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.
So, here's the math: The $99 Prime subscription works out to $8.25 per month. Netflix charges $8.99 per month (unless you're grandfathered in at the previous rate, $7.99), a price that only includes video streaming. When you consider everything else that's included with Prime, especially the newly added download options, Amazon sails to an easy bang-for-the-buck victory.