Antidepressants in urine: Dispersive microextraction with derivatisation
- Published: Jan 26, 2015
- Author: Steve Down
- Channels: Sample Preparation
Action for antidepressants
Scientists in Iran have developed a method for extracting and analysing antidepressant drugs in urine that combines the extraction and derivatisation processes in one step. Mir Ali Farajzadeh and Nina Nouri from the University of Tabriz and Ali Akbar Alizadeh Nabil from Tabriz University of Medical Sciences targeted three particular antidepressants from two different classes.
The drugs in question were nortriptyline, maprotiline and fluvoxamine. The first two are known as tricyclic antidepressants due to the three conjoined rings in their chemical structures. Fluvoxamine is a selective serotonin reuptake inhibitor (SSRI). All three act by inhibiting uptake of serotonin, which is a neurotransmitter, but acting by different mechanisms.
As with many prescription drugs, they can be misused and cases of accidental poisoning or suicide by overdose are well known. So, the research team wanted to devise a procedure for extracting the drugs from urine, one of the most common biofluids for forensic analysis, that was easier and more accurate than existing methods. They focussed on a variation of dispersive liquid-liquid microextraction and reported their findings in Biomedical Chromatography.
Heating things up
In DLLME, a liquid sample is mixed with a solvent to act as the extractant and a second liquid to act as the dispersant to form droplets of the extractant within the sample. This increases the contact surface area, thereby quickening the transfer of the analytes from the sample into the extractant.
In the new variation, Farajzadeh decided to heat the urine before it was treated which helps to increase the solubility of the extractant in urine. It was then allowed to cool as the dispersant was added and this led to the formation of new droplets that moved through the sample to increase the extraction efficiency.
In this case, simultaneous derivatisation of the drugs was also carried out during extraction by adding acetic anhydride to convert the free amino groups in each compound to acetamide derivatives.
After comparing the effectiveness of three different solvents and five dispersants, 1,1,2,2-tetrachloroethane and dimethylformamide were chosen as the best performers, respectively. After optimisation of the various volumes, temperature and solution pH, enrichment factors of 820-1070 were achieved. The final mixture was centrifuged and the sedimented organic phase was removed for analysis by GC with flame ionisation detection, giving detection limits of 2-4 ng/mL.
Urine from three female volunteers who had each been taking one of the three antidepressants regularly was tested with the new method. There were no interfering peaks in the gas chromatogram and the measured concentrations were 68-106 ng/mL.
The extraction procedure and the GC analysis performed as well as other published procedures for the drugs, and better in some cases. This was even the case for a GC/MS method which has an inherently more sensitive detection system. So, it follows that a combination of temperature assisted DLLME with GC/MS rather than GC-FID might be even more powerful.
One disadvantage of the new extraction procedure is the requirement of relatively large volumes of urine, at 50 mL, but this helped to give the high enrichment factors. The effects of heat and the simultaneous extraction and derivatisation speed up the extraction procedure, which is simple and inexpensive, factors which will endear it to clinical labs.
Biomedical Chromatography 2015 (Article in Press): "Determination of three antidepressants in urine using simultaneous derivatization and temperature-assisted dispersive liquid–liquid microextraction followed by gas chromatography–flame ionization detection"
Article by Steve Down
The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.
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