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.
After that, youâll have to pay $99/year for the Amazon Prime subscription, and a monthly fee for each independent service you add to your account. Hereâs what each of these additional TV network subscriptions will cost when purchased directly from Amazon â prices range from $2.99 per month to $9.95 per month: 1  Showtime: $8.99/month. 2  Starz: $8.99/month.  Comedy Central Stand-up Plus: $3.99/month.