Ambient ionization

FIGURE 8.9 Selectivity induced by cation adduction. Ion mobility separation of methyl-p-D-galactopyranoside from its isomer methyl-a-D-galactopyranoside using different cation adducts. (From Dwivedi et al., Rapid resolution of carbohydrate isomers by electrospray ionization ambient pressure ion mobility spectrometry-time-of-flight mass spectrometry (ESI-APIMS-TOFMS), J. Am. Soc. Mass Spectrom. 2007, 18, 1163-1175. With permission.)... 

FIGURE 9.11 Schematic of the electrospray ionization, ambient pressure, dual-gate ion mobility, quadrupole ion trap mass spectrometer. This instrument consisted of six primary units an electrospray ionization source, an ion mobility spectrometer, a vacuum interface, ion guides and lenses, a quadrupole ion trap, and a PC-based data acquisition system (not shown). " (Reprinted from Glowers and Hill, Mass analysis of mobility-selected ion populations using dual gate, ion mobility, quadrupole ion-trap mass spectrometry. Anal. Chem. 2005, 77, 5877-5885. With permission.)... 

Conventional associative ionization (AI) occurring at ambient temperature proceeds in two steps excitation of isolated atoms followed by molecular autoionization as the two atoms approach on excited molecular potentials. In sodium for example [44]... 

To examine a sample by inductively coupled plasma mass spectrometry (ICP/MS) or inductively coupled plasma atomic-emission spectroscopy (ICP/AES) the sample must be transported into the flame of a plasma torch. Once in the flame, sample molecules are literally ripped apart to form ions of their constituent elements. These fragmentation and ionization processes are described in Chapters 6 and 14. To introduce samples into the center of the (plasma) flame, they must be transported there as gases, as finely dispersed droplets of a solution, or as fine particulate matter. The various methods of sample introduction are described here in three parts — A, B, and C Chapters 15, 16, and 17 — to cover gases, solutions (liquids), and solids. Some types of sample inlets are multipurpose and can be used with gases and liquids or with liquids and solids, but others have been designed specifically for only one kind of analysis. However, the principles governing the operation of inlet systems fall into a small number of categories. This chapter discusses specifically substances that are normally liquids at ambient temperatures. This sort of inlet is the commonest in analytical work. 

To achieve sufficient vapor pressure for El and Cl, a nonvolatile liquid will have to be heated strongly, but this heating may lead to its thermal degradation. If thermal instability is a problem, then inlet/ionization systems need to be considered, since these do not require prevolatilization of the sample before mass spectrometric analysis. This problem has led to the development of inlet/ionization systems that can operate at atmospheric pressure and ambient temperatures. Successive developments have led to the introduction of techniques such as fast-atom bombardment (FAB), fast-ion bombardment (FIB), dynamic FAB, thermospray, plasmaspray, electrospray, and APCI. Only the last two techniques are in common use. Further aspects of liquids in their role as solvents for samples are considered below. 

Reference methods for criteria (19) and hazardous (20) poUutants estabHshed by the US EPA include sulfur dioxide [7446-09-5] by the West-Gaeke method carbon monoxide [630-08-0] by nondispersive infrared analysis ozone [10028-15-6] and nitrogen dioxide [10102-44-0] by chemiluminescence (qv) and hydrocarbons by gas chromatography coupled with flame-ionization detection. Gas chromatography coupled with a suitable detector can also be used to measure ambient concentrations of vinyl chloride monomer [75-01-4], halogenated hydrocarbons and aromatics, and polyacrylonitrile [25014-41-9] (21-22) (see Chromatography Trace and residue analysis). 

Polybutene can be cross-linked by irradiation at ambient temperature with y-rays or high energy electrons in the absence of air. The performance of articles manufactured from polybutene is only slightly affected by ionizing radiation at doses below 30 kGy (3 Mrad) (26). PMP is also relatively stable to P-and y-radiation employed in the sterilization of medical suppHes (27). 

Historically, measurements have classified ambient hydrocarbons in two classes methane (CH4) and all other nonmethane volatile organic compounds (NMVOCs). Analyzing hydrocarbons in the atmosphere involves a three-step process collection, separation, and quantification. Collection involves obtaining an aliquot of air, e.g., with an evacuated canister. The principal separation process is gas chromatography (GC), and the principal quantification technique is wdth a calibrated flame ionization detector (FID). Mass spectroscopy (MS) is used along with GC to identify individual hydrocarbon compounds. 

The flame ionization detector is capable of measuring only gaseous hydrocarbons, in other words, hydrocarbons that have a low boiling point. Emission gases can, however, also contain hydrocarbons in liquid form at ambient temperature and pressure. Therefore, analyzers based on flame ionization detection are generally equipped with heating elements to keep rhe sampling line and the detector at about 200 °C. 

The hydrophilic Au SR (RSH = GSH, h-GSH, (PG)SH, (SA)SH) clusters were ionized by the ESI method [15,16,18,23,24] (Figures 2 and 3c). The details of the ESI source are depicted in Figure 3c, together with typical pressures of the chambers under operation. A 50%(v/v) water-methanol solution of the fractionated Au SR cluster with a typical concentration of 0.5mg/mL was electro-sprayed into the ambient atmosphere through the stainless steel needle of a syringe biased at ca. — 3kV. The solution was delivered by a syringe pump (SP310I, World Precision... 

The recommended technique for the determination of oxime carbamates and their metabolites by HPLC/MS and HPLC/MS/MS is positive ESI. Electrospray is a soft ionization technique and is suitable for thermally labile compounds. Ions are produced in the liquid phase at quasi-ambient temperature and atmospheric pressure, thus leaving the fragile pesticides intact. For oxime carbamates, the molecular adducts that can be monitored during HPLC/MS analysis with electrospray in positive mode are [M- -H]+, [M- -Na]+, or [M- -NH4]+, depending on the nature of mobile phase used. ... 

After the desired reaction time, the stirring was stopped and the reactor cooled to ambient temperature. The reactor was slowly vented into the hood. The organic phase was typically clear and colorless and the aqueous phase yellow to red. The products were analyzed by gas chromatography using an SRI Instmments gas chromatograph with a flame ionization detector. 

Chemical ionization can be used at ambient pressures. Chemical ionization was used in tandem MS, using a triple quadrupole instrument, to characterize the antipsychotic agent 2-amino-N(4-(4-(l,2-benzisothiazol-3-yl)-l-piperazinyl)butyl)benzamide from human plasma.5... 

Z. Takats, J. M. Wiseman and R. G. Cooks, Ambient mass spectrometry using desorption electrospray ionization (DESI) instmmentation, mechanisms and applications in forensics, chemistry, and biology, J. Mass Spectrom., 40, 1261 1275 (2005). 

Recent innovations in ionization techniques have allowed the development of ambient mass spectrometry. Mass spectra can be determined for samples in their native environment without sample preparation. Although the ambient mass spectrometry technique is still in its infancy, its potential for serving as a tool of choice for high-throughput bioanalysis is very encouraging. 

A new family of ionization techniques allows ions to be created under ambient conditions and then collected and analyzed by MS. They can be divided into two major classes desorption electrospray ionization (DESI) and direct analysis in real time (DART). 

Z. Takats, I. Cotte-Rodrfguez, N. Talaty, H. Chen, and R. G. Cooks. Direct, Trace Level Detection of Explosives on Ambient Surfaces by Desorption Electrospray Ionization Mass Spectrometry. Chem. Commun., no. 15 (2005) 1950-1952. 

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