Liquid Ionization Mass Spectrometry Research Articles

Effects of Additives to Methyl Hydroperoxyoleates on the Formation of Protonated Molecules and/or Molecular Adduct Ions in Liquid Ionization Mass Spectrometry.

Effects of additives, introduced to a sample through vapor phase, on the formation of protonated molecules and/or molecular adduct ions were investigated in liquid ionization mass spectrometry for the analysis of methyl hydroperoxyoleates. Water and formic acid having small proton affinities were useful for increasing ion abundance of protonated molecules [M+H]+. 2-Aminoethanol and pyridine having slightly greater proton affinities were useful for forming molecular adduct ions [M+H+L]+ (L: additive molecule). The use of additives, acting as matrix for producing [M+H]+ and/or as reagent for forming [M+H+L]+ in liquid ionization mass spectrometry, provided useful mass spectral characteristics of the molecular weight and structure of unknown compounds.

Determination of Urinary Creatinine by Liquid Ionization Mass Spectrometry.

Determination of Urinary Creatinine by Liquid Ionization Mass Spectrometry.

Determination of xanomeline and active metabolite, N-desmethylxanomeline, in human plasma by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

We have developed a method for the determination of xanomeline and its pharmacologically active N-desmethyl metabolite. The validated method uses hexane to extract xanomeline and its N-desmethyl metabolite from basified plasma. The hexane extract is dried, reconstituted, and analyzed using a liquid chromatographic-atmospheric pressure chemical ionization tandem mass spectrometry system. The method was developed to support phase II clinical trials and has proven to be extremely sensitive, fast, and rugged. The method has a limit of quantitation of 75 and 200 pg/ml plasma for xanomeline and the N-desmethyl metabolite, respectively. Sample analysis times were less than 3 min from one injection to the next.

Compositional analysis of the phenylthiocarbamyl amino acids by liquid chromatography-atmospheric pressure ionization mass spectrometry with particular attention to the cyst(e)ine derivatives

An approach presented recently for the high-performance liquid chromatographic determination of dl- and l-cystines and cysteines as phenylthiocarbamyl (PTC) derivatives has been completed (i) with the determination of d-cystine/cysteine, (ii) by a study relating to the spectral characteristics of the PTC cystine/cysteine derivatives performed with diode-array detection and (iii) by the fragment analysis of the PTC-cyst(e)ine derivatives, applying the extremely soft conditions of the liquid chromatography-atmosphere pressure ionization mass spectrometry (LC-API-MS). In accordance with earlier experiences it has been repeatedly demonstrated that cystines and cysteines can be determined on the basis of two or four derivatives, with the same retention times and molar responses, without any special pretreatment, furnishing a simple possibility for the determination of the total cystine/cyteine in protein hydrolysates. The UV spectra of all four PTC derivatives provided by diode-array-detected purity parameters (PuP) showed that the corresponding PTC derivatives of dl-l- and d-cystine and -cysteine are identical and homogeneous, and do not show any characteristic differences. On the basis of the fragmentation patterns of seventeen PTC-amino acids and those of six PTC-cyst(e)ines, obtained under the very soft conditions of the LC-API-MS procedure, it can be stated that two characteristic PTC derivatives are formed: (i) the main product (“a” and “b” diastereoisomers, >80% of the total), shown to be the fragment of m/ z = 255, a monomeric cysteine derivative, and (ii) the other characteristic constituent (“c” and “d” stereoisomers, <20% of the total), consisting of a fragments of m/ z = 255 and its oxidised form of m/ z = 287.

Rapid Profiling of Urinary Organic Acids Due to Inherited Metabolic Disorders by Liquid Ionization Mass Spectrometry.

An application of liquid ionization (LI) mass spectrometry to the profiling of urinary organic acids due to several inherited metabolic disorders is described. A solid-phase extraction technique using DOWEX 50W-X8 was developed to remove urea and cationic species from urine matrix. This preliminary sample treatment was quite effective to detect urinary organic acids for LI mass spectrometry. LI mass spectra for dicarboxylic acidurias clearly exhibited the peaks of adipic (m/z 147), suberic (m/z 175), and sebacic (m/z 203) acids due to the disease. Those for lactic and methylmalonic acidurias exhibited the intense peaks of lactic (m/z 91) and methylmalonic (m/z 119) acids, respectively. For phenylketonuria, the peaks corresponding to phenylacetic (m/z 137) and phenyllactic (m/z 167) acids, which are diagnostic metabolites, were intensely observed. All mass spectra for the urine samples of the patients were quite indicative of the individual metabolic diseases. Furthermore, a principal component analysis was examined to classify the spectral patterns using 40 peaks selected. The mass spectra of patients with five kinds of metabolic diseases were differentiated from those of healthy newborns by the principal component plots.

Quantitative measurement of a new synthetic hetrazepine derivative, BN50730, in human plasma and urine by combined liquid chromatography-negative chemical ionization mass spectrometry using a particle beam interface.

A new simple and sensitive assay has been developed for the quantitative measurement of BN50730 at the picomole level in human plasma and urine. The drug and the internal standard (BN50765) were measured by combined liquid chromatography-negative chemical ionization mass spectrometry with methane as the reagent gas. A simple solid-liquid extraction procedure was used to isolate BN50730 from complex biological matrices. Mild operating conditions were required to assay the parent drug with a particle beam interface from Hewlett-Packard. The mass spectrometer was tuned to monitor the intense ion m/z 333, which was generated in the ion source by a dissociative capture process. This assay was performed with 1 ml of plasma or 0.1 ml of urine, and the quantification limit of the method was statistically calculated as 1 ng ml-1. The very low relative standard deviation and mean percentage of error calculated during the different within-day or between-day repeatability assays clearly demonstrate the ruggedness of the technique for the routine determination of BN50730 in the biological fluids. Some preliminary results on the pharmacokinetics of the drug are presented to illustrate the applicability of this new powerful LC-MS method.

Liquid Ionization Mass Spectrometry of Methyl Hydroperoxyoleates and Their Related Compounds.

A mixture of isomeric methyl 9-, 10-, 11-, and 12-hydroperoxyoleates was analyzed by liquid ionization (LI) mass spectrometry. LI mass spectra of the hydroperoxides exhibited [M+H]+ peaks clearly at m/z 329, while both chemical ionization and fast atom bombardment mass spectra did not show ions directly related to the molecular weight. The fragment peaks of the hydroperoxides observed at m/z 295, corresponding to the loss of H2O2 from [M+H]+, were useful to discriminate the hydroperoxides from structurally isomeric hydroxyepoxides. In addition, several characteristic fragments were observed at m/z 173, 187, 199, 201, and 213, which were also indicative of the position of the hydroperoxy group in the hydroperoxides.

Analysis of urinary organic acids by liquid chromatography-atmospheric pressure chemical ionization mass spectrometry.

We developed a new method for the rapid determination of urinary organic acids using liquid chromatography-atmospheric pressure chemical ionization mass spectrometry. Mass spectra of authentic organic acids obtained in the negative-ion mode showed intense [M-H]- ions with some fragment ions. Urine samples of patients with methylmalonic aciduria, ornithine transcarbamylase deficiency, and phenylketonuria were extracted using anion-exchange columns. The mass chromatograms of the extracts showed some dominant peaks of abnormal metabolites characteristic of each disorder. This is a useful method for the analysis of urinary organic acids for the diagnosis of organic aciduria, because the sample preparation is simple.

液体イオン化質量分析法による前生物合成生成物中の核酸塩基の同定

Nucleic acid bases in products by proton irradiation of a simulated primitive atmosphere were identified by liquid ionization (LI) mass spectrometry. In order to detect a trace amount of nucleic acid bases, the LI ion source setting was improved in terms of ionization efficiency and ion focusing. The new ion source provided better sensitivity for the analyte (uracil) and lower background of water clusters than the previous one. Addition of a certain amount of a standard compound such as adenine (1 mM) and a kind of matrix (0.2% glycerol) improved the detection limit and the linearity of calibration curves.When a mixture of carbon monoxide, nitrogen, and water (“a simulated primitive earth atmosphere”) was irradiated with high energy protons, and the nucleic acid bases in the product were analyzed. Uracil, one of the five nucleic acid bases, was identified by LI mass spectrometry using the improved ion source.

Phospholipids in middle ear effusion and serum analysed by liquid ionization mass spectrometry

Phospholipids in middle ear effusion (MEE) and serum were analysed by liquid ionization (LI) mass spectrometry. The LI mass spectra of MEE and serum measured directly without preliminary separation commonly exhibited several unknown peaks such as those at m/z 520 and 577. These peaks were also observed in 90% ethanol fractions of MEE. The mass spectrum of the 90% ethanol fraction of serum exhibited dominant peaks at m/z 551, 577 and 603 (with mass differences of 26) and also at m/z 520. Comparing this spectrum with the mass spectra of standard compounds, the ions of mass 551, 577 and 603 were identified to be [M — phosphocholine] + of dipalmitoyl, palmitoyl-oleoyl and dioleoyl-glycero-3- phosphocholine (PC), respectively. The relative abundances of these ions observed in serum were qualitatively consistent with the composition of the fatty acid residue of PCs in serum determined by gas chromatography. The ions of mass 520, observed to be more abundant in MEE than in serum, were also identified to be [ceramide + — O], which is equal in mass to [M — phosphocholine] +, of N-palmitoyl-sphingo-phosphocholine (Sph). The results strongly suggest that a part of blood permeates into the middle ear cavity, and especially Sph does this easily. LI mass spectrometry is useful for analysis of phospholipids in biological samples.

Determination of sweat constituents by liquid ionization mass spectrometry

Liquid ionization (LI) mass spectrometry was applied to the determination of organic compounds in sweat. LI mass spectra of ordinary sweat exhibited characteristic peaks of lactic acid, urea and several kinds of amino acids. The relative peak intensities of these organic compounds changed according to the sweating rate. An unknown compound giving an intense peak at m/z 107 was found in sweat produced during walking excercise and was identified as diethylene glycol (DEG) by comparison with standard compounds. This identification was confirmed by liquid chromatography (LC). The concentrations of DEG in the sweat samples changed similarly to those of inorganic cations, depending on the change in momentum of the subject. The complementary use of LI mass spectrometry and LC is one of the best methods for the analysis of complicated organic mixtures such as biological fluids.

ANALYSIS OF PRODUCTS SYNTHESIZED FROM SIMULATED PRIMITIVE PLANETARY ATMOSPHERES

Gas mixtures simulated primitive earth atmospheres were irradiated with high energy protons, and amino acids in the products were analyzed by liquid chromatography, gas-liquid chromatography and liquid ionization mass spectrometry. When a mixture of carbon monoxide, nitrogen and water was irradiated with 2.8-40MeV protons generated with accelerators, various kinds of amino acids were detected in the products. Hydrogen cyanide, which is believed to be a precursor of amino acids, was determined with a cyanide-selective electrode. G-value of glycine was about 0.02 when either methane or carbon monoxide was used as a carbon source in irradiation experiments. The present results show that cosmic rays are more effective energy sources for prebiotic synthesis of amino acids than conventionally considered energy sources like spark discharges.

ANALYSIS OF PRODUCTS SYNTHESIZED FROM SIMULATED PRIMITIVE PLANETARY ATMOSPHERES

A mixture of carbon monoxide, nitrogen and water was irradiated with high energy protons, and nucleic acid bases and related compounds in the products were analyzed. The irradiation product was separated, fractionated, and desalted by high performance liquid chromatography. Compounds in each fraction was identified by liquid ionization mass spectrometry. Uracil, one of the pyrimidine bases, and dihydrouracil were identified by the present method, and existence of some other bases were also suggested

Clusters of water under atmospheric pressure studied by field ionization and liquid ionization mass spectrometry

Cluster ion distributions of water produced at atmospheric pressure are investigated by liquid ionization mass spectrometry. Water vapor introduced in the ion source condenses on a needle held at high voltage, and cluster ions are produced either by liquid ionization or by field ionization in argon at atmospheric pressure. High electric field, temperature of the needle, and the manner of introducing water vapor are observed to cause significant effects on the cluster ion distributions. The results indicate that a supersonic free jet expansion process is not responsible for the cluster ion formation in our experiments, and that the cluster ions are produced directly at the surface of liquid water on the needle tip. Clusters of water may exist in the gas phase, as well as the liquid surface where a variety of cluster molecules of different sizes may move around. Intense ion peaks are observed at m/z 73, 181, 379 (21 molecules), and 505. Field ionization and liquid ionization mass spectrometry are useful to investigate the behavior of molecules and clusters at the surface of liquids.

液体イオン化質量分析法による新生児尿の直接分析

Liquid ionization (LI) mass spectrometry, providing mostly MH+ ions of components in a solution, was applied to screening inborn errors of metabolism using urines of newborn babys without any pretreatment.Urinary samples of healthy babys exhibited MH+ ions of urea at m/z 61 and of creatinine at m/z 114 and their related ions at m/z 121, 174, 181, 227, and so on. In contrast, the patient's urines exhibited abnormally abundant peaks of components, such as amino acids and/or organic acids, due to the errors of metabolism. All urines of babys suffering from phenyl-ketonuria clearly showed the peak at m/z 166 corresponding to phenylalanine as far as examined. Some of the other peaks at m/z 90, 104, 116, 130, 136, 141, 146, 154, 247, were observed in the mass spectra in common. The peaks assumed to be amino acids (m/z 76, 90, 104, 116, 146) were also observed in the mass spectrum of hypertyrosinemia, which is one of inborn disorders in amino acid metabolism. In the case of glycerol kinase deficiency, the peaks of glycerol (m/z 93) and 3-hydroxybutanoic acid (m/z 105) were clearly exhibited in the mass spectrum, where ammonium adduct ions with them were also observed at m/z 110 and 122 of rather intense peaks than that of MH+ ions. In the case of methylmalonic acidemia, methyl-malonic acid (m/z 119) was rather concentrated in the urine, but weakly observed by means of the direct measurement.Clear distinction was found between the mass spectra of normal and abnormal urines, although the direct analysis of urines provided rather weak peaks for organic acids. LI-MS is considered to be useful for analysis of biomedical samples like urine.

Analysis of Middle Ear Effusions by Liquid Ionization Mass Spectrometry

Analysis of Middle Ear Effusions by Liquid Ionization Mass Spectrometry

Discrimination of isomers by liquid ionization mass spectrometry with techniques of collisional activation and adduct ion formation

AbstractLiquid ionization mass spectrometry is a soft ionization technique used with liquid samples under atmospheric pressure. It facilitates the handling of reagents and the observation of ion–molecule reactions in the ion source. The differentiation of isomers by characteristic fragment ions, for example those resulting from asymmetrical cleavage of a cyclobutane ring, and by molecular adduct ion formation was studied. The samples studied were cyclobutane derivatives, alkyl 4‐(3‐oxo‐3‐pIienyl‐l‐aIkenyl)benzoate dimers, and reagents having two functional groups were used to produce adduct ions to clarify the difference between isomers. The reagents act on a sample molecule at two functional groups to form hydrogen bonds. Some correlations were observed between the structure of the sample and the relative abundances of molecular adduct ions and also fragment ions produced by collisionally activated dissociation.

Liquid ionization mass spectrometry of organometallic compounds used as lubricating oil additives

Liquid ionization mass spectrometry, a method of soft ionization at atmospheric pressure, was applied to analyze organometallic compounds used as lubricating oil additives. Alkanes such as undecane (matrix) and chloroform (solvent) were found to be better than others examined. Since proton affinities of organometallic compounds are generally larger than those of lubricating oils, zinc complexes are selectively ionized, resulting in dominant MH/sup +/ ions whose isotope peak ratios agree well with their natural abundances. Furthermore, the relative intensities of MH/sup +/ peaks coincide with the composition of a mixture of zinc complexes. Since each compound has an optimum temperature for producing MH/sup +/ ions, selective desorption of ions for each component in a mixture is also possible by increasing the sample heater current. As an example, detection of lubricating oil additives in a commercial engine oil is described. 21 references, 10 figures, 1 table.

Modification of calf thymus DNA by methyl methanesulfonate. Quantitative determination of 7-methyldeoxyguanosine by mass spectrometry

Quantitation of 7-methyldeoxyguanosine (m 7dG) produced in the in vitro methyl methanesulfonate (MeMS) action on calf-thymus DNA is achieved by enzymatic degradation, liquid chromatographic separation and chemical ionization mass spectrometry. The total degree of methylation, measured by uptake of [ 14C] MeMS was 0.35%. Mass spectral analysis shows that m 7dG constitutes 84% of the total methylated product. It is also shown that tandem mass spectrometry allows detection of m 7dG, as the protonated base, down to 1 pmol level, suggesting that MS/MS analysis can be the method of choice in quantitation of the adducts of in vivo DNA modifications.

Liquid ionization mass spectrometry of phospholipids.

Several phosphatidylcholines (PC) and a phosphatidylethanolamine (PE) were subjected to liquid ionization (LI) mass spectrometry, in which a sample is ionized through energy transfer from metastable argon atoms under atmospheric pressure. Commercially available and synthesized, saturated or unsaturated fatty acid containing phospholipids and their mixtures were studied. A sample either as a concentrated chloroform-methanol solution or with glycerol (matrix) gave characteristic peaks such as MH+ and four fragment ions. One of the fragment ions (e.g., m/z 551 of PC 16:0, 16:0) containing both fatty acid residues has been commonly observed with other ionization methods such as CI, FD, and FAB, but the other fragment ions have not been observed in other mass spectra with one exception on desorption CI. Ions b and d (e.g., m/z 464 and 328, respectively, for PC 16:0, 16:0) contain one fatty acyl residue and the other ion containing the phosphorylcholine moiety appears at m/z 196 for PC. Thus the masses of the MH+ ion and these fragment ions provide useful structural information even in the case of a mixture. The ion b (e.g., m/z 488 of PC 18:0, 18:2) observed during an early period of heating was formed mainly by the loss of one acyl group at sn-1 of the glycerol backbone and thus may be used to differentiate the positional specificities of the constituent fatty acids. The temperature of the sample, however, should be controlled precisely, because it has a significant effect on the mass spectrum. The present method (LI) also provided useful information for a mixture of PC and PE.