The ninhydrin reaction, one of the most important method of detecting amino acids, both technically and historically, has been conventionally used to detect their microgram amounts. When amino acids with a free alpha amino groups are treated with an excess of ninhydrin, they yield a purple colored product.
Update January 19: Amazon has increased the monthly price of Amazon Prime from $10.99 to $12.99 for those who opt for the month-to-month plan. However, the annual price remains untouched at $99 per year, which makes it the better option for avid Amazon shoppers.
1 Amazon Prime charges $99 per year for a membership (which equals $8.25 per month), making it very similar to the above options in terms of price. 2  You also get additional benefits including free two-day shipping for purchases made on Amazon.com.