17th International Mass Spectrometry Conference :: Prague, 2006
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|Session:||Atmospheric Pressure Ionization|
|Presentation date:||Thu, Aug 31, 2006|
|Presentation time:||14:30 – 16:00|
Andre Venter1, Huanwen Chen1, Daniella Vasconcellos Augusti2, Graham Cooks11 Purdue University, West Lafayette, United States
Correspondence address: Andre Venter, Purdue University, Chemistry, 560 Oval Dr, West Lafayette, 47906 United States.
Keywords: Extraction; Instrumentation; Ionization, Electrospray; Ionization, Micro Electrospray (Nanospray).
Novel aspect: At ionization microspray liquid-liquid extraction for direct analysis of trace compounds in complex mixtures without sample preparation.
We introduce a new electrospray-based ionization technique that permits the direct analysis of trace compounds in complex matrices such as serum, urine, milk and polluted water for long periods of time. Two separate sprayers are used, one to nebulize the sample solution and the other to produce charged microdroplets of solvent. This approach depends on liquid-liquid extraction between the colliding microdroplets. The compounds of interest are extracted from the analyte solution into the solvent spray in a continuous automatic fashion with no sample preparation steps.
Undiluted sample solutions were delivered from an infusion pump at a flow rate of 5 µL/min. The ionizing solvent spray, delivered at 10 µL/min, was a mixture of methanol/water/acetic acid (45:45:10). Both sprayers operate in a mode similar to that used in electrosonic spray ionization with dry nitrogen at 200 psi being used as the nebulizing gas. The sprayers were positioned at an angle to the Thermo LTQ mass analyzer inlet and with respect to each other in such a way that the ionized analyte molecules were directed towards the MS inlet by the combined aerodynamic effect of both sprayers. The charged ionizing spray turbulently mixes with the nebulized sample spray. The ionizing sprayer only was connected to a high voltage power supply and spray voltages of 3 to 5 kV were used in both the positive and negative ion modes. The analytes are ionized without compromising the analytical performance of the mass spectrometer, even after prolonged exposure to the complex matrix.
Low levels of RDX and atrazine were observed by microspray liquid-liquid extraction in undiluted mouse urine. Many of the components typically found in mammalian urine were observed, including creatine, glucose and urea.
2,4,6 Trinitrotoluene (TNT) was readily detected in the negative ion mode in polluted river water sample spiked with TNT. The TNT radical anion (m/z 227) occurs in the mass spectrum and was confirmed by CID. Ion/molecule reactions can be performed during the droplet collision event at atmospheric pressure as demonstrated for the formation of the diagnostic Meisenheimer complex of TNT.
Tetracyclines at typical levels could be quantified directly in undiluted milk samples.
In contrast to the rapid loss in signal intensity observed in conventional ESI/APCI ion sources when diluted urine is infused, the dual spray methodology offers good tolerance even to undiluted urine samples flowing at similar rates for long periods. No significant loss in signal was observed after many hours of analysis of raw urine. Under optimal conditions, the microspray extraction procedure provides sensitivity approaching or exceeding that of ESI-MS but with the continuous operation already noted. The inherent flexibility of the dual sprayer configuration offers the ability to perform ion/molecule reactions at atmospheric pressure to improve sensitivity and selectivity.