Interview with Christel Hempen

Detection strategies for bioassays based on liquid chromatography, fluorescence spectroscopy and mass spectrometry.

Promotion Date: 15 July 2005

What was your thesis about?

I worked with two different kinds of bioassays: On the one hand with enzymatic assays and on the other hand with the reactions of antibodies and antigens – so-called immunoassays. The aim was to develop and to apply new detection methods, which yield higher throughput of analysis and better detection limits. The techniques I worked with were based on liquid chromatography, fluorescence spectroscopy and mass spectrometry, which are also mentioned in the thesis title. By means of liquid chromatography you separate different substances of a mixture. In the case of fluorescence spectroscopy as detection method the analytes are excited by light of a certain wavelength resulting in the emission of light of another wavelength. The intensity of the emitted light is determined. With mass spectrometry you can get quantitative and structural information on the different components.

It all sounds very general. Can you give an example?

I had collaborations with different companies in industry or with other academic research groups. In collaboration with Boehringer Ingelheim (a company in Germany), for example, I developed two methods for determining the amount of a drug against high blood pressure in human blood plasma samples.

So you can actually determine the presence of the drug in the blood sample?

Yes, it is described in a part of my thesis. One method is based on an immunoassay with fluorescence detection and the other is based on liquid chromatography coupled to mass spectrometry as detection method. You can determine the concentration of the drug in the blood and how fast it is decomposed by taking various blood samples of a patient after he or she has taken the drug.

Is the company going to adopt your method?

No, I don’t think that they will do it for this drug. They have their own ways of determining the drug concentrations in blood plasma samples, which have already been optimized and validated. These methods are routinely used. But they were interested in the comparison with other methods.

What else did you do?

In my thesis, I also developed a method to determine two enzymes simultaneously, also based on fluorescence spectroscopy. In case of this assay scheme, enzymes catalyze the reaction of non-fluorescent substrates into fluorescent products.

So your research is very close to applications?

The first topic is an application and the second is at this stage more theoretical. If you really want to simultaneously determine two enzymes, you have to work with fluorescent molecules, which emission wavelengths do not overlap. This implies that it is more difficult to apply this method. But nevertheless, it was possible to determine two enzymes in parallel in a honey sample.

Which of the three methods you worked with is the most practical?

The cheapest is the fluorescence spectroscopy. The advantages are a good selectivity and sensitivity. Liquid chromatography is very often applied in analytical labs. Mass spectrometry in combination with liquid chromatography is the newest technique and also most expensive. But due to its high potential this technique still gains more and more importance in these times.

Did you experience any setbacks?

Sure, I think everybody doing science experiences moments of frustration. Mine were mostly in the first years. Some of these problems could not be solved until the end of my thesis but by trying again and again and by changing the reaction conditions and other parameters several difficulties could be overcome.

What did you like best?

I liked the work in the lab and the opportunity of going to conferences. I really enjoyed presenting my own work. I visited, for instance, the Pittcon conference twice. It took place in Orlando both times. It is a very big annual conference with approximately 20.000 visitors. I had the possibility of giving oral presentations each time.

How did you get here at MESA?

I studied chemistry at the University of Münster in Germany. When Professor Karst went to Enschede, I got the chance to come along with him and to do my PhD here in Enschede.

It is not very far, Enschede or Münster.

Yes, it is not far, but it is quite different. Here in Enschede, the atmosphere is much more international, which I liked. And as PhD students get actual contracts, your position is more secure than in Germany.

What are you going to do next?

I can stay until the end of this year to continue with some things of my projects. But I am also applying for jobs in Germany and in the Netherlands. I hope that I am lucky to find a job I like.

For the summary of the thesis, click here.