Analysis on the Go: Quantitation of Drugs of Abuse
in Dried Urine with Digital Microfluidics and Miniature Mass Spectrometry
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Abstract
We report the development of a method
coupling microfluidics and a miniature mass spectrometer, applied
to quantitation of drugs of abuse in urine. A custom digital microfluidic
system was designed to deliver droplets of solvent to dried urine
samples and then transport extracted analytes to an array of nanoelectrospray
emitters for analysis. Tandem mass spectrometry (MS/MS) detection
was performed using a fully autonomous 25 kg instrument. Using the
new method, cocaine, benzoylecgonine, and codeine can be quantified
from four samples in less than 15 min from (dried) sample to analysis.
The figures of merit for the new method suggest that it is suitable
for on-site screening; for example, the limit of quantitation (LOQ)
for cocaine is 40 ng/mL, which is compatible with the performance
criteria for laboratory analyses established by the United Nations
Office on Drugs and Crime. More importantly, the LOQ of the new method
is superior to the 300 ng/mL cutoff values used by the only other
portable analysis systems we are aware of (relying on immunoassays).
This work serves as a proof-of-concept for integration of microfluidics
with miniature mass spectrometry. The system is attractive for the
quantitation of drugs of abuse from urine and, more generally, may
be useful for a wide range of applications that would benefit from
portable, quantitative, on-site analysis