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 (NASDAQ:AMZN) Prime continues to grow in the United States. In fact, according to data from Consumer Intelligence Research Partners (CIRP), membership to the program that costs $99 a year or $10.99 a month has doubled in the United States over the last two years. The research firm estimates that Amazon now has 80 million U.S. Prime members. That's an increase from an estimated 58 million members at the end of the same period in 2016, or 38% growth in a single year. Amazon itself does not provide a Prime enrollment count.