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This paper compares static (i.e., temporally unchanging) thermal gradient gas chromatography (GC) to isothermal GC using a stochastic transport model to simulate peak characteristics for the separation of C12-C14 hydrocarbons resulting from variations in injection bandwidth. All comparisons are made using chromatographic conditions that give approximately equal analyte retention times so that the resolution and number of theoretical plates can be clearly compared between simulations. Simulations show that resolution can be significantly improved using a linear thermal gradient along the entire column length. This is mainly achieved by partially compensating for loss in resolution from the increase in mobile phase velocity, which approximates an ideal, basic separation. The slope of the linear thermal gradient required to maximize resolution is a function of the retention parameters, which are specific to each analyte pair; a single static, thermal gradient will not affect all analytes equally. A static, non-linear thermal gradient that creates constant analyte velocities at all column locations provides the largest observed gains in resolution. From the simulations performed in this study, optimized linear thermal gradient conditions are shown to improve the resolution by as much as 8.8% over comparative isothermal conditions, even with a perfect injection (i.e., zero initial bandwidth).

A simple device based on a tiny, coiled wire filament (CWF), similar in operation to solid phase microextraction (SPME), was reported almost a decade ago for sampling, concentrating, and minimizing contamination for Injection of liquid samples in gas chromatography (GC). However, the pliability of the platinum wire from which the CWF was fabricated was a hindrance when using this technique. In this work, we utilized a much stiffer stainless steel wire to form the CWF, and explored a number of ways to use it for sampling and sample introduction in GC and GC–MS. The coil radius and number of turns in the CWF (i.e., length of the coil) determined the sampling volume. The CWF was attached to a retractable plunger (part of a hand-held syringe-type holder) such that it could be retracted inside a 19 G needle for insertion into a standard GC injection port. Sampling was easily performed by either dipping the CWF in a liquid sample (i.e., sample dissolved in a solvent), which was drawn up into the wire coil by capillary action, or by applying a specific volume of liquid sample onto the CWF using a micro-syringe. Analytes trapped in/on the CWF could be introduced into the GC injection port before or after solvent evaporation. For semi-volatile compounds, the sample solvent was evaporated before injection, while for volatile compounds, some or all of the sample solvent was retained in the coil during injection. Repeatable volumes from 0.05 to 0.7 μL were sampled using CWFs with 5–70 turns, respectively, when sampling by dipping. Advantages of using a CWF compared to a conventional syringe include: (1) the chromatographic system is protected from contamination caused by accumulation of sample residues, (2) high quantitative repeatability is obtained for small volume injections (0.05–0.2 μL), (3) large sample injections can be performed for trace analysis by evaporating the solvent before injection, and (4) carryover and discrimination of semi-volatile compounds are minimized. These advantages enable easy and rapid (10 min total analysis time) trace (0.1–5 ppb) detection of a variety of different types of compounds, including polycyclic aromatic hydrocarbons, biphenyl congeners, organochlorine pesticides, pyrethroid pesticides, phthalate esters, and n -alkanes from C10 to C40 in water and waste water.

The chemical warfare agent O -ethyl S -(2-diisopropylaminoethyl) methyl phosphonothiolate (VX) and many related degradation products produce poorly diagnostic electron ionization (EI) mass spectra by transmission quadrupole mass spectrometry. Thus, chemical ionization (CI) is often used for these analytes. In this work, pseudomolecular ([M+H] + ) ion formation from self-chemical ionization (self-CI) was examined for four VX degradation products containing the diisopropylamine functional group. A person-portable toroidal ion trap mass spectrometer with a gas chromatographic inlet was used with EI, and both fixed-duration and feedback-controlled ionization time. With feedback-controlled ionization, ion cooling (reaction) times and ion formation target values were varied. Evidence for protonation of analytes was observed under all conditions, except for the largest analyte, bis(diisopropylaminoethyl)disulfide which yielded [M+H] + ions only with increased fixed ionization or ion cooling times. Analysis of triethylamine- d 15 provided evidence that [M+H] + production was likely due to self-CI. Analysis of a degraded VX sample where lengthened ion storage and feedback-controlled ionization time were used resulted in detection of [M+H] + ions for VX and several relevant degradation products. Dimer ions were also observed for two phosphonate compounds detected in this sample.

A newly developed person-portable gas chromatography-mass spectrometry (GC-MS) system was used to analyze several solvent standards, contact cement, paint thinner, and polychlorinated biphenyl samples. Passive solid phase microextraction sampling and fast chromatography with a resistively heated low thermal mass GC column were used. Results (combined sampling and analysis) were obtained in2 min for solvent, contact cement, and paint thinner samples, and in13 min for the polychlorinated biphenyl sample. Mass spectra produced by the small toroidal ion trap detector used were similar to those produced with heavily used transmission quadrupole mass spectrometers for polychlorinated biphenyl compounds, simple alkanes, and cycloalknes, while mass spectra for benzene and the ketone compounds analyzed showed evidence for ion/molecule reactions in the ion trap. For one of the contact cement samples analyzed, no evidence was found to indicate the presence of n-hexane, although the relevant material safety data sheet listed this ingredient. Specific chemical constituents corresponding to a potentially wide range of petroleum distillate compounds were identifiable from GC-MS analyses. The possibility for an improved basic characterization step in the exposure assessment process exists with the availability of fast, person-portable GC-MS, although work is needed to further refine this tool and understand the best ways it may be used.

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

A novel ion gate for electrospray-ionization atmospheric-pressure ion-mobility spectrometry (ESI-IMS) has been constructed and evaluated. The ion gate consisted of a chopper wheel with two windows--one for periodic ion passage from the ESI source into the drift region and the other for timing and synchronization purposes. The instrument contained a 45.0 cm long drift tube comprising 78 stainless steel rings (0.12 cm thick, 4.90 cm o.d., 2.55 cm i.d.). The rings were connected together in series with 3.34-MOmega resistors. The interface plate and the back plate were also connected with the first and the last rings, respectively, of the drift tube with 3.34-MOmega resistors. A potential of -20.0 kV was applied to the back plate and the interface plate was grounded. The drift tube was maintained at an electric field strength of approximately 400 V cm-1. An aperture grid was attached to the last ring in front of a Faraday plate detector, center-to-center. Several sample solutions were electrosprayed at +5.0 kV with +500 V applied to the ion gate. Baseline separations of selected benzodiazepines, antidepressants, and antibiotics were observed with moderate experimental resolution of approximately 70.

A new electron ionization source was developed for orthogonal acceleration time-of-flight mass spectrometry (TOFMS) based on the superimposition of a magnetic field around a radio frequency-only (rf-only) ion guide. The cylindrically symmetric magnetic field compresses the electron beam from the electron source into a long narrow volume along the ion guide axis. The magnetic field also helps to maintain a narrow energy distribution of electrons that penetrate the full length of the ion guide despite the influence of the radial rf field. Ionization occurs inside the ion guide with improved efficiency resulting from efficient use of electrons, prolonged interaction time, and nontraditionally large ionization volume. At the same time, the rf field effectively focuses ions radially and confines them to the axis of the ion guide by collisional focusing, leading to high ion transmission efficiency. Furthermore, the source can also be operated in a trap-and-pulse mode to improve the ion sampling duty cycle of orthogonal acceleration TOFMS. To validate the design concept of this new ion source, a simple prototype using a single set of cylindrical rods was constructed and retrofitted to an orthogonal acceleration TOFMS. A significant increase in ion signal intensity was observed by operating the source in a pulsed ion extraction mode. Low detection limits (for example, 12 fg for toluene) were determined at 12.5 spectra s(-1) in the full spectrum mode.

Electrospray ionization has grown to be one of the most commonly used ionization techniques for mass spectrometry, and efforts continue to improve its performance. Typically, the sprayer tip must be very close to the entrance orifice of the mass spectrometer in order to maximize the conduction of ions from the sprayer into the mass spectrometer. However, because of space-charge repulsion, most ions never reach the sampling orifice. In this work, an industrial air amplifier, for which the working mechanism is based on venturi and coanda effects, was added between an electrospray ionization source and a time-of-flight mass spectrometer. When a series of reserpine solutions (0.5, 1.0, 5.0, and 10.0 microM) were monitored using mass spectrometry, an over 5-fold increase in m/z 609.3 ion intensity was measured for a separation distance of 14 mm between the electrospray tip and interface capillary inlet, as compared to when the electrospray tip was in its normal position 1 mm in front of the inlet without the amplifier. When a voltage was applied to the air amplifier to further assist in focusing the electrosprayed ions, an approximately 18-fold increase in m/z 609.3 ion intensity was obtained. In addition, a 34-fold reduction in method detection limit was observed.

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.

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-efficiency separation methods such as capillary electrophoresis (CE) interfaced with structural information-producing detection systems such as mass spectrometry (MS) represent invaluable tools in analytical chemistry. Most CE applications to date have been reported using UV absorption detection. To extend the analytical power of CE, new detectors which demonstrate increased speed, sensitivity, and specificity must be developed. In this paper, we describe the design of an electrospray ionization time-of-flight mass spectrometer and its performance as a detector for CE. Emphasis is placed on fulfillment of the speed and sensitivity requirements. Low attomole and low femtomole detection limits are demonstrated for continuous infusion and CE−MS operation, respectively.

The rapid and accurate detection and identification of chemi cal 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-b ased technique, recent advan ces in GC, MS, and sampling technologies have led to the development of a hand-porta ble GC/MS system that is mo re 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 performa nce 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. Key Words: ion trap, mass spectrometer, gas chromatography, SPME, field-portable, chemical detection, toxic industrial compounds, chemical warfare agents, GCMS

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.

The design and use of a solid-phase injector for open tubular column supercritical fluid chromatography (SFC) are reported. For sample introduction, a liquid sample was loaded on a platinum wire. After the solvent had evaporated, the wire was inserted into, and sealed in, the injector. The chromatographic run was started by introducing the supercritical mobile phase into tie injector. Absolute and relative peak area reproducibilities, as well as retention time reproducibility, of the injection method were evaluated. The relative standard deviations (% RSDs) of absolute and relative peak areas were 2.0-4.5 and 0.4-1.8%, respectively, for both 1- and 2-μL injections

An electrospray interface for liquid chromatography/mass spectrometry (LC/MS) is described that combines the direct heating of High-performance liquid chromatography (HPLC) effluent that is characteristic of thermoooospray-type interfaces. This interface is called the thermally assisted electrospray interface for LC/MS. The device can accept the total effluent from a liquid chromatograph at flow rates ranging up to 500 μL/min. The HPLC effluent is nebulized into charged droplets by a combination of heat and an applied electric field. Ions emitted from charged droplets are mass-analyzed by a triple quadraupole mass spectrometer equipped with an atmospheric pressure ion sampling orifice. Singly or multiply charged ions, indicating the molecular weight of a sample, are observed with minimal fragmentation. The extent of multiple charging observed in electrospray and ion spray mass spectrometry is decreased somewhat in thermally assisted electrospray. Labile compounds which undergo thermal decomposition by conventional thermospray show no decomposition with thermally assisted electrospray.

We describe a novel radio frequency ion trap mass analyzer based on toroidal trapping geometry and microfabrication technology. The device, called the halo ion trap, consists of two parallel ceramic plates, the facing surfaces of which are imprinted with sets of concentric ring electrodes. Radii of the imprinted rings range from 5 to 12 mm, and the spacing between the plates is 4 mm. Unlike conventional ion traps, in which hyperbolic metal electrodes establish equipotential boundary conditions, electric fields in the halo ion trap are established by applying different radio frequency potentials to each ring. The potential on each ring can be independently optimized to provide the best trapping field. The halo ion trap features an open structure, allowing easy access for in situ ionization. The toroidal geometry provides a large trapping and analyzing volume, increasing the number of ions that can be stored and reducing the effects of space-charge on mass analysis. Preliminary mass spectra show resolution (m/Deltam) of 60-75 when the trap is operated at 1.9 MHz and 500 Vp-p.

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.

A method of predicting reduced ion mobility values, K0, for use in ion mobility spectrometry is described. While the method is very similar to a previously reported method based on a neural network, the method described in this paper uses a purely statistical regression approach. Furthermore, it has been applied to a wider class of compounds, including chemical agents. Various molecular parameters were evaluated in the predictive model to determine the qualitative dynamics that have the greatest effect on K0. An R2 value of 80.1% was obtained when calculated K0 values were plotted against measured K0 values for 162 compounds for which experimental K0 values were available. However, when chloroacetophenone and 3-xylyl bromide (3-methylbenzyl bromide) were removed from the set due to their large residual values, the predictability increased to an R2 value of 87.4%. This compares well with the value of 88.7%, which was obtained in a regression step of a previous neural network study for a less diverse set of 168 compounds.

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.

Alan L. Rockwood, ARUP Institute for Clinical and Experimental Pathology, 500 Chipeta Way, Salt Lake City, Utah 84108, USA, was inadvertently left out of the coauthor list of the original publication. He suggested the idea for gating the ion signal with a mechanical chopper and participated in the design of the ion mobility spectrometer. The correct sequence of authors of this contribution is: Li Zhou, David C. Collins, Edgar D. Lee, Alan L. Rockwood and Milton L. Lee.

An improved capillary zone electrophoresis (CZE)/ mass spectrometer interface comprises a liquid junction adapted to makeup the volume/flow rate of the CZE column eluent stream to be more compatible with the ion spray LC/MS interface flow rates required by mass spectrometer detectors in on-line separation/detection systems for variouscompositions and mixtures including biological fluids and environmental samples. Analytes eluting from the CZE capillary column are diluted with a suitable buffer thereby adjusting the volume and flow rates to prevent flow and pressure discrepanies which would otherwise result in peak broadening. The new liquid junction system for CZE/MS and CZE/MS/MS is useful in separating, detecting and analyzing compositions and mixtures such as amino acids, pesticides, peptides, mucleotides, sulfonated azo dyes and enzymatic digests such as tryptic digest of recombinant bovine somatotropan. Detection can be carried out in both positive and negative ion modes. High separation efficiencies ranging from 50,000 to 1,000,000 theoretical plates and peak asymmetries of 1.2 to 1.8 for tryptic digest are achieved.

Travaux du laboratoire, en particulier sur le plan du materiel, c'est un injecteur a diaphragme qui est utilise comme interface chromatographe-spectrometre. Nombreux exemples de separations

A liquid–solid extraction method suitable for rapid screening of sulfonated azo dyes in municipal wastewater has been developed. The dyes (Color Index Acid Yellow 23, Red 14 and Yellow 49) were separated on a short, reversedphase liquid chromatographic column with a water-methanol gradient containing 2 mM sulfuric acid. The column effluent was directed via a split-valve to an ion spray liquid chromatography/mass spectrometry (LC/MS) interface to an atmospheric pressure ionization mass spectrometer. The ion spray LC/MS system produced abundant [M – Na]− and [M – 2Na]2− ions according to the number of sulfonic acid substituents. Collision-induced dissociation of the parent ions for the dyes studied gave the SO3−. fragment common to sulfonated compounds plus additional daughter ion fragments characteristic of each dye. The dyes were quantified by monitoring from four to six different daughter ions of each dye. The relative abundances and the sum of the daughter ion current counts were used for confirmation and quantification with external standards. Recoveries of the dyes were in the range of 70–122%, and the relative standard deviation of replicate determinations was 5.4–12%. The method detection limit was three times higher for Acid Yellow 23 compared with the other two dyes, which could be detected down to 50 ppb in municipal wastewater.

Microbore high performance liquid chromatography-ion spray mass spectrometry is demonstrated for the determination of peptides. The ion spray mass spectra of peptides contained primarily only (M + nH)n+ ions (n is the degree of protonation). The linearity for a dilution series of leucine enkephalin was determined to be 4.9 orders of magnitude (r = 0.990), from 29 fmol to 90 pmol injected, and the smallest discernible signal (S/N of 3/1) was 65 amol. The tandem mass spectrometry daughter-ion mass spectrum of the multiply-charged molecular ion of dynorphin 1–9 exhibited daughter ions consistent with the sequence of the peptide. The micro-LC gradient elution separation for a tryptic digest of recombinant bovine somatotropin was acquired. The mass spectra obtained from the components in the tryptic digest were consistent with previously identified peptides. The mass spectrum of the tryptic fragment ISLLLIQSWLGPLQFLSR (MW 2083) contained multiply-charged ions that made it possible to detect this fragment even though its molecular weight is beyond the mass range of the mass spectrometer.

Full-scan capillary zone electrophoresis/mass spectrometry and capillary zone electrophoresis/tandem mass spectrometry (CZE/MS/MS) are demonstrated for the determination of monosulfonated and polysulfonated azo dyes at the low picomole levels. Under selected ion monitoring conditions femtomole levels of the dyes are detectable. Ion evaporation via the ion spray liquid chromatography/mass spectrometry interface is a mild form of ionization exhibiting only deprotonated singly charged or poly-deprotonated multiply charged negative molecular ions for sulfonated azo dyes. CZE/MS/MS daughter ion scanning after collision-induced dissociation of the molecular species for all sulfonated azo dyes contained the sulfonate ion (m/z 80). The presence of three sulfonated azo dyes in a wastewater extract was confirmed by parent ion scanning for the sulfonate daughter ion (m/z 80).

Sulfoconjugated anabolic steroids were separated by micro-bore high-performance liquid chromatography. The eluent was introduced into the atmospheric pressure ion source of the triple-quadrupole mass spectrometer via an ion spray liquid chromatograph/mass spectrometer interface operated in the negative ion mode. The limit of detection was 10 pg on-column by selected ion monitoring of the molecular ion and the response increased linearly over a concentration range of 2.4 orders of magnitude. Following work-up by a liquid-solid extraction procedure of equine urine samples, full-scan daughter ion spectra of boldenone sulfate could be obtained up to 17 days after a therapeutic dose of boldenone undecylenate to a horse.

Description des details experimentaux utilises pour obtenir des resultats preliminaires avec la methode citee, dans des cas simples. Etude des facteurs instrumentaux

A temperature-controlled reaction vessel was closely coupled to the ion-spray LC/MS interface on an atmospheric pressure ionization, triple quadrupole mass spectrometer and used to study mechanistic and kinetic aspects of reactions taking place in solution. Free access to the reaction vessel and temperature control as well as minimal sample consumption make continuous-introduction ion-spray mass spectrometry a useful approach for real-time measurement of reactions. The reaction medium, reactants, and products were transferred to the ion source of the mass spectrometer from the reaction vessel in less than 1 s. A variety of model reactions have been investigated to demonstrate the feasibility acd potential for continuous-introduction ion-spray mass spectrometry for real-time reaction monitoring. The half-life for the solvolysis of methandrostenolone sulfate in aqueous medium and the Michaelis-Menten constant of the enzymatic hydrolysis of 0-nitrophenyl P-D-galactopyranoside by lactase were determined. The enzymatic hydrolysis of dynorphin 1-8 by a-chymotrypsin and leucine aminopeptidase and the reduction of the disulfide bridge in oxytocin with fi-mercaptoethanol were obtained on-line to emphasize the technique's capability for peptide sequencing and structural elucidation.

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.