High sensitivity fourier transform ion cyclotron resonance mass spectrometry for biological analysis with nano-LC and microelectrospray ionization

Modifications to a 7 T nano-LC micro-ESI FT-ICR mass spectrometer, including a shorter octopole, ∼100% duty cycle, improved nano-LC micro-ESI emitter tips, and reverse-phase HPLC resins that require no ion-pairing agent, combine to achieve attomole detection limit. Three peptides in a mixture totaling 500 attomoles (amol) each in water (10 μL, 50 amol/μL) are separated and detected, demonstrating detection from a mixture at low endogenous biological concentration. Two peptides in a mixture totaling 500 amol each in artificial cerebrospinal fluid (1 μL, 500 amol/μL) are separated and detected, demonstrating detection from a mixture at a biological concentration in a biological solvent. The highest sensitivity is attained with arg⁸-vasotocin, in which a total of 300 amol is detected in artificial cerebrospinal fluid (1 μL, 300 amol/μL) and a total of 100 amol in water (1 μL, 100 amol/μL). Arg⁸-vasotocin isolated from the pineal gland of rainbow trout is detected, demonstrating the ability of FT-ICR to detect and identify a true endogenous biological analyte.