<p> Instrumental Analysis, ChFE 5503</p><p>Density by Density Meter</p><p>8-2005</p><p>The Paar DMA 40 and 45 Density Meters: The measuring principle is based on the variation of the natural frequency of a hollow oscillator (sample tube) when filled with different liquids or gases. The mass, and thus the density, of the sample changes natural frequency due to a gross mass change of the oscillator caused by the introduction of the sample.</p><p>Operating procedure: 1. Set the bath temperature control such that it will yield the required temperature at the density meter. e.g. density at 20.0C (68F).</p><p>2. Turn power switch on. Record the period inside the tube, Tair, with the light off. Clean tube and check baseline value for water & air in manual. Insure tube is free of contaminates.</p><p>3. Turn on the light, inject distilled water (1 - 2 ml) into the lower opening of the sample tube using a 3 ml disposable syringe. The sample tube should be completely full of water with no air bubbles and the upper inlet should be closed off with a plug.</p><p>4. While leaving the syringe in position, turn off the light and when a stable</p><p> reading is observed (approx. 30 sec.) record Twater.</p><p>5. Remove the pug and withdraw the sample back into the syringe.</p><p>6. Rinse the tube with acetone or alcohol, then, with the air pump switched on, connect the air hose to the upper inlet and continue the flow of air through the U tube until the displayed value repeats itself several times.</p><p>7. Switch off the pump and compare Tair with its original value (step 2), repeat if the period is not consistent. 8. Repeat 3 to 7 with decane and/or oil samples.</p><p>9. After measuring oil samples, you may need to clean the U tube with toluene, dichloromethane, and then acetone as described in step 6.</p><p>10. Density is obtained by using the formula</p><p>ρ = A (T2 - B) A and B are meter constants, T = period</p><p>A and B are determined by calibration using air and water standards (steps 2 and 4). A and B values may be given in the lab for the instrument we use. Otherwise determine them using handbook densities and the data from steps 2 and 4.</p>