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For most analytes, ESI-MS operates primarily as a concentration sensitive detector in which the signal response is a function of the analyte concentration in the mobile phase. In conventional LC-MS, analyses are performed with a packed column of 4.6 mm in diameter operating with flow rates in excess of 0.5 mL/min. To handle these high flow rates, most commercial ESI sources for mass spectrometers use pneumatic assistance for aerosol generation. The direct coupling of a conventional column to an ESI source has some disadvantages. At these high flow rates, the mass spectrometer inlet samples typically less than 0.1% of the total aerosol produced. A great deal of the sample is "wasted" because it does not contribute to ion current. To better utilize sample, it is advisable to reduce the total volume (and hence flow rate) of mobile phase exiting the column. The reduction in flow rate has the effect of increasing analyte concentration and improving the signal response, and hence sensitivity of the mass spectrometer.
Since nanospray methods permit direct operation of the electrospray source at low flow rates (nL/min), the inside diameter of the column can be reduced by orders of magnitude with virtually no analytical penalty. A 75 µm ID nanobore column operating at 250 nL/min has a volume of some 3000 times less than a conventional 4.6 mm ID column. Theoretically, one can obtain an analyte concentration factor of approx. 3000 fold, and a much higher signal-to-noise response with the mass spectrometer. Practically, the experimental number is lower, but sensitivity improvements well in excess of 500 fold are commonly obtained. The analytical challenge is then to get your sample into the smallest possible volume for the highest possible signal response. The principle analytical benefit is that samples with strict quantity limitations, such as gel-separated proteins, are now readily analyzed. With 75 um ID columns, limits of detection are typically in the sub-femtomole to attomole range.
New Objective offers nanobore columns for the highest sensitivity LC/MS, especially for proteomics. Choose from a standard nanobore column with internal frit, our IntegraFrit™ column, or eliminate the headache of coupling nanobore-LC to ESI/MS by trying a PicoFrit® column. The easy-to-use PicoChip™ provides complete performance. Columns items are available in different bed lengths and packing materials.