Voltammetric Detection of Vanillylmandelic Acid and Homovanillic Acid Using Urea-Derivative-Modified Graphite Electrode

Vanillylmandelic acid (VMA) and homovanillic acid (HVA) are diagnostic markers of neuroblastoma. The purpose of this study was to understand the reason for the discrimination of structural analogues (VMA and HVA) onto a graphite electrode coated with an electrochemically oxidized urea derivative. Density functional theory calculations (DFT), FTIR spectroscopic measurements, and electrochemical impedance spectroscopic measurements were used in this work. Density functional theory calculations (DFT) were used to identify the most suitable binding sites of the urea derivative and to describe possible differences in its interaction with the studied analytes. The FTIR measurement indicated the enhancement and disappearance of NH vibrations on graphite and platinum surfaces, respectively, that could be connected to a different orientation and thus provide accessibility of the urea moiety for the discrimination of carboxylates. Additionally, the higher the basicity of the anion, the stronger the hydrogen-bonding interaction with -NH-groups of the urea moiety: VMA (pK_b = 10.6, K_Ads = (5.18 ± 1.95) × 10⁵) and HVA (pK_b = 9.6, K_Ads = (4.78 ± 1.58) × 10⁴). The differential pulse voltammetric method was applied to detect VMA and HVA as individual species and interferents. As individual analytes, both HVA and VMA can be detected at a concentration of 1.99 × 10^-5 M (RSD ≤ 0.28, recovery 110-115%).

Comprehensive Targeted Metabolomic Assay for Urine Analysis

Among all the human biological fluids used for disease biomarker discovery or clinical chemistry, urine stands out. It can be collected easily and noninvasively, it is readily available in large volumes, it is typically free from protein contamination, and it is chemically complex-reflecting a wide range of physiological states and functions. However, the comprehensive metabolomic analysis of urine has been somewhat less studied compared to blood. Indeed, most published metabolomic assays are specifically optimized for serum or plasma. In an effort to improve this situation, we have developed a comprehensive, quantitative MS-based assay for urine analysis. The assay robustly detects and quantifies 142 urinary metabolites including 28 amino acids and derivatives, 17 organic acids, 22 biogenic amines and derivatives, 40 acylcarnitines, 34 lipids, and glucose/hexose, among which 67 metabolites are absolutely quantified and 75 metabolites are semiquantified. All the analysis methods in this assay are based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) using both positive and negative-mode multiple reaction monitoring (MRM). The recovery rates of spiked urine samples at three different concentration levels, that is, low, medium and high, are in the range of 80% to 120% with satisfactory precision values of less than 20%. This targeted metabolomic assay has been successfully applied to the analysis of large numbers of human urine samples, with results closely matching those reported in the literature as well as those obtained from orthogonal analysis via NMR spectroscopy. Moreover, the assay was specifically developed in a 96-well plate format, which enables automated, high-throughput sample analysis. The assay has already been used to analyze more than 1800 urine samples in our laboratory since early 2019.

Microbial Contribution to the Human Metabolome: Implications for Health and Disease

The human gastrointestinal tract is home to an incredibly dense population of microbes. These microbes employ unique strategies to capture energy in this largely anaerobic environment. In the process of breaking down dietary- and host-derived substrates, the gut microbiota produce a broad range of metabolic products that accumulate to high levels in the gut. Increasingly, studies are revealing that these chemicals impact host biology, either by acting on cells within the gastrointestinal tract or entering circulation and exerting their effects at distal sites within the body. Given the high level of functional diversity in the gut microbiome and the varied diets that we consume, the repertoire of microbiota-derived molecules within our bodies varies dramatically across individuals. Thus, the microbes in our gut and the metabolic end products they produce represent a phenotypic lever that we can potentially control to develop new therapeutics for personalized medicine. Here, we review current understanding of how microbes in the gastrointestinal tract contribute to the molecules within our gut and those that circulate within our bodies. We also highlight examples of how these molecules affect host physiology and discuss potential strategies for controlling their production to promote human health and to treat disease.

ISiCLE: A Quantum Chemistry Pipeline for Establishing in Silico Collision Cross Section Libraries

High-throughput, comprehensive, and confident identifications of metabolites and other chemicals in biological and environmental samples will revolutionize our understanding of the role these chemically diverse molecules play in biological systems. Despite recent technological advances, metabolomics studies still result in the detection of a disproportionate number of features that cannot be confidently assigned to a chemical structure. This inadequacy is driven by the single most significant limitation in metabolomics, the reliance on reference libraries constructed by analysis of authentic reference materials with limited commercial availability. To this end, we have developed the in silico chemical library engine (ISiCLE), a high-performance computing-friendly cheminformatics workflow for generating libraries of chemical properties. In the instantiation described here, we predict probable three-dimensional molecular conformers (i.e., conformational isomers) using chemical identifiers as input, from which collision cross sections (CCS) are derived. The approach employs first-principles simulation, distinguished by the use of molecular dynamics, quantum chemistry, and ion mobility calculations, to generate structures and chemical property libraries, all without training data. Importantly, optimization of ISiCLE included a refactoring of the popular MOBCAL code for trajectory-based mobility calculations, improving its computational efficiency by over 2 orders of magnitude. Calculated CCS values were validated against 1983 experimentally measured CCS values and compared to previously reported CCS calculation approaches. Average calculated CCS error for the validation set is 3.2% using standard parameters, outperforming other density functional theory (DFT)-based methods and machine learning methods (e.g., MetCCS). An online database is introduced for sharing both calculated and experimental CCS values ( metabolomics.pnnl.gov ), initially including a CCS library with over 1 million entries. Finally, three successful applications of molecule characterization using calculated CCS are described, including providing evidence for the presence of an environmental degradation product, the separation of molecular isomers, and an initial characterization of complex blinded mixtures of exposure chemicals. This work represents a method to address the limitations of small molecule identification and offers an alternative to generating chemical identification libraries experimentally by analyzing authentic reference materials. All code is available at github.com/pnnl .

Exploring the Role of Different Neonatal Nutrition Regimens during the First Week of Life by Urinary GC-MS Metabolomics

In this study, a gas-chromatography mass spectrometry (GC-MS) metabolomics study was applied to examine urine metabolite profiles of different classes of neonates under different nutrition regimens. The study population included 35 neonates, exclusively either breastfed or formula milk fed, in a seven-day timeframe. Urine samples were collected from intrauterine growth restriction (IUGR), large for gestational age (LGA), and appropriate gestational age (AGA) neonates. At birth, IUGR and LGA neonates showed similarities in their urine metabolite profiles that differed from AGA. When neonates started milk feeding, their metabolite excretion profile was strongly characterized by the different diet regimens. After three days of formula milk nutrition, urine had higher levels of glucose, galactose, glycine and myo-inositol, while up-regulated aconitic acid, aminomalonic acid and adipic acid were found in breast milk fed neonates. At seven days, neonates fed with formula milk shared higher levels of pseudouridine with IUGR and LGA at birth. Breastfed neonates shared up-regulated pyroglutamic acid, citric acid, and homoserine, with AGA at birth. The role of most important metabolites is herein discussed.

Synthesis and deposition of a Tröger’s base polymer on the electrode surface for potentiometric detection of a neuroblastoma tumor marker metabolite

We propose an innovative approach to detect a low molecular weight metabolite of neuroblastoma.

The human urine metabolome

Urine has long been a "favored" biofluid among metabolomics researchers. It is sterile, easy-to-obtain in large volumes, largely free from interfering proteins or lipids and chemically complex. However, this chemical complexity has also made urine a particularly difficult substrate to fully understand. As a biological waste material, urine typically contains metabolic breakdown products from a wide range of foods, drinks, drugs, environmental contaminants, endogenous waste metabolites and bacterial by-products. Many of these compounds are poorly characterized and poorly understood. In an effort to improve our understanding of this biofluid we have undertaken a comprehensive, quantitative, metabolome-wide characterization of human urine. This involved both computer-aided literature mining and comprehensive, quantitative experimental assessment/validation. The experimental portion employed NMR spectroscopy, gas chromatography mass spectrometry (GC-MS), direct flow injection mass spectrometry (DFI/LC-MS/MS), inductively coupled plasma mass spectrometry (ICP-MS) and high performance liquid chromatography (HPLC) experiments performed on multiple human urine samples. This multi-platform metabolomic analysis allowed us to identify 445 and quantify 378 unique urine metabolites or metabolite species. The different analytical platforms were able to identify (quantify) a total of: 209 (209) by NMR, 179 (85) by GC-MS, 127 (127) by DFI/LC-MS/MS, 40 (40) by ICP-MS and 10 (10) by HPLC. Our use of multiple metabolomics platforms and technologies allowed us to identify several previously unknown urine metabolites and to substantially enhance the level of metabolome coverage. It also allowed us to critically assess the relative strengths and weaknesses of different platforms or technologies. The literature review led to the identification and annotation of another 2206 urinary compounds and was used to help guide the subsequent experimental studies. An online database containing the complete set of 2651 confirmed human urine metabolite species, their structures (3079 in total), concentrations, related literature references and links to their known disease associations are freely available at http://www.urinemetabolome.ca.

Separation, quantification and identification of non-volatile organic acids in body fluids by gas chromatography

The present paper concentrates on the analysis of non-volatile organic acids in physiological fluids. The solvent extraction and DEAE-Sephadex extraction of organic acids, respectively, seem to be the most widely used methods for isolation of this group of compounds from the biological matrix. Gas chromatography-mass spectrometry (GC/MS) is the preferred method for the separation, quantification and identification. In three tables organic acids are divided into the classes according to a functional group, a survey of alkylation methods is given and retention indices of common urinary organic acids on various GC columns are summarized.

Clinical and biochemical profiles of maple syrup urine disease in malaysian children

INTRODUCTION

Maple Syrup Urine Disease (MSUD) is an autosomal recessive disorder caused by defects in the branched-chain α-ketoacid dehydrogenase complex resulting in accumulation of branched-chain amino acids (BCAAs) and corresponding branched-chain ketoacids (BCKAs) in tissues and plasma, which are neurotoxic. Early diagnosis and subsequent nutritional modification management can reduce the morbidity and mortality. Prior to 1990s, the diagnosis of MSUD and other inborn errors of metabolism (IEM) in Malaysia were merely based on clinical suspicion and qualitative one-dimensional thin layer chromatography technique. We have successfully established specific laboratory diagnostic techniques to diagnose MSUD and other IEM. We described here our experience in performing high-risk screening for IEM in Malaysia from 1999 to 2006. We analysed the clinical and biochemical profiles of 25 patients with MSUD.

METHODS

A total of 12,728 plasma and urine samples from patients suspected of having IEM were received from physicians all over Malaysia. Plasma amino acids quantitation using fully automated amino acid analyzer and identification of urinary organic acids using Gas Chromatography Mass Spectrometry (GCMS). Patients' clinical information were obtained from the request forms and case records Results: Twenty-five patients were diagnosed MSUD. Nineteen patients (76%) were affected by classical MSUD, whereas six patients had non-classical MSUD. Delayed diagnosis was common among our case series, and 80% of patients had survived with treatment with mild-to-moderate learning difficulties.

CONCLUSION

Our findings suggested that MSUD is not uncommon in Malaysia especially among the Malay and early laboratory diagnosis is crucial.

Metabolomics: an integral technique in systems biology

Metabolomics is the unbiased identification and state-specific quantification of all metabolites in a cell, tissue or whole organism, and has developed rapidly into one of the cornerstones of postgenomic techniques for the quantitative analysis of molecular phenotypes. These large-scale analyses of metabolites are intimately bound to advancements in MS technologies and have emerged in parallel with the development of novel mass analyzers and hyphenated techniques, as well as with the combination of different techniques to cope with the physicochemical diversity of a metabolome. This review gives a brief description of the development and applications of these technologies in biochemistry and systems biology, and discusses their significance in the postgenomic era. Especially, the systematic relation between high-throughput metabolomic data and their interpretation with respect to the underlying biochemical regulatory network is discussed.

Reflections on my career in analytical chemistry and biochemistry

My career has been focused in two major areas, analytical chemistry and biochemistry of complex lipids and glycoconjugates. Included here are the pioneering work on the gas chromatography of long-chain sphingolipid bases, carbohydrates, steroids and urinary organic acids. Mass spectrometry was utilized extensively in structural studies of sphingolipids, fatty acids, carbohydrates, steroids, urinary organic acids, polyisoprenoid alcohols, and juvenile hormone. Computer systems were developed for the acquisition and analysis of mass spectra, and were used for development of automated metabolic profiling of complex mixtures of metabolites. Fabry's disease was discovered to be a glycosphingolipidosis. Enzymes of lysosomal metabolism of glycosphingolipids were purified, characterized, and used in one of the first demonstrations of the feasibility of enzyme replacement therapy in a lysosomal storage disorder (Fabry's disease). Extracellular sialidases were studied to evaluate the hypothesis that they might be involved in the regulation of membrane growth factor receptors. The enzyme for hematoside synthesis was purified and characterized.

Biochemical individuality reflected in chromatographic, electrophoretic and mass-spectrometric profiles

This review discusses the current trends in molecular profiling for the emerging systems biology applications. Historically, the methodological developments in separation science were coincident with the availability of new ionization techniques in mass spectrometry. Coupling miniaturized separation techniques with technologically-advanced MS instrumentation and the modern data processing capabilities are at the heart of current platforms for proteomics, glycomics and metabolomics. These are being featured here by the examples from quantitative proteomics, glycan mapping and metabolomic profiling of physiological fluids.

The future of liquid chromatography-mass spectrometry (LC-MS) in metabolic profiling and metabolomic studies for biomarker discovery

The future utility of liquid chromatography-mass spectrometry (LC-MS) in metabolic profiling and metabolomic studies for biomarker discover will be discussed, beginning with a brief description of the evolution of metabolomics and the utilization of the three most popular analytical platforms in such studies: NMR, GC-MS, and LC-MS. Emphasis is placed on recent developments in high-efficiency LC separations, sensitive electrospray ionization approaches, and the benefits to incorporating both in LC-MS-based approaches. The advantages and disadvantages of various quantitative approaches are reviewed, followed by the current LC-MS-based tools available for candidate biomarker characterization and identification. Finally, a brief prediction on the future path of LC-MS-based methods in metabolic profiling and metabolomic studies is given.

Gas chromatographic-mass spectrometric urinary metabolome analysis to study mutations of inborn errors of metabolism

Urine contains numerous metabolites, and can provide evidence for the screening or molecular diagnosis of many inborn errors of metabolism (IEMs). The metabolomic analysis of urine by the combined use of urease pretreatment, stable-isotope dilution, and capillary gas chromatography/mass spectrometry offers reliable and quantitative data for the simultaneous screening or molecular diagnosis of more than 130 IEMs. Those IEMs include hyperammonemias and lactic acidemias, and the IEMs of amino acids, pyrimidines, purines, carbohydrates, and others including primary hyperoxalurias, hereditary fructose intolerance, propionic acidemia, and methylmalonic acidemia. Metabolite analysis is comprehensive for mutant genotypes. Enzyme dysfunction-either by the abnormal structure of an enzyme/apoenzyme, the reduced quantity of a normal enzyme/apoenzyme, or the lack of a coenzyme-is involved. Enzyme dysfunction-either by an abnormal regulatory gene, abnormal sub-cellular localization, or by abnormal post-transcriptional or post-translational modification-is included. Mutations-either known or unknown, common or uncommon-are involved. If the urine metabolome approach can accurately observe quantitative abnormality for hundreds of metabolites, reflecting 100 different disease-causing reactions in a body, then it is possible to simultaneously detect different mutant genotypes of far more than tens of thousands.

Percutaneous absorption of azelaic acid in humans

Six healthy male volunteers received a single topical treatment with 5 g of an anti-acne cream containing 20% azelaic acid (AzA) onto the face, the chest and the upper back. One week later 1 g of AzA was given orally to the same subjects as aqueous microcrystalline suspension. Following the two treatments the renal excretion of the unchanged compound was measured. Analysis included ether extraction of the urine, derivatization of extract and HPLC with UV detection. After topical application 2.2 +/- 0.7%, and after oral administration 61.2 +/- 8.8% of the dose had been excreted unchanged with the urine. By comparing both amounts, the percutaneous absorption of AzA from the cream was assessed to 3.6% of the dermally applied dose.

Basic profiles of organic acids in urine

Altogether 143 of the organic acids regularly occurring in urine of healthy individuals are identified as methyl esters by gas chromatography-mass spectrometry with respect to their complete chemical structures. They are classified as dicarboxylic acids, oxocarboxylic acids, hydroxycarboxylic acids, aromatic acids, furancarboxylic acids, nitrogen-containing acids and acid conjugates. By pre-fractionating the complex mixture of the total organic acids, peak overlap is minimized, and substances in low concentrations can also be detected and identified. The qualitative patterns of the urinary organic acids in the fractions are constant and reproducible, and in many cases a reliable identification of organic acids is possible by gas chromatography alone, using methylene units and separation on OV-1701 capillary columns.

Simultaneous assay for urinary 4-hydroxy-3-methoxy-mandelic acid, 5-hydroxyindoleacetic acid and homovanillic acid by isocratic HPLC with electrochemical detection

A method is described for the simultaneous determination of urinary HMMA, 5-HIAA and HVA by HPLC with electrochemical detection. The method was evaluated over an 8-month period and has thus far identified 2 cases of phaeochromocytoma, 1 case of neuroblastoma and 2 of carcinoid tumour.

Discovery of methoxyacetylcarbamide in the urine of normal adults and phenylketonuric children

In order to study metabolic distinctions in phenylketonuria, urinary metabolites in the form of trimethylsilyl derivatives have been characterized by high resolution gas chromatography and mass spectrometry. A previously unknown metabolite has been found in the urine of some untreated phenylketonuric infants between 2 and 5 yr of age. The metabolite was absent in healthy children of the same age. The metabolite appeared to be present in the urine of apparently healthy adults (25-32 yr old). The metabolite was identified as methoxyacetylcarbamide on the basis of mass fragmentation analysis and compared with synthetic methoxyacetylcarbamide. Their retention times and mass spectra coincided.

Determination of human fibroblasts metabolism in vitro by gas chromatography-mass spectrometry of cell-excreted metabolites

In order to develop an approach to the study of cell metabolism in vitro, we undertook the determination of metabolites excreted by human skin diploid fibroblasts into culture medium using high-resolution gas chromatography in combination with mass spectrometry. Chromatographic and mass spectrometric characteristics of 29 metabolites have been obtained, and 11 of the metabolites have been identified. The excreted metabolites reflect the activity of certain metabolic processes in fibroblasts in vitro. A comparison of chromatographic and mass spectrometric characteristics of the cell metabolites and of those excreted from the body in urine showed most of the metabolites excreted by fibroblasts to be different from the urine metabolites. The possibility of secondary conversion of cell metabolites in the organism and the specificity of metabolism in cells of different tissues are discussed.

Metabolic profiling with gas chromatography-mass spectrometry and its application to clinical medicine

Nowadays, metabolic profiling is widely applied in clinical medicine for the diagnosis and study of human diseases. The number of these applications and their diversity have increased rapidly in the past few years. This review summarizes recent advances in the methods for sample pretreatment and the clinical application of GC-MS to the study of uraemia, diabetes mellitus, dicarboxylic aciduria and other organic acidurias. High-resolution GC-MS is well suited to the profile analysis of metabolic disorders.

Gas chromatographic profiling of ketone bodies and organic acids in diabetes

Diabetes mellitus is a defect not only in glucose metabolism, but also in the metabolism of lipids and amino acids. Gas chromatographic and gas chromatographic--mass spectrometric profile analyses have contributed much to the understanding of the metabolic changes connected with this defect. Ketones are isolated by a gas-phase extraction and adsorption technique and profiled after thermal desorption. Organic acids are isolated by solvent extraction or anion exchange, derivatized and separated either as total acid profiles or subprofiles after pre-fractionation of the acid derivatives. The main results are as follows. (a) Increased total 4-heptanone is inherently connected with diabetes mellitus. Its urinary levels are elevated in therapeutically well controlled patients. (b) A general ketogenesis pathway leads to higher molecular weight ketone bodies in addition to the conventional ketone bodies. (c) During diabetic ketoacidosis, in addition to the fatty acids the following acids are elevated in serum and in urine: dicarboxylic acids resulting from omega- and beta-oxidation of monocarboxylic acids; oxomonocarboxylic acids as metabolites of the amino acids valine, leucine and isoleucine and as products of ketogenesis; and hydroxymonocarboxylic acids, also originating from amino acids and from ketogenesis.

Identification of aromatic dihydroxy acids in biological fluids

3,5-Dihydroxyphenylpropionic acid, 3,5-dihydroxycinnamic acid and 2,3-dihydroxycinnamic acid were detected for the first time to be components of human urine. In the course of this investigation all constitutional isomers of dihydroxy-benzoic, -phenylpropionic, -phenylacetic and -cinnamic acid were synthesized. Mass spectra and retention indices of methyl and trimethylsilyl (TMS) derivatives were determined. In contrast to many other substituted aromatic compounds the mass spectra of methyl and TMS derivatives of dihydroxy aromatic acids often allow a firm distinction to be made between constitutional isomers: TMS derivatives of aromatic acids containing two hydroxy groups located in the ortho position to each other can be recognized by ions resulting from a primary cleavage reaction mainly in the side chain or ester group, followed by loss of tetramethylsilane. In methyl derivatives of 1,2,3-trisubstituted isomers, methoxy groups are lost much more easily from the ions corresponding to the benzylic cleavage than in other isomers. Methyl derivatives of dihydroxycinnamic acids containing at least one methoxy group in the ortho position to the side chain are characterized by a fragmentation reaction, corresponding to the loss of dimethyl ether. TMS and methyl derivatives of 3,5-dihydroxy aromatic acids show unique structure-specific fragmentation reactions.

High-performance liquid chromatographic method for screening disorders of aromatic acid metabolism using a multi-detection system

This paper describes the use of a high-performance liquid chromatograph equipped with an ultraviolet multi-detection system for the analysis of aromatic acids to help establish a high-risk screening system for disorders of organic acid metabolism. The peak height ratios of about seventy metabolically important aromatic acids have been compiled using the multi-detection system. It may be possible to identify aromatic acids by comparing retention time and peak height ratios. The method was very effective for the diagnosis of disorders of aromatic acid metabolism.

Gas chromatographic and gas chromatographic—mass spectrometric analysis of organic acids in plasma of patients with chronic renal failure

Apart from increased concentrations of aliphatic dicarboxylic acids and phenolic aromatic acids in plasma from patients with chronic renal failure, there is large elevation of a furanoid acid, 3-carboxy-4-methyl-5-propyl-2- furanpropionic acid, and of hippuric acid. The levels of 3-hydroxy- and 4- hydroxyhippuric acid are also raised. The quantitative results are as follows: furanoid acid in hemodialysis patients, 1.4 +/- 0.6 mg/dl; in healthy individuals, 0.2 +/- 0.1 mg/dl; hippuric acid in hemodialysis patients, 9.8 +/- 6.5 mg/dl; in health individuals, 0.4 +/- 0.5 mg/dl. Both compounds are dialysable, but less effectively than creatinine and urea. The mean elimination rate of the furanoid acid is only 21%.

Application of metabolic profiling to study the effects of ethanol on metabolism in rats

Rat urine was analyzed by both gas chromatography and a combination of gas chromatography/mass spectroscopy in an attempt to apply the technique of metabolic profiling to determine if ethanol consumption produced an alteration in acid excretion products. Rats were fed a liquid diet for seven days then fed ethanol in the same diet. The 24 hr urine for the last day of control and the first day of ethanol differed greatly with respect to four compounds. These were an increase in threonic, glucuronic and an undetermined acid and a decrease in pyroglutamic acid. The biological basis for the alterations was not investigated. Glucuronic acid forms conjugates with many compounds. Possibly an acute dose of ethanol may alter the removal of some compounds from the liver.

Metabolic profiles of rats of different ages

Urine samples from 6- to 31-month-old male Fischer F344 rats were analyzed using a high performance liquid chromatograph and a unique computer-based data analysis and quality control system in order to discover substances that could be used as markers in the aging process. Metabolic profiles of the organic acids from these urines yielded 42 peaks whose areas could be measured reliably. Of the 42 peaks, 10 were found by analysis of variance to vary significantly (p less than 0.05) with age. Rats from the four ages could also be distinguished using a multivariate statistic (discriminant analysis).

Mass spectrometry: analytical capabilities and potentials

The mass range of mass spectrometers has been extended by almost an order of magnitude in the past decade, ionization procedures have been introduced which allow ionic, nonvolatile compounds to be examined, and new capabilities have been achieved through the successful integration of separation and analysis techniques. In combination with other techniques, mass spectrometry has been used in biological and environmental research to characterize constituents of mixtures, including those present in trace amounts; in metabolic profiling, where high throughput and large dynamic range are important; and in protein structure determinations. Measurements of stable isotope abundances by mass spectrometry have been used in enzymology, studies of photosynthesis, and carbon dating. Outside the area of chemical analysis, mass spectrometry has been used to study gas-phase acidities and basicities and to study organic reaction mechanisms in the gas phase. Trends in mass spectrometry include multidimensional experiments, use of ionization methods, direct analysis without extensive sample preparation, and the development of advanced instrumentation including an ion trap and an inductively coupled plasma mass spectrometer. It is likely that mass spectrometry will come to be much more widely used and that data will increasingly be other than conventional mass spectra.

Automated metabolic profiling analysis of urinary steroids by a gas chromatography mass spectrometry data system

A computer system (MSSMET), using methylene unit retention indices for an off-line reverse library search analysis of selected ion chromatograms from gas-liquid chromatographic mass spectrometric data, has been applied for the qualitative and quantitative determination of daily variations in the excreted levels of urinary steroids of two individuals, using capillary column gas-liquid chromatography. Aliquots of 24 h urine collections and morning spot urine samples were examined. The daily excretion pattern of most of the major steroid metabolites was fairly consistent from day to day (i.e. 3 alpha-hydroxy-5 alpha-androstane-17-one, androsterone; 3 alpha-hydroxy-5 beta-androstane-17-one, etiocheolanolone; 3 alpha, 17 alpha, 21-trihydroxy-5 beta-pregnane-11,20-dione, THE; 3 alpha, 11 beta, 17 alpha, 21-tetrahydroxy-5 beta-pregnane-20-one, THF; 3 alpha, 11 beta, 17 alpha, 21-tetrahydroxy-5 alpha-pregnane-20-one; allo-THF; 3 alpha, 17 alpha, 20 alpha, 21-tetrahydroxy-5 beta-pregnane-11-one, cortolone; 3 alpha, 17 alpha, 20 beta, 21-tetrahydroxy-5 beta-pregnane-11-one, beta-cortolone; 5 beta-pregnane-3 alpha, 11 beta,17 alpha,20 alpha,21-pentol, cortol; 5 beta-pregnane-3 alpha, 11 beta, 17 alpha, 20 beta, 21-pentol, beta-cortol), while certain other steroid metabolites had a less consistent excretion pattern (3 beta-hydroxy-5-androstene-17-one, for example). Advantages and disadvantages of using capillary columns for the automated metabolic profile analysis of urinary steroids by reverse library search of selected mass chromatograms.

Profile analysis of volcano field ionization mass spectra of urine from mice with sarcoma I transplanted by intraperitoneal inoculation

A group of 20 inbred mice were inoculated intraperitoneally with sarcoma I cells. Urine specimens were collected before and after inoculation from this group as well as from a group of 20 mice for controls. Mass profiles of these groups were obtained by volcano field ion mass spectrometry and compared. Significant differences in average normalized mass peaks between the two groups after inoculations are observed for most of the peaks analysed from mass 84 to 313. There is sufficient diagnostic power in the mass profiles to permit unambiguous separation of the diseased mice from the healthy ones.

Increased excretion of lactate, glutarate, 3-hydroxyisovalerate and 3-methylglutaconate during clinical episodes of propionic acidemia

Metabolic changes dependent upon clinical conditions were studied in an eight-month-old girl with propionyl CoA carboxylase deficiency. Only methylcitric acid and 2-methyl-3-oxovaleric acid were detected in the urine of the patient under clinically favorable conditions. During episodes of clinical decompensation, she excreted increased amounts of all the metabolites associated with this disorder. Four acetyl CoA precursors increased during clinical episodes: glutaric acid, a catabolic intermediate of lysine; 3-hydroxyisovaleric acid and 3-methylglutaconic acid, catabolic intermediates of leucine; and lactic acid. This suggests that under clinically favorable conditions the patient has an altered propionate metabolism which proceeds via normal acetyl CoA metabolism with sufficient capacity for acetyl CoA plus propionyl CoA metabolism. When the production of propionyl CoA exceeds the metabolic capacity, however, the catabolism of potent ketogenic amino acids is effectively suppressed in order to reduce acetyl CoA production.

Automated qualitative and quantitative metabolic profiling analysis of urinary steroids by a gas chromatography-mass spectrometry-data system

A computer system (MSSMET), using methylene unit retention indices for an off-line reverse library search analysis of selected ion chromatograms from gas chromatography-mass spectrometry data, has been applied to the qualitative and quantitative determination of urinary steroids. Several published methods for the isolation and derivatization of urinary steroids were evaluated for reproducibility using fused silica capillary column gas chromatography. Using a procedure that gave the greatest reproducibility, MSSMET analyses of urinary steroids were evaluated with packed (3-m 3% OV-101) and capillary (50-m OV-101 WCOT fused silica) columns. Most urinary steroids could be accurately quantitated using the packed column. However, urinary steroids with similar mass spectra and retention behavior on a packed column (i.e., androsterone and etiocholanolone, or 3 alpha, 11 beta, 17 alpha, 21-tetrahydroxy-5 beta-pregnane-20-one and 3 alpha, 11 beta, 17 alpha, 21-tetrahydroxy-5 alpha-pregnane-20-one) were completely separated using the capillary column and could be reproducibly quantitated with a 2-sec scan cycle time (10-15 data points across a peak) but not with a longer scan cycle time. Overloading was the major problem encountered with the fused silica capillary column.

Comparison of isolation methods of urinary organic acids by high-performance liquid chromatography

Four methods for extracting organic acids from human urine prior to analysis by high-performance liquid chromatography (HPLC) were compared. The methods were manual solvent extraction with ethyl acetate and diethyl ether, continuous solvent extraction, anion exchange with pyridinium acetate as the eluting solvent and anion exchange with hydrochloric acid as the eluting solvent. All four methods produced samples that could be analyzed by reversed-phase HPLC, but the continuous solvent extraction and anion exchange with pyridinium acetate methods gave the best reproducibilities (approximately 6% relative standard deviations). Pretreatment of the urine with barium hydroxide and hydroxylamine hydrochloride prior to anion exchange did not markedly alter the HPLC profiles.

Quantitative profiling analysis of organic acids in complex mixtures

The simultaneous detection and quantitative determination of a very large number of metabolites in physiological fluids or tissues, and the subsequent comparison of these data with reference values, is a process which has commonly been called 'metabolic profiling' analysis. Profiles generated by gas-liquid chromatography on packed or capillary columns are readily analyzed by mass spectrometry, utilizing reverse library search procedures to identify individual components. Emphasis will be given here to procedures for the pre-purification of organic acids from plasma, to the use of quartz capillaries for metabolic profiling analysis, and to the sensitivity of this method for trace components.

Studies on drug metabolism by use of isotopes XXVI: Determination of urinary metabolites of rutin in humans

Determination of urinary metabolites of orally administered rutin and rutin-2',5',6'-d3 in humans was carried out by TLC and GLC-mass spectrometry. In human urine, 3-hydroxyphenylacetic acid, 3-methoxy-4-hydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid, 3,4-dihydroxytoluene, and beta-m-hydroxyphenylhydracrylic acid were identified as rutin metabolites. Unchanged rutin and quercetin were not present in urine.

High resolution gas chromatography mass spectrometry of the methyl esters of organic acids from uremic hemofiltrates

The organic acid fraction of hemofiltrates was investigated in the form of methylates by glass capillary gas chromatography-mass spectrometry. The pattern obtained is similar to that of urinary organic acid methylates from healthy individuals. A marked difference was noted for N-phenylacetyl-alpha-aminoglutarimide, present in hemofiltrate at levels 50-100 times higher than those in urine. Analysis of hemofiltrate samples taken at different times during a hemofiltration with post-dilution technique revealed that the hemofiltrate concentration of most compounds was drastically reduced the course of the hemofiltration treatment. Compared to the other compounds, the reduction in hemofiltrate concentration of N-phenylacetyl-alpha-aminoglutarimide was extremely rapid.

Instrumentation in clinical chemistry

Major advances in instrumentation have revolutionized the clinical chemistry laboratory during the past two decades. This article focuses on some of the more recent developments in instrumentation for clinical chemistry in the areas of general chemistry, immunoassays, urinalysis, electrophoresis, chromatography, and trace metal analyses.

Pattern of aliphatic dicarboxylic acids in uremic serum including a new organic acid, 2,4-dimethyladipic acid

(1) 2,4-Dimethyladipic acid was first identified in normal human urine using gas chromatography-mass spectrometry. Urinary excretion of 2,4-dimethyladipic acid in 7 healthy adults ranged from 4.9 mumol to 14 mumol per 24 h. (2) Succinic acid, adipic acid, 3-methyladipic acid, 2,4-dimethyladipic acid, pimelic acid and azelaic acid were identified in the ultrafiltrate of the blood obtained from a chronic uremic patient using a hemodialyzer. (3) Levels of succinic acid, adipic acid, 3-methyladipic acid, 2,4-dimethyladipic acid, pimelic acid and azelaic acid in uremic serum were determined using a mass fragmentographic technique. Concentration of succinic acid in uremic serum was comparable to that in normal serum, whereas concentrations of adipic acid, 3-methyladipic acid, 2,4-dimethyladipic acid, pimelic acid and azelaic acid were highly elevated in uremic serum.