Trace Determination of Glycols by HPLC with UV and Electrospray Ionization Mass Spectrometric Detections

A high-performance liquid chromatography/mass spectrometry (HPLC/MS) method is developed for trace determination of glycols (ethylene glycol, 1,2- and 1,3-propylene glycols, and 2,3-butylene glycol) in water after derivatization with benzoyl chloride. Benzoyl esters of glycols are separated by microcolumn reversed-phase HPLC. Sensitivity and linearity of UV detection at 237 nm is compared with electrospray ionization mass spectrometric (ESI-MS) detection using selected ion monitoring. Limits of detection (LOD) and quantitation (LOQ) for UV detection are 1 and 2 mg/L, respectively. For ESI-MS detection, LOD and LOQ are in the ranges 10-25 and 20-50 μg/L, respectively. LOD obtained by ESI-MS for the determination of glycols is improved by 2-3 orders of magnitude in comparison to previously published methods. The effect of the structure of isomeric glycols on their electrospray mass spectra is discussed. The method has been applied for the determination of glycols in aqueous matrixes containing high concentrations of salts occurring in nuclear waste disposal treatment.     

Determination of iodide in seawater by ion chromatography

A simple and highly sensitive ion chromatographic method with UV detection was developed for iodide (I(-)) in seawater. A high-capacity anion-exchange resin with polystyrene-divinylbenzene matrix was used for both preconcentration and separation of iodide. Iodide in artificial seawater (salinity, 35‰) was trapped quantitatively (98.8 ± 0.6%) without peak broadening on a preconcentrator column and was separated with 0.35 M NaClO(4) + 0.01 M phosphate buffer (pH 6.1). On the other hand, the major anions in seawater, chloride and sulfate ions, were partially trapped (5-20%) and did not interfere in the determination of I(-). The detection limit for I(-) was 0.2 μg/L for 6 mL of artificial seawater. The present method was applied to determination of I(-) (ND - 18.3 μg/L) and total inorganic iodine (I(-) + IO(3)(-) - I, 50.0-52.7 μg/L) in seawater samples taken near Japan.     

Quantitative RP-HPLC Determination of Some Aldehydes and Hydroxyaldehydes as Their 2,4-Dinitrophenylhydrazone Derivatives

A high-performance liquid chromatographic (HPLC) method is described for the quantitative determination of some aliphatic aldehydes and β-hydroxyaldehydes as their 2,4-dinitrophenylhydrazone derivatives. A method is described for the preparation of derivatives for those β-hydroxyaldehydes where no reference compounds of known purity are available. The detection limit of the method was 4.3-21.0 μg/L, depending on the aldehyde.     

Analysis of free intracellular nucleotides using high-performance capillary electrophoresis.

High-performance capillary electrophoresis (HPCE) with UV absorbance detection (254 nm) has been applied for analyzing intracellular free ribonucleotides. The nucleotide profiles obtained from peripheral blood lymphocytes differ from those obtained from Molt4 human leukemic cells. With a 140 mM borate buffer, pH 9.4, a nearly complete profile can be obtained in 25 min. HPCE has comparable resolution to that of high-performance liquid chromatography (HPLC) but is faster in terms of time per sample run (25 min vs 45 min) and requires much less sample (nanoliter range for HPCE vs microliter range for HPLC).     

Lowering the UV Absorbance Detection Limit in Capillary Zone Electrophoresis Using a Single Linear Photodiode Array Detector

A new approach for lowering the UV absorbance detection limit in capillary electrophoresis is presented. This approach involves the use of a photodiode array in which each of the diodes in the array is treated as an independent detector. Over the course of a run, therefore, an electropherogram is generated for each diode in the array. Averaging the electropherograms generated from 1500 diodes in a diode array resulted in a signal-to-noise ratio 85 times that of an electropherogram generated from any one diode in the array. These signal-to-noise improvements are discussed, and the detection limits are compared to the detection limits obtained from a commercial single-point detector. The array detector improves the detection limit by a factor of 3.8 (±0.4).     

Application of rhodamine 800 for reversed phase liquid chromatographic detection using visible diode laser-induced fluorescence

This study reports the application of rhodamine 800, a far-red dye, suitable for excitation using visible diode laser-induced fluorescence (VDLIF) detection. A reagent synthesized from rhodamine 800 was evaluated as a precolumn reagent for derivatization with amino-containing analytes. The derivative of this reagent with primary amine analytes showed a loss of fluorescence. Rhodamine 800 was then applied as a mobile phase additive in the indirect mode for quantitation of valproic acid in plasma using reversed phase HPLC in combination with VDLIF detection. A visible diode laser (output power 8.50 mW) temperature-tuned to oscillate at 674.70 nm was used as a light source for a laboratory constructed HPLC fluorescence detector. A liquid/liquid extraction procedure was applied to human blank plasma. The selectivity of this method was validated by demonstration of a lack of interfering peaks in extracts of plasma (n = 3 sources). A calibration curve for valproic acid between 40 and 200 μg/mL was shown to be linear (r = 0.9932). The recoveries of valproic acid at concentrations of 50 and 100 μg/mL were evaluated and determined to be 73 and 72%, respectively. The precision and accuracy (n = 5) of the assay was within 7.0% RSD and 8.0% difference from the spiked concentration, respectively. The limits of detection (S/N = 3) for extracted and unextracted valproic acid were 15.0 and 11.54 μg/mL, respectively. The theoretical (C(lim)) and practical (C(det)) limits of detection in the detector flow cell for unextracted valproic acid at a S/N = 1 were found to be within 15%.     

反相高效液相色谱法分离分析水中一些阴离子

本文试验反相高效液相色谱法分离分析水中氯离子、硝酸根和硫酸根的条件,研究可能干扰、提高选择性和提高灵敏度的方法,建立应用于自来水和海水等实际样品的分离分析方法。     

Laser Vaporization/Ionization Interface for Capillary Electrophoresis-Time-of-Flight Mass Spectrometry

Mass spectrometry (MS) is usually coupled on-line with capillary electrophoresis (CE) to analyze biomolecules by using electrospray ionization or continuous-flow fast-atom bombardment. We present a new design for laser vaporization/ionization time-of-flight mass spectrometry. CE, with its low flow rate (<1 μL/min), is highly compatible with MS, even if the total column effluent is introduced directly. A UV laser is used to vaporize and ionize the solution eluting from the column. There is no need to have a makeup solvent. Using this system, we have analyzed a group of amines and peptides. The concentration detection limit of serotonin is in the 10(-)(7) M level. The separation and identification of an amine mixture by CE/MS demonstrates the complementary nature of the information.     

Multidimensional biochemical detection of microcystins in liquid chromatography

The coupling of antibody-, receptor-, or enzyme-based inhibition assays postcolumn to chromatographic systems provides biological detectors with extraordinary high sensitivity and specificity. Three monoclonal antibodies (MC10E7, AD4G2, M8H5) directed against microcystins and protein phosphatase 1 (PP1) were used as off-line detectors for the HPLC separation of microcystins and nodularin in comparison to UV detection. For HPLC/ELISA coupling using antibody MC10E7, a detection limit of 0.04 ng microcystin-LR was achieved. The provisional guideline value for microcystin-LR (1 microg/L, WHO) could be monitored without prior sample concentration, in contrast to UV detection. Quantification of microcystin-LR and two cross-reactants was demonstrated. Furthermore, cross-reactivity or enzyme inhibition of new microcystins, only available in small amounts, can be determined by this method. Using a cyanobacterial extract, HPLC/ELISA coupling was compared to HPLC/UV and electrospray ionization mass spectrometry (ESI-TOFMS).     

HPLC analysis of ecdysteroids in plant extracts using superheated deuterium oxide with multiple on-line spectroscopic analysis (UV, IR, 1H NMR, and MS).

HPLC, using superheated D20 as the mobile phase, combined with on-line characterization via a combination of diode array UV, 1H NMR, FT-IR spectroscopy, and mass spectrometry has been used for the analysis of a standard of 20-hydroxyecdysone- and ecdysteroid-containing plant extracts. This combination of spectrometers enabled the on-flow collection of UV, 1H NMR, IR, and mass spectra not only for pure 20-hydroxyecdysone (100-400 microg on column) but also the major ecdysteroids present in crude extracts of Silene otites, Silene nutans, and Silene frivaldiskyana. The ecdysteroids unequivocally identified in these extracts included 20-hydroxyecdysone, polypodine B, and integristerone A.     

Determination of Iodide and Iodate by Ion Chromatography with Postcolumn Reaction and UV/Visible Detection

Iodide and iodate can be determined by two new methods using anion-exchange chromatography with postcolumn reaction and UV/visible detection. Iodide is determined as IBr(2)(-) at 249 nm. Iodate is determined as I(3)(-) at 288 nm. The analyses can be run completely automatically and do not require any sample pretreatment. The detection limits for iodide and iodate are 0.1 μg/L. The methods have been successfully applied to determine iodide and iodate in several mineral waters and in drinking water as well as for the determination of iodide in table salt.     

Chiral polymeric reagents for off-line and on-line derivatizations of enantiomers in high-performance liquid chromatography with ultraviolet and fluorescence detection: an enantiomer recognition approach

Optically active and detector-sensitive polymeric reagents have been synthesized, loadings determined, derivatizations/separations/detection optimized, and applications to simple amines and amino alcohols described. Such reagents have been designed to contain different chiral centers, usually amino acids, leashed via an activated ester attachment to an insoluble, structurally rigid, organic polymer backbone. 9-Fluorenylmethyl (FMOC) moieties chemically bonded to the amino acids were used as ultraviolet (UV) and fluorescence (FL) sensitive detector probes to the final diastereomers of enantiomer substrates. Such diastereomers can be readily separated by isocratic or gradient elution normal-phase methods. The kinetics for diastereomer formation have been determined, and final UV/FL responses for known mixtures of enantiomers have been compared to demonstrate overall validity of the method. Minimum detection limits, linearity of calibration plots, dual detector responses, and linear diode array spectra and absorbance ratios have also been demonstrated. In some cases, authentic standards have been prepared to calculate absolute percent derivatizations for specific enantiomer pairs. The overall approach permits, for the very first time, off-line or on-line precolumn derivatization for the formation of diastereomers having unique detector properties. It has been proven that the rates and rate constants for such formations are identical for at least those pairs of enantiomers studied. Separations are base-line or near-base-line, permitting accurate and precise quantitative determinations, by both UV and FL, of enantiomer/optical purity and chemical purity.     

Online enzyme discrimination and determination of substrate enantiomers based on electrophoretically mediated microanalysis

We proposed the first application of an electrophoretically mediated microanalysis (EMMA) method for fast online discrimination and determination of substrate enantiomers, which was achieved by just one EMMA assay. Lactate dehydrogenase (LDH)-catalyzed reaction was studied to evaluate the feasibility and performance of the presented method. The l- and d-LDH chiral enzymatic reactions, which are highly stereoselective to the lactate enantiomers, were initiated successively in one capillary, and the corresponding products, nicotinamide adenine dinucleotide (NADH), were online discriminated and detected by UV absorption. Excellent linear dependence of the two NADH peak intensities on the concentration of the corresponding lactate enantiomers was obtained within a wide range of 0.1-10 mM. The limit of detection was 26 μM for d-lactate and 49 μM for l-lactate (S/N = 3). Good repeatability of online chiral discrimination was demonstrated with relative standard deviation (RSD) < 6.3% for NADH peak height and RSD < 1.5% for migration time (n = 5). K(m) values for l- and d-lactate were measured and were consistent with those of the off-line enzyme assays. The presented method was successfully applied to determine the l-/d-lactate in several yogurt and wine samples. Our study shows a new application of the EMMA method utilizing high stereoselectivity of enzymes for fast online chiral analysis.     

Degradation characteristics of secondary effluent of domestic wastewater by combined process of ozonation and biofiltration

The performance of the combined process of ozonation and biofiltration was studied for treating the secondary effluent from sewage treatment plant. It was found that COD, NH(3)-N, and TOC were removed from 40-52, 10-19, and 9-13 mg/L in the raw water to 18-23, 0.5-1.5, and 7-8.5 mg/L in the effluent water (removal efficiency were 58, 89, and 25%, respectively), respectively, with an ozone dose of 10 mg/L (0.7-1.1 mg O(3)/(mg TOC) and 0.2-0.25 mg O(3)/(mg COD)), and contacting time of 4 min. Under the operation conditions, ozonation enhanced the biodegradability of the organics in the secondary effluent, as illustrated by increasing biodegradable dissolved organic carbon (BDOC) value from 0.8-1.1 mg/L in the raw water to the 2.0-2.7 mg/L in the effluent water. Meanwhile, the percentage of the organics with molecular size less than 1k Da in the secondary effluent increased from 52.9 to 72.6%. The experimental results supported the expectation that the combined process of O(3)/Biofiltration might enhance the overall treatment efficiency of secondary effluent treatment.     

Simultaneous determination of ultratrace lead and cadmium by square wave stripping voltammetry with in situ depositing bismuth at Nafion-medical stone doped disposable electrode

An ultrasensitive electrochemical method for simultaneous determination of lead and cadmium was first developed using the novel bismuth-Nafion-medical stone doped disposable electrode (an improved wax-impregnated graphite electrode). Through the synergistic sensitization effect of the resulting composite material, the disposable electrode showed remarkable electrochemical responses to lead and cadmium. The oxidation of the two metals produced two well-defined and separated square wave peaks at about -0.62 V for Pb(2+) and -0.85 V for Cd(2+), respectively. The effects of the amount of medical stone, concentration of Nafion, thickness of bismuth, pH of buffer solution, deposition potential, accumulation time, voltammetric measurement and possible interferences were investigated in detail. Under the optimal conditions, the fabricated electrode exhibited linear ranges from 2.0 to 12.0 μg L(-1) with detection limit of 0.07 μg L(-1) for lead and 2.0-12.0 μg L(-1) with detection limit of 0.47 μg L(-1) for cadmium. The assay results of heavy metals in wastewater with the proposed method were in acceptable agreement with the atomic absorption spectroscopy method.     

Insecticide detection through protein engineering of Nippostrongylus brasiliensis acetylcholinesterase B

The sensitivity of acetylcholinesterase (AChE) biosensors for insecticide detection could be increased substantially by engineering AChE B of Nippostrongylus brasiliensis. The introduction of 10 single and 4 double mutations into the AChE peptide chain led to an increase in sensitivity to 10 of the 11 insecticides tested. The combination of three mutants with the wild-type enzyme in a multienzyme biosensor array enabled the detection of 11 out of the 14 most important organophosphates and carbamates at concentrations below 10 microg/kg, the maximum residue limit of infant food. The detection limit for pirimiphos methyl could be reduced from 10 microg/L to a value as low as 1 ng/L (3.5 x 10(-)(12) mol/L). The newly created biosensors exhibited an extraordinary high storage stability. There was no loss of sensitivity of N. brasiliensis AChE B, immobilized on screen-printed, disposable electrodes, even after 17-month storage at room temperature.     

A Validated Stability Indicating LC Method for Nateglinide

ABSTRACT

A simple, isocratic, rapid and accurate reverse phase high-performance liquid chromatography (RP-HPLC) method was developed for the quantitative determination of Nateglinide. The developed method is also applicable for determination of related substance in bulk drugs. The chromatographic separation was achieved on a Hypersil C18 (250 × 4.6 mm 5 μm) column using aqueous mixture of 0.025 M potassium hydrogen phosphate and 0.1% triethyl amine, v/v (pH 3.0 with dilute phosphoric acid)—methanol (25:75, v/v) as a mobile phase. Solution concentrations were measured on a weight basis to avoid the use of an internal standard. The chromatographic resolutions between Nateglinide and its potential impurities A and B were found to be greater than four. Forced degradation studies were performed for Nateglinide using acid (0.5 N hydrochloric acid), base (0.5 N sodium hydroxide), oxidation (3% hydrogen peroxide) heat (60°C) and UV light (254 nm). The limit of detection and limit of quantification of Nateglinide, impurities A and B were found to be 0.05 and 0.15 μg /mL, respectively for 20 μL injection volume. The percentage recovery of Nateglinide was ranged from 98.4 to 100.9. The percentage recovery of impurities in Nateglinide sample was ranged from 96.8 to 103.5. The developed RP-HPLC method was validated with respect to linearity, accuracy, precision, robustness, and forced degradation studies prove the stability indicating power of the method.     

High-performance liquid chromatography of lignin-derived phenols in environmental samples with diode array detection

Lignin-derived and standard phenols were successfully analyzed with reversed-phase high-performance liquid chromatography (HPLC) with diode array detection. The 11 major phenols produced by cupric oxide (CuO) oxidation were clearly and rapidly separated. Determination by diode array detection also allowed detection of interfering impurities within individual HPLC peaks. The lignin phenols were accordingly corrected and quantified. This method yields precise and reliable data for various environmental samples such as dissolved organic matter from aqueous samples and sediments and can also be applied to various particulate materials such as detritus and plant tissues. An interlaboratory method comparison with humic substance standards from the International Humic Substances Society revealed differences in lignin phenol concentrations, whereas lignin parameters better coincided.     

Minimization of transition metal interferences with hydride generation techniques

A new hydride generator has been characterized for use with the acid-NaBH(4) hydride generation systems based on the insertion of a capillary tube into the sample introduction channel of a standard Meinhard nebulizer. The acidic sample and the tetrahydroborate solution are mixed at a merge point 1.5 cm from the end of the nebulizer orifice. Nebulization of the reaction solutions into a 0.7 mL tubular "spray chamber" follows a very short mixing time (less than 0.012 s) of the reagents. This approach permits 10?000 μg/mL Ni(2+) or Cr(3+) to be present in the sample solution without producing any interferences. Additionally, in the presence of Fe(3+) added as a "releasing agent", 5000 μg/mL Co(2+) or 160 μg/mL Cu(2+) can also be tolerated without interference. An 80 ± 2% generation efficiency is attained for the test element selenium. A detection limit of 6 μg/L (3σ(b)) is achieved with ICP-AES detection. Precision of replicate measurements at the 12 μg/L level varies from 5 to 12% relative standard deviation.     

Determination of total organic carbon in water by thermal combustion-ion chromatography

A sensitive method for determining total organic carbon at microgram per liter levels in industrial, environmental, and drinking waters by thermal combustion ion chromatography was developed using tube furnace and readily accessable HPLC equipment. To achieve complete oxidation, persulfate (0.25%) was added to oxidize nonvolatile organic compounds in solution and cupric oxide heated at 900 °C to convert volatile organic compounds to CO(2), which was scrubbed in a 20 mL solution of 50 mM KOH with 10 drops of butanol added. The carbonate anion obtained was determined by nonsuppressed ion chromatography using 0.6 mM potassium hydrogen phthalate (KHP) as the eluent. Both surfactants and volatile and nonvolatile organic compounds commonly found in environmental waters give highly repeatable recoveries close to 100%. The detection limit (S/N = 2) and linear range for a 1 L water sample are 2 μg of C L(-)(1) and 10-2500 μg of C L(-)(1), respectively, and they can be adjusted using samples ranging from 100 mL to 2 L. Good repeatablity (RSD less than 10%) and close to 100% recoveries were obtained for KHP added to real samples such as deionized, mineral, tap, and river water and seawater. Compared with the ASTM D2579 method, the method developed is 3 orders of magnitude more sensitive, more accurate, and reliable in determining samples with low total organic carbon values and more flexible in adjusting the linear range and sensitivity using variable sample sizes.