Determination of phenols in wines by liquid chromatography with photodiode array and fluorescence detection

A reversed-phase LC method, optimised for the separation of trans- and cis-resveratrol, catechin, epicatechin, quercetin and rutin, is reported. Analyses were performed on a reversed-phase column by gradient elution. Detection was carried out by photodiode array, although the use of a fluorimetric detector considerably lowered the detection limits for catechin, epicatechin and both resveratrol isomers. Identification by the two different detection systems was based on retention characteristics, UV spectra and peak purity index were compared with commercial standards. The procedures were applied to the determination of the phenolic compounds in different types of wines and musts.     

Determination of components in propolis by capillary electrophoresis and photodiode array detection

The capillary electrophoretic separation of components in propolis, a commonly used natural medicine, was investigated. Optimum conditions for the separation were established. Photodiode-array detection permitted the rapid identification of the components in the samples analysed. The determination of these components, including caffeic acid, dimethylcaffeic acid, isoferulic acid and quercetin, was performed on a commercial propolis sample.     

Determination of isoflavones in nutritional supplements by HPLC with coulometric electrode array detection

In the present study eleven soy and/or red clover based supplements were analyzed after acid hydrolysis or direct extraction with 70% aqueous ethanol for their content of total isoflavone aglucones and free aglucones plus glucosides by high performance liquid chromatography in gradient elution mode coupled with coulometric electrode array detection. The ratio of the individual isoflavones and the conjugation pattern turned out to be highly variable in the investigated products. Whereas red clover based supplements contained isoflavones (mainly formononetin and biochanin A) exclusively in free form, soy containing preparations showed variable proportions of conjugated isoflavones. The total isoflavone aglucone content in products intended for direct consumption ranged from 12.0 to 45.6?mg per capsule or tablet, whereas the content of free aglucones and glucosides was between 12.2 and 51.6?mg per capsule or tablet. The experimentally determined isoflavone aglucone content was in agreement with or higher than the manufacturer’s claim in 6 of the 11 investigated products. Expression of the isoflavone content as a sum of free aglucones and glucosides raised the number of matched claims to 8.     

Simultaneous determination of phenolic acids and flavonoids in rice using solid-phase extraction and RP-HPLC with photodiode array detection

An analytical method based on an optimized solid-phase extraction procedure and followed by high-performance liquid chromatography (HPLC) separation with diode array detection was developed and validated for the simultaneous determination of phenolic acids (gallic, protocatechuic, 4-hydroxy-benzoic, vanillic, caffeic, syringic, p-coumaric, ferulic, sinapic, and cinnamic acids), flavanols (catechin and epicatechin), flavonols (myricetin, quercetin, kaempferol, quercetin-3-O-glucoside, hyperoside, and rutin), flavones (luteolin and apigenin) and flavanones (naringenin and hesperidin) in rice flour (Oryza sativa L.). Chromatographic separation was carried out on a PerfectSil Target ODS-3 (250 mm × 4.6 mm, 3 μm) column at temperature 25°C using a mobile phase, consisting of 0.5% (v/v) acetic acid in water, methanol, and acetonitrile at a flow rate 1 mL min(-1) , under gradient elution conditions. Application of optimum extraction conditions, elaborated on both Lichrolut C(18) and Oasis HLB cartridges, have led to extraction of phenolic acids and flavonoids from rice flour with mean recoveries 84.3-113.0%. The developed method was validated in terms of linearity, accuracy, precision, stability, and sensitivity. Repeatability (n = 5) and inter-day precision (n = 4) revealed relative standard deviation (RSD) <13%. The optimized method was successfully applied to the analysis of phenolic acids and flavonoids in pigmented (red and black rice) and non-pigmented rice (brown rice) samples.     

Characterization of fifty-one flavonoids in a Chinese herbal prescription Longdan Xiegan Decoction by high-performance liquid chromatography coupled to electrospray ionization tandem mass spectrometry and photodiode array detection

High-performance liquid chromatography coupled to electrospray ionization (ESI) tandem mass spectrometry and photodiode array detection (HPLC-DAD-ESI-MS(n)) was developed to identify and characterize the flavonoids in a Chinese formulated preparation, Longdan Xiegan Decoction (LXD). In total, fifty-one flavonoids (27 flavones, 10 flavanones, 7 chalcones, 5 flavonols and 2 isoflavones) were characterized. Eighteen compounds among them including a newly detected flavonoid, naringin, from the ingredient herbs, were unambiguously determined by comparing the retention times (t(R)), UV spectral data and mass fragmentation behaviors with those of the reference compounds. Another thirty-three compounds were tentatively identified by referencing to the reported data of their UV and MS spectra. The ESI-MS/MS fragmentation behavior of flavones (OMe-substituted, O-glycosides, C-glycosides), chalcones, flavonols and their appropriate characteristic pathways were proposed. In negative ion ESI-MS all the flavonoids yielded prominent [M--H](-) ions in the first order mass spectra. Fragmentation with a loss of mass of 15 Da (CH(3)), 18 Da (H(2)O), 28 Da (CO), 44 Da (CO(2)), 56 Da (2CO) and the residues of glucose and glucuronic acid observed in the MS/MS spectra were useful for aiding the structural identification of the flavonoids investigated.     

Spectral detection in thin-layer chromatography by linear photodiode array spectrometry

Summary A new method of spectral detection in thin-layer chromatography (TLC) is given. Spectral reflectance and fluorescence can be measured by use of fiber optics and a photodiode array. The possibilities of the method with respect to quantitative evaluation, background subtraction, and recognition of overlapped spots are demonstrated at examinations of dyes in comparison to conventional single wavelength detection. The apparatus, the experimental limitations, and future developments are discussed.

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Spektrale Detektion in der Dünnschicht-Chromatographie durch lineare Photodiodenarray-Spektrometrie

     

Determination of aristolochic acid in Chinese herbal medicine by capillary electrophoresis with laser-induced fluorescence detection

We have demonstrated the analysis of aristolochic acids (AAs) that are naturally occurring nephrotoxin and carcinogen by capillary electrophoresis in conjunction with laser-induced fluorescence detection (CE-LIF). Owing to lack of intrinsic fluorescence characteristics of oxidized AAs (OAAs), reduction of the analytes by iron powder in 10.0 mM HCl is required prior to CE analysis. The reduced AAs (RAAs) exhibit fluorescence at 477 nm when excited at 405 nm using a solid-state blue laser. By using 50.0 mM sodium tetraborate (pH 9.0) containing 10.0 mM SDS, the determination of AA-I and AA-II by CE-LIF has been achieved within 12 min. The CE-LIF provides the LODs of 8.2 and 5.4 nM for AA-I and AA-II, respectively. The simple CE-LIF method has been validated by the analysis of 61 Chinese herbal samples. Prior to CE analysis, OAAs were extracted by using 5.0 mL MeOH, and then the extracts were subjected to centrifugation at 3,000 rpm for 5 min. After reduction, extraction, and centrifugation, the supernatants were collected and subjected to CE analysis. Of the 61 samples, 14 samples contain AA-I and AA-II, as well as 10 samples contain either AAI or AAII. The relative standard deviation (RSD) values of the migration times for AA-I and AA-II are less than 2.5% and 2.1% for three consecutive measurements of each sample. The RSD values for the peak heights corresponding to AA-I and AA-II in most samples are about 8.0% and 10.0%, respectively. The result shows that the present CE-LIF approach is sensitive, simple, efficient, and accurate for the determination of AAs in real samples.     

Analysis of flavonoids in honey by HPLC coupled with coulometric electrode array detection and electrospray ionization mass spectrometry

The analysis of flavonoids in unifloral honeys by high-performance liquid chromatography (HPLC) coupled with coulometric electrode array detection (CEAD) is described. The compounds were extracted by a nonionic polymeric resin (Amberlite XAD-2) and then separated on a reversed phase column using gradient elution. Quercetin, naringenin, hesperetin, luteolin, kaempferol, isorhamnetin, and galangin were detected in a coulometric electrode array detection system between +300 and +800 mV against palladium reference electrodes, and their presence was additionally confirmed by HPLC coupled with electrospray ionization mass spectrometry. The method was applied to analysis of 19 honeys of different varieties and origin. The limits of detection and quantitation ranged between 1.6 and 8.3 μg/kg and 3.9 and 27.4 μg/kg, respectively. The recoveries were above 96% in fluid and above 89% in creamy honeys. Some of these honeys (melon, pumpkin, cherry blossom, dandelion, maple, and pine tree honey) were investigated for their flavonoid content and profile for the first time. Differences between honeys were observed both in flavonoid concentrations and in the flavonoid profiles. The flavonoid concentrations ranged from 0.015 to 3.4 mg/kg honey. Galangin, kaempferol, quercetin, isorhamnetin, and luteolin were detected in all investigated honeys, whereas hesperetin occurred only in lemon and orange honeys and naringenin in lemon, orange, rhododendron, rosemary, and cherry blossom honeys.     

Determination of sulphonated azo dyes in food by ion-pair liquid chromatography with photodiode array and electrospray mass spectrometry detection

An ion-pair liquid chromatography method with on-line photodiode-array and electrospray mass spectrometry detection was developed to determine 10 commonly used sulphonated azo dyes (Tartrazine, Amaranth, New Coccine, Sunset Yellow FCF, Allura Red AC, Ponceau R, Ponceau 3R, Orange I, Orange II and Metanil Yellow) in food. A reversed phase C(18) column with gradient elution was utilized to separate these compounds. Triethylamine was added in the mobile phase as an ion-pair reagent for chromatographic separation. Photodiode-array detection was employed for quantitative determination and electrospray mass spectrometry was used for identification. Good linearity (0.05-10 ppm, r(2)=0.999) and detection limit (<0.01 ppm) were determined with 5 mul injection. In addition, precision and accuracy associated with this newly developed method will be presented. A liquid extraction method was also developed to extract these dyes from different foodstuffs. The application of this method was demonstrated by analyzing sulphonated azo dyes in soft drinks, fruit jam, and salted vegetables.     

Determination of total phthalates in edible oils by high‐performance liquid chromatography coupled with photodiode array detection

The previously reported procedure for the determination of the total phthalate in fatty food involved the extraction of phthalates using chloroform/methanol followed by the removal of the solvents before alkaline hydrolysis requiring 20 h and derivatization of phthalic acid. In this study, a phase‐transfer catalyst (tetrabutylammonium chloride) was used in the liquid–liquid heterogeneous hydrolysis of phthalates in oil matrix shortening the reaction time to within 25 min. The resulting phthalic acid in the hydrolysate was extracted by a novel molecular complex based dispersive liquid–liquid microextraction method coupled with back‐extraction before high‐performance liquid chromatography coupled with photodiode array detection. Under the optimal experimental conditions, the linearity of the method was in the range of 0.5–12 nmol/g with the correlation coefficients (r) >0.997. The detection limit (S/N = 3) was 0.11 nmol/g. Intraday and interday repeatability values expressed as relative standard deviation were 3.9 and 7.1%, respectively. The recovery rates ranged from 82.4 to 99.0%. The developed method was successfully applied for the analysis of total phthalate in seven edible oils.     

HPLC with electrode array detection

Summary A fast method for the determination of amitrole in drinking and ground water is described. Amitrole is separated from other substances by HPLC. For the determination a highly sensitive coulometric electrode array detector is applied. Tap and well water with concentrations down to 0.1 g amitrole/L can be determined without any enrichment steps. The detection limit of amitrole added to Viennese tap water is 0.05 g/L.     

Determination of insulin in humans with insulin-dependent diabetes mellitus patients by HPLC with diode array detection

A simple and reliable high-performance liquid chromatographic method with diode array detection has been developed and validated for the determination of insulin in human plasma. A good chromatographic separation was achieved on a C18 column with a mobile phase consisting of acetonitrile and 0.2M sodium sulfate (pH 2.4), 25:75 (v/v). Its flow rate was 1.2 mL/min. Calibration curve was linear within the concentration range of 0.15-25 μg/mL. Intra-day and inter-day relative standard deviations for insulin in human plasma were less than 6.3 and 8.5%, respectively. The limits of detection and quantification of insulin were 0.10 and 0.15 μg/mL, respectively. Also, this assay was applied to determine the pharmacokinetic parameters of insulin in eight insulin-dependent diabetes mellitus patients after subcutaneous injection of 25 IU of Actrapid HM.     

高效液相色谱法测定茶饮料中的黄酮类化合物

建立了茶饮料中六种黄酮类化合物的高效液相色谱检测方法。流动相采用梯度洗脱。结果表明芦丁、漆黄素、木犀草素、芹菜素在0.025~20 mg·L-1范围内呈现良好线性关系,桑色素、槲皮素在0.050~20 mg·L-1范围内呈现良好线性关系。加标回收率在84.5%~107.5%。该方法精密度良好(六种黄酮类化合物的相对标准偏差均不大于3.2%),检测限为6.2~34μg·L-1。该方法简便,灵敏、重现性好,可用于同时分析茶饮料中的黄酮化合物。     

高效液相色谱-光电二极管阵列检测法测定柴油中芳烃的类型

在采用美国试验与材料学会(ASTM) D6591标准方法测定柴油芳烃含量的过程中,通过光电二极管阵列检测器(PDAD)检测得到的色谱保留时间值及光谱特征吸收曲线,观察柴油中各类芳烃在极性氨基柱上的分离情况;用PDAD检测器考察了根据ASTM D6591确定的反冲洗时间点B对分析结果的影响,结果发现其允许的变化范围为B±0.2 min。在单环芳烃和双环芳烃分界不明显时,用PDAD检测器可以确定其切割点。     

Determination of iodide and thiocyanate in powdered milk and infant formula by on-line enrichment ion chromatography with photodiode array detection

Automated ultra-performance liquid chromatography (LC) with a radiometric detection system has been developed to analyze compounds labeled with short-lived positron (beta(+))-emitting radionuclides in microdialysates. This system involves (1) on-line microdialysis sampling to submit dialysates directly into the LC, (2) ultra-performance LC for improving sensitivity, resolution and speed of analysis, and (3) tandem flow-through of beta(+) and electrochemical detectors for real-time monitoring of radioactive and endogenous compounds simultaneously. This system permitted ultrasensitive measurement of radioactive compounds at the lowest detection limit of about 1Bq with a high-temporal resolution of sampling and less operator attention. The developed system was used for the continuous monitoring of l-[beta-(11)C]-3,4-dihydroxyphenylalanine (l-[beta-(11)C]DOPA) metabolites in the rat brain.     

Determination of flavonoids as complexes with Al3+ in microemulsion media by HPLC method with fluorescence detection

The scheme of postcolumn complexation reaction of flavonoids with aluminum (III) ions in various microemulsion media followed by fluorimetric detection is proposed. It is shown that fluorescence intensity of such complexes is five, three, and three times higher for quercetin, isorhamnetin, and kaempferol, respectively, when compared with the complexes obtained by dissolving flavonoids in MeCN/0.1 M HCl (30/70) and AlCl₃ in H₂O. The prospect of using microemulsions for quantitative quercetin extraction from plant raw material is demonstrated. Recovery of quercetin from onion peel is 98% with detection limits being 100, 45, and 15 ng/L for quercetin, isorhamnetin, and kaempferol, respectively. Quercetin content in three types of onion peel is determined. This content is found to be 34 ± 3 and 5 ± 1 mg/g for yellow and purple onion peel, respectively, while the content in white onion peel is below the detection limit.     

Determination of nitrofurans in animal feeds by liquid chromatography-UV photodiode array detection and liquid chromatography-ionspray tandem mass spectrometry

Within the EU, the use of nitrofurans is prohibited in food production animals. For this reason detection of these compounds in feedingstuffs, at whatever limit, constitutes an offence under EU legislation. This detection generally involves the use of analytical methods with limits of quantification lowers than 1 mg kg(-1). These procedures are unsuitable for the detection and confirmation of trace amounts of nitrofurans in feedingstuffs due to contamination. It is well known that very low concentrations of these compounds can be the source of residues of nitrofuran metabolites in meat and other edible products obtained from animals consuming the contaminated feed. The present multi-compound method was capable of measuring very low concentrations of nitrofurantoin (NFT), nitrofurazone (NFZ), furazolidone (FZD) and furaltadone (FTD) in animal feed using nifuroxazide (NXZ) as internal standard. Following ethyl acetate extraction at mild alkaline conditions and purification on NH2 column, the nitrofurans are determined using liquid chromatography with photodiode-array detection (LC-DAD). It was observed a CCalpha ranged from 50 to 100 microg kg(-1). The liquid chromatography-tandem mass spectrometric (LC-MS/MS) procedure was used to confirm the identity of the suspected presence of any of the nitrofuran compounds.     

藏药达乌里秦艽中环烯醚萜苷的HPLC测定

采用HPLc法同时测定了藏药达乌里秦艽中龙胆苦苷(gentiopicroside)、獐牙菜苦苷(swertiamarin)、獐牙菜苷(sweroside)和落干酸(loganic acid)4种主要环烯醚萜苷类成分,利用在线质谱(MS)进行了定性分析,并与同属藏药麻花艽进行了比较.色谱柱为Eclipse XDB-C8(4.6 mm×150 mm i.d.,5 μm),流动相A:体积分数5%乙腈(含10 mmol甲酸)水溶液,流动相B:体积分数95%乙腈水溶液,以流动相A在0～15 min内由100%线性减至90%,15～20 min内保持90%不变线性梯度洗脱.流速1.0 mL/min,检测波长240 nm,柱温30℃.结果表明,4种成分均达到了基线分离,具有较好的线性关系和回收率.本法可作为达乌里秦艽药材有效成分的测定方法,为其有效成分的进一步开发利用提供依据.