Ion-pair chromatography of polythionates and thiosulfate with detection based on their catalytic effects on the postcolumn azide–iodine reaction

The reduction of iodine with azide, catalyzed by polythionates (tri-, tetra-, penta- and hexathionate) and thiosulfate, has been utilized as a postcolumn reaction for chromatographic determination of these sulfur oxyanions. The method is based on the separation of polythionates and thiosulfate on an octadecylsilica column with an acetonitrile–water (20:80, v/v) mobile phase (pH 5.0) containing 3 mM tetrapropylammonium hydroxide and 6 mM acetic acid, followed by photometric measurement of the residual iodine (as triiodide) from the catalytic postcolumn azide–iodine reaction after mixing a reaction solution containing azide and iodine with the column effluent. Chromatograms obtained for the sulfur oxyanions showed negative peaks as a result of the decrease in absorbance of background. The conditions for the catalytic postcolumn reaction of the sulfur oxyanions in the column effluents were established by varying the concentrations of azide, iodine, iodide and acetic acid in the reaction solution, and varying the flow-rate, reaction temperature and length of the reaction tube. The detection limits (defined as S/N=3) were 4.3 μM for trithionate, 0.10 μM for tetrathionate, 2.7 nM for pentathionate, 5.0 nM for hexathionate and 1.1 nM for thiosulfate. When compared with earlier methods, the proposed method gave a much higher sensitivity for the determination of two polythionates (penta- and hexathionate) and thiosulfate. This method was applied successfully to the analysis of polythionates and thiosulfate added to hot-spring water samples.     

Determination of trace concentrations of bromate in municipal and bottled drinking waters using a hydroxide-selective column with ion chromatography

The International Agency for Research on Cancer determined that bromate is a potential human carcinogen, even at low micro/l levels in drinking water. Bromate is commonly produced from the ozonation of source water containing naturally occurring bromide. Traditionally, trace concentrations of bromate and other oxyhalides in environmental waters have been determined by anion exchange chromatography with an IonPac AS9-HC column using a carbonate eluent and suppressed conductivity detection, as described in EPA Method 300.1 B. However, a hydroxide eluent has lower suppressed background conductivity and lower noise compared to a carbonate eluent and this can reduce the detection limit and practical quantitation limit for bromate. In this paper, we examine the effect of using an electrolytically generated hydroxide eluent combined with a novel hydroxide-selective anion exchange column for the determination of disinfection byproduct anions and bromide in municipal and bottled drinking water samples. EPA Methods 300.1 B and 317.0 were used as test criteria to evaluate the new anion exchange column. The combination of a hydroxide eluent with a high capacity hydroxide-selective column allowed sub-microg/l detection limits for chlorite, bromate, chlorate, and bromide with a practical quantitation limit of 1 microg/l bromate using suppressed conductivity detection and 0.5 microg/l using postcolumn addition of o-dianisidine followed by visible detection. The linearity, method detection limits, robustness, and accuracy of the methods for spiked municipal and bottled water samples will be discussed.     

Determination of atropine in biological specimens by high-performance liquid chromatography

A sensitive and selective method for the determination of atropine in biological specimens has been developed. Samples alkalinized with sodium hydroxide were extracted with dichloromethane, and the organic phase was evaporated in a water-bath at 50 degrees C for ca. 10 min. The residue was dissolved in the mobile phase and injected into a reversed-phase column (TSK gel ODS-120A). The retention time for atropine could be varied by changing either the acetonitrile-water ratio in the mobile phase or the pH of the mobile phase. Acetonitrile-water (2:8, v/v) containing 6 mM phosphoric acid was used as mobile phase. Samples of 200 microliters or less were injected into the chromatography and measured at 215 nm. The recoveries of atropine added to drug-free specimens were satisfactory with coefficients of variation of 4% or less. Ninety-two compounds tested did not interfere with the assay of atropine. The method has been applied for monitoring atropine concentrations in cases of organophosphate and drug poisoning.     

Liquid chromatographic determination of penicillins by postcolumn degradation with sodium hypochlorite using an hollow-fibre membrane reactor

A sensitive, high-performance liquid chromatographic method involving postcolumn degradation with sodium hypochlorite and using a hollow-fibre membrane as a reactor is described for the determination of penicillins. Penicillins were separated on a C18 column followed by postcolumn reaction with sodium hypochlorite and sodium hydroxide using aminated and sulphonated hollow-fibre membrane reactors immersed in each solution, and detected at 270-280 nm based on the UV absorbances of the degradation products. At penicillin concentrations of 2 micrograms/ml, the precisions (relative standard deviation) were 2.28-4.78%. The detection limits of the proposed method were 2.5-25 ng for each penicillin at a signal-to-noise ratio of 3. Ampicillin and its metabolites [(5R,6R)-ampicilloic acid, the (5S,6R)-epimer and (2R)-pierazine-2',5'-dione] in human serum and urine were simultaneously determined by this method.     

Use of Alkaline Degradation for the Analysis of Dihydrotriazines via High Pressure Liquid Chromatography

Abstract

An HPLC method is described for the determination of 4,6-diamino-1,2-dihydro-2,2-dimethyl-1-(3′,4′-dichlorobenzyloxy)-1,3,5-triazine hydrochloride (WR 38839). The procedure required the isomerization of the drug sample by alkaline treatment with sodium hydroxide, as the parent compound was retained by the column. The reaction product of the drug was analyzed by HPLC using a strong cation exchange resin as the stationary phase and glycine buffer, pH 10.4 as the mobile phase. The product was isolated and identified by TLC, UV, IR, mass spectroscopy and elemental analysis. The postulated mechanism indicates that this would be a general analytical method for dihydrotriazine compounds. This technique, developed for the assay of the dihydrotriazine in an aqueous system, was successfully applied to rat urine samples spiked with the drug.     

Application of Iodine-Azide Reaction as Postcolumn Reaction in HPLC for Determination of 2-Thiobarbituric Acid

The reaction between iodine and azide ion induced by 2-thiobarbituric acid (TBA) has been utilized as a postcolumn reaction for chromatographic determination of this sulphur compound. The method is based on the separation of thiobarbituric acid on an Nova-Pak® CN HP column with an acetonitrile–aqueous solution of sodium azide mobile phase. The separation stage is followed by spectrophotometric measurement of the residual iodine (λ=350 nm) from the postcolumn iodine-azide reaction induced by thiobarbituric acid after mixing iodine solution containing iodide with the column effluent containing azide ions and the inductor. Chromatograms obtained for thiobarbituric acid showed negative peaks as a result of the decrease in absorbance of background. The detection limit (defined as S/N=3) was 0.16 pmol (22.9 pg) for thiobarbituric acid. Calibration graphs, plotted as peak heights or peak area vs. concentrations, were linear up to 1 nM.     

HPLC-photolysis-electrochemical detection in pharmaceutical analysis: application to the determination of spironolactone and hydrochlorothiazide in tablets

To extend the applicability of electrochemical detection in pharmaceutical analysis, an on-line postcolumn photochemical reactor is used to produce electroactive photoderivatives of selected cardiovascular drugs. This system is applied to the analysis of dosage forms containing spironolactone in both single-component formulation and in combination with hydrochlorothiazide. The pH of the mobile phase and irradiation time within the reactor are optimized to produce maximum amperometric response. Spironolactone, hydrochlorothiazide, and 4-amino-6-chloro-1,3-benzenedisulfonamide, the synthetic precursor and hydrolysis product of hydrochlorothiazide, are separated by reversed-phase chromatography on a 5-microns cyano bonded phase column within nine minutes by using a methanol-phosphate buffer mobile phase. Minimum detectable levels are in the low ng range.     

A universal peroxyoxalate-chemiluminescence detection system for mobile phases of differing pH.

A universal peroxyoxalate-chemiluminescence detection system for high performance liquid chromatography, available for a variety of mobile phases, has been developed. The system consisted of a dual-head short-stroke pump and a chemiluminescence detector. The standard conditions using bis(2,4,6-trichlorophenyl) oxalate (TCPO) as aryl oxalate were as follows. The first postcolumn solution was the mixture of 0.5 M imidazole-nitric acid (pH 7.5) and acetonitrile (1:4, v/v). The second was acetonitrile containing TCPO-hydrogen peroxide. These two solutions were delivered by the two pump-heads. After the pH of the column eluate was adjusted to the optimum range (6.5-7.5) by the first postcolumn solution, the solution was mixed with the second postcolumn solution. After flowing through a reaction coil, the chemiluminescence of the mixture was monitored. Using this system, a high sensitivity (fmol level) was obtained for perylene as an analyte with mobile phases having different pH values (2.0-8.0). Polycyclic aromatic hydrocarbons became detectable to a high sensitivity even after the column separation using an acidic mobile phase. The detection sensitivity of nitrated pyrenes after on-line electrochemical reduction using an acidic mobile phase was also increased. This system might be available for other aryl oxalates by some modifications of the postcolumn solutions.     

Liquid chromatography and postcolumn indirect detection of glyphosate.

Glyphosate [N-(phosphonomethyl)glycine] and its metabolite aminomethylphosphonic acid (AMPA) were separated and detected by a postcolumn indirect detection strategy. Separation can be done on a cation-exchange column, where glyphosate elutes before AMPA, or on an anion-exchange column, where the elution order is reversed. Detection was achieved by using a fluorescent Al(3+)-morin postcolumn reagent. When the postcolumn reagent combines with the column effluent in a mixing tee, the fluorescence decreases in the presence of both analytes. Variables affecting the postcolumn indirect fluorescence detection were established and optimized; the major factors were postcolumn pH and volume and temperature of the postcolumn reaction coil. Detection limits, defined as three times the background noise, for glyphosate and AMPA separated on an anion-exchange column were 14 and 40 ng, respectively.     

Determination of bovine blood oleandrin by high-performance liquid chromatography and postcolumn derivatization

A high-performance liquid chromatographic procedure with a postcolumn fluorescence derivatization is developed for the analysis of oleandrin in bovine blood. Oleandrin is separated by an octadecylsilane-bonded column with a mobile phase containing dehydroascorbic acid. The effluent of the column is mixed with concentrated hydrochloric acid and passed through poly(tetrafluoroethylene) tubing maintained at 70 degrees C. The resultant fluorophores are detected at 465 nm with excitation at 348 nm. Simple solid-phase extraction using Sep-Pak tC2 is effective for sample purification. We found the minimal detectable quantity of oleandrin in plasma to be 1.5 ng/mL at a signal-to-noise ratio of 3:1.     

Automated flow system on-line to LC with postcolumn derivatisation for determination of sugars in carbohydrate-rich foods

Summary A method for the direct determination of carbohydrates in foods using an automated-flow system coupled on-line to a high-performance liquid chromatograph is proposed. The method is based on postcolumn derivatisation of reducing sugars with p-aminobenzoic acid hydrazide in an alkaline medium following elution from the chromatographic column with an acetonitrile: water gradient as mobile phase. The manifold allows non-reducing sugars to be hydrolysed prior to insertion into the chromatograph, thus making them compatible with the derivatisation reaction and with continuous decolorisation of the sample on an activated carbon column. The method allows determination of six sugars in contents between 0.005 and 4% (w/v) with high precision (3.8–5.0%RSD). For analytical validation, it was applied to determination of fructose, sucrose, maltose, lactose and maltotriose in two reference materials (milk powder and sugar). Finally, the method was used to determine sugars in a variety of carbohydrate-rich foods.     

Immunoaffinity column cleanup with liquid chromatography for determination of aflatoxin B1 in corn samples: interlaboratory study

An interlaboratory study was conducted to evaluate the effectiveness of an immunoaffinity column cleanup liquid chromatography (LC) method for the determination of aflatoxin B1 levels in corn samples, enforced by European Union legislation. A test portion was extracted with methanol-water (80 + 20); the extract was filtered, diluted with phosphate-buffered saline solution, filtered on a microfiber glass filter, and applied to an immunoaffinity column. The column was washed with deionized water to remove interfering compounds, and the purified aflatoxin B1 was eluted with methanol. Aflatoxin B1 was separated and determined by reversed-phase LC with fluorescence detection after either pre- or postcolumn derivatization. Precolumn derivatization was achieved by generating the trifluoroacetic acid derivative, used by 8 laboratories. The postcolumn derivatization was achieved either with pyridinium hydrobromide perbromide, used by 16 laboratories, or with an electrochemical cell by the addition of bromide to the mobile phase, used by 5 laboratories. The derivatization techniques used were not significantly different when compared by the Student's t-test; the method was statistically evaluated for all the laboratories. Five corn sample materials, both spiked and naturally contaminated, were sent to 29 laboratories (22 Italian and 7 European). Test portions were spiked with aflatoxin B1 at levels of 2.00 and 5.00 ng/g. The mean values for recovery were 82% for the low level and 84% for the high contamination level. Based on results for spiked samples (blind pairs at 2 levels) as well as naturally contaminated samples (blind pairs at 3 levels), the values for relative standard deviation for repeatability (RSDr) ranged from 9.9 to 28.7%. The values for relative standard deviation for reproducibility (RSDR) ranged from 18.6 to 36.8%. The method demonstrated acceptable within- and between-laboratory precision for this matrix, as evidenced by the HorRat values.     

烯丙基乙基醚接枝聚硅氧烷气相色谱固定相的研究

合成了侧链为烯丙基乙基醚的聚硅氧烷气相色谱固定相,静态法涂柱,评价了其色谱性能.该固定相柱效高,易于涂渍,耐温达290℃,分离选择性好,适用于醇类和酯类的分离以及白酒样品的分析.     

Determination of aflatoxin in processed dried cassava root: validation of a new analytical method for cassava flour

A new method that uses HPLC with a photochemical reactor for enhanced detection was developed and validated for the determination of aflatoxins in cassava flour. Samples were spiked with a mixture of four aflatoxins at 5, 10, and 20 microg/kg mixed with either 1 or 5 g NaCI and extracted with methanol-water (80 + 20, v/v) by shaking for 10 or 30 min. An immunoaffinity column was used for cleanup. HPLC with postcolumn derivatization, for enhancement of aflatoxin fluorescence, and fluorescence determination were used for quantitation of the toxin concentration. The method was validated for recovery, linearity, and precision at the three concentrations tested. Recovery ranges were 52-70, 69-85, and 80-89% for the spiking levels of 5.0, 10.0, and 20.0 microg/kg, respectively. It appears that the amount of salt (NaCl) and the shaking time are critical factors in this method; optimal performance was obtained when 1 g salt was used and the shaking time was 10 min. The good linearity and precision of the method allowed baseline separation from interferences, e.g., coumarins.     

Validation of a column liquid chromatographic method for phytate

A column liquid chromatographic method that uses a spectrophotometric detector for the analysis of phytate and other inositol phosphates in foodstuffs and seeds is described. It has been tested thoroughly and sent to 6 other laboratories where there was an interest in such an analytical method and the equipment was available for performing it. These samples were blinded to the individual collaborators. Also sent was a standard wheat bran sample available from the American Association of Cereal Chemists with a standard phytate value reported as 3.2%. The postcolumn sulfosalicylic acid reaction was developed in the 1950s as an analytical method for ferric ion. All reagents are aqueous solutions and the specific pH values of each are important. The column separation is at pH 4, which dissociates all phosphate analogs. The ferric sulfosalicylate is at pH 1.8. The postcolumn reaction is then at pH 2.0-2.3. At this pH, the sulfosalicylate complexes one ferric ion and will yield it to a stronger complexing agent such as a phosphate ester. At higher pH values, sulfosalicylate complexes 2 ferric ions and will yield neither to these anions. The method sensitivity is 8-12 nmoles/injection.     

分散固相萃取净化/高效液相色谱-串联质谱法测定水产品中的5种硝基咪唑类药物残留

建立了水产品中5种硝基咪唑类药物的高效液相色谱-串联质谱检测方法。样品经含0.1%氨水乙腈提取,加无水硫酸钠、C18-N以及NH2-PSA净化剂后涡旋振荡对样品进行净化,以Merck Chromolith Performance RP-18e(4.6 mm×100 mm)色谱柱分离,甲醇和0.1%甲酸水溶液为流动相梯度洗脱,正离子模式电喷雾电离,配合多反应离子扫描(MRM)定性定量分析目标化合物。考察了提取剂中氨水和净化剂的用量对加标回收率的影响,在优化实验条件下,5种硝基咪唑类药物在20~500μg/L范围内线性关系良好,r2≥0.998 9;3个加标水平下的方法回收率为77.2%~94.8%;定量下限为0.7~2.0μg/kg。该方法快速、简单、准确,适用于水产品中5种硝基咪唑类药物残留的检测。     

Differential Measurement of Cortisol and Cortisone in Human Saliva by HPLC with Uv Detection

Abstract

Both cortisol and its dehydro metabolite cortisone are present in normal human saliva. A method for differential Measurement of both compounds in 1 ml samples of saliva by HPLC/UV is described. the method uses an extraction column having a cyclodextrin bonded phase to retain the compounds of interest while allowing elution of interfering compounds. A steroid-bearing fraction is eluted from the cyclodextrin column, dried, reconstituted in a weak mobile phase, and injected on a reversed phase HPLC/UV system provided with an injector-mounted reversed phase extraction column. Samples containing corticosteroid concentrations as low as 0.5 ng/ml can be effectively analyzed by this method.     

Regeneration of tetrabutylammonium ion-pairing reagent distribution in a gradient elution of reversed phase ion-pair chromatography

The regeneration of ion-pairing reagent distribution on liquid chromatography columns after gradient elution has been well recognized as the cause for long column equilibration time, a major drawback associated with gradient elution reverse phase ion-pair chromatography. To date, the majority of studies have focused on optimizing the separation conditions to shorten the equilibration time. There is limited understanding of the ion-pairing reagent distribution process between the mobile phase and stationary phase in the course of gradient elution, and subsequent column re-equilibration. The focus of this work is to gain a better understanding of this process. An ion-pair chromatographic system, equipped with a YMC ODS C(18) column and a mobile phase containing tetrabutylammonium (TBA) hydroxide as the ion-pairing reagent, was used in the study. The TBA distribution profile was established by measuring its concentration in the eluent fractions collected during the gradient cycle using different column equilibration times with an ion chromatographic method. Furthermore, the analyte retention time was evaluated as the function of the column equilibration time and TBA concentration in the mobile phase. The column equilibration and its impact on the method robustness will also be discussed.     

Determination of biotin by high-performance liquid chromatography in infant formula, medical nutritional products, and vitamin premixes

A solid-phase extraction sample preparation procedure was developed for use with a high-performance liquid chromatography (HPLC) method for biotin analysis. The HPLC method used a reversed-phase C18 column; chromatography run time was 8.5 min. After eluting from the column, biotin went through postcolumn reaction to form a conjugate with streptavidin-fluorescein isothiocyanate, which was then detected by a fluorescence detector. This method was tested with infant formula, medical nutritional products, and vitamin premix samples.     

高效液相色谱法同时测定化妆品中七种性激素

建立了化妆品中7种性激素(雌二醇、雌三醇、雌酮、睾酮、甲基睾酮、孕酮、己烯雌酚)同时测定的高效液相色谱法。先在试样中加入20 g/L氢氧化钠溶液与油脂进行皂化反应,然后用二氯甲烷-乙酸乙酯(体积比为40∶1)混合液在酸性条件下(pH 3)萃取,选择XTerraTMRP18色谱柱,以水-甲醇-乙腈(体积比为50∶32∶18)混合液为流动相,在波长230 nm处检测。7种性激素分离良好并排除了样品中杂质峰的干扰,低、高浓度平均回收率范围为75.6%~97.8%;相对标准偏差为1.9%~7.2%;检出限为3.7