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.
Amazon Prime's Â£7.99 a month subscription will offer users the chance to sign up without the hefty one-off fee - but over the year it will cost users Â£16.88 MORE than paying upfront. The total yearly cost of paying monthly is Â£95.88 compared to the Â£79 annual fee.