Positive-ion thermospray liquid chromatography-mass spectrometry: detection of organic acidurias

Mass probe-assisted ionization method for total analysis of biomolecules with electrospray ionization-mass spectrometry

In this paper, we review the mass probes used for the derivation of a variety of biomolecules efficiently detected by the electrospray ionization-mass spectrometry and mass probe-assisted ionization method for total analysis and determination by consecutive detection with a single instrument. We describe mass probes for a variety of molecules including proteins, nucleobases, metallic cations, and other small molecules.

Contemporary clinical usage of LC/MS: analysis of biologically important carboxylic acids

OBJECTIVES

This review summarizes the current role of LC/MS in the diagnosis and screening of clinical conditions involving the analysis of biologically important carboxylic acids.

DESIGN AND METHODS

Carboxylic acids are divided into six logical categories of acid size and function. Details of chromatographic separation methods and modes of mass spectrometer operation are described for each category.

RESULTS

The use of LC/MS in clinical applications such as the diagnosis of inherited and acquired metabolic disorders, gastrointestinal disorders, cancer and diabetes and therapeutic drug monitoring is discussed.

CONCLUSIONS

The mild conditions, speed and sensitivity advantages of LC/MS analysis, over alternatives, are highlighted. The sensitivity and specificity afforded by the combination of tertiary and quaternary ammonium derivatives and tandem mass spectrometry for the analysis of carboxylic acids is emphasized. Potential for a greater range of LC/MS carboxylic analyses, including stereoisomeric intermediates, is predicted.

Design and Synthesis of Labeling Reagents (MS Probes) for Highly Sensitive Electrospray Ionization Mass Spectrometry and Their Application to the Detection of Carbonyl, Alcohol, Carboxylic Acid and Primary Amine Samples

Novel labeling reagents, called MS probes, which possess a positively charged quaternary amine moiety and can transform a neutral analyte into a charged compound by simply mixing with the analyte and allowing the mixture to stand from several minutes to 30 min at room temperature or while heating to 50 degrees C, were designed and synthesized for the highly sensitive detection of carbonyl, alcohol, carboxylic acid and primary amine samples by electrospray ionization mass spectrometry (ESI-MS). The positively charged products can be detected with high sensitivity in an ESI-MS system, which is the most popular liquid MS instrument. All of the labeled products showed a remarkably large increase in the molecular-ion peak abundance detection sensitivity of over 500-fold at picomolar concentration levels compared to that of unlabeled analytes in an ESI-MS system. These MS probes, used together with liquid MS detection, are widely applicable as a convenient method for the highly sensitive detection of less than picomolar levels of analytes, and therefore greatly enhance the power of ESI-MS analysis.

Analysis of Dicarboxylic Acids by Tandem Mass Spectrometry. High-Throughput Quantitative Measurement of Methylmalonic Acid in Serum, Plasma, and Urine

Background: Methylmalonic acid (MMA) is a dicarboxylic acid whose concentration can be increased in blood and urine in patients with an inborn error of metabolism or vitamin B12 deficiency. We developed a method for the selective analysis of dicarboxylic acids that exploits the high specificity of tandem mass spectrometry (MS/MS) and the substantial difference in fragmentation patterns of the isomers methylmalonic (MMA) and succinic acid (SA).

Methods: Dicarboxylic acids were extracted from samples with methyl-tert-butyl ether and derivatized with butanolic HCl to form dibutyl esters. The derivative was injected into the liquid chromatography (LC)-MS/MS system using TurboIonSprayTM (nebulizer-assisted electrospray) ionization and quantified by the multiple reaction monitoring mode of MS/MS.

Results: The assay for MMA was linear up to 150 μmol/L. The total imprecision was ≤7.5% at both low and high concentrations. The limits of quantification and detection were 0.1 and 0.05 μmol/L, respectively. The degree of interference from SA could be predicted from the branching ratios of the major product ions.

Conclusions: The method is specific for dicarboxylic acids. The LC-MS/MS analysis for MMA requires minimal chromatographic separation and takes <60 s per sample. The entire analysis, including sample preparation, for a batch of 100 specimens can be performed in <4 h.

13C NMR spectroscopy: a convenient tool for detection of argininosuccinic aciduria

Proton decoupled high resolution 13C NMR spectra of argininosuccinic acid have been measured in a series of dilute water solutions of various acidity. These data have provided a basis for unequivocal determination of the presence of this metabolite in the investigated sample. The method additionally enables simultaneous rough estimation of the metabolite concentration. In order to check the practicability of the usage of this spectroscopy for diagnostic purposes, the spectra of several unprocessed urine samples have been recorded including three from patients with argininosuccinic aciduria. It has been concluded that 13C NMR spectroscopy can be a convenient method of recognising the above syndrome and probably many other inborn metabolic errors which manifest themselves with the excretion of the marker metabolite in amounts comparable to (or larger than) creatinine.

Application of electrospray tandem mass spectrometry to neonatal screening

For the past 30 years, neonatal screening programs have been performed largely by using the bacterial inhibition assays developed by Dr Robert Guthrie. These programs focused on a small number of diseases such as phenylketonuria and maple syrup urine disease and involved one test for each disease. During the same period many new diseases were discovered, such as organic acidemias and fatty acid oxidation defects, and they presented a diagnostic challenge to biochemical laboratories. Different mass spectrometric approaches have been the main tools for the diagnosis; however, each has its own limitation. Recently, electrospray tandem mass spectrometry (MS/MS) has provided an alternative automated high throughput, specific, and broad-spectrum approach to screening for a relatively large number of disorders, including those covered by bacterial inhibition assays tests. By using specific scan functions, a large number of amino acids and acylcarnitines in blood spots are quantified in 2 minutes analytical time. A new scan function is described here for quantification and screening for argininosuccinic acid in blood spots, which is a key metabolite in the diagnosis of argininosuccinase deficiency. We describe the results of a 3-year tandem MS/MS-based neonatal study that was performed in our newborn population. We screened 27,624 blood spots and identified 20 cases yielding a frequency of 1:1,381. No false-negative cases were identified, but several false-positive cases were eliminated by repeat analysis by MS/MS of blood or by other means. We also used MS/MS analysis of urine or blood either for confirmation of initial positive results or for follow-up of treatment, such as in glutaric acidemia, citrullinemia, argininosuccinase deficiency, and biopterin-dependent phenylketonuria.

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.