Re: How do you measure vitamin content?

Hello, Riya.

Most vitamins are difficult to assay by the layman. Highly technological methods are used in laboratories to determine the content of most vitamins. For example, there are many types of carotenoids. These are fat-soluble precursors of Vitamin A. Their activity is usually determined by spectrophotometric techniques.

Vitamin B6, which also exists in a few biologically active forms, is often joined with other substances in food, and is usually derived by microbiological assays. Similar techniques are used to determine Vitamin B12 content.

Vitamin D is determined by its ultraviolet absorption capacity, as measured by spectrophotometers, or even more accurately by liquid chromatography. The latter method also is used for analysis of Vitamin K.

Having said that, I've come across a method that could give you a good means of measuring Vitamin C, otherwise known as ascorbic acid. Here it is: Make an indicator using 1 gram of dichloroindophenol (DCIP), and mix it with 100 ml. of distilled water. This will be your solution.

Fill several test tubes half way with the DCIP solution. Place them in a rack. Take some fruit juice, (i.e. from orange, grapefruit, lime, lemon, etc.) and put each on the side in a seperate container. Make sure you label each one.

Add pure ascorbic acid into your first test tube of the DCIP solution with a dropper. Count the number of drops needed to change its color from blue to clear.

Into each remaining test tube, add one of your juices with a dropper. Note the number of drops needed to change the color of your indicator solution. The lower the number of drops needed, the higher the amount of Vitamin C in your fruit juice sample.

Hope that helps,

Peter Bosani.

Reference: McGraw-Hill Encyclopedia of Science & Technology.