Let's face it, the whole solid phase extraction method development process can be time consuming and expensive. So Dilute-and-Shoot methods end up being the choice in some laboratories. The problem is that these methods are dirty and lead to a lot of other issues. In this blog post, I'll be discussing filtration methods and how those are a superior option to Dilute-and-Shoot.
While an extraction method like solid phase extraction or supported liquid extraction are the preferred techniques for sample clean up, sometimes they are not immediately practical due to cost constraints in a lab.
Researchers from ARUP Institute for Clinical and Experimental Pathology and the University of Utah say that Dilute-and-Shoot underestimated oxycodone concentrations in a sample as much as 45% compared to the existing method utilising SPE sample preparation. As Zlatuse Clark shown during MSACL 2018, Dilute-and-Shoot methods also tend to have greater variation between sample replicates.
Using filtration methods are always a good alternative to Dilute-and-Shoot. Many companies make filter devices that can be used as an additional sample clean up step. Biotage makes ISOLUTE FILTER+ plates.
For these plates, you load the sample into the plate and apply positive pressure or a vacuum to filter the sample through the plate.
One benefit of the FILTER+ plates is that the filter is 0.2 um filter, which is recommended for LC-MS/MS analysis. This means that the bigger particulates are being filtered out of the sample, which leads to a cleaner sample and a cleaner LC column. These FILTER+ plates can be used with sample volumes from 50 uL to 1.5 mL, which is great for a range of sample types and LOQs.
So now that we know the idea behind filtration devices, how do we actually filter our samples with them?
With the FILTER+ plates, you can filter:
- even blood samples
For urine samples, if hydrolysis is necessary, you add your sample, enzyme, hydrolysis buffer, and internal standard and incubate the sample (incubation time varies depending on the enzyme that you use).
You can then do one of two things:
- You can dilute your sample with water and apply it to the FILTER+ plate
- You can just apply the sample to the FILTER+ plate
Just remember, when you dilute your sample with water, your area counts for your analytes of interest will be lower. However, the samples are cleaner than they would have been without the dilution or in a dilute-and-shoot method.
Using a filtration device like the FILTER+ plates can save a lot of sample preparation time when compared to dilute-and-shoot. There is no need to centrifuge the sample to get rid of any particulates, nor is there a sample transfer step. Just filter with the ISOLUTE FILTER+ plates and you're good to go!