Resolution measurement for ion mobility spectrometry

Rokushika, Souji; Hatano, Hiroyuki; Baim, Michael A.; Hill, Herbert H.

doi:10.1021/ac00286a023

Cited by 119 publications

(94 citation statements)

References 18 publications

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“…Mobility resolution has been derived for lowfield conditions [16 -19]; however, high applied fields have a distinct effect on mobility resolution. The mobility peak width depends on four broadening terms: the initial pulse, diffusion, space-charge effects, and ion-molecule reactions [17,18]. If we assume that the initial ion gate width is narrow with respect to the peak width, the number of ions in each ion packet is low, and ion-neutral interaction potentials with the dirft gas are negligible, then we can assume that band broadening is limited to the diffusion term.…”

Section: Theorymentioning

confidence: 99%

Resolution equations for high-field ion mobility

Verbeck

Ruotolo

Gillig

et al. 2004

J. Am. Soc. Mass Spectrom.

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An extension of current mobility resolution equations as they apply to high-field ion mobility spectrometry is presented. The new resolution expression is applied to arrival time distributions for ions having a large range of ion mobilities and mass-to-charge ratios (m/z). The results indicate that the new equation can be utilized to predict the mobility resolution over a broader range of applied electric fields than previous ion mobility resolution expressions. (J Am Soc Mass Spectrom 2004, 15, 1320 -1324) © 2004 American Society for Mass Spectrometry S eparation based on the mobility of an ion through a neutral buffer gas (i.e., ion mobility spectrometry (IMS)) [1,2] is an important technology for studying long-lived electronic states of gas-phase ions and a sensitive method for detection of air-borne species [3, 4]. Recent work, which demonstrates the utility of IMS for analyzing gas-phase ionized biopolymers (i.e., peptides, proteins, DNA, etc.), has renewed interest in the analytical applications of IMS and led to the development of several high-resolution drift tubes in combination with mass spectrometry [5][6][7][8][9][10][11]. In order to perform a gas-phase separation of near thermal, structurally isomeric gas-phase ion populations, most IMS separations are performed near the low-field limit. Low-field conditions are important for studies of gas-phase peptide/protein structure because collisional activation can, in some cases, lead to structural rearrangement and/or fragmentation.In addition to the distinctions drawn for IMS operation in terms of separation field strength, the use of IMS can be divided into two pressure regimes, viz. high pressure (typically low-field) and low pressure (either low or high applied fields), and there are distinct advantages associated with both pressure regimes. At high pressure, the number of ion-neutral collisions is high, i.e., C 60 ϩ⅐ undergoes 10 10 collisions/s at 760 torr He compared with about 10 7 collisions/s for the same ion at 1 torr He. It is also important to consider that collisions with low-level impurities may significantly influence the separation and total drift time of an analyte ion. For example, in a 30 cm drift cell maintained at 760 torr He, C 60 ϩ⅐ will undergo 10 5 -10 6 collisions with a of 0.01% impurity, compared with ca. 10 collisions with the same level of impurity at 1 torr He. Another advantage of low-pressure drift tubes is the ease of coupling ion mobility with high vacuum mass spectrometers. Lastly, low-pressure (or high-field) mobility decreases ion separation times, leading to higher throughput analysis (approximately 3 orders of magnitude faster for analysis times at 1 torr over 760 torr).Low-field mobility conditions are defined in terms of the kinetic energy acquired by the ion in the presence of an applied field (E o ). That is, the translational energy gained by the ion between collisions should be less than the thermal energy of the collision gas [12, 13],where m is the mass of the ion, M is the mass of the neutral drift gas, ...

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Section: Theorymentioning

confidence: 99%

Resolution equations for high-field ion mobility

Verbeck

Ruotolo

Gillig

et al. 2004

J. Am. Soc. Mass Spectrom.

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“…Equation 4 is interesting because it suggests that all ions with the same charge will have the same spatial peak width in the plasmagram, which is consistent with [12]. To convert Eq.…”

mentioning

confidence: 76%

“…This definition of peak width has been used for defining a resolution metric for a given ion and an ideal IMS instrument using the total peak width based on a height equivalent to a theoretical plate (HETP), following similar resolution definitions from chromatography [12].…”

mentioning

confidence: 99%

Decomposition of overlapping plasmagram peaks by spectral subtraction

Swanson

2011

Int. J. Ion Mobil. Spec.

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Low field atmospheric pressure Ion Mobility Spectroscopy (IMS) involves the careful analysis of plasmagrams with multiple peaks which can mask one another when they are closely spaced in drift time or corresponding reduced mobility. A typical signal processing approach to decomposing overlapped peaks would be to use an orthogonal decomposition technique, but unfortunately Gaussian-like functions are not orthogonal, so no unique decomposition can be guaranteed. However, each ion species in the drift tube will arrive at the Faraday plate with a known statistical distribution determined by the IMS instrument's drift tube design, electric field strength, reagent gas flow and other instrument-specific factors such as the ion gate function. This paper presents a straightforward algorithm for decomposing plasmagrams into distinct peaks using a subtractive technique that independently estimates the statistical parameters of each peak, rejecting spurious peaks and electrical noise. The results show that for relatively short gate times, the plasmagram peaks are nearly Gaussian-shaped, but slightly fatter and asymmetric. We show that including of the gate rise and fall times is also significant in matching the plasmagram peak shape. We also show that the diffusion effects on resolution can be attributed to combinations of non-uniform ion distributions in the reaction chamber as well as detritus effects in the drift tube. Given the known peaks statistical parameters, one can then separate overlapping peaks using a straightforward spectral subtractive technique.

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“…At higher fields, the peak resolution continues to improve and three distinct ion distributions are baseline resolved at the highest field investigated (23 V cm -1 Torr -1 ). The change in ion mobility resolution with increasing voltage has been noted previously [53,54]. Hill and coworkers have combined several experimental parameters into an analytical expression for conditional ion mobility resolving power which predicts that the optimum resolution would be voltage-dependent and change with respect to the drift gas temperature [55].…”

Section: Torrmentioning

confidence: 90%

A Mass-Selective Variable-Temperature Drift Tube Ion Mobility-Mass Spectrometer for Temperature Dependent Ion Mobility Studies

May

Russell

2011

J. Am. Soc. Mass Spectrom.

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A hybrid ion mobility-mass spectrometer (IM-MS) incorporating a variable-temperature (80-400 K) drift tube is presented. The instrument utilizes an electron ionization (EI) source for fundamental small molecule studies. Ions are transferred to the IM-MS analyzer stages through a quadrupole, which can operate in either broad transmission or mass-selective mode. Ion beam modulation for the ion mobility experiment is accomplished by an electronic shutter gate. The variable-temperature ion mobility spectrometer consists of a 30.2 cm uniform field drift tube enclosed within a thermal envelope. Subambient temperatures down to 80 K are achievable through cryogenic cooling with liquid nitrogen, while elevated temperatures can be accessed through resistive heating of the envelope. Mobility separated ions are mass analyzed by an orthogonal time-of-flight (TOF) mass spectrometer. This report describes the technological considerations for operating the instrument at variable temperature, and preliminary results are presented for IM-MS analysis of several small mass ions. Specifically, mobility separations of benzene fragment ions generated by EI are used to illustrate significantly improved (greater than 50%) ion mobility resolution at low temperatures resulting from decreased diffusional broadening. Preliminary results on the separation of long-lived electronic states of Ti + formed by EI of TiCl 4 and hydration reactions of Ti + with residual water are presented.

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Resolution measurement for ion mobility spectrometry

Cited by 119 publications

References 18 publications

Resolution equations for high-field ion mobility

Resolution equations for high-field ion mobility

Decomposition of overlapping plasmagram peaks by spectral subtraction

A Mass-Selective Variable-Temperature Drift Tube Ion Mobility-Mass Spectrometer for Temperature Dependent Ion Mobility Studies

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