What are the advantages and disadvantages of the different measuring techniques for density and refractometry?
What are the major applications ?
Please find the answers below:
What are the major applications ?
Please find the answers below:
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Pycnometer Hydrometer (aerometer) ABBE refractometer Handheld refractometer Density kit Digital density meter Digital refractometer Combination of density and refractometry
Pycnometer
A pycnometer is a glass beaker of defined volume. It is weighed without sample (M1), then filled with the sample and weighed again (M2). The difference between M1 and M2 (=Mass of the sample) divided by the volume of the beaker is the density of the sample.
A pycnometer is a glass beaker of defined volume. It is weighed without sample (M1), then filled with the sample and weighed again (M2). The difference between M1 and M2 (=Mass of the sample) divided by the volume of the beaker is the density of the sample.
| Advantages: | Disadvantages: | Main applications: |
| simple method | breakable glassware | educational: what is density, how to measure density |
| relatively inexpensive instrument | long and difficult thermostating | production control: where more precision is required |
| inexpensive instrument | density must be calculated (some balances include this calculation) | analytical labs: where GLP is not required |
| special instruments with direct readings in Alcohol%, Sugar% (BRIX) or other density relatedvalues available | operator dependent readings, therefore limited accuracy | not suitable for expensive samples (large volume required). |
| (*) if no thermostating required | no measurement protocol (not suitable for GLP) | |
| large sample volume required | ||
Hydrometer
The hydrometer (aerometer) is a glass body which is dipped into the sample. After a short equilibration time it will swim at a certain level (when the mass of the hydrometer is equal to the buoyancy effect). The higher the density of the sample, the less the aerometers will sink. The level of equlibration reads the density on the calibrated scale.
The hydrometer (aerometer) is a glass body which is dipped into the sample. After a short equilibration time it will swim at a certain level (when the mass of the hydrometer is equal to the buoyancy effect). The higher the density of the sample, the less the aerometers will sink. The level of equlibration reads the density on the calibrated scale.
| Advantages: | Disadvantages: | Main applications: |
| simple method | breakable glassware | quick control of a "rough" density value, mainly for process control |
| quick measurement (*) | long and difficult thermostating | suitable for the measurement of the same kind of sample (wine, beer) due to the limited measuring range |
| inexpensive instrument | very small measuring range (requires several hydrometers to cover a wider range, typically 20 units) | not suitable for expensive samples (large volume required). |
| special instruments with direct readings in Alcohol%, Sugar% (BRIX) or other density related values available | operator dependent readings, therefore limited accuracy | |
| (*) if no thermostating required | no measurement protocol (not suitable for GLP) | |
| large sample volume required | ||
| difficult to clean and dry | ||
ABBE refractometer (benchtop)
A few drops of the liquid to be measured are put on the prism. The refractive index can be read directly from the built-in scale, looking into the refractometer. Connection to an external water bath allows thermostating required for accurate refractive index measurements. Some models use natural light, the most advanced a light source with defined wave length.
A few drops of the liquid to be measured are put on the prism. The refractive index can be read directly from the built-in scale, looking into the refractometer. Connection to an external water bath allows thermostating required for accurate refractive index measurements. Some models use natural light, the most advanced a light source with defined wave length.
| Advantages: | Disadvantages: | Main applications: |
| relatively inexpensive instrument | long and difficult thermostating (requires external water bath) | production control |
| operator dependent readings, therefore limited accuracy | raw material control | |
| no measurement protocol (not suitable for GLP/GMP) | ||
| tedious calibration | ||
Handheld refractometer
A few drops of the liquid to be measured are put on the prism. The refractive index can be read directly from the built-in scale, looking into the refractometer. Some models feature a temperature compensation scale. There are refractometers for specific concentration measurement with dedicated concentration scales (BRIX, salinity).
A few drops of the liquid to be measured are put on the prism. The refractive index can be read directly from the built-in scale, looking into the refractometer. Some models feature a temperature compensation scale. There are refractometers for specific concentration measurement with dedicated concentration scales (BRIX, salinity).
| Advantages: | Disadvantages: | Main applications: |
| simple method | small measuring range(requires several refractometers to cover a wide range) | quick control of a "rough" density value, especially for BRIX measurements |
| no thermostating | ||
| inexpensive instrument | operator dependent readings, therefore limited accuracy | sugar control in wine production |
| special instruments with direct readings in BRIX° or salinity | no measurement protocol | |
Density kit
The density kit is used together with a balance. A glass body of defined volume is weighed in air (M1), dipped into the sample and weighed again in the sample (M2). The difference between M1 and M2 (buoyancy) divided by the volume of the glass body is the density of the sample. A special holder can also be used to measure density of solids, using a reference liquid (water, ethanol or user defined).
The density kit is used together with a balance. A glass body of defined volume is weighed in air (M1), dipped into the sample and weighed again in the sample (M2). The difference between M1 and M2 (buoyancy) divided by the volume of the glass body is the density of the sample. A special holder can also be used to measure density of solids, using a reference liquid (water, ethanol or user defined).
| Advantages: | Disadvantages: | Main applications: |
| no manual reading | long and difficult thermostating | density of solids |
| GLP printout | large sample volume required | density of porous materials |
| just an accessory to a balance, therefore relatively inexpensive | density of viscous material (using a gamma sphere) | |
Digital density meter
A hollow glass tube vibrates at a certain frequency. This frequency changes when the tube is filled with the sample: the higher the mass of the sample, the lower the frequency. This frequency is measured and converted into density. Calibration is carried out with air and distilled water. A built-in Peltier thermostat controls the temperature very precisely, without using a water bath.
A hollow glass tube vibrates at a certain frequency. This frequency changes when the tube is filled with the sample: the higher the mass of the sample, the lower the frequency. This frequency is measured and converted into density. Calibration is carried out with air and distilled water. A built-in Peltier thermostat controls the temperature very precisely, without using a water bath.
| Advantages: | Disadvantages: | Main applications: |
| built-in thermostat | relatively expensive | high accuracy measurements |
| quick measurement (Approx 1 min.) | GLP measurements, where protocols are required | |
| very high accuracy | perfumes, fragrances: where small sample volume required | |
| small sample volumes (1,2 ml) | soft drinks, cola drinks: BRIX measurements | |
| GLP: operator independent | alcoholic beverages: Alcohol measurement | |
| special instruments with direct readings in Alcohol%, Sugar% (BRIX) or other density related values available | petroleum: API measurements | |
Digital refractometer
The latest in refractive index measurement. A high resolution optical sensor measures the total reflection of a light beam emitted by a special LED light source after hitting the sample. This total reflection is converted into refractive index, BRIX, HFCS or user defined concentrations. A built-in Peltier thermostat controls the temperature (no water bath required).
The latest in refractive index measurement. A high resolution optical sensor measures the total reflection of a light beam emitted by a special LED light source after hitting the sample. This total reflection is converted into refractive index, BRIX, HFCS or user defined concentrations. A built-in Peltier thermostat controls the temperature (no water bath required).
| Advantages: | Disadvantages: | Main applications: |
| built-in thermostat | relatively expensive | high accuracy measurements |
| very high accuracy | production control, raw materials | |
| GLP: Operator independent results | perfumes, fragrances | |
| Automation (sample changer, computer) | BRIX: Fruit juices, sugar, soft drinks | |
Combination of density and refractometry
Our digital density meters and refractometers can be combined for simultaneous measurement of density, refractive index and related values:
Our digital density meters and refractometers can be combined for simultaneous measurement of density, refractive index and related values:
- No need of water circulator: built-in Peltier thermostat.
- The sample is measured simultaneously in the density meter and in the refractometer.
- Both results (and related values) can be printed out or transferred to a PC.
- Easy calibration with air and water on one keystroke.
- To be used together with a sampling unit or sample changer.