Sampling Efficiency Improvement to an Electrospray Ionization Mass Spectrometer and Its Implications for Liquid Chromatography Based Inlet Systems in the Nanoliter to Milliliter per Minute Flow Range

Abstract

This paper describes electrospray sampling efficiency measurements obtained on a triple quadrupole mass spectrometer equipped with a large atmosphere to vacuum sampling aperture and modified ion optics designed to confine the ions traveling in the intense expanding gas beam and prevent scattering losses in the entrance optics of the mass analyzer. Sampling efficiency, defined as the ratio of the number of ions captured in the first vacuum stage of the entrance optics to the number of analyte molecules entering the ion source, is a measure of sensitivity that takes into account both ionization efficiency at atmospheric pressure, the efficiency of transporting the ions from atmosphere to vacuum, and the efficiency of confining them in the subsequent gas expansion before mass analysis. Sampling efficiency measurements were conducted under high-performance liquid chromatography sample introduction conditions using columns and flow rates spanning the nanoflow (300 nL/min), microflow (3–60 μL/min), and milliflow (100–500 μL/min) ranges. The results show a convergence in the sampling efficiencies across this range, narrowing the sensitivity gap between the nanoflow and higher flow rate ranges largely because nanoflow sampling efficiency has been shown to be close to 100% for more than a decade, leaving little room for improvement. Under situations where sample volumes are not limiting, lower concentration detection limits can now be achieved with the higher flow rate systems versus nanoflow as a direct consequence of the higher sample loading capacity of the columns and the reduction in the difference in their ion sampling efficiencies.

Open Port Interface for Coupling Capillary Electrophoresis and Mass Spectrometry: Performance Evaluation for Capillary Isoelectric Focusing

“…These results are consistent with previous publications that have mapped the electrospray sampling efficiency as a function of liquid flow rate for the same amount of injected sample. For instance, Schneider and coauthors found approximately 3-fold sampling efficiency difference when comparing flow rates of 100 μl/min and 5 μl/min for reserpine ions . Therefore, the actual reduction in the intensity of the signal in the OPI caused by the dilution is relatively small.…”

“…For instance, Schneider and coauthors found approximately 3-fold sampling efficiency difference when comparing flow rates of 100 μl/min and 5 μl/min for reserpine ions. 57 Therefore, the actual reduction in the intensity of the signal in the OPI caused by the dilution is relatively small. However, by operation with a high dilution rate, the effects of ion suppression can be reduced or eliminated.…”

Numerical Analysis and Quantification of Transfer Efficiency Coupled with Capillary and Quadrupole Ion Guide in an API-MS System

“…16,17 The novel dodecapole ion guide device called "Djet" could increase ion transfer efficiency from the ion source using a larger inlet orifice, and scatter losses in the shock waves of the accelerating gas are minimized to yield a signal improvement. 16,18 The stacked ring ion guide (SRIG) has advantages in trapping ions because of pseudopotential well scales as e r . 19,20 The SRIG, the ion tunnel, 21,22 and the S-lens 23 were used to improve ion transport efficiency in the first vacuum of commercial MS.…”

“…This study described increasing the MS orifice and used a 150 mm long radio frequency quadrupole (RFQ) ion guide in an ∼10-fold elevated bulk gas pressure to deliver ions into the mass analyzer with good transfer efficiency. Many studies were published to improve the sensitivity by using RF ion guides with acceptance radius which could entrain a spatially dispersed ion cloud, such as quadrupole, , sextupole, , octupole, − and dodecapole. , The novel dodecapole ion guide device called “Djet” could increase ion transfer efficiency from the ion source using a larger inlet orifice, and scatter losses in the shock waves of the accelerating gas are minimized to yield a signal improvement. , The stacked ring ion guide (SRIG) has advantages in trapping ions because of pseudopotential well scales as e r . , The SRIG, the ion tunnel, , and the S-lens were used to improve ion transport efficiency in the first vacuum of commercial MS. In contrast to a conjoined stepped RF ion guide, the electrodynamic ion funnel (EDIF) included a single stack of annular lenses and had the same achievement in ion transfer …”