Evaluation of automatically generated substructure identification rules from tandem mass spectra.

Substructure identification rules for phenothiazine and barbiturate substructures were generated by using a new version of the Method for Analyzing Patterns in Spectra (MAPS) software. This software uses tandem mass spectra and known substructure content of reference compounds to provide "feature-combination" rules. A feature-combination is a series of tandem mass spectral features which are completely unique to compounds containing a specified substructure. The current reference databases contain over 11,000 daughter spectra of 100 compounds acquired at two different collision gas pressures (i.e., single- and multiple-collision conditions). The results of rule evaluation procedures are presented and include a comparison of the spectral features developed in rule generation to those identified in documented fragmentation pathways of the indicated substructure. Two potential sources of error due to spectral feature and substructure "cross-correlation" were identified. If errors occur, they can be detected by calculating cross-correlation coefficients and edited from the rules. A beneficial cross-correlation involving feature-combinations was also discovered. The rules obtained by using single- and multiple-collision data were further evaluated by applying them to tandem mass spectra of 20 test compounds (compounds not in the reference database). The results of these evaluations give a good indication of the utility of the rules for use in an automated structure elucidation system for tandem mass spectrometry data.

Reflections on the modified simplex-I.

The modified simplex method is a well-known method of optimization. In this study several changes have been made to it. These include an adaptive weighted centroid and a Lagrange interpolation procedure. The latter is used to get a better value of the reflected point when a contraction succeeds or an expansion fails. The new method, called the composite modified simplex method (CMS) has been rigorously evaluated by means of mathematical functions, maps and chemical experimentation. The effect of the starting point and the size of the simplex have been investigated in detail. For flow-injection analysis it has proved possible to optimize 2-12 variables. The method has proved most suitable for rapid and effective optimization of polarography, flow-injection analysis and chemical synthesis. This paper describes the evaluation procedures and reviews the results obtained.

Reflections on the modified simplex-II.

This paper discusses the details of the composite modified simplex, critically compares it with other simplex methods, and reviews the value of this type of optimization procedure.

Thermosonimetry of the phase II/III transition of hexachloroethane.

A thermosonimetric study has shown that the Phase II/III polymorphic transition of hexachloroethane emits acoustic signals. This solid-solid phase transition is known to occur by a nucleation-growth process during which a nucleus of the new phase, once formed, grows at the expense of the mother phase to form a complete crystal without fracture. Acoustic emissions from a conditioned multi-crystal sample have been used to study the transition. Acoustic activity correlated well with dilatometric measurements. Frequency analysis on waveforms of many hundreds of individual acoustic emissions revealed marked differences between individual signals. Principal-components analysis on 24 signal features revealed a single dispersed cluster with a highly non-uniform distribution of signals. These experiments provided highly reproducible average power spectra. Time-resolved acoustic power spectra were also generated. These additional types of information cannot be obtained by other techniques.

Simplex optimization of conditions for the determination of arsenic in environmental samples by using electrothermal atomic absorption spectrometry.

Simplex optimization was used to efficiently delineate the optimum experimental conditions to be used for the electrothermal atomic absorption spectrometric analysis of arsenic in a standard reference material of marine origin. Four experimental variables, were considered: ashing temperature, atomization temperature, modifier concentration, and atomization ramping time. This combination of methods and materials provides a powerful means of rapidly improving the experimental conditions used for analysis of arsenic in a wide variety of samples of environmental origin. Excellent recoveries of arsenic were obtained when using the optimum electrothermal atomic absorption spectrometry conditions to analyze standard solutions of arsenobetaine, arsenocholine and tetramethylarsonium iodide.

Spectrophotometric method for determination of sulfide with iron(III) and nitrilotriacetic acid by flow injection.

A manual colorimetric method for determination of sulfide has been adapted to flow injection, systematically optimized, and more fully characterized. Its intended application is for measurement of sodium sulfide reagent strength in pulp process streams, and sulfide contamination in effluent from Kraft pulp mills. In the flow-injection method developed, a sample solution containing sulfide is reacted with a mixture of iron(III) and nitrilotriacetic acid under ammoniacal conditions. The absorbance of the intensely-colored green product of this reaction is measured at 636 nm. Excess sulfite is present as a color stabilizer. A linear dynamic range of 20-100 ppm sulfide is readily achieved; the relative standard deviation is less than 1.2% (n = 10) throughout this range, and 0.37% (n = 10) midrange at 60 ppm. The usable dynamic range is 8-250 ppm sulfide. Long-term stability of the method is ensured by periodically performing an automatic cleaning cycle using a hydrochloric acid wash solution. This prevents tube discoloration and removes any precipitates which are formed under strongly alkaline conditions. The sample throuhput rate is at least 30/hr, given alternate acid wash cycles.

Spectrophotometric determination of palladium with sulfochlorophenolazorhodanine by flow injection.

Sulfochlorophenolazorhodanine (as its sodium salt) has been used in the automated development of a sensitive flow-injection procedure for the spectrophotometric determination of palladium. The resulting method has high sample throughput, good precision, and low consumption of both sample and reagents. The optimum pH for the reaction is 5.0 and the response is constant at pH between 4.7 and 5.3. The sensitivity (calibration slope) of the procedure is 4.4 x 10(3) l./mole. The linear dynamic range is 0.045-30.0 mug/ml. The sample throughput is at least 120/hr. An automated procedure for optimization of analytical variables is described and a two-variable response surface for the system is given. Interference studies on 19 metal ions show that the method has good selectivity.

Computer-assisted optimization of HPLC with post-column reaction for the determination of amino-acids.

Computer-assisted optimization of a high-performance liquid chromatograph and associated post-column reactor is reported for the determination of six amino-acids. First six, then seven, experimental variables were considered. Non-standard experimental conditions were found which gave significantly improved colour development in the ninhydrin reaction. The composite modified simplex method for experimental optimization and a novel system-response function facilitated rapid and simultaneous improvement of separation, sensitivity and analysis time. The approach described is directly applicable to many similar systems.

Optimization of automatically generated rules for predicting the presence and absence of substructures from MS and MS/MS data.

A pattern-recognition/artificial-intelligence program, referred to as MAPS (Method for Analyzing Patterns in Spectra), was recently developed to identify the relationships that exist between substructures and the characteristic features they produce in the spectra from mass spectrometry (MS) and successive mass spectrometry (MS/MS). MAPS has been extended to utilize these relationships to formulate exclusion rules as well as inclusion rules, so that the absence of recognized substructures can be predicted as well as their presence. The potential usefulness of each MS and MS/MS spectral feature in such rule formulation is characterized by correlation and uniqueness factors. The correlation factor expresses the degree of correlation between a feature and a specific substructure; the uniqueness factor expresses the uniqueness of a feature with respect to that substructure. Features with high correlation factors are most use for predicting the absence of substructures, whereas features with high uniqueness factors are most useful for predicting their presence. Feature intensity-data have been found to improve the inclusion-rule performance and degrade the exclusion-rule performance. Criteria for optimizing the predictive abilities of both rule types are discussed.

Synthesis of deuterium labeled cholesterol and steroids and their use for metabolic studies.

A simple method is described for the preparation of [6,7,7(-2)H3] sterols and steroids. The synthesis starts with a Δ(5)-sterol or steroid and involves preparation of the 6-oxo-3α,5α-cyclosteroid, base exchange in the presence of deuterium oxide to introduce two deuteriums at the C-7 position and sodium borodeuteride reduction of the 6-oxo group to introduce the third deuterium atom at C-6. Rearrangement of the [6,7,7(-2)H3]6α-hydroxy-3α,5α-cyclosteroid then gives the desired [6,7,7(-2)H3]-Δ(5) sterol or steroid. [6,7,7(-2)H3]Cholesterol, [6,7,7(-2)H3]pregnenolone and [6,7,7(-2)H3]3ß-hydroxyandrost-5-en-17-one were synthesized in this fashion and [6,7,7(-2)H3]progesterone was prepared from the [6,7,7(-2)H3]pregnenolone. Three examples of the use of these deuchromatography-mass spectrometry. The chrysophyte alga,Ochromonas malhamensis, was shown to be capable of introducing an extra methyl or ethyl group at C-24 of the side chain of [6,7,7(-2)H3]cholesterol to yield brassicasterol and poriferasterol, respectively. The ovary of the echinoderm,Asterias rubens, was demonstrated to metabolize [6,7,7(-2)H3]progesterone to yield mainly the 5α-isomers of pregnane-3,20-dione and 3ß-hydroxypregnan-20-one. However, the 5ß-isomers of these compounds were also detected as minor products for the first time as progesterone metabolites in this animal. Isolated oocytes of the frog,Xenopus laevis, produced a number of metabolites of [6,7,7(-2)H3]progesterone. In this report, two of them were shown to be 17α-hydroxy-pregn-4-en-3,20-dione and 20α-hydroxypregn-4-en-3-one.

The isolation, characterization and structure of uroterpenol, a monoterpene from human urine.

Human urine is shown to contain, in a conjugated form, a compound of molecular formula C(10)H(18)O(2), which is named uroterpenol. Details are reported of the isolation procedure, the preparation of derivatives and the chemical and physical properties, together with a proof that the compound is p-menth-1-ene-8,9-diol.

Versatile IEEE-488 data acquisition and control routines for a diode array spectrophotometer.

The UV-visible diode array spectrophotometer is a work-horse instrument for many laboratories. This article provides simple data acquisition and control routines in Microsoft QuickBasic for a HP-8452A diode array spectrophotometer interfaced to an IBM PC/XT/AT, or compatible, microcomputer. These allow capture of full spectra and measure absorbance at one or several wavelengths at preset time intervals. The variance in absorbance at each wavelength is available as an option.

Umbilical vein cortisol after spontaneous and induced labour and at elective Caesarean section.

Umbilical vein (UV) plasma cortisol levels were assayed at delivery after spontaneous labour, oxytocin-induced labour, prostaglandin E2-induced labour and after delivery by elective Caesarean section. Higher mean UV cortisol levels were observed after vaginal delivery than after delivery by elective Caesarean section. The highest mean UV cortisol level was observed in the PGE2 group which accords with the known ability of prostaglandins to increase steroid production. The significance of these findings is discussed.