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.
How much is Amazon Prime? A subscription to Amazon Prime costs $99 per year. You are charged annually, from the date you sign up to the same date next year. If you're looking to compare that to other per-month billing schemes, Amazon Prime's cost averages out to $8.25 per month. You can, however, get a 30-day free trial when you first sign up for Amazon Prime. See our How to Sign Up for an Amazon Prime Free Trial tutorial to learn how.