In normal phase HPLC, the mobile phase is relatively non-polar and the. stationary phase is relatively polar. Other more general types of HPLC include partition, adsorption, ion-exchange, size-exclusion, and thin-layer chromatography.
This particular guitar loop pedal is the Boss RC-30. Simply put, a loop pedal is a device used to capture sound clips which are then played over and over again (looped) and often overdubbed. While loop machines have been around for quite a while, the idea of a guitar loop pedal is relatively recent. Instead of the traditional box controlled by the hands of a DJ, loop pedals allow guitarists to control the looping and overdub features via foot switches.
Mayer also tends to play barre chords in the same style as Hendrix, using the thumb to fret the base note and mute the A-string of the guitar. This way, his remaining four fingers can easier do fills and small licks. John reportedly has over 200 guitars in his collection. A great guitar to use if you want to emulate Mayer's single-coil sound is the 2012 Gibson Les Paul Standard, which has push/pull pots that turn the humbuckers into single-coils. That way you get both the crunch and power of a Les Paul, and the smooth melodic sounds of a single-coil pickup.