pH in Fruit Juices
Smartphone-based determination of pH after reaction with a chemically bound pH indicator

Introduction

The pH value of beverages such as fruit juices is one of the most important parameters that gives information about the quality of the product. The pH value of fruit juices typically ranges from pH 2.5–4.0.

An easy way to check the pH of your soft drinks are test strips.

Analyze your MQuant^® test strips with your smartphone for fast, convenient, and precise results. Test the simplest way to determine pH in aqueous solutions. This low-priced and easy-to-use analytical detection system provides reliable quantification of water, food & beverage samples for customers from research, industry, environment and diagnostics.

The following application note describes the determination of the pH value in fruit juices using the MQuant® pH test strips in combination with the MQuant® StripScan app.

Experimental Method

Special indicator dyes are covalently bound to the reagent papers and change their colors depending on the pH value of the sample.

Sample Material

Fruit Juices

Measuring Range

pH 0 - 14

Reagents and Accessories

Reagents

MQuant^® pH-indicator strips pH 0 – 14 Universal indicator (1.09535)

Accessories

• MQuant^® Card (provided with the test strip box)
• MQuant^® StripScan app (can be downloaded via Apple App Store or Google Play Store)

Sample Preparation

The sample can be analysed in its original form.

Sample Analysis

For analysis, follow this procedure:

1. Start the app.
2. Get your MQuant^® pH indicator test strip and the
   MQuant^® Card ready.
3. Dip the test strip into the undiluted sample (15 – 25 °C) for approx. 2 seconds, ensuring that the reaction zones are completely immersed.
4. Shake off excess liquid from the strip and dry the backside of the strip using a paper towel.
5. Select the parameter pH (1.09535) in the app. A countdown is displayed on the screen, which begins immediately after selecting the parameter pH.
6. Just before the end of the countdown, place the test strip on the MQuant^® Card.
7. After the waiting time is elapsed, place the MQuant^® Card with the test strip within the viewfinder on your phone screen, and align the camera along the reference points.
8. The picture is captured automatically by the camera of the smartphone.
9. The result is displayed on the screen.

Results

In Table 1 is a comparison shown for the pH determination of 8 fruit juices with test strips using a visual and StripScan read out and the measurement with a pH electrode.

pH Value

Table 1. Comparison with visual evaluation and pH electrode.

Sample	StripScan*	Visual Readout*	pH Electrode
Cherry Juice	3.5	3	3.40
Grape Juice Red	3.5	3	3.14
Grape Juice White	3.1	3	3.34
Cranberry Juice	3.0	2	2.67
Currant Spritzer	2.5	3	3.04
Apple Juice	3.5	3	3.44
Pineapple Juice	3.5	4	3.5
Smoothie Juice Tree (Red)	3.5	3	3.57
*Results are based on the average of a 5-fold determination Note: Result graduation provided by MQuant® StripScan is identical with graduation on test strip package.

Conclusion

The MQuant^® pH test strip in combination with the MQuant^® StripScan app is a quick and easy way to analyze the pH-values of fruit juices. The measured values are comparable to those measured with the pH electrode.

As always, (whenever trying a new method of analysis) it is recommended to do plausibility checks and to compare the results with a reference method.

For More Information

• MQuant^® StripScan see SigmaAldrich.com/mquant-stripscan
• MQuant^® Test Strips see SigmaAldrich.com/mquant
• Applications see SigmaAldrich.com/wfa-applications