Knauer membrane osmometer

Figure 4.4.17. Description of the principal construction of a Knauer membrane osmometer A 300 1 - head thermostat, 2 - channel for syringe, 3 - calibration device with suction tube, 4 - calibration glass, 5 - c illary position MEASUREMENT, 6 - capillary position CALIBRATION, 7 - tension screws, 8 - cell retaining disc, 9 - upper half of measuring cell, 10 - sample introduction system, 11 -semipermeable membrane, 12 - lower half of measuring cell, 13 -pressure measuring system, 14 - cell thermostat, 15 - suction of calibration bottle. [Reprinted from the operating manual with permission from Dr. H. Knauer GmbH (Germany)].

Technical details of the different apparatuses will not be presented here, however, the principle construction of the measuring cell and the heating thermostat of the Knauer membrane osmometer A 300 is shown in Figure 4.4.17 for illustration and as example. 

Kucharikova [16] noticed that the agreement between the values of Mn by VPO and those given by the manufacturers in Table 5.2 was better than that which had been first indicated by Kamide et al., because the molecular weights used by Kamide et al. [14] were not but My,., The M value in the parentheses for sample la in Table 5.2 was determined by Kucharikova [16] by using a Knauer membrane osmometer in toluene at 37°C, and that for sample 1 la was obtained by Adams et al. [17] using GPC. These values are in good agreement with the Mn determined by VPO reported by Kamide et al, [14]. 

Membrane osomometry The number average molar masses of humic acid and Na-humate (sample from Tatabanya) were determined at 5 and 500 mmol dm NaCl by membrane osmometry (Knauer membrane osmometer, Sartorius superfine membrane), using the extrapolation procedure described in [32]. 

Laboratory designed instruments were developed in the 40 s and 50 s, e.g. by Zimm or by Flory. Later on, high speed membrane osmometers are commercially available, e.g., from Knauer, Hewlett-Packard or Wescan Instruments. External pressures may be applied to balance the osmotic pressure if necessary, e.g., Vink. The principle scheme of a membrane osmometer together with the corresponding... 

The vapour pressure osmometer (Dr. Knauer, Berlin) was provided with a universal-two-thermistor-probe for all kinds of liquids. The probe is one part of a Wheatstone-bridge, which is connected with an external amplifier, an analog meter and a recorder. The membrane osmometer is from the same producer. 

Number average molecular weights of the samples were measured by the osmotic pressure measurements. The Knauer high-speed membrane osmometer was used with Sartorius Ultra-cellafliter sd as a semipermeable membrane. 

The simplest static osmometers are of the basic form indicated schematically in Fig. 3.9 (e.g. Pinner-Stabin osmometer) and have relatively large cell volumes (typically 3-20cm ). The volume of solvent transported across the membrane at equilibrium is reduced by using capillaries for the pressure head. However, these capillary osmometers are cumbersome to use and give relatively long equilibration times (typically several hours). Modern static osmometers have much smaller cell volumes and pressure sensors which monitor the pressure in the solution cell, usually indirectly (e.g. Wescan and Knauer osmometers). It normally is not necessary to correct the solution concentration for dilution due to movement of solvent into the solution cell because the effect is usually negligible. 

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