Simultaneous determination of nucleosides and nucleotides in dietary foods and beverages using ion-pairing liquid chromatography-electrospray ionization-mass spectrometry

Dicationic imidazole ionic liquid stationary phase for preservative detection and its application under mixed mode of HILIC/RPLC/IEC

BACKGROUND

Food safety has always been a great concern, and the detection of additives is vital to ensuring food safety. Therefore, there is a necessity to develop a method that can quickly and efficiently separate and detect additives in food. High performance liquid chromatography is widely used in the analysis and testing of food additives. Ionic liquids have attracted wide attention in the preparation of high performance liquid chromatography stationary phases owing to their high stability, low vapor pressure and adjustable structure.

RESULTS

We developed a novel dicationic imidazole ionic liquid stationary phase for the simultaneous determination of organic preservatives (sodium benzoate, potassium sorbate) and inorganic preservatives (nitrate and nitrite) in foodstuffs under mixed-mode chromatography. The method had the advantages of easy operation, high reproducibility, good linearity and precision. In the detection of these four preservatives, the limit of detection ≤0.4740 mg⋅L-1 and the limit of quantification ≤1.5800 mg⋅L-1. The intra-day and inter-day precision were less than 4.02%, and the recovery rate was 95.90∼100.19 %. At the same time, we also characterized the stationary phase, explored the mechanism and evaluated the chromatographic performance. The stationary phase was able to operate under the mixed mode of reversed phase/hydrophilic interaction/ion exchange chromatography, and it was capable of separating hydrophilic substances, hydrophobic substances, acids, and inorganic anionic substances with good separation efficiency and had high column efficiency.

SIGNIFICANCE

In summary, the stationary phase has a promising application in the routine analysis of organic and inorganic preservatives in food. In addition, the stationary phase has good separation ability for hydrophilic, hydrophobic, ionic substances and complex samples, making it a prospective material for chromatographic separation.

A liquid chromatography-tandem mass spectrometry method for comprehensive determination of metabolites in the purine pathway of rat plasma and its application in anti-gout effects of Lycium ruthenicum Murr

It has been proved that purine metabolites are implicated in various biological syndromes and disorders. Therefore, the realization of panoramic detection of purine metabolites will be of great significance to the pathogenesis of purine metabolic disorders. In the present study, an ultra-high performance liquid chromatography with tandem mass spectrometry method was developed for the comprehensive quantification of purine metabolites in rat plasma. The 17 purine metabolites were separated and quantified in the short running time of 15 min. The proposed method was strictly validated by applying SeraSub solution as a matrix and proved to be linear (R2 ≥ 0.9944), accurate (the recoveries of all analytes ranged from 85.3% to 103.0%, with relative standard deviation values ≤ 9.3%), and precise (the intra- and inter-day precisions were less than 10.8% and 12.4%, respectively). The method was then successfully applied to the qualification of the endogenous purine metabolites in acute gouty arthritis rats, as well as colchicine and anthocyanin-intervened rats. Results showed that uric acid, xanthine, hypoxanthine, and xanthine were considered the key factors of acute gouty arthritis. The established method and measurement of purines in rat plasma might help the investigation of the action mechanisms between purine disorders and related diseases.

The integrated metabolomics and sensory analyses unravel the peculiarities of mountain grassland-based cheese production: The case of Parmigiano Reggiano PDO

Untargeted metabolomics based on ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry was combined with sensory analysis to provide new insights into the impact of the feeding system from mountain regions (grassland deriving from permanent meadows) on the chemical fingerprint of Parmigiano Reggiano PDO hard cheese. In the framework of a representative investigation, two different ripening times (12 and 24 months) were also considered. Multivariate statistics allowed discriminating cheese samples from different feeding regimens according to their metabolomics signatures. Interestingly, mountain grassland-based cheese samples were characterized by a more favourable fatty acid profile, recording also feed-derived compounds (such as terpenoids and linoleic acid derivatives) potentially associated with both beneficial effects on human health and sensory properties. According to the sensory analysis, the impact of herbs and grass enhanced the colour and retro-olfactive complexity of Parmigiano Reggiano PDO cheese, with spicy, umami and intense vegetal aromatic notes representing distinctive features.

Application of a HPLC-Q/TOF method with post-column compensation for separation and identification of polar impurities in Cytidine disodium triphosphate for injection

Background:

Cytidine Disodium Triphosphate (CTP-2Na) for injection is mainly used for treating nervous system diseases. Currently, there are few studies focused on the separation and identification of polar impurities in CTP-2Na for injection, which is important for ensuring drug safety and efficacy.

Objective:

The study aimed to establish an HPLC-Q/TOF method for the separation and identification of polar impurities in CTP-2Na for injection.

Methods:

Chromatographic separation was achieved on a Waters Atlantis T3 column using 5 mM aqueous ammonium acetate solution as the mobile phase in an isocratic elution mode. A postcolumn compensation technology was used to improve the ionization efficiency of impurities in the spray chamber.

Results:

Three polar impurities (disodium cytidine tetraphosphate, disodium cytidine diphosphate, disodium cytidine monophosphate) were detected in CTP-2Na for injection. The former one is probably the overreaction product during the production of CTP-2Na, the latter two were reported as degradation products. The fragmentation patterns of cytidine phosphate compounds in negative ion mode are summarized.

Conclusion:

This study provides a good reference for the separation and identification of polar impurities in nucleotide drugs.

An Overview of Pretreatment and Analysis of Nucleotides in Different Samples (Update since 2010)

Nucleotides, which are important low-molecular-weight compounds present in organisms, are precursors of nucleic acids and participate in various regulatory and metabolic functions. Sensitive and valid methods for monitoring and determining nucleotides and nucleosides in different samples are urgently required. Due to the presence of numerous endogenous interferences in complex matrices and the high polarity of the molecules of the phosphate moiety, the determination of nucleotide content is challenging. This review summarizes the pretreatment and analysis methods of nucleotides in different samples. Advanced pretreatment methods, including different microextraction methods, solid-phase extraction based on novel materials, QuEChERS, are clearly displayed, and continuous progress which has been made in LC, LC-MS/MS and capillary electrophoresis methods are discussed. Moreover, the strengths and weaknesses of different methods are discussed and compared. Highlight:Advanced pretreatment and detection methods of nucleotides were critically reviewed.Microextraction technology was one of the trends of nucleotides pretreatment in the future.Applications of novel materials and supercritical fluid were highlighted.The evolution and advance of HRMS analyzers were in detailed.

Preparation of a boronate-affinity monolithic column for adsorption of nucleosides

Chitosan is a considerably versatile and promising biomaterial and can easily form a 3D hierarchical porous scaffold. In this work, a novel boronate-affinity monolithic column modified with a boronic acid-chitosan complex was prepared and characterized by different methods such as Fourier transform infrared spectroscopy, scanning electron microscopy, thermal gravimetric analysis, specific surface area analysis and pore size distribution analysis. The synthesized monolithic column was used for polymer monolithic microextraction combined with high performance liquid chromatography for the simultaneous determination of cytidine, uridine, inosine, and guanosine in milk powder samples. Several parameters affecting extraction efficiency, including the eluent proportion, eluent flow rate, sample flow rate, sample volume, and sample pH were investigated. The boronate-affinity monolithic column showed high enrichment ability due to the selective formation of cyclic borate esters between nucleosides and boronic acid groups at high pH and the release of cyclic borates at low pH values. Under the optimum operating conditions, the linear range was 0.1-50 μg mL^-1, and the correlation coefficients were in the range of 0.9993-0.9994. The LOD and LOQ were in the range of 0.0027-0.0034 and 0.0090-0.011 μg mL^-1, respectively. In addition, the results of recovery and relative standard deviation were satisfactory.

Anti-Microbiological, Anti-Hyperglycemic and Anti-Obesity Potency of Natural Antioxidants in Fruit Fractions of Saskatoon Berry

The aim of the present work was to evaluate for content of phytochemicals (monophosphate nucleotides, free amino acids, polyphenols), and for anti-microbiological, anti-diabetic (ability to inhibit pancreatic lipase, α-glucosidase, and α-amylase), and antioxidant activities in seven selected fruit and fruit fractions of Amelanchier alnifolia. Most of the fruit and fruit fractions analyzed in this study have not been examined in this respect until now. The content of monophosphate nucleotides and free amino acids were tested by ultra-performance liquid chromatography coupled with photodiode array detector and electrospray ionization-mass spectrometry (UPLC-PDA-ESI-MS). The distribution of the examined compounds and biological activity differed significantly depending on the tested fruit and parts of the fruit. Cultivars “Smoky” and “Thiessen” had a high content of essential free amino acids, monophosphate nucleotides, and the highest antioxidant activity. They were also accountable for the high ability to inhibit Enterococcus hirae (anti-bacterial activity), of activity toward α-amylase, α-glucosidase, and pancreatic lipase. Moreover, the fruit peel was abundant in polyphenolic compounds and showed the highest antioxidative activity, which were strongly correlated with each other. In addition, the peel was characterized by a high concentration of monophosphate nucleotides, free amino acids, and were responsible above all for the strong ability to inhibit pancreatic lipase enzymes contributing to the development of obesity. The seeds were rich in uridine 5’-monophosphate, and total essential and non-essential free amino acids, whose contents correlated with the inhibitory activity toward α-amylase and α-glucosidase. The fruit flesh showed a high content of total free amino acids (hydroxy-L-proline, O-phosphoethanolamine, L-citruline). There was a positive correlation between antioxidant capacity and the content of polyphenolic compounds, nucleotide, and ability to inhibit pancreatic lipase, and between anti-hyperglycemic and free amino acids in fruits and fruit fractions. Therefore, the tested fruit of A. alnifolia and their fractions could be essential ingredients of new functional products and/or probiotic food.

Metabolic Profiling of Water-Soluble Compounds from the Extracts of Dark Septate Endophytic Fungi (DSE) Isolated from Scots Pine (Pinus sylvestris L.) Seedlings Using UPLC-Orbitrap-MS

Endophytes are microorganisms living inside plant hosts and are known to be beneficial for the host plant vitality. In this study, we isolated three endophytic fungus species from the roots of Scots pine seedlings growing on Finnish drained peatland setting. The isolated fungi belonged to dark septate endophytes (DSE). The metabolic profiles of the hot water extracts of the fungi were investigated using Ultrahigh Performance Liquid Chromatography with Diode Array Detection and Electron Spray Ionization source Mass Spectrometry with Orbitrap analyzer (UPLC-DAD-ESI-MS-Orbitrap). Out of 318 metabolites, we were able to identify 220, of which a majority was amino acids and peptides. Additionally, opine amino acids, amino acid quinones, Amadori compounds, cholines, nucleobases, nucleosides, nucleotides, siderophores, sugars, sugar alcohols and disaccharides were found, as well as other previously reported metabolites from plants or endophytes. Some differences of the metabolic profiles, regarding the amount and identity of the found metabolites, were observed even though the fungi were isolated from the same host. Many of the discovered metabolites have been described possessing biological activities and properties, which may make a favorable contribution to the host plant nutrient availability or abiotic and biotic stress tolerance.

A rapid UHPLC-HILIC method for algal guanosine 5'-diphosphate 3'-diphosphate (ppGpp) and the potential separation mechanism

A fast and facile hydrophilic interaction liquid chromatography (HILIC) method was developed and applied to quantify physiologically important ppGpp and its analogues in a tough sample, the astaxanthin-accumulating alga Hameatococcus pluvialis. The method is able to analyze simultaneously seven nucleotides, including ppGpp at the order of pmol g^-1 cells within 12 min. Mechanism on the elution order was investigated. It was found that 1) phosphate salt competed for the amide groups on the HILIC column with the phosphate groups of the nucleotides; 2) intramolecular hydrogen bonds might contribute to the elution order by offsetting and reducing the number of free hydrogen acceptor/donor of the nucleotide molecules interacting with the amide groups. This is the first HILIC method for ppGpp, which is feasible and applicable to a wide range of samples, especially tough samples, e.g., algae and plants.

Capillary electrophoresis coupled to mass spectrometry employing hexafluoro-2-propanol for the determination of nucleosides and nucleotide mono-, di- and tri-phosphates in baby foods

The present work describes a method for the simultaneous determination of unmodified nucleosides and nucleotide mono-, di- and tri-phosphates by capillary electrophoresis coupled to mass spectrometry (CE-MS). The use of hexafluoro-2-propanol (HFIP) in the separation medium, and as an additive to the sheath liquid of the electrospray interface (ESI), generated a highly efficient and sensitive method. Instrumental limits of detection in the range of 14-53ngmL^-1 for nucleosides and 7-23, 20-49 and 64-124ngmL^-1 for nucleotide mono-, di-, and tri-phosphates, respectively, were found. Sample treatment involved diluting an aliquot of baby food with ultra-high quality water and applying centrifugation-assisted ultrafiltration (CUF). The proposed method was validated and used to analyse a variety of baby food samples (16 in total) such as fish, meat, fruits, and baby dairy desserts that may endogenously contain these analytes.

Analysis of Intra- and Extracellular Levels of Purine Bases, Nucleosides, and Nucleotides in HepG2 Cells by High-performance Liquid Chromatography

To evaluate cellular uptake and purine transport, we developed a high-performance liquid chromatography method for intra- and extracellular purine quantification. Our aim was to develop an effective method for simultaneously quantifying the substrate and metabolites with high sensitivity. C18 columns from different manufacturers were tested for simultaneous quantification of 22 different purine bases, nucleosides, and nucleotides. We used a YMC-Triart C18 column. The analysis conditions, including extraction solutions for the cells and cell culture medium, were optimized to achieve good quantification. Linearity, accuracy, determination limits, and recovery were assessed and showed good performance. The developed HPLC method was successfully applied to the qualitative analysis of 22 different intra- and extracellular purines, demonstrating that it is useful for studying the overall pattern of purine metabolism. This method could also be useful for evaluating metabolic dynamics of purines under a variety of stimulatory conditions of culture cells.

Determination of nucleosides and nucleotides in baby foods by hydrophilic interaction chromatography coupled to tandem mass spectrometry in the presence of hydrophilic ion-pairing reagents

In this work we propose a rapid and efficient method for the joint determination of nucleosides and nucleotides in dairy and non-dairy baby foods based on hydrophilic interaction chromatography coupled to tandem mass spectrometry in the presence of diethylammonium (DEA) as a hydrophilic ion-pairing reagent (IP-HILIC-MS/MS). Sample treatment of the baby food included dilution with water and centrifugal ultrafiltration (CUF) with an additional washing step that notably improved the global performance of the process. Later dilution of the extract with acetonitrile allowed adequate separation in the HILIC system. With the proposed treatment, we obtained extraction recoveries higher than 80% and, additionally, no matrix effects were observed. The CUF-IP-HILIC-MS/MS method was validated according to the 2002/657/EC decision and was used for the quantification of nucleotides and nucleosides in sixteen samples of commercial baby foods.

Hydrophilic interaction chromatography coupled to tandem mass spectrometry in the presence of hydrophilic ion-pairing reagents for the separation of nucleosides and nucleotide mono-, di- and triphosphates

A fast and efficient method for the simultaneous separation of highly polar compounds, in this case nucleosides and nucleotide mono-, di- and triphosphates, using hydrophilic interaction chromatography coupled with tandem mass spectrometry (HILIC-MS/MS) is proposed. This new separation method revealed the possibilities of the formation of hydrophilic ion-pairing compounds. Three stationary phases (HILIC XBridge-Amide, HILIC-CoreShell and ZIC-HILIC) were assayed for the separation of 20 target analytes, and a detailed study of the composition of the mobile phase was made using different salts at different concentrations in a organic-rich mobile phase. We report that in order to prevent the adsorption of nucleotides on the LC-MS setup and to enhance their retention on the HILIC stationary phase, a mobile phase containing hexafluoro-2-propanol and different cations should be used. Four cations were evaluated: ammonium, diethylammonium, triethylammonium and tetrabutylammonium. The results revealed the formation of an ionic-association compound between the phosphorylated analytes and the cationic ion-pairing reagents, whose retention increased with the polarity of the cationic ion-pairing reagent. HILIC XBridge-Amide was found to be the most suitable column for the separation of these analytes, and the optimized mobile phase consisted of an ACN/UHQ water mixture (3min of isocratic elution using 82:18%, v/v and then a fast gradient from 18% to 22% of water) with 100mM hexafluoro-2-propanol and 50mM diethylamine (w(w)pH 9-w(s)pH 10). In a total analysis time of 8min, good results were achieved in terms of resolution. Under these optimum conditions, a further comprehensive study of the retention mechanism was carried out.

Evaluation of umami taste in mushroom extracts by chemical analysis, sensory evaluation, and an electronic tongue system

Seventeen edible mushrooms commercially available in Korea were analysed for their umami taste compounds (5'-nucleotides: AMP, GMP, IMP, UMP, XMP; free amino acids: aspartic, glutamic acid) and subjected to human sensory evaluation and electronic tongue measurements. Amanita virgineoides featured the highest total 5'-nucleotide content (36.9 ± 1.50 mg/g), while monosodium glutamate-like components (42.4 ± 6.90 mg/g) were highest in Agaricus bisporus. The equivalent umami concentration (EUC) ranged from 1.51 ± 0.42 to 3890 ± 833 mg MSG/g dry weight; most mushrooms exhibited a high umami taste. Pleurotus ostreatus scored the highest in the human sensory evaluation, while Flammulina velutipes obtained the maximum score in the electronic tongue measurement. The EUC and the sensory score from the electronic tongue test were highly correlated, and also showed significant correlation with the human sensory evaluation score. These results suggest that the electronic tongue is suitable to determine the characteristic umami taste of mushrooms.

Quantitation of endogenous nucleoside triphosphates and nucleosides in human cells by liquid chromatography tandem mass spectrometry

Nucleosides and nucleoside triphosphates are the building blocks of nucleic acids and important bioactive metabolites, existing in all living cells. In the present study, two liquid chromatography tandem mass spectrometry methods were developed to quantify both groups of compounds from the same sample with a shared extraction procedure. After a simple protein precipitation with methanol, the nucleosides were separated with reversed phase chromatography on an Atlantis T3 column while for the separation of the nucleoside triphosphates, an anion exchange column (BioBasic AX) was used. No addition of ion pair reagent was required. A 5500 QTrap was used as analyzer, operating as triple quadrupole. The analytical method for the nucleoside triphosphates has been validated according to the guidelines of the US Food and Drug Administration. The lower limit of quantification values were determined as 10 pg on column (0.5 ng/mL in the injection solution) for deoxyadenosine triphosphate and deoxyguanosine triphosphate, 20 pg (1 ng/mL) for deoxycytidine triphosphate and thymidine triphosphate, 100 pg (5 ng/mL) for cytidine triphosphate and guanosine triphosphate, and 500 pg (25 ng/mL) for adenosine triphosphate und uridine triphosphate respectively. This methodology has been applied to the quantitation of nucleosides and nucleoside triphosphates in primary human CD4 T lymphocytes and macrophages. As expected, the concentrations for ribonucleosides and ribonucleoside triphophates were considerably higher than those obtained for the deoxy derivatives. Upon T cell receptor activation, the levels of all analytes, with the notable exceptions of deoxyadenosine triphosphate and deoxyguanosine triphosphate, were found to be elevated in CD4 T cells.

Determination and profiling of purines in foods by using HPLC and LC-MS

Purines in food are known to raise serum uric acid levels. We determined the purine content of sweet potato and beef by high-performance liquid chromatography and liquid chromatography-mass spectrometry. The purine content of the samples was 118-1,034 μmol/100 g. The total purine content was also divided into purine bases, nucleosides, nucleotides, and nucleic acids. Our results suggest that differences in total purine content and in the ratio of purine types between vegetables and beef cause a difference in elevation of serum uric acid levels.

Assessment of capillary anion exchange ion chromatography tandem mass spectrometry for the quantitative profiling of the phosphometabolome and organic acids in biological extracts

Metabolic profiling has become an important tool in biological research, and the chromatographic separation of metabolites coupled with mass spectrometric detection is the most frequently used approach for such studies. The establishment of robust chromatographic methods for comprehensive coverage of the anionic metabolite pool is especially challenging. In this study, the development of a capillary ion exchange chromatography (capIC) - negative ESI tandem mass spectrometry (MS/MS) workflow for the quantitative profiling of the phosphometabolome (e.g., sugar phosphates and nucleotides) is presented. The chromatographic separation and MS/MS conditions were optimized, and the precision of repetitive injections and accuracy in terms of error percentage to true concentration were assessed. The precision is excellent for a capillary flow system with an average CV% of 8.5% for a 50-fmol standard injection and in the lower 2.4-4.4% range for higher concentrations (500-7,500 fmol). The limit of detection (LOD) ranges from 1 to 100 nM (5-500 fmol injected on column), and the limit of quantitation (LOQ) ranges from 1 to 500 nM (5-2,500 fmol injected on column). A fast gradient method with the injection of 50% methanol in water between analytical samples is needed to eliminate carry-over and ensure optimal re-equilibration of the column. Finally, the quantitative applicability of the system was tested on real biological matrices using the constant-volume standard addition method (SAM). Extracts of the human kidney Hek293 cell line were spiked with increasing concentrations of standards to determine the concentration of each metabolite in the sample. Forty-four metabolites were detected with an average uncertainty of 4.1%. Thus, the capIC-MS/MS method exhibits excellent selectivity, sensitivity and precision for the quantitative profiling of the phosphometabolome.

Comprehensive quantitative analysis of purines and pyrimidines in the human malaria parasite using ion-pairing ultra-performance liquid chromatography-mass spectrometry

Targeted metabolite profiling has aided in the understanding of a variety of biological processes in the malaria parasite as well as in drug discovery. A fast and sensitive analytical method, based on ion-pairing reversed phase ultra-high performance liquid chromatography tandem mass spectrometry (IP-RP-UPLC-MS/MS), was optimized for the simultaneous analysis of intracellular levels of 35 purine and pyrimidine nucleobases, nucleosides, and nucleotides. This analytical method allows for chromatographic separation of highly polar metabolites using reverse phase chemistry within 15 min. The analytical performance of the method was evaluated and successfully applied to the quantification of purines and pyrimidines in Plasmodium falciparum and its host cell, the human erythrocyte. In addition, this method can be customized to include other related metabolites such as NADPH and NADP, among others.

Mass spectrometry analysis of nucleosides and nucleotides

Mass spectrometry has been widely utilised in the study of nucleobases, nucleosides and nucleotides as components of nucleic acids and as bioactive metabolites in their own right. In this review, the application of mass spectrometry to such analysis is overviewed in relation to various aspects regarding the analytical mass spectrometric and chromatographic techniques applied and also the various applications of such analysis.

Fully validated assay for the quantification of endogenous nucleoside mono- and triphosphates using online extraction coupled with liquid chromatography-tandem mass spectrometry

An analytical method coupling online solid-phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed to quantify 16 endogenous nucleoside mono- and triphosphates in cellular samples. Separation was achieved on a porous graphitic carbon (PGC) column without ion-pairing agent in the mobile phase. Low levels of the ion-pairing agent diethylamine (DEA) added to the reconstitution solution were necessary to prevent peak tailing of nucleoside triphosphates. The mass spectrometer, a triple quadrupole with an electrospray ionisation source, was operated in positive mode. Two multiple reaction monitoring (MRM) segments were programmed, each an internal standard. Extraction and separation of nucleoside mono- and triphosphates were obtained within 20 min. The total duration of a single run was 37 min. Calibration curves, performed with labelled nucleotides added to the sample matrix, ranged from 0.29 to 18.8 pmol injected for deoxyribonucleotides and from 3.9 to 3,156 pmol for ribonucleotides. Accuracy did not deviate more than -14.6 and 10.2 % from nominal values for all compounds at all levels. CV results were all lower than 17.0 % for the LLOQ level and 14.6 % for the other levels. Quality control (QC) samples were also in agreement with acceptance criteria, except for the lower QC of GMP. Ion suppression, matrix effect, extraction recoveries and stability were assessed. After validation, the method was applied to the evaluation of the effects of gemcitabine and hydroxyurea on nucleotide pools in Messa cells.

Determination of nucleotides in infant milk formulas using novel dendrimer ion-exchangers

The main aim of the present study was to develop a method for the separation of 5'-monophosphate nucleotides with the use of ion chromatography. Novel dendrimeric stationary phases were used for this purpose. The effects exerted by the type of anion-exchanger support (silica or polymeric) and the number of stationary phase layers on nucleotide retention were studied. A silica-based dendrimeric anion-exchanger was most suitable for analyzing the studied compounds. An increase in the number of layers enhanced nucleotide retention inside the column. The separation efficiency of the studied compounds was tested at various concentrations of the mobile phase buffer. At higher phosphate buffer concentrations, nucleotide resolutions were achieved in 6min. Three commercially available infant milk formulas were analyzed to verify the applicability of the studied method. Solid phase extraction was used for sample cleanup and concentration. The limit of quantification of nucleotides was 0.40μg/ml, and the method was linear in the concentration range of 0.40-20.6μgml(-1.)

Separation of nucleotides by hydrophilic interaction chromatography using the FRULIC-N column

A stationary phase composed of silica-bonded cyclofructan 6 (FRULIC-N) was evaluated for the separation of four cyclic nucleotides, six nucleoside monophosphates, four nucleoside diphosphates, and five nucleoside triphosphates via hydrophilic interaction chromatography (HILIC) in both isocratic and gradient conditions. The gradient conditions gave significantly better separations by narrowing peak widths. Sixteen out of nineteen nucleotides were baseline separated on the FRULIC-N column in one run. Unlike other known HILIC stationary phases, there can be dual-retention mechanisms unique to this media. Traditional hydrogen bonding/dipolar interactions can be supplemented by dynamic ion interaction effects for anionic analytes. This occurs because the FRULIC-N stationary phase is able to bind certain buffer cations. The extent of the ion interaction is tunable, in comparison to stationary phases with embedded charged groups, where the inherent ionic properties are fixed. The best mobile phase conditions were determined by varying the organic modifier (acetonitrile) content, as well as salt type/concentration and electrolyte pH. The thermodynamic characteristic of the FRULIC-N column was investigated by evaluating the column temperature effect on retention and utilizing van't Hoff plots. This study shows that there is a greater entropic contribution for the retention of nucleotide di and triphosphates, whereas there is a greater enthalphic contribution for the cyclic nucleotides with the FRULIC-N column.

Analysis of nucleosides and nucleotides in infant formula by liquid chromatography-tandem mass spectrometry

A method for the simultaneous analysis of nucleosides and nucleotides in infant formula using reversed-phase liquid chromatography-tandem mass spectrometry is described. This approach is advantageous for compliance testing of infant formula over other LC-MS methods in which only nucleotides or nucleosides are measured. Following sample dissolution, protein was removed by centrifugal ultrafiltration. Chromatographic analyses were performed using a C18 stationary phase and gradient elution of an ammonium acetate/bicarbonate buffer, mass spectrometric detection and quantitation by a stable isotope-labelled internal standard technique. A single laboratory validation was performed, with spike recoveries of 80.1-112.9% and repeatability relative standard deviations of 1.9-7.2%. Accuracy as bias was demonstrated against reference values for NIST1849a certified reference material. The method has been validated for the analysis of bovine milk-based, soy-based, caprine milk-based and hydrolysed milk protein-based infant formulae.

Effect of mobile phase pH on the retention of nucleotides on different stationary phases for high-performance liquid chromatography

The main aim of the present investigation was to study the retention and separation of eight nucleotides with the use of seven stationary phases in RP HPLC mode. Two octadecyl columns were used; however, aminopropyl, alkylamide, cholesterol, alkyl-phosphate, and phenyl were also studied. Special attention was paid to the mobile phase buffer pH, since it appears that this factor is very influential in the case of chromatographic separation of nucleotides. The retention of nucleotides was greater for mobile phase pH 4.0 in comparison with pH 7.0 (except for octadecyl and phenyl packing). This is a consequence of protonization of polar groups present on the stationary phase surface. It was proved that aminopropyl, alkyl phosphate, alkylamide packing materials are not suitable for the resolution of nucleotides. On the other hand, cholesterol and phenyl stationary phases are alternatives for conventional octadecyl phases. Application of cholesterol packing allows separation of small, polar nucleotides, which is impossible to achieve in the case of octadecyl phase. Moreover, a phenyl support allows separation of nucleotides in a shorter time in comparison with octadecyl packing.

Quantitation of intracellular purine intermediates in different Corynebacteria using electrospray LC-MS/MS

Intermediates of the purine biosynthesis pathway play key roles in cellular metabolism including nucleic acid synthesis and signal mediation. In addition, they are also of major interest to the biotechnological industry as several intermediates either possess flavor-enhancing characteristics or are applied in medical therapy. In this study, we have developed an analytical method for quantitation of 12 intermediates from the purine biosynthesis pathway including important nucleotides and their corresponding nucleosides and nucleobases. The approach comprised a single-step acidic extraction/quenching procedure, followed by quantitative electrospray LC-MS/MS analysis. The assay was validated in terms of accuracy, precision, reproducibility, and applicability for complex biological matrices. The method was subsequently applied for determination of free intracellular pool sizes of purine biosynthetic pathway intermediates in the two Gram-positive bacteria Corynebacterium glutamicum and Corynebacterium ammoniagenes. Importantly, no ion pair reagents were applied in this approach as usually required for liquid chromatography analysis of large classes of diverse metabolites.

Mass spectrometry based analysis of nucleotides, nucleosides, and nucleobases--application to feed supplements

In this work, accurate MS-based methods for quantitative profiling of nucleotides, nucleosides, and nucleobases in yeast extracts used as additives in animal feedstuff are presented. Reversed-phase chromatography utilizing a stationary phase compatible with 100% aqueous mobile phases resulted in superior analytical figures of merit than HILIC or ion-pair reversed-phase separation. The novel separation method was combined with both molecular and elemental mass spectrometry. By use of RP-LC-MS-MS, excellent limits of detection <1 μmol L(-1) could be obtained for all the compounds investigated. The elemental speciation analysis approach enabled determination of nucleotides by phosphorus detection. Sensitivity of LC-ICP-MS was 1-2 orders of magnitude lower than that of LC-MS-MS. Quantitative analysis of yeast products using complementary MS detection furnished values in good agreement.

Simultaneous quantification of 12 different nucleotides and nucleosides released from renal epithelium and in human urine samples using ion-pair reversed-phase HPLC

Nucleotides and nucleosides are not only involved in cellular metabolism but also act extracellularly via P1 and P2 receptors, to elicit a wide variety of physiological and pathophysiological responses through paracrine and autocrine signalling pathways. For the first time, we have used an ion-pair reversed-phase high-performance liquid chromatography ultraviolet (UV)-coupled method to rapidly and simultaneously quantify 12 different nucleotides and nucleosides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, adenosine, uridine triphosphate, uridine diphosphate, uridine monophosphate, uridine, guanosine triphosphate, guanosine diphosphate, guanosine monophosphate, guanosine): (1) released from a mouse renal cell line (M1 cortical collecting duct) and (2) in human biological samples (i.e., urine). To facilitate analysis of urine samples, a solid-phase extraction step was incorporated (overall recovery rate ≥ 98 %). All samples were analyzed following injection (100 μl) into a Synergi Polar-RP 80 Å (250 × 4.6 mm) reversed-phase column with a particle size of 10 μm, protected with a guard column. A gradient elution profile was run with a mobile phase (phosphate buffer plus ion-pairing agent tetrabutylammonium hydrogen sulfate; pH 6) in 2-30 % acetonitrile (v/v) for 35 min (including equilibration time) at 1 ml min(-1) flow rate. Eluted compounds were detected by UV absorbance at 254 nm and quantified using standard curves for nucleotide and nucleoside mixtures of known concentration. Following validation (specificity, linearity, limits of detection and quantitation, system precision, accuracy, and intermediate precision parameters), this protocol was successfully and reproducibly used to quantify picomolar to nanomolar concentrations of nucleosides and nucleotides in isotonic and hypotonic cell buffers that transiently bathed M1 cells, and urine samples from normal subjects and overactive bladder patients.

Simultaneous determination of purine and pyrimidine metabolites in HPRT-deficient cell lines

Genetic mutations in the purine salvage enzyme, hypoxanthine-guanine phosphoribosyltransferase (HPRT), are known to cause Lesch-Nyhan syndrome and Kelley-Seegmiller syndrome. In patients, purine metabolism is different from that of normal persons. We have previously developed a method for simultaneously determining the concentration of purine and pyrimidine nucleosides and nucleotides. This system was applied to determine the concentrations of nucleosides and nucleotides in HPRT-deficient cell lines. The amount of inosine 5'-monophosphate (IMP) was different in Lesch-Nyhan syndrome, Kelley-Seegmiller syndrome, and control cell lines. The difference in the amount of IMP confirmed the mutation of the enzyme.