Derivatization in mass spectrometry-3. Alkylation (arylation)

The review is devoted to alkylation (arylation) as a widely employed derivatization procedure for the protection of OH (carboxylic acids, phosphoric acids, sulfonic acids, alcohols, polyols, phenols, enols), SH (thiols) and NH (amines, amides) groups in order to increase volatility, to improve the chromatographic properties and, if possible, mass spectral properties of derivatives. Chemical aspects of derivatization and various alkylation (arylation) reagents and reaction procedures are described. Specific mass spectral (electron ionization, chemical ionization) features of derivatives helpful in identification, structure elucidation, profiling and quantitative determination of the above-mentioned polar compounds by coupled gas chromatography or high-performance liquid chromatography are discussed. Some common analytical applications of the procedures in organic chemistry, clinical chemistry, environmental chemistry etc. are briefly summarized.     

Application of the novel 5-chloro-2,2,3,3,4,4,5,5-octafluoro-1-pentyl chloroformate derivatizing agent for the direct determination of highly polar water disinfection byproducts

A novel derivatizing agent, 5-chloro-2,2,3,3,4,4,5,5-octafluoropentyl chloroformate (ClOFPCF), was synthesized and tested as a reagent for direct water derivatization of highly polar and hydrophilic analytes. Its analytical performance satisfactorily compared to a perfluorinated chloroformate previously described, namely 2,2,3,3,4,4,5,5-octafluoropentyl chloroformate (OFPCF). The chemical properties (reactivity, selectivity, derivatization products, and their chromatographic and spectral features) for ClOFPCF were investigated using a set of 39 highly polar standard analytes, including, among others, hydroxylamine, malic and succinic acids, resorcinol, hydroxybenzaldehyde, and dihydroxybenzoic acid. Upon derivatization, the analytes were extracted from the aqueous solvent and analyzed by gas chromatography (GC)-mass spectrometry (MS) in the electron-capture negative ionization (ECNI) mode. Positive chemical ionization (PCI)-MS was used for confirming the molecular ions, which were virtually absent in the ECNI mass spectra. ClOFPCF showed good reaction efficiency, good chromatographic and spectroscopic properties (better than with OFPCF), good linearity in calibration curves, and low detection limits (0.3–1 μg/L). A unique feature of the derivatizations with ClOFPCF, and, in general, highly fluorinated chloroformates, is their effectiveness in reacting with carboxylic, hydroxylic, and aminic groups at once, forming multiply-substituted non-polar derivatives that can be easily extracted from the aqueous phase and determined by GC-ECNI-MS. The entire procedure from raw aqueous sample to ready-to-inject hexane solution of the derivatives requires less than 10 min. Another benefit of this procedure is that it produced stable derivatives, with optimal volatility for GC separation, and high electron affinity, which allows their detection as negative ions at trace level. In addition, their mass spectra exhibits chlorine isotopic patterns that clearly indicate how many polar hydrogens of the analyte undergo derivatization. Finally, derivatization with ClOFPCF was used successfully to identify 13 unknown highly polar disinfection byproducts (DBPs) in ozonated fulvic and humic acid aqueous solutions and in real ozonated drinking water.     

Mechanism Based Design of Amine Fluorogenic Derivatization Reagents: Proof of Concept, Physical–Chemical Characterization and Initial Analytical Derivatization Protocols

Herein, are described initial efforts in the design of a fluorogenic reagent applicable for the derivatization of primary and secondary amines. The initial reagent, 3-isothiocyanato-2-chloropyridine was based on physical–organic reactivity considerations to redirect the initial product of reaction between an amine and the isothiocyanate functional group, long established as a robust first step in Edman sequencing of peptides. The proposed chemistry results in the formation of a class of bicyclic fluorescent heterocycle (N,N-di-substituted [5,4-b] pyridine amines) bearing the amine analyte as substituents. Reported are the results regarding reaction kinetics in various relevant media, the ionization constants for a number of derivatives, and the associate UV and fluorescence spectral properties. These data and properties are utilized in the development of a derivatization protocol that is used in the establishment of calibration plots for several substances, with detection limits in the picomole mass range using liquid chromatography with fluorescence detection.     

Derivatization in mass spectrometry--8. Soft ionization mass spectrometry of small molecules

This is the first of two reviews devoted to derivatization approaches for "soft" ionization mass spectrometry (FAB, MALDI, ESI, APCI) and deals, in particular, with small molecules. The principles of the main "soft" ionization mass spectrometric methods as well as the reasons for derivatizing small molecules are briefly described. Derivatization methods for modification of amines, carboxylic acids, amino acids, alcohols, carbonyl compounds, monosaccharides, thiols, unsaturated and aromatic compounds etc. to improve their ionizability and to enhance structure information content are discussed. The use of "fixed"-charge bearing derivatization reagents is especially emphasized. Chemical aspects of derivatization and "soft" ionization mass spectrometric properties of derivatives are considered.     

Comparison of highly-fluorinated chloroformates as direct aqueous sample derivatizing agents for hydrophilic analytes and drinking-water disinfection by-products

Four highly-fluorinated alkyl and aryl chloroformates, including 2,2,3,3,4,4,5,5-octafluoro-1-pentyl chloroformate (OFPCF), 2,3,4,5,6-pentafluorobenzyl chloroformate (PFBCF), 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octyl chloroformate (TDFOCF), and 2-(2,3,4,5,6-pentafluorophenoxy)-ethyl chloroformate (PFPECF), were synthesized and tested as reagents for the direct water derivatization of polar and hydrophilic analytes. The goal of this research was to develop an optimal derivatizing agent to aid in the identification of highly polar ozonation drinking water disinfection by-products (DBPs) that are believed to be missed with current analytical procedures. The chemical properties (reactivity, selectivity, derivatization products, and their chromatographic and spectral features) for the four chloroformates were investigated using a set of highly polar standard analytes, including malic and tartaric acids, hydroxylamine, valine, 2-aminoethanol, resorcinol, 1,3,5-trihydroxybenzene, and 2,4-dihydroxybenzoic acid. Upon derivatization, the analytes were extracted from the aqueous solvent and analyzed by gas chromatography (GC)-mass spectrometry (MS) in the electron capture negative ionization (ECNI) mode. Positive chemical ionization (PCI)-MS was used for confirmation of molecular ions that were weak or absent in ECNI mass spectra. Of the four derivatizing reagents tested, OFPCF showed the best performance, with good reaction efficiency, good chromatographic and spectroscopic properties, low detection limits (10-100 fmol), and a linear response more than two orders of magnitude. Further, the entire procedure from raw aqueous sample to ready-to-inject hexane solutions of the derivatives requires less than 10 min. PFBCF showed ideal applicability for derivatizing aminoalcohols and aminoacids. The two chloroformates with the highest intrinsic stability (TDFOCF and PFPECF) failed to derivatize some of the analytes. Finally, the OFPCF derivatizing agent was tested with simulated ozonated drinking water (aqueous fulvic acid treated with ozone), and three highly polar reaction by-products were determined.     

Derivatization for electrospray ionization-mass spectrometry. 4. Alkenes and alkynes

A survey of derivatization strategies and prospective derivatization reactions for conversion of simple alkenes and alkynes to 'electrospray-active' species is presented. General synthetic strategies are discussed and illustrative examples of prospective derivatives prepared from model compounds are presented along with their electrospray ionization (ES) mass spectra. The identified derivatives of these neutral, nonpolar analytes are either ionic or are ionizable in solution through Bronsted acid/base chemistry, by Lewis acid/base chemistry, or by chemical or electrochemical electron-transfer chemistry. Once ionized, the derivatives are expected to be amenable to detection by electrospray ionization-mass spectrometry. Derivatives are identified for positive and negative ion analysis of both alkenes and alkynes. Copyright 2000 John Wiley & Sons, Ltd.     

Alternative procedure for charged derivatization to enhance detection responses of steroids in electrospray ionization-MS

A derivatization procedure has been examined to enhance the electrospray ionization (ESI)-MS detectabilities of steroids that charged derivatization is not suitable for. The derivatization procedure with 2-hydrazinopyridine or isonicotinoyl azide was very effective for the sensitive detection of di-oxosteroids or di-hydroxysteroids, respectively, and the detection limits of the resulting derivatives were as low as about 2 fmol. The derivatives also provided intense characteristic product ions in the MS-MS, which are expected to be usable for the selected reaction monitoring mode.     

Review: Derivatization in mass spectrometry--4. Formation of cyclic derivatives

This fourth in a series of reviews describes a further common derivatization approach, namely, the formation of cyclic derivatives (cyclic acetals and ketals, boronates, siliconides, carbonates and other miscellaneous derivatives) that can be used to increase volatility and to improve chromatographic and, if possible, the mass spectral properties of various di- and polyfunctional compounds. Some chemical aspects of this type of derivatization are briefly discussed. Characteristic mass spectral features of various cyclic derivatives that are helpful in the structure determination, profiling and quantitation of multifunctional organic compounds are presented. Some recent analytical applications of mass spectrometry in conjunction with preliminary cyclic derivative formation are given.     

Mass spectrometry of partially methylated alditol acetates derived from hydroxyethyl starch

The degradation and derivatization of hydroxyethyl starch to partially methylated alditol acetates (PMAAs) allows its detection by gas chromatography/mass spectrometry. The derivatization was performed by permethylation of the carbohydrate, hydrolysis of the permethylated polysaccharide, reduction of the resulting monosaccharides to alditoles and finally acetylation. A close similarity in the fragmentation of the PMAAs obtained was observed in both electron ionization (EI) and chemical ionization (CI) mass spectra owing to the comparable structures of the derivatives. CI measurements permitted the recognition of introduced hydroxyethyl groups in the glucose residues by detection of [M(+)+1]-60 signals. Investigations concerning the EI fragmentation schemes allowed secure determinations of monohydroxyethyl monosaccharides and differentiations between the possible positions (C-2, C-3 and C-6) of the substituted hydroxyethyl groups. Proposed generations of the main fragment ions are presented.     

Mass spectral studies of perfluorooctane sulfonate derivatives separated by high-resolution gas chromatography

The mass spectral characteristics of perfluorooctane sulfonate (PFOS, C(8)F(17)SO(3)-) isomers present in technical PFOS were obtained using high-resolution gas chromatography (HRGC) combined with mass spectrometry (MS). To make PFOS amenable to HRGC separation, a simple derivatization procedure was developed. The method involved the conversion of PFOS into the iso-propyl ester using iso-propanol as the derivatization reagent under acidic conditions. Mass spectra were generated employing electron ionization (EI) and negative chemical ionization (NCI). Interpretation of fragment ions was possible due to the use of deuterium-labeled iso-propanol as derivatization reagent, which induced mass shifts in the electron ionization (EI) and negative chemical ionization (NCI) mass spectra. HRMS allowed the accurate mass measurement of important EI fragments and confirmed the derivatization reaction as well as the proposed fragmentation pathway involving rearrangement. Moreover, the high resolution provided by HRGC enabled the separation of eleven PFOS isomers present in the technical product. This is an improvement over the previously reported high-performance liquid chromatography (HPLC) separation. A complete identification of all isomers was not possible due to lack of pure reference materials. Finally, the developed derivatization procedure was successfully applied to perfluoroalkyl carboxylates (PFCA) and corresponding fragmentation involving rearrangement of the derivatized PFCA was observed. The described qualitative derivatization offers a promising alternative technique for the separation and identification of isomers of perfluoroalkyl sulfonates and carboxylates by HRGC/MS.     

Novel approach for the simultaneous analysis of glyphosate and its metabolites

A novel approach for the simultaneous analysis of glyphosate (PMG), and aminomethylphosphonic (AMPA, GlyP), N-methylaminomethylphosphonic (MAMPA. SarP) and methylphosphonic (MPA) acids is presented. This includes a preliminary 31P NMR analysis of mixtures of PMG, MPA, AMPA and MAMPA, their further derivatization to volatile phosphonates by means of the trifluoroacetic acid-trifluoroacetic anhydride-trimethyl orthoacetate reagent and subsequent MS [chemical ionization (CI) MS, GC-CI-MS, GC-electron impact ionization MS] and/or GC-flame ionization detection (FID) analysis of the products of derivatization. The detection limits of PMG, AMPA, MAMPA and MPA by means of GC-CI-MS and GC-FID were determined. The calibration graphs (GC-FID) for these derivatives were in the range 0.1 to 100 nmol linear and sufficiently reproducible for quantitative determinations. The applicability of the method was demonstrated during the analysis of water samples fortified with PMG, AMPA and MAMPA, characterized by recoveries of >95%.     

1-苯基-3-甲基-5-吡唑啉酮(PMP)柱前衍生化寡糖链的HPLC分离及其激光解吸电离质谱分析

以1-苯基-3-甲基-5-吡唑啉酮(PMP)为衍生化试剂对寡糖链进行标记, 用氨水替代氢氧化钠溶液作碱性介质, 衍生化反应后氨水可通过干燥除去, 省去了脱盐处理过程, 衍生化的寡糖可直接进行激光解吸电离质谱分析. 建立起了PMP衍生化寡糖的RP-HPLC分离分析模式, 在此HPLC分析条件下, 可以对标记的寡糖链进行样品分离及制备.     

Characterization of oxygenated derivatives of isoprene related to 2-methyltetrols in Amazonian aerosols using trimethylsilylation and gas chromatography/ion trap mass spectrometry

In the present study, we have tentatively identified the structures of three oxygenated derivatives of isoprene in Amazonian rain forest aerosols as the C(5) alkene triols, 2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene. The formation of these oxygenated derivatives of isoprene can be explained by acid-catalyzed ring opening of epoxydiol derivatives of isoprene, namely, 1,2-epoxy-2-methyl-3,4-dihydroxybutane and 1,2-dihydroxy-2-methyl-3,4-epoxybutane. The structural proposals of the C(5) alkene triols were based on chemical derivatization reactions and detailed interpretation of electron and chemical ionization mass spectral data, including data obtained from first-order mass spectra, deuterium labeling of the trimethylsilyl methyl groups, and MS(2) ion trap experiments. The characterization of 2-methyl-1,3,4-trihydroxy-1-butene (cis and trans) and 3-methyl-2,3,4-trihydroxy-1-butene in forest aerosols is important from an atmospheric chemistry viewpoint in that these compounds hint at the formation of intermediate isomeric epoxydiol derivatives of isoprene and as such provide mechanistic insights into the formation of the previously reported 2-methyltetrols through photooxidation of isoprene.     

Determination of pentachlorophenol by negative ion chemical ionization with membrane introduction mass spectrometry

Pentachlorophenol (PCP) was used as a model compound to explore the potential of desorption chemical ionization (DCI) in the determination of polychlorinated pesticides using membrane introduction mass spectrometry (MIMS). A direct insertion membrane probe was modified so that a chemical ionization plasma could be established at the membrane surface. Using selected ion monitoring (SIM) in a tandem triple quadrupole mass spectrometer with isobutane chemical ionization (CI), the PCP detection limit under positive chemical ionization is 20 ppb whereas negative CI gives detection limits in the low ppb range. This performance is achieved without any pre-treatment or derivatization of the sample. Negative ion CI gives a signal that is linear over a concentration range of 2-1000 ppb. Comparison of data obtained with low ppb samples of 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol suggests that the sensitivity of this analytical procedure increases with increase in the number of electronegative substituents in the molecule.     

Dispersive derivatization liquid-liquid extraction of degradation products/precursors of mustards and V-agents from aqueous samples

A new derivatization and extraction technique termed as dispersive derivatization liquid-liquid extraction (DDLLE) speeds up the analysis process by removing the requirement for drying of the sample. The derivatization process takes place at the interface between the analyte containing aqueous phase and derivatization agent laden organic phase. The organic phase is highly dispersed using disperser solvent so that the total surface area is large. The derivatizing agent used is 1-(heptafluorobutyryl)imidazole and the resulting heptafluorobutyryl (HFB) derivatized analytes are partitioned into the organic phase. In addition to reduced sample preparation time, for some of the analytes, the HFB derivatives provide better spectral differentiation between isomers than conventional trimethylsilyl (TMS) derivatives. Method parameters for the DDLLE, such as extraction, and disperser solvent and their volume, type and amount of base, amount of heptafluorobutyrylimidazole and extraction time were optimized on diisopropylaminoethanol (DiPAE), ethyldiethanolamine (EDEA), triethanolamine (TEA) and thiodiglycol (TDG). The DDLLE was also used on various real world samples, which also includes few OPCW organized proficiency test and a spiked urine sample. The observed limit of detection (LOD) with 1mL of sample for DDLLE in full scan with AMDIS was 10ng/mL and with methane chemical ionization, multiple reaction monitoring (MRM) was 100pg/mL, i.e., 100fg on-column.     

Review: derivatization in mass spectrometry-6. Formation of mixed derivatives of polyfunctional compounds

The review describes chemical transformations of multifunctional compounds (amino acids and peptides, amino alcohols, amino thiols, hydroxy acids, oxo acids, oxo alcohols, compounds containing simultaneously three or more different groups etc.) by using step-wise or one-step modification or protection of functional groups. Some chemical aspects of mixed derivatization performed for improving the physical-chemical properties and mass spectral characteristics are discussed. Application of mixed derivatization to qualitative and quantitative analysis of various multifunctional compounds mainly in biological fluids and other matrices by gas chromatography/mass spectrometry in electron ionization, chemical ionization, negative-ion chemical ionization and selected ion monitoring modes is considered.     

Review: derivatization in mass spectrometry--5. Specific derivatization of monofunctional compounds

The present paper is complementary to the foregoing reviews and describes some additional methods of the derivatization of particular functional groups mainly to enhance the structural information content of electron ionization and chemical ionization mass spectra. Derivatization approaches for the modification of unsaturated compounds, alcoholic, carboxylic, carbonyl, amine and other functional groups, are discussed. Derivatization for separation and quantitative determination of chiral enantiomeric compounds is also considered. Preliminary chemical and physicalchemical degradation for structure elucidation of high molecular weight compounds (biopolymers, synthetic polymers) is mentioned. Chemical aspects of derivatizations and characteristic mass spectral features of derivatives are described briefly. Some particular applications of chemical modification, in conjunction with mass spectral measurements for the analysis of various important bioorganic compounds and compounds in biological fluids, air, environmental etc., are considered.     

Chromatographic and mass spectral studies on methoxy methyl methamphetamines related to 3,4-methylenedioxymethamphetamine

The methoxy methyl methamphetamines are a unique set of compounds having an isobaric relationship with the controlled drug substance 3,4-methylenedioxymethamphetamine (3,4-MDMA or Ecstasy). The various isomeric forms of the methoxy methyl methamphetamines have mass spectra essentially equivalent to 3,4-MDMA, all have molecular weight of 193 and major fragment ions in their electron ionization mass spectra at m/z 58 and 135/136. Mass spectral differentiation of 3,4-MDMA from some of the methoxy methyl methamphetamines was possible after formation of the perfluoroacyl derivatives, pentafluoropropionamides (PFPA) and heptafluorobutyramides (HFBA). Perfluoroacyl derivatization provided unique and characteristic mass spectral fragment ions when the methoxy group is substituted at the 2- or 4-position of the aromatic ring relative to the alkylamine side chain group. Perfluoroacyl derivatization did not offer any characteristic ions for discrimination of 3,4-MDMA from the 3-methoxy ring substituted methyl methamphetamines. Gas chromatographic separation on non-polar stationary phases successfully resolved subsets of the methoxy methyl methamphetamines, based on ring position of the methoxy group, from 2,3- and 3,4-MDMA as the PFPA and HFBA derivatives.     

Perfluoroalkyl ketones: novel derivatization products for the sensitive determination of fatty acids by gas chromatography/mass spectrometry in electron impact and negative chemical ionization modes

Analytically useful pentafluoro ketone derivatives of fatty acids are described. The gas chromatographic/mass spectrometric characteristics of these new derivatives are compared with those of methyl, trimethylsilyl and pentafluorobenzyl esters. Pentafluoro ketones exhibit excellent chromatographic properties and significantly shorter chromatographic retention times than these other esters. The electron impact mass spectra of these new compounds show informative acylium ions, whose intensity decreases with the degree of unsaturation of the parent fatty acid. The formation of strong and informative fragment ions in negative chemical ionization (CH(4)) mass spectra of pentafluoro ketone derivatives allows the detection and the characterization (length of the chain and number of double bonds) of fatty acids at trace levels (femtomole), even in the case of polyunsaturated compounds. The scope and limitations of this new derivatization technique are also discussed.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of oligosaccharides derivatized by reductive amination and N,N-dimethylation

Oligosaccharides were derivatized by reductive amination with benzylamine followed by N,N-dimethylation with methyl iodide and analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and MALDI post-source decay (PSD) TOFMS. The resulting derivatives have a positive charge localized to the modified reducing end. The derivatization methodology was tested on maltoheptaose and three different human milk oligosaccharides. The approximate detection limit for the resulting carbohydrate derivatives was determined to be 50 fmol of the derivative loaded onto the target, corresponding to a tenfold increase in sensitivity compared with underivatized oligosaccharides. When the derivatives were analyzed by MALDI-PSD TOFMS the observed fragmentation pattern was dominated by fragment ions retaining the modified reducing terminus, thus simplifying the interpretation of the mass spectral data.