Claude R Mallet, Waters Corporation, Milford, MA, USA
Introduction
This technical note describes the method for the analysis of water samples using Waters® UPLC® with online SPE MS/MS technology .
The platform has many advantages:
1 Simplified laboratory workflow
2 Reduced manual operations and improved work efficiency
3 Minimize operator error and increase confidence in results
4 Accelerated sample turn-over and improved laboratory performance The system can be used as a complete UPLC online SPE system or as a daily LC-MS system to speed up the turnaround.
Traditional analytical method
With existing LC/MS/MS or GC/MS/MS systems, the sample must be converted from the original form to the appropriate form for easy injection analysis. Sample preparation is carried out by various manual extraction methods for enrichment or purification purposes. These extraction methods are quite time consuming and labor intensive. The number of repetitions of the extraction step depends to a large extent on the complexity of the sample and the target detection limit (LOD).
For trace levels of application, it is common practice to extract 1 liter of sample into a final volume of 500 microliters.
Online SPE method
In the online SPE method, the analyte of interest is first adsorbed onto the extraction column, washed, and then directly eluted onto the LC/MS/MS system. The evaporation and reconstitution steps in the extraction process are omitted. The sample utilization of this method is higher and the required sample volume is smaller.
As long as 20 ml of sample is available, the results of the offline method with 1 liter of sample can be achieved. By coupling two extraction columns, Waters UPLC with online SPE technology can also generate parallel events. With this two-column configuration, the loading, washing, and elution steps can be completed on the second extraction column while the equilibrium step is completed on the first extraction column. This reduces overall uptime and increases productivity. The SPE spool is cleaned after each injection, so it can be reused without reducing efficiency.
Figure 1. UPLC with online SPE technology .
From personal communication about the use of off-line SPE to analyze organic contaminants in water, we learned that a chemist can prepare 24 LC/MS/MS samples in an eight-hour shift. In this way, there are 120 samples in a week. In contrast, Waters UPLC with online SPE technology was used in our lab, and more than 500 water samples were processed in a week with very little user intervention.
Figure 2. Schematic diagram of UPLC using online SPE technology .
instructions
Shown in Figure 1 is a UPLC with online SPE technology consisting of a switching valve, pump, extraction column, analytical column, automated sampler, and mass spectrometer. Figure 2 shows a schematic of the system.
The analysis begins with loading the sample and loading the sample through the SPE injector port (valve A in Figure 2). The loading pump is an ACQUITY® Quaternary Solvent Manager (QSM) set to a 2 ml/min 100% aqueous solution. It moves the sample from the sample loop to the extraction column A. After the target analyte is adsorbed, the extraction process continues with a mild cleaning solution (< 20% organic solvent) to remove weaker interfering substances. After the cleaning step is completed, the adsorbed analyte on the extraction column A is eluted onto the UPLC analytical column using a backflush gradient elution (ACQUITY Binary Solvent Manager (BSM)) to perform refocusing of the peak. During the elution of extraction column A, extraction column B is regenerated and then re-equilibrated to the original conditions for the next analysis.
Online SPE systems can be arranged in a variety of ways for continuous operation, even when SPE and LC require different conditions and adsorbents. Using an additional solvent line, you can further optimize the extraction method by selecting the best solvent mixing method for the cleaning step prior to elution and selecting an efficient solvent mixing method for residue management. In addition, the system has a unique feature that bypasses the entire SPE path (valve C) for use as a standard UPLC/MS/MS system.
Online SPE schematic
For application success, careful selection of chemicals for extraction (SPE) and separation (LC) is also required. This choice is entirely dependent on the physical and chemical properties of the analyte of interest. The choice of SPE and LC chemistry must be able to achieve a seamless bond between extraction and separation conditions. Waters Oasis® HLB and XBridgeTM columns and ACQUITY UPLC BEH analytical columns provide the most efficient and effective performance because of their excellent repeatability and stability over a wide pH range. These products allow the analysis of a large number of types of compounds in complex mixtures.
in conclusion
Waters UPLC with online SPE technology provides additional functionality based on existing online SPE/HPLC systems.
1 This system can perform multitasking in direct UPLC/MS/MS or SPE/UPLC injection mode.
2 Parallel SPE configurations allow the system to align multiple methods with the same set of SPE chemicals or with different SPE sorbents for analyte screening.
3 A wide range of SPE and chromatographic chemistries are available to ensure the best solution for a wide range of applications.
4 The small sample size required for trace level analysis (low ppt) allows the laboratory to significantly reduce manual handling of sample processing and analysis, thereby increasing productivity.
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