How is the vitamin content in food determined？ Most labs determine the vitamin content of

How is the vitamin content in food determined？

Most labs determine the vitamin content of foods using a combination of two technologies —chromotography, which sorts food molecules based on their molecular weight, and a light emission detector that identifies molecules based on their interaction with light。

To test the vitamin A content in an apple, for example, laboratories first grind the fruit to a pulpy liquid and drop a small sample through a device known as a vertical chromotography column. As the sample falls through the column, smaller molecules move faster while heavier molecules move more slowly. As each molecule drops from the bottom of the column, a monitor sounds out like the blips on an electrocardiogram that ring out each time the heart beats. All molecules pass through the column at specific speeds— vitamin A typically takes 10 minutes — a characteristic that has been previously determined.

When 10 minutes have elapsed, a machine shoots a beam of light through the bottom end of the column and records the wavelength and intensity of light the molecule reemits. If vitamin A is present, it should have reemitted the light at a characteristic 325-nanometer wavelength. The intensity of the light given off is a measure of how much vitamin A is present. So by comparing the intensity of the light given off in the apple sample to the intensity of a known amount of vitamin A, scientists can calculate the amount present in the sample.

To determine vitamin A content in an apple,_____.

A．it has to be ground first

B．it has-to be weighed first

C．it has to be X-rayed first

D．it has to be first treated in a chemical liquid