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.
Also, if a Prime-eligible package arrives after the two-day shipping guarantee and you reach out to customer service, Amazon may extend your Prime membership by a month. MORE: 15 Best Amazon Prime Perks. Q.: How much does Amazon Prime cost? A.: The membership fee for Amazon Prime is $99 per year or $12.99 per month. The first 30 days of the annual subscription are free, and you can cancel anytime. Students can get a generous price break, however.