Direct spectrophotometric observation of intracellular nitro-blue tetrazolium and its formazan by multiple internal reflectance infrared spectroscopy.

A technique is described which permits the direct, infrared (IR) spectrophotometric observation of peripheral leukocytes by utilizing multiple internal reflectance (MIR) spectroscopy on zinc selenide prisms. The IR spectra of nitro-blue tetrazolium (NBT) and its derivative, nitro-blue diformazan (NBF), are described and examined and these spectra are compared with those of the intracellular NBT and NBF yielding several peaks which may prove to be analytically useful. Additionally, the presence of unreduced NBT in leukocytes is demonstrated, which microscopic and chemical "NBT tests" have not previously done.