Final answer:
The most probable cause of high column pressure and abnormal peaks in an HPLC system is air bubbles in the system. Air bubbles can obstruct the flow and disrupt the detector's response, leading to increased pressure and abnormal peaks.
Step-by-step explanation:
The question posed by the student relates to a scenario where an HPLC operator is experiencing issues with the column pressure being too high and rising too rapidly, as well as abnormal peaks in the recorder output. Among the given options, the most probable cause of the problem is D) Air bubbles in the system. The presence of air bubbles in the HPLC system can lead to an abnormal increase in backpressure because they can obstruct the flow of the mobile phase through the packed column. Not only do air bubbles cause high pressure, but they can also disrupt the detector's ability to produce a smooth baseline, resulting in distorted peaks or erratic detector response. On the contrary, column overloading would result in broad, distorted peaks due to too much sample being injected, but might not necessarily cause rapid pressure increase. Mobile phase contamination could cause abnormal peaks, but would typically cause a baseline drift rather than a pressure issue. Lastly, a detector malfunction would impact the shape of the peaks and the response signal, but would not have a direct effect on the pressure within the column.