Chromatograph-mass Spectrometer-computer System Research Articles

Gas chromatographic—mass spectrometric analysis of amine metabolites in urine

An analytical method for the separation and identification of amine metabolites in human urine has been developed using a gas chromatograph—mass spectrometer—computer system. The sample preparation consists of organic solvent extraction, adsorption on a cation-exchange resin, evaporation, and acylation. N-3-Hydroxypropyl-1, 4-diaminobutane was identified for the first time in urine. Methylguanidine, guanidine, putrescine, cadaverine, p-tyramine, 3-methoxytyramine, spermidine, and spermine were detected in normal urine with good gas chromatographic separation.

The importance of cyanide and organic nitriles in fire fatalities

AbstractA study of fire deaths in the Glasgow area has been in operation for 2½ years. Detailed pathological and toxicological examinations have been carried out on 127 fatalities, arising primarily in domestic fires. Cyanide and thiocyanate, the principal metabolite of cyanide in blood, were measured in blood samples from 100 fatalities and from groups of non‐fatal fire casualties, firemen and normal and post‐mortem controls. Cyanide concentrations in the blood of fatal and non‐fatal casualties were elevated to statistically significant levels compared to controls and 6% of fatalities had cyanide levels above 100 μmol 1−1 blood. No evidence was obtained for the operation of additive or synergistic effects in fire deaths between cyanide, carbon monoxide and ethyl alcohol. Thiocyanate was of value as an index of metabolized cyanide in non‐fatal subject groups but not in fatalities. Organic volatiles in blood from fire victims were analysed with a gas chromatograph mass spectrometer computer system and for the first time the presence of toxic nitriles other than cyanide has been demonstrated.

Application and evaluation of limited mass monitoring with a gas chromatograph mass spectrometer computer system.

The technique of scanning a preselected set of ions employing a combined gas chromatography mass spectrometer computer system has been investigated to ascertain the advantages and disadvantages of such a procedure. This technique allows one to determine gas chromatographic retention data with with a high degree of precision and accuracy, in rapid temperature programming operation, due to shortening of the mas spectral scanning interval. Signal-to-noise ratio in ion abundance recordings can be enhanced by increasing the dwell time for as many as 100 ions without lenghtening the scanning interval. The utility of such an approach was demonstrated by analysis of complex mixtures isolated form human urine and cerebrospinal fluid.

Polypeptide sequencing by liquid chromatography mass spectrometry.

Key steps in a proposed automated system for polypeptide sequencing utilizing a liquid chromatograph mass spectrometer computer system have been tested with mixtures containing up to six model oligopeptides. At the low nanomole level it was possible to obtain complete sequence information for all components in many, but not all, of the mixtures tried. Interpretation of the results is complicated by the presence of numerous side-products formed in the derivatization process. Minimization of such impurities will be necessary to reduce the ambiguity of the sequence information resulting from more complex mixtures, such as those expected from the degradation of larger polypeptides, and to reduce sample requirements to the subnanomole level. However, the present system appears to have unique advantages over other proposed automated methods.

Polypeptide sequencing by a gas chromatograph mass spectrometer computer system: II—characterization of complex mixtures of oligopeptides as trimethylsilylated polyamino alcohols

Complex mixtures of O-trimethylsilylated polyamino alcohols, which have been generated by either acid or enzymatic hydrolysis of polypeptides and subsequent derivatization, are completely characterized by a gas chromatograph mass spectrometer computer system. These peptide derivatives possess excellent gas chromatographic properties; a wide range of derivatives from di- to hexapeptides may be separated in a single chromatographic experiment. The identification of these compounds, either manually or with the assistance of the computer, is based on three sets of data which are automatically generated after the g.c.m.s. computer experiment: (1) mass spectra, which exhibit sequence-determining ions of high abundance; (2) selected ion records, which allow efficient location of peptide derivatives in the gas chromatogram as well as resolution of incompletely separated fractions; (3) retention indices, which can be calculated from values which have been assigned to each amino acid residue.

Polypeptide sequencing by a gas chromatograph mass spectrometer computer system: I—generation and derivatization of complex mixtures of oligopeptides

A generally applicable strategy for polypeptide sequencing has been developed which involves cleavage of a large peptide (for example, primary degradation peptides obtained by tryptic or cyanogen bromide cleavage of a protein) to a mixture of small peptides whose individual amino acid sequences are then determined without their prior isolation. This is accomplished by conversion of the peptide mixture into the corresponding mixture of O-trimethylsilylated polyamino alcohols through reduction of the N-acetylated peptide esters with lithium aluminum deuteride, followed by treatment with trimethylsilyldiethylamine. The conditions for the enzymatic or chemical cleavage were optimized to yield mixtures of peptides best suited for this technique and which represented complete overlap. Limited acid hydrolysis combined with a second experimen utilizing either an enzyme with broad specificity, a set of enzymes, or dipeptidyl aminopeptidase I on the original and/or Edman-degraded molecule was found to be the best choice. This sequencing strategy was evaluated using 0.4 to 1.4 μmol of peptides with known structures (ribonuclease S-peptide, glucagon) and then applied to primary degradation peptides of rabbit skeletal muscle actin up to twenty amino acids long (0.4 to 1 μmol per experiment).

Rapid computerized identification of compounds in complex biological mixtures by gas chromatography—mass spectrometry

A new method has been developed for rapid identification of compounds in complex mixtures by gas chromatograph—mass spectrometer—computer system. The method uses a gas chromatographic retention index in conjunction with a small set of discriminating ions to identify each compound. The retention index predicts to within 1% the location of a time-dependent “window” within which a specific compound may appear, while the accuracy of the peak identification is dependent primarily upon the specificity of the ion set chosen. Optimum specificity is obtained by selecting ions which not only are chracteristic of the compound to be identified, but which also differentiate it from other compounds likely to elute at similar retention times. Utilizing the data files created by repetitive scanning during a single elution by gas-liquid chromatography, the present algorithm permits the automated identification of approximately eight compounds per minute. Examples of the identification of acidic urinary metabolites are given; however, the method is sufficiently general to be applied to any group of volatile compounds.

Gas Chromatograph—Mass Spectrometer—Computer System for Detection and Identification of Abnormal Metabolic Products in Physiological Fluids

Abstract A gas chromatograph—mass spectrometer—computer system was developed to rapidly separate and identify metabolic products of low molecular weight in microliter quantities of physiological fluids. For sample preparation, the silyl derivative extraction method was used, in which extraction, derivative formation, and concentration are achieved in a single step, and components with widely different chemical structures can be analyzed in a single run. Gas-chromatographic peaks were identified by the computer output of high-resolution mass measurements or low-resolution fragmentation patterns. Application is illustrated by a case of inborn metabolic error. The system appears well suited for screening for metabolic disorders.