Min In Borate Buffer Research Articles

Determination of paroxetine in serum treated with simple pretreatment by pre‐column high‐performance liquid chromatography using 4‐(5,6‐dimethoxy‐2‐phthalimidinyl)‐2‐methoxyphenylsulfonyl chloride as a fluorescent labeling reagent

The therapeutic drug monitoring of paroxetine could be used to optimize the pharmacological treatment of depressed patients. A simple and sensitive high-performance liquid chromatography procedure was developed for the determination of paroxetine in serum. After simple pretreatment of serum (50 μL) with acetonitrile and o-phthalaldehyde, paroxetine was derivatized with 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride at 70°C for 20 min in borate buffer (0.1 mol/L, pH 8.0) to produce a fluorescent product. The derivative was separated on a reversed-phase column at 40°C for stepwise elution with (A) acetic acid (10 mmol/L) and (B) acetonitrile. The flow rate was 1.0 mL/min. The fluorescence intensity was monitored at excitation and emission wavelengths of 320 and 400 nm, respectively. The within-day and day-to-day relative standard deviations were 3.0-3.4 and 2.7-8.3%, respectively. The detection limit of paroxetine was 8.3 fmol at a signal-to-noise ratio of 3. As the proposed method that only requires a small quantity of serum (50 μL) is simple, sensitive and reproducible, it would be useful for clinical and biochemical research as well as drug monitoring.

Micellar electrokinetic chromatographic analysis for in vitro accumulation of anthracyclines enhanced by inhibitors of cell membrane transporter-proteins in cancer cells

Cell membrane transporter-proteins have been partly implicated in lowering the accumulation of drugs in cancer cells, leading to multidrug resistance (MDR). Two cancer cell lines, A549 and RDES, were continuously exposed to subclinical concentration (250 nM) of anthracyclines and micellar electrokinetic chromatography was used to investigate their in vitro accumulation after treatment with inhibitors of membrane transporter-proteins. The four anthracylines [doxorubicin (DOX), epirubicin (EPI), daunorubicin (DNR), and idarubicin (IDA)] were separated within a short analysis time of less than 15 min in borate buffer (80 mM, pH 9.22) containing sodium taurodeoxycholate (35 mM), 2-hydroxypropyl-γ-cyclodextrin (3.5% wt/v), and sodium dodecylsulfate (20 mM). Laser-induced fluorescence was used for detection of the anthracyclines. Three inhibitors, verapamil, cyclosporine A and probenecid, were examined by adding each inhibitor independently or two inhibitors simultaneously to the culture medium. It was found that independent use of each inhibitor leads to more efficient accumulation than combined use of verapamil and probenecid. In addition, the results show that effect of inhibitors on the accumulation of anthracyclines depended on type of cell: in RDES, inhibitors enhanced accumulation of all four anthracyclines, while in A549, inhibitors showed different accumulation behavior for each anthracycline. Generally higher accumulation of anthracyclines was observed in RDES cells than A549, as evidenced by dead cells (7-16%) after 24 h of continuous exposure to subclinical concentration.

Sensitive determination of carnosine in urine by high-performance liquid chromatography using 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride as a fluorescent labeling reagent

A simple and highly sensitive high-performance liquid chromatography procedure was developed for the determination of carnosine in urine. Carnosine was derivatized with 4-(5,6-dimethoxy-2-phthalimidinyl)-2-methoxyphenylsulfonyl chloride at 70 degrees C for 15 min in borate buffer (20 mmol l(-1), pH 9.0) to produce fluorescent sulfonamides. After hydrolysis of the reaction mixture with formic acid at 100 degrees C for 15 min, the fluorescent derivative of carnosine was separated on a reversed-phase column with a linear gradient elution using solvents of (A) acetate buffer (0.1 mmol l(-1), pH 7.0) and (B) acetonitrile at a flow-rate of 1.0 ml/min and was detected at excitation and emission wavelengths of 318 and 400 nm, respectively. The detection limit of carnosine was 4 fmol at a signal-to-noise ratio of 3. The within-day and day-to-day relative standard deviations were 2.7-4.6% and 0.4-5.2%, respectively. The concentration of carnosine in normal human urine was found to be 4.6-125 nmol (mg creatinine)(-1) (mean+/-SD: 21.6+/-26.6 nmol (mg creatinine)(-1), n=20).

Quantification of biogenic amines in human plasma based on the derivatization with N‐hydroxy‐succinimidyl fluorescein‐O‐acetate by high‐performance liquid chromatography

An HPLC method for the determination of biogenic amines based on the precolumn derivatization with N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA) has been developed. The derivatization was performed at 45 degrees C for 30 min in borate buffer (pH 8.0). The derivatives were separated on a ZORBAX Eclipse XDB-C8 column (150 mm x 4.6 mm id; 5 mum) and monitored by fluorescence detection (excitation, 469 nm; emission, 512 nm). The LODs (S/N = 3) for spermine, spermidine, putrescine, cadaverine, and phenethylamine were 0.4, 0.2, 0.3, 0.5, and 0.4 nM, respectively. The developed method has been successfully applied to the determination of biogenic amines in human plasma of three healthy volunteers and four cancer patients. Average recoveries for plasma samples ranged from 94 to 106% and coefficients of variation ranged from 1.8 to 4.6%. Deproteinization of plasma was accomplished with ACN to precipitate interfering substances and the centrifuged supernatant was used directly for analysis.

Liquid chromatographic analysis of phosphoamino acids at femtomole level using chemical derivatization with N-hydroxysuccinimidyl fluorescein- O-acetate

Phosphorylation of amino acid residues in proteins plays a major role in biological systems. In this paper, a reversed-phase high performance liquid chromatographic (HPLC) method based on chemical derivatization has been described for the separation and quantification of phosphoamino acids at femtomole level, using fluorimetric detection (FLD). The protocol involved pre-column derivatization of phosphoamino acids with N-hydroxysuccinimidyl fluorescein- O-acetate (SIFA) and subsequent separation on ZORBAX Eclipse XDB-C8 column. Several experimental factors that influenced derivatization and separation were carefully investigated. The derivatization was performed at 40 °C for 40 min in borate buffer (pH 8.5). Under the optimum conditions, phosphoserine (P-Ser), phosphothreonine (P-Thr) and phosphotyrosine (P-Tyr) were satisfactorily separated in 8 min. The detection limits (signal-to-noise ratio = 3) for the phosphoamino acids could reach 10–20 fmol, which was the lowest value reported for HPLC methods and comparable to those obtained by capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection methods. The proposed method has been validated and used to characterize the phosphoamino acids in the hydrolyzed phosphorylated protein samples. The results clearly demonstrated the potential of this technique to study phosphoamino acids as well as provided a new analytical methodology that should be applicable to the study of phosphorylation of protein in biological system.

Pre-column Derivatization High Performance Liquid Chromatography Tandem Mass Spectrometric Determination of Trace Level of Amino Acids in Rat Serum

A simple and sensitive method based on the derivatization of 20 amino acids with 1,2-benzo-3,4-dihydrocarbazole-9- ethyl chloroformate (BCEOC) as derivatization reagent on a reversed-phase Hypersil BDS C 18 column (4.6 mm × 200 mm, 5 μm) with a gradient elution followed by high performance liquid chromatography (HPLC) via fluorescence detection at 390 nm (excitation wavelength of 333 nm) and tandem mass spectrometric identification has been developed. Optimum derivatization, giving the corresponding stable fluorescent derivatives, was obtained by reacting amino acids with BCEOC at 40 ° for 10 min in borate buffer (pH 9.0) with four times excess of molar reagent. The linear range of 20 amino acids were 51.6 fmol–105.6 pmol, all correlation coefficients >0.9995, detection limits were 6.3–177.6 fmol (at signal to noise 3:1, S/N=3:1). The identification of amino acid derivatives was carried out by post-column tandem mass spectrometry with electrospray ion (ESI) source, and the MS/MS cleavage mode of representative tyrosine derivative was analyzed. Under all the above optimum experimental conditions, the contents of 20 amino acids in rat serum of 3 groups (A: Quiet, B: At exercising exhaust, C: 12 h after exercising exhaust) were determined. It was indicated that the contents of 20 amino acids in group B were obviously higher than those in group A, and the contents of amino acids of group C and group A were almost the same. The established method exhibited high sensitivity and excellent reproducibility, and provided a new technology for the determination of amino acids in rat serum.

Existence of low‐molecular‐weight thiols in Caenorhabditis elegans demonstrated by HPLC‐fluorescene detection utilizing 7‐chloro‐N‐[2‐(dimethylamino)ethyl]‐2,1,3‐benzoxadiazole‐4‐sulfonamide

A highly sensitive and simple method using HPLC-fluorescence detection with 7-chloro-N-[2-(dimethylamino)ethyl]-2,1,3-benzoxadiazole-4-sulfonamide (DAABD-Cl) as a fluorogenic reagent demonstrated the existence of the low-molecular-weight thiols in the extract of Caenorhabditis elegans (C. elegans). The method includes derivatization of the thiols with DAABD-Cl at 40 degrees C for 10 min in borate buffer (pH 9.0) containing TCEP, CHAPS and EDTA, separation of the derivatives on an ODS column and fluorometric determination of the derivatives at 510 +/- 15 nm with excitation at 400 +/- 15 nm. The identification of the thiols was made by HPLC-electrospray ionization mass spectrometry (LC-MS) following isolation of the derivatives using HPLC-fluorescence detection. Low-molecular-weight thiols were found to exist in the extract of C. elegans, such as cysteine, cysteinylglycine, gamma-glutamylcysteine, reduced glutathione and two other unidentified thiol compounds, confirming the existence of the 'glutathione cycle' in C. elegans similar to the mammalian body.

Suppression of thiol exchange reaction in the determination of reduced‐form thiols by high‐performance liquid chromatography with fluorescence detection after derivatization with fluorogenic benzofurazan reagent, 7‐fluoro‐2,1,3‐benzoxadiazole‐4‐sulfonate and 4‐aminosulfonyl‐7‐fluoro‐2,1,3‐benzoxadiazole

The derivatization of the reduced-form thiols with SBD-F (7-fluoro-2,1,3-benzoxadiazole-4-sulfonate) and ABD-F (4-aminosulfonyl-7-fluoro-2,1,3-benzoxadiazole) was studied. The yields of the derivatives of the reduced-form thiols (cysteine, homocysteine, reduced-form glutathione) with SBD-F at 60 degrees C for 45 min in the borate buffer (pH 9.3) were significantly decreased in the presence of the oxidized-form thiols (cystine, homocystine, oxidized-form glutathione) because of the thiol exchange reaction between the reduced-form and the oxidized-form thiols. The use of ABD-F at low temperature enabled the suppression of these thiol exchange reactions, and the recommended conditions were below 5 degrees C for 90 min in borate buffer (pH 9.3). These results suggest that ABD-F is a preferred derivatization reagent for the accurate determination of the reduced-form thiols in samples containing the oxidized-form thiols. In addition, it was also suggested that the derivatization of the reduced-form thiols should also be performed at low temperature when derivatization reagents such as o-phthalaldehyde (OPA) and monobromobimane (BrB) are used.

Determination of Phosphoamino Acids by 6-Oxy-(N-succinimidyl acetate)-9-(2′-methoxycarbonyl)fluorescein and MEKC with LIF Detection

The fluorescent reagent 6-oxy-(N-succinimidyl acetate)-9-(2′-methoxycarbonyl)fluorescein (SAMF), has been newly synthesized for use as a label for characterization of phosphoamino acids by micellar electrokinetic capillary electrophoresis (MEKC) with laser-induced fluorescence (LIF) detection. The conditions for derivatization and separation of the phosphoamino acids, including pH, concentration of electrolyte, and Brij-35 concentration were optimized in detail. Derivatization was performed at 35 °C for 10min in borate buffer (pH 8.0). The derivatives were separated to baseline by use of running buffer containing 50 mM borate and 20 mM Brij-35 at pH 9.3. Detection limits ranged from 5 × 10−11 to 1 × 10−9 mol L−1 (signal to noise ratio = 3). The method was used for characterization of the phosphoamino acids in a sample from hydrolysis of a novel protein kinase from tobacco cells.

Determination of Bisphenol-A in Water by Semi-Micro Column High-Performance Liquid Chromatography Using 2-Methoxy-4-(2-phthalimidinyl)-phenylsulfonyl Chloride as a Fluorescent Labeling Reagent

A highly sensitive method for the determination of bisphenol-A in water with semi-micro column high-performance liquid chromatography using 2-methoxy-4-(2-phthalimidinyl)phenylsulfonyl chloride as a fluorescent labeling reagent has been developed. The labeling reaction was carried out at 70 degrees C for 20 min in borate buffer (pH 9.5). The derivative eluted at 11.6 min on a reversed-phase column with methanol-water (78:22, v/v) at a flow-rate of 0.2 ml/min. The fluorescence was monitored at 308 nm for excitation and 410 nm for emission. The detection limit (S/N = 3) was 10 fmol per injection. The labeling yield was about 95%.

Exocytic Trafficking Is Required for Nicotine-induced Up-regulation of α4β2 Nicotinic Acetylcholine Receptors

The primary target for nicotine in the brain is the neuronal nicotinic acetylcholine receptor (nAChR). It has been well documented that nAChRs respond to chronic nicotine exposure by up-regulation of receptor numbers, which may underlie some aspects of nicotine addiction. In order to investigate the mechanism of nicotine-induced nAChR up-regulation, we have developed a cell culture system to assess membrane trafficking and nicotine-induced up-regulation of surface-expressed alpha(4)beta(2) nAChRs. Previous reports have implicated stabilization of the nAChRs at the plasma membrane as the potential mechanism of up-regulation. We have found that whereas nicotine exposure results in up-regulation of surface receptors in our system, it does not alter surface receptor internalization from the plasma membrane, postendocytic trafficking, or lysosomal degradation. Instead, we find that transport of nAChRs through the secretory pathway to the plasma membrane is required for nicotine-induced up-regulation of surface receptors. Therefore, nicotine appears to regulate surface receptor levels at a step prior to initial insertion in the plasma membrane rather than by altering their endocytic trafficking or degradation rates as had been previously suggested.

Determination of biogenic amines in fermented beverages and vinegars by pre-column derivatization withpara-nitrobenzyloxycarbonyl chloride (PNZ-Cl) and reversed-phase LC

The reagentp-nitrobenzyloxycarbonyl chloride (PNZ-CI) was used for pre-column derivatization of biogenic amines (BAs) at ambient temperature followed by reversed-phase, liquid-chromatographic separation of the derivatives. Optimized derivatization of samples was achieved within 10 min in borate buffer by adding PNZ-Cl in acetonitrile (MeCN). Excess reagent was scavenged by subsequent addition of glycine in water. For LC a Superspher® RP-18e column and gradient elution using a ternary gradient system containing sodium acetabe buffer (pH 6.1), sodium acetate buffer (pH 4.3) and MeCN, were used. The PNZ-derivatives were quantified by their UV-absorption at 265 nm. Detection limits of BAs were approximately 62–1000 μg L−1 (injected amounts: 53–850 pg) at a signal-to-noise ratio of 3:1. The coefficients of determination were 0.9906–0.9992. Diaminohexane was used as internal standard. Recoveries of BAs ranged from 78–93% depending on the food matrix. This method was applied to the quantitative determination of 2-phenylethylamine, tryptamine, serotonin, putrescine, histamine, cadaverine, tyramine, spermidine, and spermine, in beer, wine, vinegars, and lactic fermented cabbage juice.

High-performance liquid chromatographic determination of erdosteine and its optical active metabolite utilizing a fluorescent chiral tagging reagent, R-(−)-4-( N, N-dimethylaminosulfonyl)-7-(3-aminopyrrolidin-1-yl)-2,1,3-benzoxadiazole

Chiral separation of racemic M1 metabolized from erdosteine was investigated by reversed-phase chromatography. The sensitive determination of M1 and erdosteine with UV detection was difficult because of their low absorptivity in the effective wavelength region. To improve the sensitivity and separatability, one thiol and two carboxyl groups in the M1 structure were labelled with DBD-F and R-(−)-DBD-APy, respectively. Non-fluorescent DBD-F quantitatively reacted with thiol in M1 at room temperature for 30 min in borate buffer (pH 9.3) to produce the fluorescent derivative. On the other hand, the labelling of two carboxyls was carried out with a chiral fluorescent reagent, R-(−)-DBD-APy, in acetonitrile containing DPPA. The derivatives corresponding to a pair of the enantiomers were completely separated with water–acetonitrile containing 0.1% TFA as the mobile phase by an ODS column. Erdosteine with a carboxyl group was also labelled with R-(−)-DBD-APy and separated together with M1 derivatives. The detection limits ( S/ N=3) of erdosteine and M1 were 0.37 and 0.22 pmol, respectively. The proposed derivatization and separation methods were applied to simultaneous determination of racemic M1 and erdosteine in rat plasma after administration of erdosteine. The amounts of both enantiomers of M1 were essentially the same in oral and intravenous administrations. In contrast, total amounts (reduced-form and oxidized-form) of S-(−)-M1 in rat plasma were higher than those of R(+)-M1 in both administrations.

High-performance capillary electrophoresis of O-glycosidically linked sialic acid-containing oligosaccharides in glycoproteins as their alditol derivatives with low-wavelength UV monitoring

Several O-glycosidically linked monosialooligosaccharides from glycoproteins were separated as their alditol derivatives in ca. 10 min in borate buffer (pH 9.6) containing sodium dodecyl sulfate (SDS), and sensitively detected at the 10 −4 M level by measuring absorption at 185 nm. Oligosaccharides having higher degree of polymerizations migrated faster, and N-acetyl- and N-glycolylneuraminic acid-containing oligosaccharide analogues could be resolved from each other under the conditions employed. Good linearity was demonstrated between 0.9 and 20 m M concentrations for relative response of N-acetylneuraminyllactose as a model compound to lactobionic acid as an internal standard. The detection limit was 0.2 m M, which corresponded to 0.80 pmol as the injected amount. The relative standard deviation of relative response at 9 m M was 1.97% ( n = 7). The established system was successfully applied to microanalysis of sialooligosaccharides in bovine submaxillary mucin and swallow nest material.