The Importance of Filtration in Liquid Chromatography-Mass Spectrometry (LC-MS) Workflows

Sample filtration can significantly improve LC-MS results but not all filters are created equal and some can introduce unwanted errors

September 2, 2021

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Sample filtration has been shown to be an important tool for improving the results from LC-MS. In part 1 of this two-part blog series, we review the results of some recent studies that looked at the improvements made possible by sample filtration with syringe filters prior to HPLC, and how to obtain these improvements without introducing other unwanted errors and effects.

 

LC-MS is a powerful analytical technique used for various qualitative and quantitative applications. Detection is achieved in the mass spectrometry (MS) via ionization of the analytes in the chromatographic effluent. About 75% of LC-MS users utilize Electrospray Ionization (ESI) as the interface between liquid chromatography and MS. However, despite the versatility of ESI, this ionization technique suffers from a phenomenon known as the matrix effect.

 

Matrix effect is typically attributable to components present in the sample matrix that co-elute with the compounds of interest. This competition may either suppress (ion suppression) or enhance (ion enhancement) the detection efficiency of the target analytes, which often leads to poor accuracy and precision of quantitative results. One way to minimize the matrix effect is by improving the method for analytical sample preparation, which typically includes sample filtration prior to analysis. If sample filtration is required, it is critical that the filters do not contribute any extractable/leachable materials that may influence the ionization efficiency of the target analytes.

 

High Performance, Low Leachable Syringe Filters 

 

In the first study, syringe filters from three suppliers were compared head-to-head to assess the contribution of undesirable, leachable compounds the filters contributed to the filtered effluent before it was loaded onto the HPLC column. The first study compared the cleanliness of the effluents from the three following filters:

 

 

Further details of the study can be seen in the Pall App note “Low Extractable Syringe Filters for LCMS Applications

 

Figure 1: Overlaid TIC Chromatograms showing the control (unfiltered test fluid) and the effluents from Pall Acrodisc MS Syringe Filters, Competitor A filters, and Competitor B filters. 10 samples were tested of each. Results may vary

 

As can be seen in fig 1., the Acrodisc MS Syringe Filter demonstrates a significantly lower level of leachable compounds in the effluent after the sample filtration step. In all three graphs, the Acrodisc Syringe Filter shows almost no discernible difference from the unfiltered control media. In contrast, the traces for the other two filter types show that both have contributed leached compounds into the matrix, with knock-on effects on the mass spec results.

 

In a second study, the same three filters were compared for their level of matrix effect, using samples of three different pharmaceutical substances spiked into HPLC grade methanol. The samples were then analyzed using ultra-high-performance liquid chromatography coupled to electrospray mass chromatography. 

 

Figure 2: Comparison of % Matrix Effect (ME) Observed at Different Concentrations in the Effluents from 3 Different Filters. Dash lines on each chart indicate no matrix effect (i.e. % ME = 100%).  25 samples were tested of each.  Results may vary.

 

As can be seen in figure 2, the Acrodisc MS Syringe Filters consistently outperform the other two filters, with lower levels of matrix effect seen in above data. For real-world sample analysis, this reduced matrix effect from the Acrodisc filters means that users can have the benefit of prefiltration without worrying about distorting their results. Further details of the study can be seen in the Pall app note “Reduction of Matrix Effects from Filter Effluents Using Pall Acrodisc MS Syringe Filters for LCMS Sample Preparation

 

If you are interested in improving your LC-MS/MS sample prep, please check out Pall’s Acrodisc MS Syringe Filters which are available in 13 mm diameter (cat # MS-3301) and 25 mm diameter (cat # MS-3201) with 0.2 µm rated wwPTFE membrane and HDPE housings.

 

Stay tuned for part 2 of this blog series which will focus on high throughput sample prep in LC-MS and a novel technique that shaves three hours off a typical LC-MS workflow.

 

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