Electrospray ionization using a bamboo pen nib

A novel and highly sensitive electrospray ionization method, nib spray-mass spectrometry (Nibs-MS), is described. A bamboo pen nib was shaped and used for sample loading and ionization. The nib can be directly connected to the ESI ion sources of various mass spectrometers. The sample solution can be loaded onto the nib by normal pipetting, or simply dipping the nib into a sample solution. The sample solution enters the seam (width ∼7.5 μm) of the nib by capillary attraction. Meanwhile, the seam functions as a micro reservoir and prevents the sample solution from spreading to the surface. When a high voltage is applied to the nib, the sample solution is rapidly ejected and ionized toward the mass inlet. Since ionization occurs within a very short period, an abundance of ions is formed, leading to a dramatic improvement in the limit of detection. Using 4-chloro-amphetamine as a model compound, the limit of detection was determined to be 10 ng/mL. In contrast to this, when the traditional methods, including paper-spray and wooden tip-spray were used, the limits of detection were 100 and 50 ng/mL, respectively. Detailed information on how to prepare a suitable bamboo pen nib, the optimized position for ionization and its application to the analysis of a saliva sample are also reported.