research update

I’ve been meaning to write a post for a couple of weeks detailing the state of play of my current analytical projects but I’ve been awfully busy helping my MSc student get the last of her LC-MS data on cherry anthocyanins and phenolics. We managed it in the end and she has a lovely result so I spent last week broadening my focus again and picking up some of the projects I’d had to put aside. Most of last week I also spent trying to derivatise reducing sugars for a collaboration with some lovely people from the Human Potential Centre at AUT’s Millenium Institute. This is a really exciting capability as sugars are notoriously hard targets to analyse chromatographically. We currently use a gas chromatographic method which involves a quite lengthy and fiddly acetylation procedure but I’ve found a compound that works really nicely for liquid chromatography with a relatively simple derivatisation procedure. There’s also lots of potential to push the analysis into larger oligosaccharides and glycans, with at least two exciting projects already on the table. I’m hoping this might result in two publications, the first being method development and the second an application.

I’ve also started developing a quantitative method for bile acids and have been approached to quantify lignin-derived phenolic compounds in sediment and plant material from estuarine habitats across the South Pacific. Very exotic! At some point I’d like to get some more method development done on neonicotinoid pesticides as I’ve developed a very cool and powerful extraction method which may solve the recovery and sensitivity problems. Again, definite options to present this as a method development and validation paper so no details yet.

😉

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I love HPLC – High Pressure Liquid Chromatography

HPLC is my favourite analytical technique because it can be applied to pretty much anything soluble. Which includes, well, pretty much everything. This is in contrast to Gas Chromatography (GC), which only works for compounds which are volatile at temperature below about 350C. This is only about 5% of molecules so that’s a fairly restrictive condition, although as us scientific types are jolly clever we’ve worked out cunning ways of changing non-volatile molecules we want to analyse by GC to make them volatile.

Here’s a link to one of the HPLC systems we use in our labs, including some of the applications for this technique. In addition I’d like to present a bit of my history with this technique to provide some examples of what it can achieve.

I used HPLC during my PhD to quantify glutathione ratios in the polychaete worm I was studying. Glutahione ratios are a very useful indicator of oxidative stress as glutathione is the first line of defence against the toxic effects of many metals and is a substrate or cofactor in many antioxidant and other enzymes.

Whilst working on my PhD I also used HPLC to quantify hormones in monkey pooh! This was a quick bit of work to validate a friend’s work looking at social hierarchies in communities of monkeys in zoos. The hormones in their pooh were correlated with their health and with their place in the hierarchy!

Nowadays you tend to find HPLC systems coupled to Mass Spectrometers, harnessing the resolving power of this technology to enhance the capabilities of liquid chromatography. This allows you to identify and quantify many different compounds in very short runs and in very complex matrices such as urine, blood and cell or tissue homogenates. SoAs was lucky enough to acquire an Agilent 6420 triple quadrupole mass spectrometer and an Agilent 1200 series LC stack a couple of years ago and this has become the workhorse of our lab.

During my PhD I first managed to get time on an LC-MS instrument when I was based at Plymouth University, where I worked as Research Assistant on a project characterising the metabolism of a common biocide, 2-hydroxybiphenyl [HBP], in common shore crabs. This was incredibly valuable experience and I was lucky to have an oustanding LC-MS mentor in the form of Dr Claire Redshaw. Claire helped me develop a method to extract HBP and its metabolites from urine we collected from the crabs (that’s a post for another day). The LC-MS allowed us to confirm that the metabolites were mostly sulphate-conjugates of either the parent molecule or of a monooxygenated product of Phase 1 detoxification.

Other pieces of LC-MS work I’ve been involved in or conducted myself include the extraction and quantification of bisphenol A from human urine, profiling of triglycerides in edible oils and in human plasma and the quantification of neonicotinoid pesticides in pollen and honey. I have been working on the latter piece of work for several years now, starting with a postdoc position at Exeter University studying the toxicity of this class of pesticides to bees and continuing now here at AUT.

Hopefully these examples of HPLC and LC-MS applications illustrate why I love the technique so much. One reason which may not be obvious is that LC is a notoriously challenging technique and can be incredibly complex to get right. So much so that it is often referred to as a “Black Art”. I have a favourite joke I tell to all the students when their analysis isn’t working as it should: I ask them how big their chicken was that morning. When they look baffled or alarmed I follow up with the question: “Well, you did sacrifice a chicken this morning, didn’t you?”

LOL!