Petrel Probe: An Integrated In Situ Sampling and Injection Interface for Fast, High-Efficiency Liquid...

Herein, we describe an in situ analysis probe, Petrel probe, highly integrating multiple functions of in situ sampling, in situ sample injection, high-performance liquid chromatography (HPLC) separation, and mass spectrometry (MS) electrospray. The Petrel probe was fabricated based on a single capillary, which consists of a micrometer-sized hole for sampling, a packed column for LC separation, and a tapered tip for MS electrospray. The design of the Petrel probe was optimized to obtain higher structural strength, and a polytetrafluoroethylene (PTFE) chip was used for sealing the probe-sampling hole to meet the high-pressure (∼30 MPa) requirement of LC manifold. On the basis of the Petrel probe, we developed a novel valveless LC injection method, that is, the probe pressing microamount in situ (PPMI) injection method, which performs sample injection by pressing the probe-sampling hole on the PTFE chip, using the mobile phase to dissolve the sample dry spot in the sampling area on the chip, and injecting it into the LC column under high-pressure conditions for separation and subsequent MS analysis. The LC-MS system with the PPMI injection method exhibits rapid injection and separation speed, as well as minimum injection dead volume. It can yield a high separation efficiency comparable to those of conventional HPLC systems. The present system was optimized using standard peptide samples, and four peptides were separated within 11 min in a probe with an effective column length of 5 cm, achieving the highest theoretical plate number up to ∼5,500,000/m. The system was also applied in the separation of cytochrome C digest to demonstrate its separation ability for complex samples, and 21 peptides were detected in 8 min with an amino-acid coverage of 83%.