Instrumental Analysis, Chfe 5503

Instrumental Analysis, ChFE 5503

Density by Density Meter

8-2005

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.

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).

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.

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.

4. While leaving the syringe in position, turn off the light and when a stable

reading is observed (approx. 30 sec.) record Twater.

5. Remove the pug and withdraw the sample back into the syringe.

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.

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.

9. After measuring oil samples, you may need to clean the U tube with toluene, dichloromethane, and then acetone as described in step 6.

10. Density is obtained by using the formula

ρ = A (T2 - B) A and B are meter constants, T = period

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.