( ion ...)Improved Quantitative Selectivity of Clenbuterol in Human Urine using ,,, High Resolution on the TSQ Quantum Mass Spectrometer

ion Analysis, in SRM mode, of the spiked urine samples at a resolution setting of 0.7 Da FWHM resulted in a Clenbuterol peak eluting from the column upon a broad chemical noise background signal containing interferent peaks from the urine.

The same urine samples analysed at a peak resolution setting of 0.1 Da FWHM resulted in elimination of the interfering isobaric mass peaks and the broad background chemical noise previously seen in the analysis at a peak width setting of 0.7 Da FWHM. The selected reaction monitoring analysis performed at a higher resolution setting of 0.1 Da FWHM resulted in increased selectivity of the assay and hence an increase in the precision could be achieved.

The increase in selectivity at a peak width setting of 0.1 Da FWHM is due to the fact that Clenbuterol is a chlorinated compound and thus the negative mass deficiency can be used to eliminate interferents from the urine matrix in SRM mode. This increased selectivity can be achieved without detrimental loss of transmission. Typically only a factor of two to three fold decrease in peak area is observed between analyses performed at 0.7 and 0.1 Da FWHM, however, greater selectivity could then be achieved.

The calibration curves for Clenbuterol concentrations of between 0.1 to 100 pg/L at resolution settings of 0.1 and 0.7 Da FWHM both demonstrate excellent linearity. The calibration line at 0.7 Da FWHM showed a high intercept due to chemical background in the urine blank. This was significantly reduced by the use of high resolution.

The use of higher resolution to increase selectivity and precision could enable the limit of quantitation of an assay to be lowered and achieves a higher degree of confidence in identification of analytes in biological matrices.
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