Why should I filter my samples instead of doing dilute-and-shoot?

Let’s face it, the whole method development process can be time consuming and expensive. Using solid phase extraction, while a much cleaner extraction method, can require a bit more time and evaluation. So dilute-and-shoot methods end up being the method of choice in some laboratories. The problem is that these methods are dirty and lead to a lot of other issues (dirty mass spec, clogged injection ports, frequent changing of LC columns,…). In this blog post, I’ll be discussing filtration methods and how those are a superior option 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? For the FILTER+ plates, you can filter urine, serum, plasma, or 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. If you need some enzyme tips, check out my previous blog post on hydrolysis!). You can then do one of two things. You can dilute your sample with water and apply it to the FILTER+ plate or 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. Dilute-and-shoot methods also tend to have greater variation between sample replicates, as was shown by ARUP Institute in this article.

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!

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. Using filtration methods are always a good alternative to dilute-and-shoot.

 

Should we use vacuum or positive pressure for processing samples in our lab?

Solid-phase extractions (SPE) can be a long and sometimes complicated process. So, we want to make sure that everything works the first time we extract. There are several different techniques we can use to extract. We can use a manual vacuum extraction or we can use manual or automated positive pressure to extract. In this blog post, I will be discussing some of the benefits that we see when using positive pressure for SPE.

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How can we extract and analyze for ever-present contaminants of interest?

It happens to all of us. We’re getting a new method developed and validated and then it comes time to run our negative urines. And everything comes up as positive! There are peaks for our analytes of interest in every urine that we run! How is that possible? In this blog post, I’m going to discuss some of the more troublesome analytes that I’ve encountered as far as finding an actual blank sample and what I’ve done to try and fix the issue.

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Urine hydrolysis: how did I choose which enzyme to use?

Urine hydrolysis is a part of sample preparation that we do to eliminate glucuronides. So first, what are glucuronides? And why do we want to get rid of them? Glucuronides are formed during metabolism. These glucuronide compounds attach to drugs to make them more water-soluble. This allows for easier excretion of the drugs in urine. However, this is not what we want to analyze when looking for our drugs of interest. We would rather look for just morphine or just oxazepam instead of morphine-3-β-D glucuronide or the oxazepam glucuronide. The process of removing these glucuronides from our analytes of interest is called hydrolysis.

In this post, I’ll tell you about my experience with urine hydrolysis and my success (or lack of success) when using different enzymes.

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