Equipment osmometers

Figure 3 Membrane osmometry. Top concentration series with multiple injection of polystyrene (PS, 5,250 g/mol) in toluene. Concentrations 1.07,1.91, 2.94, 4.11, and 5.03 g/L. Multiple solvent injections establish the baseline (subtracted). Inset data evaluation for concentration series of PS (5,250 g/mol) and PS (47,400 g/mol) in toluene. Bottom design of osmometer equipped with flow cell. Reproduced with permission from Lehmann et al. [16]. Copyright 1996 American Chemical Society.

Two grams of HSPAN was added to 500 ml of water, the pH was adjusted from 9 to 6.5 with dilute hydrochloric acid, and 0.1 ml of Thermamyl 60L enzyme solution (Novo Enzyme Corp.) was added. The resulting mixture was heated at 95°C for 21 hr, and the clear yellow solution was exhaustively dialyzed against distilled water. Freeze drying yielded 1.235 g of polymer, which contained only about 5% residual carbohydrate (by infrared analysis). The number average molecular weight of this polymer was 44,000, as determined in 0.15N sodium chloride solution on a Melabs Model CSM-2 membrane osmometer equipped with a B-19 membrane (Schleicher and Schuell Co.). 

Apparatus Use a suitable vapor pressure osmometer, such as the Hewlett-Packard Model 302A, or equivalent, equipped with dual thermistor beads. 

Osmometers consist basically of a solvent compartment and a solution compartment separated by a semipermeable membrane and equipped with a... 

The calcein release from the vesicles was measured as follows the vesicle suspensions of HCO-10 were prepared in 100 mM calcein/20mM Tris buffer (pH 7.4, 388 mOsm), in which the fluorescence intensity of calcein is self-quenched. The vesicles were separated from un-trapped calcein by gel-permeation chromatograph using a Sephadex G-75 gel (0.5 x10 cm column) equilibrated with an isotonic buffer, glucose/20mM Tris buffer (pH 7.4). The osmolarity of buffers was monitored with an Osmometer (Semi-micro Osmometer, Knauer). The separated vesicles, suspended in a cold isotonic buffer, were rapidly diluted (1 200) into the well-stirred isotonic buffer equilibrated to the experimental temperature. The fluorescence emission intensity of a sample was recorded continuously subsequent to this dilution (zero time) on a RF-5000 fluorescence spectrophotometer, Shimadzu (excitation A = 490 nm, emission X = 520 nm) equipped with temperature control accessories and a magnetic stirrer [11]. 

Molecular Weights by Vapor Pressure Osmometry (VPO) A Jupiter Instrument Co. model 833 vapor pressure osmometer was used to determine the molecular weights by VPO, using nitrobenzene as the solvent at a working temperature of 100 °C. The constant of the equipment was calculated using pyrene (202 g/mol) as the standard. The solutions analyzed were prepared in concentrations ranging from 1 to 6 g/L. 

Modern osmometers are equipped with a servo-control, which compensates the increase of the osmotic pressure by a hydrostatic backpressure. With such equipment, equilibrium is attained in a few minutes instead of several hours. 

A vapor pressure osmometer is available from H. Knauer and Co., Berlin, West Germany. The manufacture of the Mechrolab instrument previously lefciu d to in this footnote has been discontinued. Ilotvcver, some nuKlels may lx available from slocks on hand at laboratory supply houses, or as used equipment from laboratory instrument exchanges. 

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