The main ingredient in the edible vinegar is acetic acid (the content of acetic acid is more than 3.5%). The edible vinegar also contains a few other organic acids. According to national hygienic standard, free mineral acid (sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid and other inorganic acid and oxalic acid) should not be detectable. The vinegar which is made up of unedible acid or contaminated contains free mineral acid and it would cause indigestion and diarrhea. Long-term consumption of the unqualified vinegar is severely harmful for the health of human beings. National standard GB/T5009.41 provides two methods to test the free mineral acid of edible vinegar. They are thymol blue test paper and methyl violet test paper.

1. Using method and results

1.1 Thymol blue test paper (yellow color)

1.1.1Take a piece of thymol blue test paper, uncover the film on the surface, use a capillary tube or a glass rod to dip a little detected sample onto the test paper, then observe the color.

1.1.2 It is positive results that there are purple spots or purple circles (light purple inside the circles) on the test paper. It means the vinegar contains free mineral acid. It is negative results that there is not any purple spots or no purple circles (yellow or white inside the circles) on the test paper. Don’t observe the color variation until the test paper is a little dry when detecting the white vinegar.

1.2 Methyl violet test paper (purple color)

1.2.1Take a piece of methyl violet test paper, uncover the film on the surface, use a capillary tube or a glass rod to dip the detected sample onto the test paper, then observe the color.

1.2.2 It is positive results that the test paper turns blue or green (it means the vinegar contains free mineral acid).It is negative result that the color of test paper still keeps purple.

2. Application scope

Suitable for rapid detection of free mineral acid in vinegar.

3. The lower limit of detection:

0.50%

4. Matters need attention:

The thymol blue test paper (yellow color) is suitable for detecting some dark color vinegar, and the methyl violet test paper (purple color) is suitable for detecting white vinegar and light color vinegar.

5. Preservation condition

Keep them at room temperature in aeration-drying condition. The expiration time is one year.