A stacking tray for electrical components, such as integrated circuits, particularly those of the ball grid array includes an upper side and a lower side. Cysteine concentration is quantitated by contacting cysteine with a coumarin dye capable of conjugating with cysteine but not to O-acetyl serine or sulfide; exciting the conjugate with UV light; and detecting fluorescent light emitted by the conjugate. The locking tabs can be formed by punching a hole in the sidewall, such that each locking tab remains integral with the sidewall, the locking tab projecting from an edge of the hole distal the flange and at angle toward the flange.