Determination of triazines in water samples by high-performance liquid chromatography with diode-array detection

Triazines are widely used herbicides that can be detected in the environment at trace level. A preconcentration step is necessary to determinate them before analysis. In this study, carbonaceous and polymeric adsorbents are compared with C18 for the solid-phase extraction of simazine, atrazine, and propazine in water samples in order to quantitate their levels by high-performance liquid chromatography using photodiode-array detection.     

Profiling of Alternaria mycotoxins in foodstuffs by high-performance liquid chromatography with diode-array ultraviolet detection

The potential of high-performance liquid chromatography (HPLC) with diode-array detection for the profiling of mycotoxins in food samples has been demonstrated. A gradient elution reversed-phase chromatographic method coupled with a suitable extraction procedure was devised for the separation and detection of major Alternaria mycotoxins in foodstuffs. Altenuene, alternariol, alternariol methyl ether (dibenzo-alpha-pyrone derivatives), altertoxin-I and altertoxin-II (perylene derivatives) were profiled in extracts of artificially infected maize, rice and tomato samples and naturally contaminated sunflower seeds. First evidence of the occurrence of a new dibenzo-alpha-pyrone derivative in Alternaria cultures is also reported.     

Determination of vitamin A in pharmaceutical preparations by high-performance liquid chromatography with diode-array detection

Summary A very simple high-performance liquid chromatographic method for determination of Vitamin A in pharmaceutical preparations without the need for saponification was developed. A reversed-phase (Nova-Pack C₁₈, 4 m) column was used with a mobile phase of acetonitrile-tetrahydrofuran-water (55378) and a flowrate of 1.5 ml/min. Sample treatment only consisted of the extraction of retinol acetate content from capsules or tablets with methanol. Total extraction was achieved by shaking vigorously with the aid of magnetic stirring for three hours at room temperature. No change of solvent is necessary to introduce the sample in the chromatographic system. This method is suitable for routine quantification of Vitamin A.     

Determination of formaldehyde in spirits by high-performance liquid chromatography with diode-array detection after derivatization

A high-performance liquid chromatography (HPLC) method with diode-array detection (DAD) to identify and quantify formaldehyde (FA) in spirits is described. Formaldehyde was quantified with DAD after derivatization with ethyl 3-oxobutanoate and ammonia to yield the diethyl 2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate. The response of the detection system was linear within the range of 0.25-2.00 μg/ml with a correlation coefficient of 0.9998. The average formaldehyde concentration in the samples ranged between 0.27 and 3.01 mg/l. The coefficient of variation was lower than 4.84% and recoveries ranged from 93.4 to 100.4%. Purity of formaldehyde derivative peak was confirmed by spectral data.     

Screening for coumatetralyl in soft drinks by solid-matrix extraction and high-performance liquid chromatography with diode-array detection.

A method was developed for the rapid determination coumatetralyl in cola- and orange-type soft drinks, which includes extraction using solid-matrix column, clean-up by silica cartridge chromatography and reversed-phase high-performance liquid chromatography with diode-array detection. The recovery of coumatetralyl from 50 ml of soft drinks was better than 80% at spiking levels down to 50 micrograms/kg (ppb).     

Determination of β-adrenoreceptor antagonists in urine by high-performance liquid chromatography with diode-array spectrophotometric detection

The determination of pindolol, oxprenolol and propranolol in human urine is described. The drugs are isolated with a GDX-502 resin-packed column, separated on a C₁₈ (5-μm) reversed-phase column with methanol/aqueous acetic acid as mobile phase and quantified with diode-array spectrophotometric detector. The recovery was > 93%, and detection limits were 2 ng for pindolol, 12 ng for oxprenolol and 2 ng for propranolol. Results are given for urine from healthy volunteers who had received the drugs orally.     

Gradient separations of complex mixtures by micro high-performance liquid chromatography

High-performance micro packed fused-silica and open-tubular glass capillary columns were prepared and applied to separations of complex mixtures. Solvent-gradient elution proved quite useful for the separation of solutes with wide polarity. Instruments and some applications are described.     

液相色谱法检测水果蔬菜中的烟碱类农药残留

建立了果蔬样品中5种烟碱类农药(噻虫嗪、吡虫啉、啶虫脒、噻虫啉、噻虫胺)残留的液相色谱快速检测方法。样品采用乙腈提取,浓缩,水转溶后经ENVI-18固相萃取柱净化,0.02 mol/L NaOH预淋洗除去柱上中等极性干扰物,100%乙腈1 mL洗脱5种烟碱类残留,反相高效液相色谱-二极管阵列检测器检测。在黄瓜空白基质中0.1~1.0 mg/kg的加标浓度范围内,5种农药的回收率为50.8%~108.9%,相对标准偏差(RSD)小于15%;而苹果、梨、香蕉、西红柿和韭菜空白基质在0.1~1.0 mg/kg添加水平下,5种农药的回收率均大于80%,RSD小于11%。所测试的6种果蔬样品中噻虫嗪、噻虫胺、吡虫啉的检出限(LOD)为0.01~0.02 mg/kg,啶虫咪和噻虫啉的LOD为0.03~0.05 mg/kg,方法可满足水果蔬菜中烟碱类农药多残留分析的要求。     

A chromatospectroscopic method for analyzing the signals generated during high-performance liquid chromatography with diode-array detection

A "chromatospectroscopic" technique has been developed to quantitate two compounds that coelute in high-performance liquid chromatography. The method uses a diode-array detector with Millenium 32 software to extract spectra at regular time intervals during the elution of the unique peak and recover spectral data (absorbance versus wavelength), which can then be processed using the Excel software package. The method is applied to mixtures of two coeluting UV filters. Both could be accurately quantitated even when the mixture consisted of 99.5% of one and only 0.5% of the other.     

Quantitative trace analysis of surfactant mixtures by reversed-phase high-performance liquid chromatography with refractometric detection

Reversed-phase partition liquid chromatography on an octyl column allowed the separation of complex non-ionic poly(ethylene oxide)-type (PEO) surfactant mixtures resulting from the condensation of ethylene oxide with saturated fatty alcohols. As these compounds have no chromophoric group, they were detected by differential refractometry. Accurate quantitation of each oligomer (C_mE_n) allowed the main characteristics of each non-ionic surfactant, i.e., the nature and percentage of the different alkyl chains (with m = number of carbons) and the average number of ethylene oxide units ( ) to be obtained in one analysis. Preparative liquid chromatography was used to isolate pure oligomers with a higher degree of ethoxylation (n =10, 11, 12, 14 and more) than the commercially available standards, in order to determine a wide range of refractometric response factors. It appeared that they are constant as a function of alkyl chain length (C₁₀-C₁₆ range) but that they vary significantly and non-linearly as a function of the degree of ethoxylation, n. It was found that neglecting the variation of response factors can result in a distortion of the average ethoxylation number and in an unsatisfactory quantitative analysis. This chromatographic method, involving a quantitative and reproducible trace enrichment procedure with liquid-solid extraction, allowed the analysis of very dilute PEO mixtures in water. The components of complex PEO mixtures in water were determined at concentrations as low as 0.5 mg 1⁻¹, without any distortion of the distribution, the detection limit being 0.25 μg 1⁻¹ for the less abundant oligomers.     

Algorithms for the assessment of peak purity in liquid chromatography with photodiode-array detection. Part II

Two modifications of the algorithm based on the Gram-Schmidt orthogonalization technique for the assessment of peak purity are presented. The performance of this approah is investigated for liquid chromatography with photodiode-array detection (LC-DAD) data, although its applicability is not restricted to this experimental model. This method is applied to simulated and experimental data where two compounds are eluting, but can be applied when more compounds are eluting. The results are compared with the ones obtained previously with the first version of this algorithm.     

Determination of imidacloprid and its metabolite 6-chloronicotinic acid in greenhouse air by high-performance liquid chromatography with diode-array detection

A method is described for analysing and sampling imidacloprid and its metabolite 6-chloronicotinic acid in greenhouse air by high-performance liquid chromatography (HPLC) with diode-array detection (DAD). The trapping efficiency of two solid sorbents, Amberlite XAD-2 and Amberlite XAD-4 and the use of different desorption procedures have been tested. To validate the methodology, standard atmospheres containing known concentrations of these pesticides and with different relative humidities were generated. No breakthrough was observed in the range of concentrations studied. Dissipation of analytes was investigated in a 24 h period after application by using personal samplers in a field experiment.     

Characterisation of complex amphiphilic cyclodextrin mixtures by high-performance liquid chromatography and mass spectrometry

It is established that amphiphilic beta-cyclodextrins chemically modified with alkyl chains on the secondary face exhibit self-organisation properties yielding stable nanospheres or nanoparticles. The ability of these promising colloidal drug carriers to encapsulate drugs being partly related to the internal structure of nanosystems, precise characterisation methods are required to control their synthesis procedure. The present work describes the development of complementary analytical methods based on reversed-phase high-performance liquid chromatography (RPLC) coupled to evaporative light-scattering detection (ELSD) and electrospray ionisation-mass spectrometry (ESI-MS) to characterize various beta-cyclodextrins enzymatically transesterified by vinyl-acyl fatty esters (the number of carbon atom in the acyl chain varying from 4 to 12). LC-ELSD has been used in a preliminary step to optimize the separation on a monolithic octadecylsiloxane-bonded silica stationary phase. A complex fingerprint was achieved for each mixture, revealing the presence of isomers unnoticed by the sole spectrometric (NMR and MS) techniques.     

Determination of enrofloxacin and its metabolite ciprofloxacin in goat milk by high-performance liquid chromatography with diode-array detection. Optimization and validation

A high-performance liquid chromatography-diode array detection method (HPLC-DAD) combined with liquid chromatography-mass spectrometry was developed for the determination of enrofloxacin and its metabolite ciprofloxacin in goat milk. The HPLC-DAD method validation was compliant with the "DG SANCO 1805/2000" European regulation. The residues were extracted from milk with phosphate buffer, purified on a C18 Speedisk cartridge SPE (Baker) and then analysed using HPLC-DAD set at 277 nm. The decision limit (CCa) calculated by spiking samples at 100 microg/kg with both analytes, taking into account the maximum residue limit (MRL) of 100 microg/kg established by the European Union for the sum of enrofloxacin and its metabolite ciprofloxacin in milk, was 105.3 microg/kg for enrofloxacin and 105.5 microg/kg for ciprofloxacin. The detection capability (CCbeta) was 110.7 and 110.9 microg/kg for enrofloxacin and ciprofloxacin, respectively. The mean recoveries of the method, calculated by spiking samples at 50, 100 and 150 microg/kg were 84% for enrofloxacin and 88% for ciprofloxacin. The limit of quantification was 20 microg/kg for both analytes. The HPLC-DAD validated method was successfully applied for the first time in goats milk, and proved to be suitable for the sensitive and accurate quantification and confirmation analysis of enrofloxacin and ciprofloxacin for regulatory purposes.     

Fast separation of (poly)phenolic compounds from apples and pears by high-performance liquid chromatography with diode-array detection

Polyphenolic compounds in apples and pears were analysed by HPLC on C₁₈-modified silica. Gradient elution with phosphoric acid–methanol mixtures and phosphoric acid–acetonitrile mixtures gave complete separation of all polyphenolics of interest. The use of methanol as modifier was preferred because it provides a more rapid separation (20 min). Diode-array detection was used for the provisional identification of polyphenolic compounds not available as standards.     

Bio-analysis of vinorelbine by high-performance liquid chromatography with fluorescence detection.

A simple and selective procedure for the determination of vinorelbine, a new semi-synthetic vinca alkaloid, is presented. The method is based on ion-exchange high-performance liquid chromatography on normal-phase silica with fluorescence detection, combined with liquid-liquid extraction using diethyl ether for sample clean-up. The absence of endogenous interferences and the excellent chromatographic behaviour of vinca alkaloids provides accurate results even at low concentrations. The limit of determination in plasma is 1.5 micrograms/l (500-microliters sample). Reproducible recoveries in urine were obtained if 10-50 microliters of sample were processed supplemented with 500 microliters of blank plasma.     

Implications of column peak capacity on the separation of complex peptide mixtures in single- and two-dimensional high-performance liquid chromatography

Column peak capacity was utilized as a measure of column efficiency for gradient elution conditions. Peak capacity was evaluated experimentally for reversed-phase (RP) and cation-exchange high-performance liquid chromatography (HPLC) columns, and compared to the values predicted from RP-HPLC gradient theory. The model was found to be useful for the prediction of peak capacity and productivity in single- and two-dimensional (2D) chromatography. Both theoretical prediction and experimental data suggest that the number of peaks separated in HPLC reaches an upper limit, despite using highly efficient columns or very shallow gradients. The practical peak capacity value is about several hundred for state-of-the-art RP-HPLC columns. Doubling the column length (efficiency) improves the peak capacity by only 40%, and proportionally increases both the separation time and the backpressure. Similarly, extremely shallow gradients have a positive effect on the peak capacity, but analysis becomes unacceptably long. The model predicts that a 2D-HPLC peak capacity of 15,000 can be achieved in 8 h using multiple fraction collection in the first dimension followed by fast RP-HPLC gradients employing short, but efficient columns in the second dimension.     

Characterization and identification of multiple constituents in Yinhuang granules by high-performance liquid chromatography with diode-array and time-of-flight mass spectrometry detection

A fast high-performance liquid chromatography (HPLC) method with diode-array detection (DAD) and time-of-flight mass spectrometry (TOF/MS) has been developed for the analysis of multi-constituent in Yinhuang granules, a well-known combined herbal remedy prepared from the extract mixtures of Flos Lonicerae and Radix Scutellariae. The fast HPLC analysis was performed on an Agilent ZorBax SB-C(18) column (4.6×50 mm, 1.8 μm) and 0.2% aqueous formic acid and acetonitrile was the optimum mobile phase for gradient elution in 17 min, which is five times faster than the performance of conventional columns packed with 5.0 μm particles. With various fragmentor voltages in TOF/MS, accurate mass measurements (<5 ppm error) for molecular ions and characteristic fragment ions represented reliable identification criteria for different constituents. A total of 28 compounds, including nine phenolic acids, three iridoid glycosides and nine saponins from Flos Lonicerae and seven flavonoids from Radix Scutellariae, were identified or tentatively characterized in the extract of Yinhuang granules. The established fast HPLC-DAD-TOF/MS method turns out to be useful and efficient for quality control of this commonly used Chinese herbal preparation.