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 is a no-brainer for those heavily invested in the Amazon ecosystem. And if $99 per year seems like too much of a commitment, you can opt for the monthly $10.99. But read this first. That said, starting a 30-day free trial gives you early access to deals, plus free two-day shipping.