You may be asking “Why is my test strip Ascorbic Acid Test Strip turning pink or purple instead of blue?” Here’s the answer!
The Ascorbic Acid test strip is based on discoloration of blue red-ox indicator, depending on the concentration of ascorbic acid. The Ascorbic Acid test strip is calibrated from 0.01% (10 mg/100 ml) to 0.1% (100 mg/100 ml). Red-ox indicator is also sensitive to acidic compounds, and its blue color turns to purple in the presence of acids.
The Vitamin C strips are buffered to a certain extent to keep the blue color of the pad, but in the presence of strong acids, contained in some fruits or juices, the color can turn to a purple-pink instead of a blue-white. In such cases, we recommend using a special color chart (See “Ascorbic Acid Color Changes” chart below) which shows results for Vitamin C in the presence of different concentrations of citric acid. Lemons and limes contain the highest amount of citric acid at about 5 percent. Grapefruits and oranges also have high content of citric acid at about 2.5 and 2 percent, respectively.
In the “Ascorbic Acid Color Changes” chart, the values are as follows:
Low = 0.5%; Medium = 1%; High = 5%