Atmospheric-pressure photoionization

Last updated
Atmospheric pressure photoionization chamber Atmospheric pressure photoionization chamber.jpg
Atmospheric pressure photoionization chamber

Atmospheric pressure photoionization (APPI) is a soft ionization method used in mass spectrometry (MS) usually coupled to liquid chromatography (LC). Molecules are ionized using a vacuum ultraviolet (VUV) light source operating at atmospheric pressure (105 Pa), either by direct absorption followed by electron ejection or through ionization of a dopant molecule that leads to chemical ionization of target molecules. The sample is usually a solvent spray that is vaporized by nebulization and heat. The benefit of APPI is that it ionizes molecules across a broad range of polarity and is particularly useful for ionization of low polarity molecules for which other popular ionization methods such as electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are less suitable. It is also less prone to ion suppression and matrix effects compared to ESI and APCI and typically has a wide linear dynamic range. The application of APPI with LC/MS is commonly used for analysis of petroleum compounds, pesticides, steroids, and drug metabolites lacking polar functional groups and is being extensively deployed for ambient ionization particularly for explosives detection in security applications. [1] [2]

Contents

Instrument configuration

Atmospheric pressure photoionization interface.png

The figure shows the main components of an APPI source: a nebulizer probe which can be heated to 350–500 °C, an ionization region with a VUV photon source, and an ion-transfer region under intermediate pressure that introduces ions into the MS analyzer. The analyte(s) in solution from the HPLC flows into the nebulizer at a flow rate that can range from μL/min to mL/min range. The liquid flow is vaporized by nebulization and heat. The vaporized sample then enters into the radiation zone of the VUV source. Sample ions then enter into the MS interface region, frequently a capillary through the combination of a decreasing pressure gradient and electric fields.

APPI has been commercially developed as dual ionization sources more commonly with APCI, but also with ESI. [3]

Ionization mechanisms

The photoionization mechanism is simplified under vacuum conditions: photon absorption by the analyte molecule, leading to electron ejection, forming a molecular radical cation, M•+. This process is similar to electron ionization common to GC/MS, except that the ionization process is soft, i.e., less fragmentation. In the atmospheric region of an LC/MS system, the ionization mechanism becomes more complex. The unpredictable fate of ions is generally detrimental to LC/MS analysis, but like most processes, once they are better understood, these properties can be exploited to enhance performance. For example, the role of dopant in APPI, first developed and patented for the atmospheric ion source of ion mobility spectrometry (IMS), [4] [5] was adapted to APPI for LC/MS. The basic APPI mechanisms can be summarized by the following scheme:

Direct positive ion APPI

M + hν → M•+ + e−Analyte molecule M is ionized to a molecular radical ion M•+. The radical cation can then abstract an H atom from the abundant solvent to form [M+H]+.
M•+ + S → [M + H]+ + S[-H]•Hydrogen abstraction from solvent

Dopant or solvent-assisted positive ion APPI

D + hν → D•+ + e−A photoionizable dopant or solvent D is delivered in large concentration to yield many D•+ ions. Photoionizable solvent molecules achieve the same affect.
D•+ + M → → [M+H]+ + D[-H]•·D•+ ionizes analyte M by proton transfer
D•+ + M → → M•+ + DD•+ ionizes analyte M by electron transfer

The fundamental process in photoionization is the absorption of a high-energy photon by the molecule and subsequent ejection of an electron. In direct APPI, this process occurs for the analyte molecule, forming the molecular radical cation M•+. The analyte radical cation can be detected as M•+ or it can react with surrounding molecules and be detected as another ion. The most common reaction is the abstraction of a hydrogen atom from the abundant solvent to form the stable [M+H]+ cation, which is usually the observed ion. [6]

In dopant-APPI (or photoionization-induced APCI), a quantity of photoionizable molecules (e.g., toluene or acetone) is introduced into the sample stream to create a source of charge carriers. Use of a photoionizable solvent can also achieve the same effect. The dopant or solvent ions can then react with neutral analyte molecules via proton transfer or charge exchange reactions. The above table simplifies the dopant process. In fact, there may be extensive ion-molecule chemistry between dopant and solvent before the analyte becomes ionized. APPI can also produce negative ions by creating a high abundance of thermal electrons from dopant or solvent ionization or by photons striking metal surfaces in the ionization source. The cascade of reactions that can lead to M− or dissociative negative ions [M-X]− often involve O2 as an electron charge carrier. [7] Examples of negative ionization mechanisms include:

Direct or dopant-assisted negative ion APPI

M + O2•−→ [M − H]− + HO2•Deprotonation by superoxide O2•−
M + e–  →  M–  Electron capture
M + O2•−→ M− + O2

M + O2•−→ (M − X)− + X• + O2

M + O2•−→ (M − X + O)− + OX•   Where X = H, Cl, Br, or NO2

Electron transfer

Dissociative electron transfer

Dissociative electron capture and substitution

M + X–  →  [M + X]–        

Where X = Br, Cl, or OAc

Anion attachment

History

Photoionization has a long history of use in mass spectrometry experiments, though mostly for research purposes and not for sensitive analytical applications. Pulsed lasers have been used for non-resonant multiphoton ionization (MPI), [8] resonance-enhanced MPI (REMPI) using tunable wavelengths, [9] and single-photon ionization using sum frequency generation in non-linear media (usually gas cells). [10] [11] Non-laser sources of photoionization include discharge lamps and synchrotron radiation. [12] The former sources were not adaptable to high sensitivity analytical applications because of low spectral brightness in the former case and large "facility-size" in the latter case. Meanwhile, photoionization has been used for GC detection and as a source for ion mobility spectrometry for many years suggesting the potential for use in mass spectrometry. [13]

The first development of APPI for LC/MS was reported by Robb, Covey, and Bruins [14] and by Syage, Evans, and Hanold in 2000. [15] APPI sources were commercialized shortly thereafter by Syagen Technology and made available for most commercial MS systems and by Sciex for their line of MS instruments. Concurrent to the development of APPI was a similar use of a VUV source for low pressure photoionization (LPPI) by Syage and coworkers that accepted atmospheric pressure gas phase samples but stepped down the pressure for ionization to about 1 torr (~100 Pa) before further pressure reduction for introduction into a MS analyzer. This photoionization method is well suited as an interface between gas chromatography (GC) and MS. [16] [17]

Advantages

APPI is most used for LC/MS although it has recently found widespread use in ambient applications such as detection of explosives and narcotics compounds for security applications using ion mobility spectrometry. Compared to the more commonly used predecessor ionization sources ESI and APCI, APPI ionizes a broader range of compounds with the benefit increasing toward the non-polar end of the scale. It also has relatively low susceptibility to ion suppression and matrix effects, which makes APPI very effective in detecting compounds quantitatively in complex matrices. APPI has other advantages including a broader linear range and dynamic range than ESI as seen by the example in the left figure. [18] It is also generally more selective than APCI with reduced background ion signals as shown in the right figure. This latter example also highlights the benefit of APPI vs. ESI in that the HPLC conditions were for non-polar normal-phase in this case using n-hexane solvent. ESI requires polar solvents and further hexane could pose an ignition hazard for ESI and APCI that use high voltages. APPI works well under normal-phase conditions since many of the solvents are photoionizable and serve as dopant ions, which allows specialized applications such as separation of enantiomers (right figure). [19]

Atmospheric pressure photoionization advantages chart.png

Diarachidin (lipid) linearity plots.png LC separation of benzoin enantiomers.png

Regarding applicability to a range of HPLC flow rates, the signal level of analytes by APPI has been observed to saturate and even decay at higher solvent flow rates (above 200 μl/min), and therefore, much lower flow rates are recommended for APPI than for ESI and APCI. This has been suggested to be due to absorption of photons by the increasing density of solvent molecules., [20] [21] However, this leads to the benefit that APPI can extend to very low flow rates (e.g., 1 μL/min domain) allowing for effective use with capillary LC and capillary-electrophoresis. [22]

Application

The application of APPI with LC/MS is commonly used for analysis of low polarity compounds such as petroleums, [23] polyatomic hydrocarbons, [24] pesticides, [25] steroids, [26] lipids, [27] and drug metabolites lacking polar functional groups. [28] Excellent review articles can be found in the References. [2] [29]

Schematic of DAPPI source.png

APPI has also been effectively applied for ambient ionization applications lending itself to several practical configurations. One configuration termed desorption APPI (DAPPI) was developed by Haapala et al. and is pictured in the figure here. This device has been applied to the analysis of drugs of abuse in various solid phases, drug metabolites and steroids in urine, pesticides in plant material, etc. [29] [30] APPI has also been interfaced to a DART (direct analysis in real time) source and shown for non-polar compounds such as steroids and pesticides to enhance signal by up to an order of magnitude for N2 flow, which is preferred for DART because it is significantly cheaper and easier to generate then the higher performing use of He. Commercial APPI sources have also been adapted to accept an insertable sampling probe that can deliver or liquid or solid sample to the nebulizer for vaporization and ionization. This configuration is similar to atmospheric solid analysis probe (ASAP) that is based on the use of APCI and therefore is referred to as APPI-ASAP. The benefits of APPI-ASAP vs. APCI-ASAP are similar to those observed in LC/MS, namely higher sensitivity to lower polarity compounds and less background signal for samples in complex matrices. [31] Though ambient ionization has experienced a renaissance in the last decades, it has been used in the security industry for many decades, for example in swab detections at airports. The swabs collect condensed phase material from surfaces and are then inserted into a thermal desorber and ionizer assembly that then flows into the ion detector, which in most cases are an ion mobility spectrometer (IMS), but in later cases have been MS analyzers. A picture of a swab-APPI-IMS system used in airports and other security venues is given in the left figure

Swab-APPI-IMS security detector.png Swab-APPI-MS sample collection.png

In fact, a swab-APPI-MS system designed for explosives and narcotics detection for security applications performs very well for all types of ambient analysis using a sampling wand and swab (right figure). A particular demonstration (unpublished) showed excellent sensitivity and specificity for detection of pesticide compounds on a variety of fruits and vegetables showing detection limits for 37 priority pesticides ranging from 0.02 to 3.0 ng well below safe limits. [32]

See also

Related Research Articles

<span class="mw-page-title-main">Ion source</span> Device that creates charged atoms and molecules (ions)

An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.

<span class="mw-page-title-main">Electrospray ionization</span> Technique used in mass spectroscopy

Electrospray ionization (ESI) is a technique used in mass spectrometry to produce ions using an electrospray in which a high voltage is applied to a liquid to create an aerosol. It is especially useful in producing ions from macromolecules because it overcomes the propensity of these molecules to fragment when ionized. ESI is different from other ionization processes since it may produce multiple-charged ions, effectively extending the mass range of the analyser to accommodate the kDa-MDa orders of magnitude observed in proteins and their associated polypeptide fragments.

<span class="mw-page-title-main">Chemical ionization</span> Ionization technique used in mass [[spectroscopy]]

Chemical ionization (CI) is a soft ionization technique used in mass spectrometry. This was first introduced by Burnaby Munson and Frank H. Field in 1966. This technique is a branch of gaseous ion-molecule chemistry. Reagent gas molecules are ionized by electron ionization to form reagent ions, which subsequently react with analyte molecules in the gas phase to create analyte ions for analysis by mass spectrometry. Negative chemical ionization (NCI), charge-exchange chemical ionization, atmospheric-pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) are some of the common variants of the technique. CI mass spectrometry finds general application in the identification, structure elucidation and quantitation of organic compounds as well as some utility in biochemical analysis. Samples to be analyzed must be in vapour form, or else, must be vapourized before introduction into the source.

<span class="mw-page-title-main">Matrix-assisted laser desorption/ionization</span> Ionization technique

In mass spectrometry, matrix-assisted laser desorption/ionization (MALDI) is an ionization technique that uses a laser energy-absorbing matrix to create ions from large molecules with minimal fragmentation. It has been applied to the analysis of biomolecules and various organic molecules, which tend to be fragile and fragment when ionized by more conventional ionization methods. It is similar in character to electrospray ionization (ESI) in that both techniques are relatively soft ways of obtaining ions of large molecules in the gas phase, though MALDI typically produces far fewer multi-charged ions.

<span class="mw-page-title-main">Liquid chromatography–mass spectrometry</span> Analytical chemistry technique

Liquid chromatography–mass spectrometry (LC–MS) is an analytical chemistry technique that combines the physical separation capabilities of liquid chromatography with the mass analysis capabilities of mass spectrometry (MS). Coupled chromatography – MS systems are popular in chemical analysis because the individual capabilities of each technique are enhanced synergistically. While liquid chromatography separates mixtures with multiple components, mass spectrometry provides spectral information that may help to identify each separated component. MS is not only sensitive, but provides selective detection, relieving the need for complete chromatographic separation. LC–MS is also appropriate for metabolomics because of its good coverage of a wide range of chemicals. This tandem technique can be used to analyze biochemical, organic, and inorganic compounds commonly found in complex samples of environmental and biological origin. Therefore, LC–MS may be applied in a wide range of sectors including biotechnology, environment monitoring, food processing, and pharmaceutical, agrochemical, and cosmetic industries. Since the early 2000s, LC–MS has also begun to be used in clinical applications.

<span class="mw-page-title-main">Atmospheric-pressure chemical ionization</span> Ionization method

Atmospheric pressure chemical ionization (APCI) is an ionization method used in mass spectrometry which utilizes gas-phase ion-molecule reactions at atmospheric pressure (105 Pa), commonly coupled with high-performance liquid chromatography (HPLC). APCI is a soft ionization method similar to chemical ionization where primary ions are produced on a solvent spray. The main usage of APCI is for polar and relatively less polar thermally stable compounds with molecular weight less than 1500 Da. The application of APCI with HPLC has gained a large popularity in trace analysis detection such as steroids, pesticides and also in pharmacology for drug metabolites.

In mass spectrometry, direct analysis in real time (DART) is an ion source that produces electronically or vibronically excited-state species from gases such as helium, argon, or nitrogen that ionize atmospheric molecules or dopant molecules. The ions generated from atmospheric or dopant molecules undergo ion-molecule reactions with the sample molecules to produce analyte ions. Analytes with low ionization energy may be ionized directly. The DART ionization process can produce positive or negative ions depending on the potential applied to the exit electrode.

<span class="mw-page-title-main">Thermospray</span>

Thermospray is a soft ionization source by which a solvent flow of liquid sample passes through a very thin heated column to become a spray of fine liquid droplets. As a form of atmospheric pressure ionization in mass spectrometry these droplets are then ionized via a low-current discharge electrode to create a solvent ion plasma. A repeller then directs these charged particles through the skimmer and acceleration region to introduce the aerosolized sample to a mass spectrometer. It is particularly useful in liquid chromatography-mass spectrometry (LC-MS).

<span class="mw-page-title-main">Desorption electrospray ionization</span>

Desorption electrospray ionization (DESI) is an ambient ionization technique that can be coupled to mass spectrometry (MS) for chemical analysis of samples at atmospheric conditions. Coupled ionization sources-MS systems are popular in chemical analysis because the individual capabilities of various sources combined with different MS systems allow for chemical determinations of samples. DESI employs a fast-moving charged solvent stream, at an angle relative to the sample surface, to extract analytes from the surfaces and propel the secondary ions toward the mass analyzer. This tandem technique can be used to analyze forensics analyses, pharmaceuticals, plant tissues, fruits, intact biological tissues, enzyme-substrate complexes, metabolites and polymers. Therefore, DESI-MS may be applied in a wide variety of sectors including food and drug administration, pharmaceuticals, environmental monitoring, and biotechnology.

Sample preparation for mass spectrometry is used for the optimization of a sample for analysis in a mass spectrometer (MS). Each ionization method has certain factors that must be considered for that method to be successful, such as volume, concentration, sample phase, and composition of the analyte solution. Quite possibly the most important consideration in sample preparation is knowing what phase the sample must be in for analysis to be successful. In some cases the analyte itself must be purified before entering the ion source. In other situations, the matrix, or everything in the solution surrounding the analyte, is the most important factor to consider and adjust. Often, sample preparation itself for mass spectrometry can be avoided by coupling mass spectrometry to a chromatography method, or some other form of separation before entering the mass spectrometer. In some cases, the analyte itself must be adjusted so that analysis is possible, such as in protein mass spectrometry, where usually the protein of interest is cleaved into peptides before analysis, either by in-gel digestion or by proteolysis in solution.

<span class="mw-page-title-main">Desorption atmospheric pressure photoionization</span>

Desorption atmospheric pressure photoionization (DAPPI) is an ambient ionization technique for mass spectrometry that uses hot solvent vapor for desorption in conjunction with photoionization. Ambient Ionization techniques allow for direct analysis of samples without pretreatment. The direct analysis technique, such as DAPPI, eliminates the extraction steps seen in most nontraditional samples. DAPPI can be used to analyze bulkier samples, such as, tablets, powders, resins, plants, and tissues. The first step of this technique utilizes a jet of hot solvent vapor. The hot jet thermally desorbs the sample from a surface. The vaporized sample is then ionized by the vacuum ultraviolet light and consequently sampled into a mass spectrometer. DAPPI can detect a range of both polar and non-polar compounds, but is most sensitive when analyzing neutral or non-polar compounds. This technique also offers a selective and soft ionization for highly conjugated compounds.

<span class="mw-page-title-main">Ambient ionization</span>

Ambient ionization is a form of ionization in which ions are formed in an ion source outside the mass spectrometer without sample preparation or separation. Ions can be formed by extraction into charged electrospray droplets, thermally desorbed and ionized by chemical ionization, or laser desorbed or ablated and post-ionized before they enter the mass spectrometer.

Atmospheric pressure laser ionization is an atmospheric pressure ionization method for mass spectrometry (MS). Laser light in the UV range is used to ionize molecules in a resonance-enhanced multiphoton ionization (REMPI) process. It is a selective and sensitive ionization method for aromatic and polyaromatic compounds. Atmospheric photoionization is the latest in development of atmospheric ionization methods.

Ion suppression in LC-MS and LC-MS/MS refers to reduced detector response, or signal:noise as a manifested effect of competition for ionisation efficiency in the ionisation source, between the analyte(s) of interest and other endogenous or exogenous species which have not been removed from the sample matrix during sample preparation. Ion suppression is not strictly a problem unless interfering compounds elute at the same time as the analyte of interest. In cases where ion suppressing species do co-elute with an analyte, the effects on the important analytical parameters including precision, accuracy and limit of detection can be extensive, severely limiting the validity of an assay's results.

Petroleomics is the identification of the totality of the constituents of naturally occurring petroleum and crude oil using high resolution mass spectrometry. In addition to mass determination, petroleomic analysis sorts the chemical compounds into heteroatom class, type. The name is a combination of petroleum and -omics.

<span class="mw-page-title-main">Desorption/ionization on silicon</span> Soft laser desorption method

Desorption/ionization on silicon (DIOS) is a soft laser desorption method used to generate gas-phase ions for mass spectrometry analysis. DIOS is considered the first surface-based surface-assisted laser desorption/ionization (SALDI-MS) approach. Prior approaches were accomplished using nanoparticles in a matrix of glycerol, while DIOS is a matrix-free technique in which a sample is deposited on a nanostructured surface and the sample desorbed directly from the nanostructured surface through the adsorption of laser light energy. DIOS has been used to analyze organic molecules, metabolites, biomolecules and peptides, and, ultimately, to image tissues and cells.

<span class="mw-page-title-main">Matrix-assisted ionization</span>

In mass spectrometry, matrix-assisted ionization is a low fragmentation (soft) ionization technique which involves the transfer of particles of the analyte and matrix sample from atmospheric pressure (AP) to the heated inlet tube connecting the AP region to the vacuum of the mass analyzer.

Probe electrospray ionization (PESI) is an electrospray-based ambient ionization technique which is coupled with mass spectrometry for sample analysis. Unlike traditional mass spectrometry ion sources which must be maintained in a vacuum, ambient ionization techniques permit sample ionization under ambient conditions, allowing for the high-throughput analysis of samples in their native state, often with minimal or no sample pre-treatment. The PESI ion source simply consists of a needle to which a high voltage is applied following sample pick-up, initiating electrospray directly from the solid needle.

<span class="mw-page-title-main">Laser diode thermal desorption</span>

Laser diode thermal desorption (LDTD) is an ionization technique that is coupled to mass spectrometry to analyze samples with atmospheric pressure chemical ionization (APCI). It uses a laser to thermally desorb analytes that are deposited on a stainless steel sheet sample holder, called LazWell. The coupling of LDTD and APCI is considered to be a soft-ionization technique. With LDTD-APCI, it is possible to analyze samples in forensics, pharmaceuticals, environment, food and clinical studies. LDTD is suitable for small molecules between 0 and 1200 Da and some peptides such as cyclosporine.

References

  1. ↑ Hanold, Karl A.; Fischer, Stephen M.; Cormia, Patricia H.; Miller, Christine E.; Syage, Jack A. (2004). "Atmospheric Pressure Photoionization. 1. General Properties for LC/MS". Analytical Chemistry. 76 (10): 2842–2851. doi:10.1021/ac035442i. ISSN   0003-2700. PMID   15144196.
  2. 1 2 Kauppila, Tiina J.; Syage, Jack A.; Benter, Thorsten (2015-05-18). "Recent developments in atmospheric pressure photoionization-mass spectrometry". Mass Spectrometry Reviews. 36 (3): 423–449. doi:10.1002/mas.21477. ISSN   0277-7037. PMID   25988849.
  3. ↑ SYAGE, J; HANOLD, K; LYNN, T; HORNER, J; THAKUR, R (2004-10-01). "Atmospheric pressure photoionization☆II. Dual source ionization". Journal of Chromatography A. 1050 (2): 137–149. doi:10.1016/s0021-9673(04)01362-7. ISSN   0021-9673. PMID   15508306.
  4. ↑ "Bond, Ralph Norman, (31 Aug. 1900–6 Aug. 1984)", Who Was Who, Oxford University Press, 2007-12-01, doi:10.1093/ww/9780199540884.013.u162167 , retrieved 2021-06-30
  5. ↑ Kuckartz, Michael; Rauhut, Arnold (1999). "European Patent Organisation support for efficiency-boosting projects at German patent information centres". World Patent Information. 21 (1): 9–11. doi:10.1016/s0172-2190(99)00018-6. ISSN   0172-2190.
  6. ↑ Syage, Jack A. (2004). "Mechanism of [M + H]+ formation in photoionization mass spectrometry". Journal of the American Society for Mass Spectrometry. 15 (11): 1521–1533. doi: 10.1016/j.jasms.2004.07.006 . ISSN   1044-0305. PMID   15519219. S2CID   25780142.
  7. ↑ Kauppila, Tiina J.; Kotiaho, Tapio; Kostiainen, Risto; Bruins, Andries P. (2004). "Negative ion-atmospheric pressure photoionization-mass spectrometry". Journal of the American Society for Mass Spectrometry. 15 (2): 203–211. doi: 10.1016/j.jasms.2003.10.012 . ISSN   1044-0305. PMID   14766288. S2CID   45209180.
  8. ↑ Stansky, Peter (1991). "H. C. G. Matthew, editor. The Gladstone Diaries with Cabinet Minutes and Prime-Ministerial Correspondence. Volume Ten, January 1881–June 1883. New York: The Clarendon Press, Oxford University Press. 1990. Pp. cxcii, 479. $110.00. - H. C. G. Matthew, editor. The Gladstone Diaries with Cabinet Minutes and Prime-Ministerial Correspondence. Volume Eleven, July 1883–December 1886. New York: The Clarendon Press, Oxford University Press. 1990. Pp. vi, 702. $110.00". Albion. 23 (4): 786–788. doi:10.2307/4050787. ISSN   0095-1390. JSTOR   4050787.
  9. ↑ Syage, Jack A. (1990-04-01). "REAL-TIME DETECTION of Chemical Agents Using Molecular Beam Laser Mass Spectrometry". Analytical Chemistry. 62 (8): 505A–509A. doi:10.1021/ac00207a740. ISSN   0003-2700.
  10. ↑ Boesl, U.; Weinkauf, R.; Weickhardt, C.; Schlag, E.W. (1994), "Laser ion sources for time-of-flight mass spectrometry", Time-of-Flight Mass Spectrometry and its Applications, Elsevier, pp. 87–124, doi:10.1016/b978-0-444-81875-1.50008-2, ISBN   978-0-444-81875-1 , retrieved 2021-06-30
  11. ↑ Tonkyn, Russell G.; White, Michael G. (1989). "Compact vacuum ultraviolet source for photoelectron spectroscopy". Review of Scientific Instruments. 60 (7): 1245–1251. Bibcode:1989RScI...60.1245T. doi:10.1063/1.1140298. ISSN   0034-6748.
  12. ↑ Berkowitz, Joseph (1979), "Partial Cross Sections", Photoabsorption, Photoionization, and Photoelectron Spectroscopy, Elsevier, pp. 155–357, doi:10.1016/b978-0-12-091650-4.50012-8, ISBN   978-0-12-091650-4 , retrieved 2021-06-30
  13. ↑ Driscoll, John N. (2005-11-14), "Photoionization", Environmental Instrumentation and Analysis Handbook, Hoboken, NJ, USA: John Wiley & Sons, Inc., pp. 221–235, doi:10.1002/0471473332.ch10, ISBN   978-0-471-47333-6 , retrieved 2021-06-30
  14. ↑ Robb, Damon B.; Covey, Thomas R.; Bruins, Andries P. (2000). "Atmospheric Pressure Photoionization: An Ionization Method for Liquid Chromatography−Mass Spectrometry". Analytical Chemistry. 72 (15): 3653–3659. doi:10.1021/ac0001636. ISSN   0003-2700. PMID   10952556.
  15. ↑ Syage, Jack A.; Hanning-Lee, Mark A.; Hanold, Karl A. (2000). <204::aid-fact5>3.0.co;2-7 "A man-portable, photoionization time-of-flight mass spectrometer". Field Analytical Chemistry & Technology. 4 (4): 204–215. doi:10.1002/1520-6521(2000)4:4<204::aid-fact5>3.0.co;2-7. ISSN   1086-900X.
  16. ↑ Syage, Jack A.; Nies, Brian J.; Evans, Matthew D.; Hanold, Karl A. (2001). "Field-portable, high-speed GC/TOFMS". Journal of the American Society for Mass Spectrometry. 12 (6): 648–655. doi: 10.1016/s1044-0305(01)80210-5 . ISSN   1044-0305. PMID   11401156. S2CID   22426271.
  17. ↑ Syage, Jack A.; Cai, Sheng-Suan; Li, Jianwei; Evans, Matthew D. (2006-03-31). "Direct Sampling of Chemical Weapons in Water by Photoionization Mass Spectrometry". Analytical Chemistry. 78 (9): 2967–2976. doi:10.1021/ac0518506. ISSN   0003-2700. PMID   16642982.
  18. ↑ Hakala, Kati S.; Laitinen, Leena; Kaukonen, Ann Marie; Hirvonen, Jouni; Kostiainen, Risto; Kotiaho, Tapio (2003). "Development of LC/MS/MS Methods for Cocktail Dosed Caco-2 Samples Using Atmospheric Pressure Photoionization and Electrospray Ionization". Analytical Chemistry. 75 (21): 5969–5977. doi:10.1021/ac034679b. ISSN   0003-2700. PMID   14588039.
  19. ↑ Cai, Sheng-Suan; Hanold, Karl A.; Syage, Jack A. (2007). "Comparison of Atmospheric Pressure Photoionization and Atmospheric Pressure Chemical Ionization for Normal-Phase LC/MS Chiral Analysis of Pharmaceuticals". Analytical Chemistry. 79 (6): 2491–2498. doi:10.1021/ac0620009. ISSN   0003-2700. PMID   17288463.
  20. ↑ Kauppila, Tiina J.; Bruins, Andries P.; Kostiainen, Risto (2005). "Effect of the Solvent Flow Rate on the Ionization Efficiency in Atmospheric Pressure Photoionization-Mass Spectrometry". Journal of the American Society for Mass Spectrometry. 16 (8): 1399–1407. doi: 10.1016/j.jasms.2005.03.051 . ISSN   1044-0305. S2CID   95770095.
  21. ↑ Robb, Damon B.; Blades, Michael W. (2005). "Effects of solvent flow, dopant flow, and lamp current on dopant-assisted atmospheric pressure photoionization (DA-APPI) for LC-MS. Ionizationvia proton transfer". Journal of the American Society for Mass Spectrometry. 16 (8): 1275–1290. doi: 10.1016/j.jasms.2005.03.017 . ISSN   1044-0305. S2CID   97098539.
  22. ↑ Kauppila, Tiina J.; Östman, Pekka; Marttila, Seppo; Ketola, Raimo A.; Kotiaho, Tapio; Franssila, Sami; Kostiainen, Risto (2004). "Atmospheric Pressure Photoionization-Mass Spectrometry with a Microchip Heated Nebulizer". Analytical Chemistry. 76 (22): 6797–6801. doi:10.1021/ac049058c. ISSN   0003-2700. PMID   15538806.
  23. ↑ Purcell, Jeremiah M.; Rodgers, Ryan P.; Hendrickson, Christopher L.; Marshall, Alan G. (2007). "Speciation of nitrogen containing aromatics by atmospheric pressure photoionization or electrospray ionization fourier transform ion cyclotron resonance mass spectrometry". Journal of the American Society for Mass Spectrometry. 18 (7): 1265–1273. doi: 10.1016/j.jasms.2007.03.030 . ISSN   1044-0305. PMID   17482835. S2CID   10117894.
  24. ↑ Cai, Sheng-Suan; Syage, Jack A.; Hanold, Karl A.; Balogh, Michael P. (2009-02-19). "Ultra Performance Liquid Chromatography−Atmospheric Pressure Photoionization-Tandem Mass Spectrometry for High-Sensitivity and High-Throughput Analysis of U.S. Environmental Protection Agency 16 Priority Pollutants Polynuclear Aromatic Hydrocarbons". Analytical Chemistry. 81 (6): 2123–2128. doi:10.1021/ac802275e. ISSN   0003-2700. PMID   19227980.
  25. ↑ Kruve, Anneli; Haapala, Markus; Saarela, Ville; Franssila, Sami; Kostiainen, Risto; Kotiaho, Tapio; Ketola, Raimo A. (2011). "Feasibility of capillary liquid chromatography–microchip-atmospheric pressure photoionization–mass spectrometry for pesticide analysis in tomato". Analytica Chimica Acta. 696 (1–2): 77–83. doi:10.1016/j.aca.2011.04.006. ISSN   0003-2670. PMID   21621035.
  26. ↑ Leinonen, Antti; Kuuranne, Tiia; Kostiainen, Risto (2002). "Liquid chromatography/mass spectrometry in anabolic steroid analysis?optimization and comparison of three ionization techniques: electrospray ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization". Journal of Mass Spectrometry. 37 (7): 693–698. Bibcode:2002JMSp...37..693L. doi:10.1002/jms.328. ISSN   1076-5174. PMID   12125002.
  27. ↑ Cai, Sheng-Suan; Syage, Jack A. (2006). "Atmospheric pressure photoionization mass spectrometry for analysis of fatty acid and acylglycerol lipids". Journal of Chromatography A. 1110 (1–2): 15–26. doi:10.1016/j.chroma.2006.01.050. ISSN   0021-9673. PMID   16472815.
  28. ↑ Cai, Yanxuan; Kingery, David; McConnell, Oliver; Bach, Alvin C. (2005). "Advantages of atmospheric pressure photoionization mass spectrometry in support of drug discovery". Rapid Communications in Mass Spectrometry. 19 (12): 1717–1724. Bibcode:2005RCMS...19.1717C. doi:10.1002/rcm.1981. ISSN   0951-4198. PMID   15912481.
  29. 1 2 Kauppila, Tiina J.; Syage, Jack (2020-10-09). "Photoionization at Elevated or Atmospheric Pressure: Applications of APPI and LPPI". Photoionization and Photo‐Induced Processes in Mass Spectrometry. pp. 267–303. doi:10.1002/9783527682201.ch8. ISBN   9783527682201.
  30. ↑ Haapala, Markus; Pól, Jaroslav; Saarela, Ville; Arvola, Ville; Kotiaho, Tapio; Ketola, Raimo A.; Franssila, Sami; Kauppila, Tiina J.; Kostiainen, Risto (2007-09-06). "Desorption Atmospheric Pressure Photoionization". Analytical Chemistry. 79 (20): 7867–7872. doi:10.1021/ac071152g. ISSN   0003-2700. PMID   17803282.
  31. ↑ Cody, Robert B.; Laramée, James A.; Durst, H. Dupont (2005). "Versatile New Ion Source for the Analysis of Materials in Open Air under Ambient Conditions". Analytical Chemistry. 77 (8): 2297–2302. doi:10.1021/ac050162j. ISSN   0003-2700. PMID   15828760.
  32. ↑ Syage, Jack; Jorabchi, Kaveh (2014), "Chapter 5. Ambient Analysis by Thermal Desorption Atmospheric-Pressure Photoionization", Ambient Ionization Mass Spectrometry, Cambridge: Royal Society of Chemistry, pp. 120–136, doi:10.1039/9781782628026-00120, ISBN   978-1-84973-926-9 , retrieved 2021-06-30
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.