Edgar D. Lee

On-line capillary zone electrophoresis-ion spray tandem mass spectrometry for the determination of dynorphins

Capillary zone electrophoresis-mass spectrometry and capillary zone electrophoresis-tandem mass spectrometry with ionization at atmospheric pressure are demonstrated as being feasible for the separation and determination of small peptides such as dynorphins (1-6, 1-7, 1-8, 1-9) and leucine enkephalin at low picomole levels by full-scan mass spectrometry and tandem mass spectrometry and at the low femtomole range under selected ion monitoring conditions. Ion evaporation resulting from the ion spray liquid chromatography-mass spectrometry interface exhibits primarily molecular weight information as singly and multiply charged ions and is shown to be a sensitive and mild ionization method for peptides. The full-scan daughter ion mass spectrum of leucine enkephalin is shown to contain fragment ions consistent with the sequence of the peptide. Parent ion scanning in the tandem mass spectrometry mode is a promising technique for the screening of related peptides.

Hand-portable gas chromatograph-toroidal ion trap mass spectrometer (GC-TMS) for detection of hazardous compounds

A novel gas chromatograph-mass spectrometer (GC-MS) based on a miniature toroidal ion trap mass analyzer (TMS) and a low thermal mass GC is described. The TMS system has an effective mass/charge (m/z) range of 50–442 with mass resolution at full-width half-maximum (FWHM) of 0.55 at m/z 91 and 0.80 at m/z 222. A solid-phase microextraction (SPME) fiber mounted in a simple syringe-style holder is used for sample collection and introduction into a specially designed low thermal mass GC injection port. This portable GC-TMS system weighs <13 kg (28 lb), including batteries and helium carrier gas cartridge, and is totally self-contained within dimensions of 47×36×18 cm (18.5×14×7in.). System start-up takes about 3 min and sample analysis with library matching typically takes about 5 min, including time for column cool-down. Peak power consumption during sample analysis is about 80 W. Battery power and helium supply cartridges allow 50 and 100 consecutive analyses, respectively. Both can be easily replaced. An on-board library of target analytes is used to provide detection and identification of chemical compounds based on their characteristic retention times and mass spectra. The GC-TMS can detect 200 pg of methyl salicylate on-column. n-Butylbenzene and naphthalene can be detected at a concentration of 100 ppt in water from solid-phase microextraction (SPME) analysis of the headspace. The GC-TMS system has been designed to easily make measurements in a variety of complex and harsh environments.

Miniature toroidal radio frequency ion trap mass analyzer.

A miniature ion trap mass analyzer is reported. The described analyzer is a 1/5-scale version of a previously reported toroidal radio frequency (rf) ion trap mass analyzer. The toroidal ion trap operates with maximum rf trapping voltages about 1 kVp-p or less; however despite the reduced dimensions, it retains roughly the same ion trapping capacity as conventional 3D quadrupole ion traps. The curved geometry provides for a compact mass analyzer. Unit-mass resolved mass spectra for n-butylbenzene, xenon, and naphthalene are reported and preliminary sensitivity data are shown for naphthalene. The expected linear mass scale with rf amplitude scan is obtained when scanned using a conventional mass-selective instability scan mode combined with resonance ejection.

General considerations for optimizing a capillary electrophoresis-electrospray ionization time-of-flight mass spectrometry system

Abstract Modern analytical instrumentation must be able to perform rapid, reliable, and sensitive analysis. The on-line combination of analytical techniques such as capillary electrophoresis (CE), electrospray ionization (ESI) and mass spectrometry (MS) can provide solutions to numerous problems related to complex mixtures of organic/inorganic, or biological materials. Optimum performance of complex instrumentation such as this can be achieved only if each individual component operates with maximum proficiency, and is in full harmony/compatibility with the other components. The present paper reports on the evaluation and optimization of a CE-ESI time-of-flight mass spectrometry (TOF-MS) system. The main features of the instrument are speed and sensitivity. Low amol (3–11) detection limits have been achieved with continuous infusion experiments, and the acquisition rate can be as high as 10 000 spectra s −1 . For CE–TOF-MS, minimum detection was in the very-low fmol (1–10) range. The major contributing factors to high quality analysis characteristic to each separate technique are considered, relevant examples are discussed, and fast, and sensitive analysis is demonstrated.

Evaluation of an electrospray interface for capillary electrophoresis-time-of-flight mass spectrometry

The electrospray technique has developed into a widely used ionization source for interfacing capillary electrophoresis (CE) to mass spectrometry (MS). However, its implementation is not always straightforward. A large number of factors have been found to be important contributors to the production of a high quality spray, and the efficient transfer of analytes from the CE column into the mass spectrometer can become, in certain cases, troublesome. An electrospray device which can accommodate operation with a liquid sheath, nebulizing gas and make-up gas, as well as operation without a liquid sheath in the microelectrospray mode, was constructed. The electrospray source was evaluated for efficient CE separations, which require the best performance.

High-Speed TOFMS Detection for Capillary Electrophoresis.

A new, high-speed data acquisition system was tested for high storage rate time-of-flight mass spectrometry (TOFMS) detection in capillary electrophoresis (CE). For high spectral acquisition rates of 4 kHz, a spectral storage rate of 80 spectra s(-)(1) was achieved. The resulting detection limit was in the low amol range (10-25 amol) for continuous infusion investigations.

Design and Optimization of a Corona Discharge Ion Source for Supercritical Fluid Chromatography Time-of-Flight Mass Spectrometry

The interfacing of capillary column supercritical fluid chromatography (SFC) to time-of-flight mass spectrometry (TOFMS) through atmospheric pressure chemical ionization (APCI) was investigated. An ion source chamber and a new, flexible, and efficient transfer line from the SFC to the TOFMS system were designed to accommodate the requirements of this study. Ionization of analytes was performed using a corona discharge needle. The interface was equipped with two multiple-axis translation stages for positioning of the transfer line tip and the discharge needle inside the ion chamber. The investigations were oriented toward the optimization of parameters which have a strong effect on the intensity and stability of the analyte signal, including background stability, corona discharge needle positioning in the ion source, transfer line tip and discharge needle relative positioning, curtain gas and makeup gas flow interactions, ion chamber temperature, and elution pressure of analytes from the SFC system.

Rapid analysis of organophosphonate compounds recovered from vinyl floor tile using vacuum extraction coupled with a fast-duty cycle GC/MS

In a terrorist event or industrial accident, environmental toxins will be inhomogeneously distributed on surfaces. A field vacuum extractor (FVE) can be used to sample contamination on fixed surfaces in a non-destructive fashion, but application to heterogeneously contaminated environments tends to be limited by the sampling time and time required for analysis, which is ∼15 to 30 min for a laboratory gas chromatograph/mass spectrometer (GC/MS). In the present study, FVE surface sampling was combined with a portable, fast-duty cycle GC/MS that enables analysis of a surface sample approximately every 3 minutes. Employing multiple FVE devices enables rapid measurement of many samples as might be required for characterizing contamination that is inhomogeneously distributed in a release environment. The FVE utilizes solid phase microextraction (SPME) fibers to sorb volatilized compounds from an evacuated headspace enclosed over the surface to be sampled (vinyl floor tile in the present study), over the course of a 30 min sampling time. Recovery of organophosphonate compounds in quantities sufficient to enable identification was achieved sampling floor tile exposed to as little as 30 ng. The amount detected was found to increase in a linear fashion with quantity applied to the floor tile, over three orders of magnitude. Carboxen–polydimethylsiloxane (PDMS) was used as the SPME sorbent phase and was sufficiently robust for multiple sampling and analysis cycles. The carboxen–PDMS retained 2–5% of the organophosphonate compounds after the initial GC/MS analysis, and this fraction could be readily measured in a subsequent re-analysis of the same sample. The re-analysis showed identifiable quantities of the organophosphonate compounds in all experiments except those with the lowest exposure quantities. Thus, once-analyzed carboxen–PDMS fibers may be archived for re-analysis at a later date if desired.

Advances in field-portable ion trap GC/MS instrumentation

The rapid and accurate detection and identification of chemical warfare agents and toxic industrial chemicals can be critical to the protection of military and civilian personnel. The use of gas chromatography (GC) - mass spectrometry (MS) can provide both the sensitivity and selectivity required to identify unknown chemicals in complex (i.e. real-world) environments. While most widely used as a laboratory-based technique, recent advances in GC, MS, and sampling technologies have led to the development of a hand-portable GC/MS system that is more practical for field-based analyses. The unique toroidal ion trap mass spectrometer (TMS) used in this instrument has multiple benefits related to size, weight, start-up time, ruggedness, and power consumption. Sample separation is achieved in record time (~ 3 minutes) and with high resolution using a state-of-the-art high-performance low-thermal-mass GC column. In addition to providing a system overview highlighting its most important features, the presentation will focus on the chromatographic and mass spectral performance of the system. Results from exhaustive performance testing of the new instrument will be introduced to validate its unique robustness and ability to identify targeted and unknown chemicals.