This section summarizes the research of Karsten Levsen from 1968 up to now (The numbers in parentheses refer to the list of publications)

     Kinetics of unimolecular decomposition processes or organic ions in the gas phase
   The kinetics of unimolecular decay processes of organic ions in the gas phase can be studied by field ionisation (FI) mass spectrometry, where decomposition times ranging from pico- to microseconds can be resolved (2,4,60). This approach has been used to compare rearrangement reaction and direct bond cleavages (5-6,16,27), hydrogen/deuterium exchange reactions (13,27) and isomerization reactions in cycloalkanes and alkenes (44,47). Thus alkylcycloalkanes with three-, four-and five membered rings undergo a ring opening reaction within about one ns after ionisation, leading originally to the corresponding 1-alkenes which undergo further isomerization reactions (double bond migration) (45).  Similarely it was demonstrated that ionized 1-, 2-, 3- and 4-octenes isomerize to a mixture of interconverting structures after about  1 ns after ionisation (47).

   Structure of organic ions in the gas phase
  The structure of organic ions in the gas phase can be investigated by studying their collisional activation spectra (29,30,94)which at the same time sheds light on the reaction mechanisms involved in their formation (8-12,14,17-19,21-26,29-33,37,38,40-43,45-50,54,56,62,63,65,67,72,74,75,77,85,
87,91-93,95,99,102,104,114). For example it was demonstrated by a combination of electron impact and field ionisation mass spectrometry with collisional activation that fragmentation of ionised beta-phenoxyethylamines by loss of a phenoxy radical leads to the cyclic protonated aziridine ion (56).

  Analysis of polar, non volatile compounds by a combination of field desorption mass spectrometry and collision induced decomposition
  Polar, non volatile organic compounds cannot be analyzed by electron impact mass spectrometry. An unequivocal identification of such compounds is, however, possible by field desorption mass spectrometry combined with collision induced decomposition as shown for peptides (81), quarternary phosphonium and tertiary sulfonium salts (55) as well as cationic, non ionic and anionic surfactants (107,108, 110). Using this approach a direct mixture analysis of polar compounds is possible (96). Thus, different cationic and anionic surfactants have been determined simultaneously in river Rhein water(116). and their biodegradation was studied (120).

   Coupling of high performance liquid chromatography-mass spectrometry (HPLC-MS)
   In the early days of the development of interfaces for the coupling of HPLC to MS interfaces (135) based on the direct introduction of the HPLC effluent via a capillary into the mass spectrometer or by the use of a modified moving belt interface have been tested and used for the analysis of phenylureas and non ionic surfactants (97,101,111, 112, 113, 115, 122). The coupling of HPLC to MS using a thermospray ion source was applied to the analysis of pesticides (155,159,168,171,177-179,184). Thus, a method for the multiresidue analysis of 128 pesticides in aqueous samples was developed (159).

   Polycyclic aromatic hydrocarbons (PAHs) in environmental samples
   Methods for the analysis of polycyclic aromatic hydrocarbons and their nitrated derivatives in diesel soot (125,127,131) were developed.

   Organic compounds in precipitation
  Methods for the analysis of organic compound in precipitation (rain and cloud water), were developed (130,132,133,134) and used to quantify such compounds (in particular alkanes, polycylic aromatic hydrocarbons, phenols and nitrophenols, low molecular weight organic acids, fatty acids and aldehydes in rain water (137,138,140-142) and cloud water (152). In particular the occurrence and formation of phenols nitrated phenols in and outside of clouds and their partitioning between the gas and liquid phase was studied (193,194, 221). The  results supported the assumption of a formation of nitrophenols and in particular dinitrophenols in the liquid phase of cloud droplets (193,221). Moreover, pesticides and their photodegradation products were determined (199, 210).

   Indoor air pollution
   Organic pollutants in the indoor air were identified and quantified with emphasis on organic emissions from textile floor coverings (147, 148, 166). Methods were developed for the analysis of indoor insecticides, in particular pyrethrins and pyrethroides and these compounds were determined in model studies and  the indoor air (181, 182, 203 – 206,,214, 234,237, 244 – 246). Aromatic hydrocarbon (in particular benzene) were determined in a large field study in both the indoor air the urban outdoor air (205, 211, 215, 229, 232, 233).

   Explosives and their degradation products in ammunition waste water
   Methods were developed for the analysis of explosives and their degradation products in ammunition waste water,  polluted groundwater and soil (153, 154, 165, 167, 172, 190, 191, 198, 201, 202, 207, 208, 209, 212, 216, 220)

   Coupling of high performance liquid chromatography  – nuclear magnetic resonance  - mass spectrometry (HPLC-NMR/MS)
   Methods were developed for the analysis of complex organic mixtures by HPLC-NMR, HPLC/MS and HPLC-NMR/MS/MS (208, 209, 226, 230, 247). These methods were applied to the analysis of explosives in waste water (208, 209) and the screening of natural products and in particular the identification (230)asterosaponines in starfish (247).

     Solid phase microextraction (SPME)
    The method of solid phase microextraction  (SPME) was developed and validated for the extraction of organic pollutants from polluted water (185 – 187, 189, 200, 222) and used for the development of an automatic analyser for the detection of  organic pollutants in surface water (213, 231).

   Platinum emissions from automobile converters
   The emission of platinum from automobile converters was determined in engine test bench experiments (217 – 219, 224, 225).

   Drug metabolism
   New metabolites were identified in various organs of laboratory animals and humans and advanced methods for their analysis developed (238, 241, 242, 243, 248, 249, 250).

   Reviews
   Reviews have been published on field ionisation mass spectrometry (4, 68), collisional activation mass spectrometry (29, 30), ESCA (35), field ionisation kinetics (60), HPLC/MS coupling (88, 112, 119, 122, 135 ), tandem mass spectrometry (94), the analysis of diesel particulate (127), solid phase micro extraction (147, 186, 200, 235), the analysis of explosives in waste water (212, 220), HPLC-NMR/MS (226)