Baseline drift
Baseline drift is a common problem in DSC experiments, mainly caused by temperature fluctuations, uneven mobile phase, or system contamination.
Temperature control: Column temperature fluctuations are one of the main causes of baseline drift. High precision column temperature chambers are required to ensure temperature fluctuations of ≤ ± 0.5 ℃, and a heat exchanger should be installed in front of the detector to stabilize the temperature of the mobile phase.
Mobile phase treatment: HPLC grade solvents should be used for the mobile phase, avoiding the use of low-quality reagents or circulating solvents. After preparation, it is necessary to fully degas (such as ultrasonic degassing for 20 minutes) and replace it regularly to prevent contamination. If the baseline drifts due to uneven mobile phase, pure water can be injected for testing. If the baseline returns to a stable state, the mobile phase needs to be replaced.
System cleaning and sealing: Check whether the circulation pool is contaminated or has gas, and use 1N nitric acid for cleaning (hydrochloric acid is prohibited); If the detector outlet is blocked and causes high pressure, the flow pool window needs to be replaced. At the same time, check the sealing of the furnace body, replace the aging O-ring, and confirm that the gas flow rate is stable (such as nitrogen flow rate of 20-50mL/min).
Abnormal peak shape
Abnormal peak shapes include tailing peaks, branching peaks, ghost peaks, etc., which require targeted investigation:
Tail peak: often caused by loss or contamination of the stationary phase in the chromatographic column. High proportion organic solvents are required to rinse the chromatography column, and gradient elution deep cleaning is used when severe contamination occurs; If the chromatographic column ages, it needs to be replaced in a timely manner. In addition, calibrate the pH value of the mobile phase to the tolerance range of the chromatographic column to avoid degradation of the stationary phase.
Fork peak: commonly seen in chromatographic column head damage or injection technique issues. Minor damage to the column head can be removed and reinstalled; Optimize the injection speed to ensure uniform injection volume and avoid sample diffusion at the injection port.
Ghost peak: usually caused by mobile phase contamination or residual in the injector. High purity reagents should be used to prepare the mobile phase, and the injector should be regularly replaced and cleaned (such as rinsing the quantitative ring with methanol). If the chromatographic column is severely contaminated, regeneration technology can be used to restore its performance.
Dome wide peak: often caused by decreased column efficiency or low flow rate. It is necessary to maintain or replace the chromatography column and optimize the flow rate, balance column efficiency and analysis time through the VanDeemter equation.
General troubleshooting steps
Pre experiment inspection: Confirm that the sample is dry and free of oxides, and protect it with an inert atmosphere; Check the sealing of the instrument to avoid air or liquid leakage.
Condition optimization: Adjust the heating rate (such as 10 ℃/min), flow ratio, and flow rate according to the properties of the sample to reduce mass transfer resistance.
Regular maintenance: monthly inspection of gas pipelines, sensor connection wires, and moving parts of the furnace body; Annual dismantling of furnace body by professional engineers, cleaning of sensor deposits, and replacement of aging circuit boards.
By systematically investigating temperature, mobile phase, chromatographic column, and operating conditions, baseline drift and peak shape anomalies in DSC experiments can be effectively resolved, improving data accuracy.