of the 1980s, some effective experimental approaches based on new principles have been invented for the study of interfacial reactions in solvent extraction chemistry. Recently, some methods were developed from our laboratory, the highspeed stirring (HSS) method [4,5], the two-phase stopped flow method [6], the capillary plate method [7], the reflection spectrometry [8], and the centrifugal liquid membrane (CLM) method [9]. 

A high specific interfacial area and a direct spectroscopic observation of the interface were attained by the centrifugal liquid membrane (CLM) method shown in Fig. 2. A two-phase system of about 100/rL in each volume is introduced into a cylindrical glass cell with a diameter of 19 mm. The cell is rotated at a speed of 5000-10,000 rpm. By this procedure, a two-phase liquid membrane with a thickness of 50-100 fim. is produced inside the cell wall which attains the specific interfacial area over 100 cm. UV/VIS spectrometry, spectro-fluorometry, and other spectroscopic methods can be used for the measurement of the interfacial species and its concentration as well as those in the thin bulk phases. This is an excellent method for determining interfacial reaction rates on the order of seconds. 

FIGURE 10.2. Schematic diagram of the centrifugal liquid membrane (CLM) method apparatus. The glass cylinder cell (i.d., 19 cm) was rotated at a speed of 7000-10,000 rpm. Introduction of 50-200 pi of the organic and the aqueous phase generated a two-liquid layer system with a thickness of 50-100 pm for each phase. 

Both the requirements of a high specific interfacial area and a direct spectroscopic observation of the interface were attained by the centrifugal liquid membrane (CLM) method... 

The CLM method is a new technique, developed by Nagatani and Watarai [61]. This method produces a stable, ultrathin two-phase liquid membrane by the centrifugal force due to the rotation of a cylindrical cell, using the arrangement shown in Fig. 11. The inner diameter and inner height of the cylindrical cell were 19 and 29 mm, respectively. The rotation speed was controlled in the range 6000-7500 rpm. The summation of the absorption spectra of both interfacial and bulk organic phase species was measured in the direction perpendicular to the rotation axis with a diode array spectrophotometer. 

Porcine brains, which were obtained within 30 min after death of the animals from a local slaughterhouse, were used to prepare receptor-rich membranes. The brains were immediately frozen in liquid N2 50 g brain per 200 mL ice-cold buffer (0.32 M sucrose, 10 mM potassium phosphate buffer, pH 7.0, 1 mM EDTA) were homogenized twice for 15 sec in a blender and then for 1 min with an ultraturrax. The homogenate was centrifuged three times for 15 min at 1.400 g and 4°C to separate cellular debris. The supernatant was spun down at 100.000 g for 60 min. The resulting pellet was resuspended in buffer (as above but without sucrose). Aliquots were stored frozen at -80°C. Protein content was determined by the Lowry method, using bovine serum albumin as a standard.32 35... 

Self-supporting inorganic membranes can be formed with or without a substrate. In either case the precursor sol, consisting of either a colloidal suspension or a polymeric solution, must be formed. To produce a membrane supported on a substrate (i.e. a supported membrane), a preformed porous support is dipped in the precursor sol and a gel forms at the surface of the support typically by the slipcasting method [48]. Another approach is spin coating, in which an excess amount of liquid is deposited onto a substrate and then thinned uniformly by centrifugal force [12]. To produce a non-supported membrane, the liquid is simply poured into a mold of appropriate shape and allowed to dry. All these processes need to be done before the gel point which is accompanied by a large increase in viscosity. 

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