Ethylation, chemical ionization

Although the conventional mass spectra of the five C- nitro derivatives of indazole are nearly identical, the corresponding metastable peak shapes associated with the loss of NO-can be used to differentiate the five isomers (790MS114). The protonation and ethylation occurring in a methane chemical ionization source have been studied for a variety of aromatic amines, including indazoles (80OMS144). As in solution (Section 4.04.2.1.3), the N-2 atom is the more basic and the more nucleophilic (Scheme 5). 

An on-line chromatography/atmospheric pressure chemical ionization tandem mass spectrometry (LC-APCI/MS/MS) methods was developed for rapid screen of pharmacokinetics of different drugs, including 5 (98RCM1216). The electron impact mass spectrum of 5 and ethyl 9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7Ff-pyrido[l,2,3- fe]-l,4-benzoxazine-6-carboxylate was reported (97MI28). Electron impact/Fourier transform... 

Temperature Effects. The chemical ionization spectra of three paraffins (n-decane, 2,2,3,3-tetramethylhexane (compound 13), and 2,2,5,5-tetramethylhexane (compound 14) have been determined at several different temperatures of the mass spectrometer ionization chamber, and the relative intensities obtained for the MW — 1 ions are give in Table VII. The relative intensities decrease for all three compounds as the temperature increases, in accordance with the behavior found for the chemical ionization spectrum of ethyl-/3-chloropropionate... 

Protonated thiomorpholine loses ethylene in chemical ionization giving the cation CzH NS as main peak (ot/z 76). Methylated and ethylated derivatives lose ethylene in a similar manner (Scheme 3) <19840MS539>. 

A simple cleanup procedure based on acidic protein precipitation and LLE with ethyl acetate was used for the determination of OXA, CLO, and DICL in bovine muscle. The detection was accomplished with particle-beam MS with negative-ion chemical ionization, which was found more sensitive than electron-impact mode. Deviation from the linearity of response was observed, which could be caused by the phenomenon of coeluting carrying analyte particles through the particle beam (60). 

Derivatization was conducted by the addition of a 10% H-ethyl-diiso-propylethylamine solution and a-bromo-2,3,4,5,6-pentafluorotoluene. Sample obtained from the derivatization procedure were dissolved in ethyl acetate prior to injection in splitless mode using a DB-1 capillary column. Helium was used as the mobile phase, and the injector temperature was set at 290 °C with a transfer line temperature of 270 °C. Sample detection used ion trap MS for detection, with the detector being set at negative chemical ionization with m/z = 262 (for CCA) and m/z = 286 (for the internal standard). The limit of quantitation was 5 ng/ml, and the average recovery ranged from 92.0% to 114%. In addition, the extraction efficiency ranged from 48.2% to 55.6% for concentrations of 5, 50, and 250 ng/ml. Samples were reported to be stable for up to 6 months when stored at 18 °C. 

Notes LOD, limit of detection MeOH, methanol EtOH, ethanol ACN, acetonitrile EtAC, ethyl acetate SPE, solid phase extraction HLB (hydrophilic lipophilic balanced) TFA, trifluoroacetic acid GC, gas chromatography TMS, trimethylsilyl MS, mass spectrometry HPLC, high-performance liquid chromatography DAD, diode array detector NMR, nuclear magnetic resonance ESI, electrospray ionization APCI, atmospheric pressure chemical ionization CE, capillary electrophoresis ECD, electrochemical detector CD, conductivity detector TLC, thin layer chromatography PDA, photodiode array detector. 

You J, Zhao H, Sun Z, Suo Y, Chen G (2009) 10-Ethyl-acridine-2-sulfonyl chloride a new derivatization agent for enhancement of atmospheric pressure chemical ionization of estrogens in urine. Chromatographia 70 45-55... 

D.K. Rohrbaugh, Methanol chemical ionization quadrupole ion trap mass spectrometry of O-ethyl S-[2-(diisopropylamino)cthyl methylphos-phonothiolate (VX) and its degradation products, J. Chromatogr., A, 893, 393-400 (2000). 

Another product of esterase cleavage is p-nitrophenol (PNP), which is generated in the human body by the degradation of parathion, parathion-methyl and parathion-ethyl. Some methods for the determination of PNP in urine are summarized in Table 9.5. PNP can, for example, be determined in the urine of occupationally exposed subjects by means of GC-ECD. Sample preparation involves acid hydrolysis, extraction with diethyl ether, derivatization with diazoethane and purification on silica gel columns. The LOD was 20 pg L with a recovery of 85-98%. This method has also been used in a study on selected pesticide residues and metabolites in urine from a survey of the US general population.In the context of another survey study, a more complicated technique to detect PNP in urine has recently been used by Hill et involving GC-MS-MS with positive chemical ionization after derivatization with l-chloro-3-iodopropane. The authors also used this method for the determination of the metabolite TCP and 10 other analytes in urine.Sample preparation involved hydrolysis with p-glucuronidase, several extraction steps using different solvents and purification by SPE (silica gel column). The LOD was 1 pg L with an inter-assay RSD... 

Derivatization is also useful to detect volatile metabolites. Liu et al. [282] described a specific, rapid, and sensitive in situ derivatization solid-phase microextraction (SPME) method for determination of volatile trichloroethylene (TCE) metabolites, trichloroacetic acid (TCA), dichloroacetic acid (DCA), and trichloroethanol (TCOH), in rat blood. The metabolites were derivatized to their ethyl esters with acidic ethanol, extracted by SPME and then analyzed by gas chromatography/negative chemical ionization mass spectrometry (GC-NCI-MS). After validation, the method was successfully applied to investigate the toxicokinetic behavior of TCE metabolites following an oral dose of TCE. Some of the common derivatization reagents include acetyl chloride and TV-methyl-iV- ft-b u (y Idi methyl si I y I) tro (1 uoroacctam i nc (MTBSTFA) for phenols and aliphatic alcohols and amines, dansyl chloride and diazomethane for phenols, dansyl chloride for amines, acidic ethanol and diazomethane for carboxylic acids, and hydrazine for aldehydes. 

The mechanism in solution and in the gas phase appears to be the same, except that an alkyl substituent stabilizes the anion in the gas phase and destabilizes it in solution. The mass spectral decomposition of diethyl 2-methylheptanedioate under negative chemical ionization (NCI) conditions shows formation of the methyl-substituted enolate, ring closure and then loss of ethyl methyl ether. 

The method (27) describes the measurement of clonidine in human plasma and urine by combined gas chromatography-mass spectrometry with ammonia chemical ionization. Addition of [ 84] clonidine to plasma or urine is followed by ethylacetate extraction of clonidine from alkaline medium, back extraction into acid extraction into ethyl ether from alkaline medium and evaporation of the extract to dryness. Trimethylanilinium hydroxide is added to the residue, and dimethyl derivatives of clonidine are formed by on column methylation with an injection-port temperature of 250 for g.c. -70-eV m.s., the glass column (1.8 m X 2 mm) packed with 3% of OV-17 on Gas-Chrom Q (100 to 120 mesh) is operated at 245 . With He s carrier gas (15 ml min" ) NH3 is admitted to an ion-source pressure of 0.2 Torr, and ions are monitored at m/e 258 and 264. Graphs of peak height ratios (m/e 258 to 264) vs amounts of clonidine in urine (up to 40 ng ml-i) and in plasma (up to 5 ng ml i) are rectilinear. The precision for assay of clonidine in plasma is 11% at 0.25 ng ml" and 5% at 0.5 ng ml" and the lower limit of determination is 0.1 ng ml. ... 

Figure 3 SPE-LC-APCI-MS chromatogram of 200 ml tap water spiked with 0.04 ng ml of pesticides and 0.05 ng ml IS tert-butylazine in positive-ion mode and dinoterb in negative-ion mode). Peak identification 1, bentazone 2, Vamidothion 3,4-nitrophenol 4, MCPA 5, mecoprop 6, dinoseb 7, atrazine 8, isoproturon 9, ametryn 10, malathion 11, fenotrothion 12, molinate 13, prometryn 14, terbutryn and 15, parathion-ethyl. (Reprinted with permission from Aguilar C, Ferrer I, Bormll F, Marce RM, and Barcelo D (1998) Comparison of automated on-line solid-phase extraction followed by liquid chromatography-mass spectrometry with atmospheric-pressure chemical ionization and particle-beam mass spectrometry for the determination of a priority group of pesticides in environmental waters. Journal of Chromatography A 794 147-163 Elsevier.)...

Niwa, M. Watanabe, N. Ochiai, H. Yamashita, K. Determination of testosterone concentrations in rat plasma using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry combined with ethyl oxime and acetyl ester derivahzation. J. Chromatogr. B, 2005, 824 (1-2), 258-266. 

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