An indicator test is a way to detect the presence or absence of a specific substance in a sample based on observable changes, such as color changes. Indicators are substances that undergo distinct color changes under specific conditions, signaling the presence or absence of a particular substance.
Here are examples of indicator tests:
Starch Test with Iodine:
Indicator: Iodine solution
Purpose: Detect the presence of starch
Result: If starch is present, the iodine solution changes from yellow-brown to blue-black or dark purple.
Biuret Test for Protein:
Indicator: Biuret reagent (copper sulfate and sodium hydroxide solution)
Purpose: Detect the presence of proteins
Result: A positive test results in a color change from blue to violet or lavender.
Sudan Red Test for Lipids:
Indicator: Sudan Red solution
Purpose: Detect the presence of lipids (fats and oils)
Result: A positive test results in the substance turning reddish due to lipids absorbing the dye.
Brown Paper Bag Test for Lipids:
Indicator: Brown paper bag
Purpose: Detect the presence of lipids
Result: A positive test results in the paper becoming translucent or showing greasy marks due to lipid absorption.
Benedict's Test for Glucose:
Indicator: Benedict's solution (copper sulfate solution)
Purpose: Detect the presence of reducing sugars, like glucose
Result: A positive test results in a color change from blue to green, yellow, orange, or even brick-red, depending on the amount of sugar present.
Indicator tests are often used in biology and chemistry to quickly identify the presence of specific molecules or substances. They are simple and useful tools for students and scientists to perform qualitative analyses, such as determining the presence of certain nutrients, molecules, or compounds in various samples. The color changes in indicator tests provide a visual cue that helps researchers draw conclusions about the composition of the substances being tested.