HPLC-fluorescence determination of amino acids in pharmaceuticals after pre-column derivatization with phanquinone

A multi-functional probe to discriminate Lys, Arg, His, Cys, Hcy and GSH from common amino acids

A smart probe to classify and differentiate basic amino acids, thiol-containing amino acids and GSH in selected environments.

Analysis of amino acid composition in proteins of animal tissues and foods as pre-column o-phthaldialdehyde derivatives by HPLC with fluorescence detection

Studies of protein nutrition and biochemistry require reliable methods for analysis of amino acid (AA) composition in polypeptides of animal tissues and foods. Proteins are hydrolyzed by 6M HCl (110°C for 24h), 4.2M NaOH (105°C for 20 h), or proteases. Analytical techniques that require high-performance liquid chromatography (HPLC) include pre-column derivatization with 4-chloro-7-nitrobenzofurazan, 9-fluorenyl methylchloroformate, phenylisothiocyanate, naphthalene-2,3-dicarboxaldehyde, 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate, and o-phthaldialdehyde (OPA). OPA reacts with primary AA (except cysteine or cystine) in the presence of 2-mercaptoethanol or 3-mercaptopropionic acid to form a highly fluorescent adduct. OPA also reacts with 4-amino-1-butanol and 4-aminobutane-1,3-diol produced from oxidation of proline and 4-hydroxyproline, respectively, in the presence of chloramine-T plus sodium borohydride at 60°C, or with S-carboxymethyl-cysteine formed from cysteine and iodoacetic acid at 25°C. Fluorescence of OPA derivatives is monitored at excitation and emission wavelengths of 340 and 455 nm, respectively. Detection limits are 50 fmol for AA. This technique offers the following advantages: simple procedures for preparation of samples, reagents, and mobile-phase solutions; rapid pre-column formation of OPA-AA derivatives and their efficient separation at room temperature (e.g., 20-25°C); high sensitivity of detection; easy automation on the HPLC apparatus; few interfering side reactions; a stable chromatography baseline for accurate integration of peak areas; and rapid regeneration of guard and analytical columns. Thus, the OPA method provides a useful tool to determine AA composition in proteins of animal tissues (e.g., skeletal muscle, liver, intestine, placenta, brain, and body homogenates) and foods (e.g., milk, corn grain, meat, and soybean meal).

Digestive recovery of sulfur-methyl-L-methionine and its bioaccessibility in Kimchi cabbages using a simulated in vitro digestion model system

BACKGROUND

Sulfur-methyl-L-methionine (SMM) has been known to provide various biological functions such as radical scavenging effect, inhibition of adipocyte differentiation, and prevention of gastric mucosal damage. Kimchi cabbages are known to be a major food source providing SMM but its bioaccessibility has not been studied. The objective of current study was to determine both the digestive stability of SMM and the amount released from Kimchi cabbages under a simulated in vitro digestion model system.

RESULTS

The in vitro digestion model system simulating a human gastrointestinal tract was carried out for measuring digestive recovery and bioaccessibility of SMM. SMM was quantified by using high-performance liquid chromatography with a fluorescence detector. Recovery of an SMM standard after digestion was 0.68 and 0.65% for fasted and fed conditions, respectively, indicating that the digestive stability of the SMM standard was not affected by dietary energy or co-ingested food matrix. The SMM standard was also significantly stable in acidic pH (P < 0.05). The bioaccessibility of SMM from Kimchi cabbages was measured under a fasted condition, resulted in 8.83, 14.71 and 10.88%, for salivary, gastric and small intestinal phases, respectively.

CONCLUSION

Results from our study suggest that SMM from Kimchi cabbages, a component of food sources, is more bioavailable than SMM by itself.

Highly sensitive and selective pre-column derivatization high-performance liquid chromatography approach for rapid determination of triterpenes oleanolic and ursolic acids and application to Swertia species: optimization of triterpenic acids extraction and pre-column derivatization using response surface methodology

Oleanolic acid (OA) and ursolic acid (UA) are the ubiquitous triterpenic acids in plant kingdom and have multiple biological effects. In the present study, a highly sensitive and selective method using a dual-sensitive probe 2-(5-benzoacridine)ethyl-p-toluenesulfonate (BAETS) as pre-column labeling reagent has been developed for rapid determination of the triterpenes OA and UA by HPLC with fluorescence detection (FLD) and online mass spectrometry identification. Response surface methodology as an efficient tool was employed to optimize the ultrasonic-assisted extraction of triterpenic acids from Swertia plants and the pre-column derivatization reaction, respectively, which ensured the highest triterpenic acids recoveries within the shortest extraction time and the sufficient labeling of the analyzed components. Fast separation of the isomers OA and UA could be achieved on a Hypersil BDS C8 column within 7 min. Both of OA and UA gave the good correlation coefficients of 0.9999. This developed method offered the satisfactory detection limits of 1.10 and 1.30 ng mL(-1) for UA and OA, respectively. When applied to Swertia species, it showed good reproducibility.

A sensitive fluorescence reagent, 2-[2-(7H-dibenzo[a,g]carbazol-7-yl)-ethoxy]ethyl chloroformate, for amino acids determination in Saussurea involucrate and Artemisia capillaris Thunb using high-performance liquid chromatography with fluorescence detection and identification with mass spectroscopy/electrospray ionization source

Recent researches shows that amino acids (AA) are not only cell signaling molecules but are also regulators of gene expression and the protein phosphorylation cascade. More precise analysis of AA composition is reckoned to be one of the most important applications in the biomedical and pharmaceutical fields. In this paper, we develop a sample, sensitive and mild method using 2-[2-(7H-dibenzo[a,g]carbazol-7-yl)-ethoxy]ethyl chloroformate (DBCEC) as A labeling reagent for AA determination by high-performance liquid chromatography (HPLC) with fluorescence detection (FLD) and identification with mass spectroscopy. The maximum excitation and emission wavelengths for DBCEC-AA derivatives were 300 and 395 nm, respectively. This method, in conjunction with a gradient elution, offered a baseline resolution of 20 AA on a reversed-phase Hypersil BDS C(18) column. LC separation for the derivatized AA showed good reproducibility, and all AA were found to give excellent linear responses with correlation coefficients > 0.9993. The calculated detection limits with a 25.0 fmol injection of each AA (at a signal-to-noise ratio of 3:1) ranged from 2.62 to 22.6 fmol. This method was applied to determine the AA composition in Saussurea involucrate and Artemisia capillaris Thunb. Meanwhile, this method exhibits a powerful potential for trace analysis of AA from biomedicine, foodstuff and other complex samples.

High-performance liquid chromatographic method for determination of amino acids by precolumn derivatization with 4-chloro-3,5-dinitrobenzotrifluoride

This work presents an high-performance liquid chromatography method for the determination of amino acids after precolumn derivatization with 4-chloro-3,5-dinitrobenzotrifluoride (CNBF) which can readily react with both primary and secondary amines. The precolumn derivatization conditions, including the CNBF concentration, reaction pH, temperature and reaction time were investigated for method optimization. In pH 9.0 borate buffer, the reaction of amino acids with CNBF was carried out at 60 degrees C for 30min, the optimized concentration of CNBF was 70mmol L(-1) and the molar ratio of amino acids to CNBF was 1:5.25. The chromatographic separation of 19 amino acids derivatives was performed on a Kromasil ODS C(18) column (250mm x 4.6mm, 5microm) with good reproducibility, and ultraviolet detection was applied at 260 nm. The mobile phase was a mixture of phase A (acetonitrile) and phase B (acetate buffer, acetonitrile, triethylamine; 82.8:17:0.2, pH 4.9), and the flow rate was 0.4mL min(-1). The separation of all the labeled amino acids was achieved within 45min at room temperature by gradient elution mode. The method linearity, calculated for each amino acid, had a correlation coefficient higher than 0.9979, in concentrations ranging from 9.60 to 3330.00 micromol L(-1). The detection limits of amino acids were 2.40-6.50micromol L(-1), at a signal-to-noise ratio of 3. The proposed method was applied for the determination of amino acids in beer with recoveries of 97.0-103.9% and relative standard deviations of 2.62-4.22%, respectively. This method showed good accuracy and repeatability that can be used for the quantification of amino acids in real samples.

2,7-Dimethyl-3,8-dinitrodipyrazolo[1,5-a:1′,5′-d]pyrazine-4,9-dione: A new labelling reagent for liquid chromatographic analysis of amino acids

The use of 2,7-dimethyl-3,8-dinitrodipyrazolo[1,5-a:1',5'-d]pyrazine-4,9-dione as pre-column reagent for LC analysis of amino acids is proposed. The compound reacts (30 min at 68 degrees C in presence of 0.04 M triethylamine in a dimethylsulfoxide-water mixture) with primary and secondary amino function and the stable resulting adducts can be chromatographed under reversed-phase conditions and detected at lambda=280 nm. The derivatization conditions were optimized by a series of experiments. The effect of temperature, triethylamine concentration and reagent on the reaction was investigated. The yield of the glycine derivative was found to be quantitative at a reagent amino acid molar ratio of about 6 by comparison with an authentic specimen of synthesized glycine adduct. Application of the method to quality control of commercially available oral polyaminoacid formulations is described.

Phanquinone as a suitable derivatization reagent in micellar electrokinetic chromatography and HPLC analysis of amino acids

Phanquinone (chemically: 4,7-phenanthroline-5,6-dione) was applied as an original precolumn derivatization reagent for amino acids followed by separation using MEKC with UV detection (240 nm). The derivatization reaction was carried out at 68 degrees C in the presence of aqueous phosphate buffer (pH 8.0) and it was found to be complete after 30 min. Twelve derivatized standard amino acids were separated in about 22 min under MEKC conditions using sodium cholate (250 mM) as the surfactant in phosphate buffer (20 mM, pH 9.0). The developed method was validated for the analysis of D,L-phosphoserine (D,L-p-Ser) and L-glutamine (L-Gln); good linearity (r > 0.999) was achieved in the calibration range of 0.25-2.5 micromol/mL. The sensitivity of the MEKC method (LOD 0.1 micromol/mL; LOQ 0.25 micromol/mL, RSD% <5.0%, n = 3) was found to be adequate for quantitation of amino acids in pharmaceuticals. Quantitative applications of the validated MEKC method were carried out by the analysis of commercially available oral polyaminoacid formulations (tablets and extemporaneous solutions) containing L-Gln and D,L-p-Ser; the obtained results were found to be in agreement with those from a validated reference RP-HPLC method.

Validated method forl-ornithine-l-aspartate analysis in human plasma by capillary electrophoresis

A rapid capillary electrophoresis method for routine determination of two amino acids, L-ornithine and L-aspartic acid, in human plasma is reported. The method runs automatically, requires a minimum of sample preparation and moreover includes no extensive extraction and no gradient or derivatization procedure. Analyses were performed on an uncoated silica capillary using buffer solution composed with 10 mM sodium tetraborate and 1 M sodium hydroxide (pH=10.0). A capillary electrophoresis P/ACE system equipped with UV detection (200 nm), an automatic injector, a fluid cooled cartridge and System Gold data station was used in this study. The total analysis time under these conditions was 8.0 min. The calibration curve was linear in the range 10-280 microg mL-1 for L-aspartic acid and 20-280 microg mL-1 for L-ornithine (for both amino acids, r=0.999). The method was validated by inaccuracy (bias) and precision (RSD) studies by analysing samples. The method was successfully applied to the quantitative determination of L-ornithine-L-aspartate in human plasma and could be useful for clinical and bioavailability investigations.

A novel method using high-performance liquid chromatography with fluorescence detection for the determination of betaxanthins

Betaxanthins are natural water-soluble yellow pigments present in plants of the order Caryophyllales. The native fluorescence of these compounds is extensively characterized in this work, with study of the fluorescent properties of 14 different betaxanthins. All the species showed a similar behavior, with excitation maxima between 463 and 475 nm and emission maxima between 506 and 515 nm. Thus, betaxanthins absorb light corresponding to the blue color and emit visible green light. Similarities in excitation and emission spectra point to the responsibility of betalamic acid in fluorescence. The influence of the amine moiety is discussed. For the first time fluorescent properties of betaxanthins are applied to the detection of these pigments after separation by high-performance liquid chromatography. Wavelengths used were 460 nm for excitation and 510 nm for emission, which were suitable for detecting the native fluorescence of all the pigments assayed. Calibration was performed in each case and it exhibited linearity within the range considered, at least 20 microM. The lowest detection limit was 100 nM, corresponding to betaxanthins derived from methionine sulfoxide and leucine. Fluorescence detection was applied to the quantification of betaxanthins present in Carpobrotus acinaciformis. The present work opens up new possibilities for the analysis of betaxanthins by improving existing protocols through fluorescence detection.

LC determination of leuprolide component amino acids in injectable solution by phanquinone pre-column derivatization labelling procedure

A sensitive LC method for the determination of leuprolide acetate component amino acids in injectable solution with fluorogenic pre-column derivatization has been developed. The derivatization reaction with phanquinone was optimised by a series of experiments. Histidine, arginine, serine, tryptophan, glutamic acid, tyrosine, methionine, isoleucine, leucine and phenylalanine were separated on a reversed-phase ODS column using as eluent a binary mixture of triethylammonium phosphate buffer-methanol, under gradient elution conditions. The derivatives were eluted in 30 min with good reproducibility. The hydrolysis reaction of the peptide was carried out at reflux with 12 N hydrochloric acid for 2 h 30 min. The intra-day accuracy of the entire procedure (hydrolysis, derivatization, LC separation) ranged from 80.5 to 109.5% of the nominal concentration of leuprolide acetate and the precision (%R.S.D.) was less than 5.8%; the inter-day accuracy was in the range 81.5-107.2% and corresponding R.S.D. values were less than 4.6%. The detection limits (signal-to-noise ratio=3) for the adducts are 30-800 fmol.