Enhancing the Sensitivity of Atmospheric Pressure Ionization Mass Spectrometry Using Flow Modulated Gas Chromatography
Peak intensity enhancement is one highly desirable outcome of comprehensive two-dimensional gas chromatography (GC×GC). When coupled to mass spectrometry (MS), such enhancement is usually achieved with a thermal modulator using a technique called cryogenic zone compression (CZC). Differential flow modulation is a simple and cost-effective alternative to thermal modulation, but the requisite high flow rates are generally perceived as being incompatible with most (electron ionization [EI] and chemical ionization [CI]) mass spectrometers. The past decade has witnessed resurgent interest in coupling GC to atmospheric pressure chemical ionization (APCI), which requires high gas flows to assist ionization. This article reports on the modification of a GC–APCI system with a flow modulator and evaluates its potential to enhance the sensitivity towards selected trace organics.