Contaminated Milli-Q water causes unknown peak - WKB75016

SYMPTOMS

• Contaminant peaks show up in chromatogram after aggressively washing out the entire system
• New solvent bottles, mobile phase, and column tried, but contaminant peaks remain
• Needle wash pump is working
• Needle wash filter was replaced
• Peak grows the longer initial conditions are held

ENVIRONMENT

• Alliance HPLC System
• 2998 Photodiode Array Detector
• 2489 UV/Vis Detector
• 2475 Multi-Wavelength Fluorescence Detector
• 2795 Separations Module

CAUSE

Contaminated water source (DI water)

Mobile phase contains contaminant from the MilliQ water system.

FIX or WORKAROUND

1. Flush system with organic mix of 1/3 ACN, 1/3 IPA, 1/3 MeOH
2. Switch system over to clean water source for example MilliQ water.

ADDITIONAL INFORMATION

To determine if the contaminant is in the pump or the injector, hook up the column directly to the outlet of the pump and connect it to the detector. This will bypass the injector. Run a 0-µL injection using the method that is in question. If no contaminant peak is visible, then the contamination is in the injector. If the contaminant peak is present, then contamination is coming from the pump or mobile phase.

A good test to see if the the mobile phase is contaminated is to set up the initial conditions of the pump. Let it flow through the column for five minutes and then run an injection. Note the height of the contamination peak. Then let the pump flow through the column for 30 minutes or longer, again at initial conditions. After the 30 minutes or so, run another injection. If the contamination peak height is higher than the first injection, mobile phase is likely the source of the contamination.