This application note describes an automated method for the measurement of pH, Brix and acidity, incorporating a METTLER TOLEDO T90 Titrator, DM45 Density Meter, Rondo60 autosampler and LabX® titration software (Figure 1).
In quality control of juices, pH, acidity and sugar content affect both taste and shelf life. Discrete separate analyzers for each of these parameters have been used for years. Presented here is an analyzer which will measure these three parameters on a series of samples and deliver the results to a LIMS system.
The sample is pulled from a test tube on a multi-sampler by a peristaltic pump through separate flow-through density and pH measuring cells. After measuring these two parameters, it is transferred to a fixed volume loop where the contents of the loop are pumped into a titration beaker. The acidity is determined by potentiometric titration with sodium hydroxide. The workflow is as follows:
- The analyst selects a method by one click on the shortcut. The sample list opens.
- The sample ID is entered or bar-coded in. Sample is poured into a 30 mL test tube and placed in the first position on the Rondo sample changer. Up to 120 samples can be entered this way. The titrator can be started at any point after the first sample is entered.
- The Rondo sample changer brings a sample to the tower position. The sampling tube goes into the test tube, whereby a pump transfers sample from the test tube into the density meter or refractometer cell, then into the flow through pH chamber.
- The titrator signals LabX to start the density or refractive index measurement.
- When the reading is stable, the result is posted to LabX and sent to the titrator. The titrator then records the pH in the flow through chamber.
- The sample is pumped through the 10 mL sample loop. The TV6 valve is switched to transfer the sample into titration vessel and to allow solvent to be added.
- The water pump pushes the sample in the loop to the titration vessel and follows with about 40 mL water.
- The acidity in the sample is titrated with sodium hydroxide to an end point of 8.2 pH.
- The result of the pH measurement and the acidity are sent to LabX.
- LabX prints a report and sends the results to a LIMS system.
- The Rondo advances to the next sample and the workflow repeats.
Table 1 to the right lists the results of some samples that were taken for analysis.
This procedure provides a reliable method for the automated analysis of these parameters and requires minimal user interaction. The system can also be modified to incorporate color measurement, an additional parameter often measured in the quality control of flavors and fragrances.
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