Getting Incorrect string value error with a 3-byte character that seems to be UTF-8 [closed]

I got a Ruby On Rails project and a MySQL table/column with utf8 character set (collation utf8_unicode_ci), and I want to keep it this way for now.I wrote some code to clean invalid characters from strings before saving the records to the DB and avoid "Invalid string value" errors:

value.each_char.select{|c| c.bytes.count < 4 }.join('')

This worked fine with emojis. However, I found a case where the character is 3 bytes and the db still crashes:\xE2\x86\x92, which is the character →

I also tried this: "→".force_encoding("UTF-8") but it returns the string unchanged.

How can I detect these invalid characters using ruby?I use ruby 1.9.3,