A comparison of the gas chromatographic and mass spectrometric properties of the pentafluoropropionyl and heptafluorobutyryl derivatives of the methyl, trifluoroethyl, pentafluoropropyl and hexafluoroisopropyl esters of twelve acidic metabolites of biogenic amines

Amino acids in inflammatory bowel diseases: Modern diagnostic tools and methodologies

Amino acids are crucial building blocks of living organisms. Together with their derivatives, they participate in many intracellular processes to act as hormones, neuromodulators, and neurotransmitters. For several decades amino acids have been studied for their potential as markers of various diseases, including inflammatory bowel diseases. Subsequent improvements in sample pretreatment, separation, and detection methods have enabled the specific and very sensitive determination of these molecules in multicomponent matrices-biological fluids and tissues. The information obtained from targeted amino acid analysis (biomarker-based analytical strategy) can be further used for early diagnostics, to monitor the course of the disease or compliance of the patients. This review will provide an insight into current knowledge about inflammatory bowel diseases, the role of proteinogenic amino acids in intestinal inflammation and modern analytical techniques used in its diagnosis and disease activity monitoring. Current advances in the analysis of amino acids focused on sample pretreatment, separation strategy, or detection methods are highlighted, and their potential in clinical laboratories is discussed. In addition, the latest clinical data obtained from the metabolomic profiling of patients suffering from inflammatory bowel diseases are summarized with a focus on proteinogenic amino acids.

Amino acid analysis using chromatography-mass spectrometry: An inter platform comparison study

The analysis of amino acids has become a central task in many aspects. While amino acid analysis has traditionally mainly been carried out using either gas chromatography (GC) in combination with flame ionization detection or liquid chromatography (LC) with either post-column derivatization using ninhydrin or pre-column derivatization using o-phthalaldehyde, many of today's analysis platforms are based on chromatography in combination with mass spectrometry (MS). While derivatization is mandatory for the GC-based analysis of amino acids, several LC platforms have emerged, particularly in the dawn of targeted metabolite profiling using hydrophilic interaction liquid chromatography (HILIC) coupled to MS, allowing the analysis of underivatized amino acids. Among the numerous analytical platforms available for amino acid analysis today, we here compare three prominent approaches, being GC-MS and LC-MS after amino acid derivatization using chloroformate and HILIC-MS of underivatized amino acids. We compare and discuss practical issues as well as performance characteristics, e.g., the use of (13)C-labeled internal standards, of the different platforms and present data on their practical implementation in our laboratory. Finally, we compare the real-life applicability of all three platforms for a complex biological sample. While all three platforms are very-well suited for the analysis of complex biological samples they all show advantages and disadvantages for some analytes as discussed in detail in this manuscript.

Distribution of stable free radicals among amino acids of isolated soy proteins

Application of deuterium sulfide to powdered isolated soy proteins (ISP) was used to quench stable free radicals and produce a single deuterium label on amino acids where free radicals reside. The deuterium labels rendered increases of isotope ratio for the specific ions of radical-bearing amino acids. Isotope ratio measurements were achieved by gas chromatography/mass spectrometry (GC/MS) analyses after the amino acids were released by acidic hydrolysis and converted to volatile derivatives with propyl chloroformate. The isotope enrichment data showed the stable free radicals were located on Ala, Gly, Leu, Ile, Asx (Asp+Asn), Glx (Glu+Gln), and Trp but not on Val, Pro, Met, Phe, Lys, and His. Due to the low abundance of Ser, Thr, and Cys derivatives and the impossibility to accurately measure their isotope ratios, the radical bearing status for these amino acids remained undetermined even though their derivatives were positively identified from ISP hydrolysates. The relative isotope enrichment for radical-bearing amino acids Ala, Gly, Leu, Ile, Asx (Asp+Asn), Glx (Glu+Gln), and Trp were 8.67%, 2.96%, 2.90%, 3.94%, 6.03%, 3.91%, and 21.48%, respectively. Isotope ratio increase for Tyr was also observed but further investigation revealed such increase was mainly from nonspecific deuterium-hydrogen exchange not free radical quenching. The results obtained from the present study provide important information for a better understanding of the mechanisms of free radical formation and stabilization in "dry" ISP.

Sarcosine as a marker in prostate cancer progression: a rapid and simple method for its quantification in human urine by solid-phase microextraction-gas chromatography-triple quadrupole mass spectrometry

Sarcosine is an amino acid derivative of N-methylglycine and is involved in the amino acid metabolism and methylation processes that are enriched during prostate cancer progression. It could also serve as a new target to be measured during therapeutic interventions and help in the identification of aggressive tumors for radical treatment. In this study, we present a new urine test that can help early diagnosis of prostate cancer. The method for the quantification of sarcosine in urine consists of a solid-phase microextraction (SPME) step followed by gas chromatography-triple quadrupole mass spectrometry analysis. We used a preliminary derivatization step with ethyl chloroformate/ethanol and the corresponding ester was then extracted by SPME in immersion mode. Several fibers were evaluated and the optimization of the parameters affecting the SPME process was carried out using an experimental design. The optimal values were 20 min extraction time, 10% NaCl, and 270°C using a divinylbenzene/Carboxen/polydimethylsiloxane fiber. The triple quadrupole analyzer acquired data in selected reaction monitoring mode, allowing us to obtain reconstructed chromatograms with well-defined chromatographic peaks. The accuracy and precision of this method were evaluated at concentrations of 70, 250, and 800 ng/ml and were found to be acceptable. Very satisfactory values (0.10 and 0.16 ng/ml, respectively) were also achieved for the limit of detection and the limit of quantification. The proposed protocol represents a rapid, simple, selective, and sensitive tool to quantify sarcosine in urine samples for prostate cancer diagnosis and for a screening test.

Automated GC-MS analysis of free amino acids in biological fluids

A gas chromatography-mass spectrometry (GC-MS) method was developed for the quantitative analysis of free amino acids as their propyl chloroformate derivatives in biological fluids. Derivatization with propyl chloroformate is carried out directly in the biological samples without prior protein precipitation or solid-phase extraction of the amino acids, thereby allowing automation of the entire procedure, including addition of reagents, extraction and injection into the GC-MS. The total analysis time was 30 min and 30 amino acids could be reliably quantified using 19 stable isotope-labeled amino acids as internal standards. Limits of detection (LOD) and lower limits of quantification (LLOQ) were in the range of 0.03-12 microM and 0.3-30 microM, respectively. The method was validated using a certified amino acid standard and reference plasma, and its applicability to different biological fluids was shown. Intra-day precision for the analysis of human urine, blood plasma, and cell culture medium was 2.0-8.8%, 0.9-8.3%, and 2.0-14.3%, respectively, while the inter-day precision for human urine was 1.5-14.1%.

Selected-ion monitoring gas chromatographic-mass spectrometric analysis of catecholamines: enhancement of sensitivity by a simple clean-up step on Sephadex G-10

The sensitivity of catecholamines using selected-ion monitoring gas chromatography-mass spectrometry (SIM GC-MS) has been enhanced by employing a simple clean-up step using Sephadex G-10 columns. This procedure allows for the detection of extremely small amounts (1-10 pg) of biogenic amines (e.g., epinine) which corresponds to a 25-fold increase in detection limits compared to electron ionization GC-MS or high-performance liquid chromatography with electrochemical detection (HPLC-ED). The SIM GC-MS assay was used to monitor the dopamine-beta-hydroxylase-mediated conversion of epinine d6 to epinephrine d6 in rat hypothalamus and brainstem in vitro and the results were compared to those obtained by HPLC-ED.