Rapid separation and analysis of six organic acids in Bayer liquors by RP-HPLC after solid-phase extraction

A rapid revised phase high-performance liquid chromatographic (RP-HPLC) method for the determination of six organic acids in Bayer liquors is reported. Oxalic, tartaric, acetic, succinic, glutaric and butene dicarboxylic acid were separated and quantified in 10 min. First time repeatability, reproducibility and recoveries were determined out for these acids in Bayer liquors. The organic acids were removed from Bayer liquor by using a solid-phase extraction procedure with anion-exchange cartridges. The chromatographic separation was achieved with only one Kromasil RP-C18 column thermo stated at 25 degrees C. Organic acids were detected with a UV-vis detector (215 nm). The precision results showed that the relative standard deviations of the repeatability and reproducibility were < 2.80% and < 3.74%, respectively. The accuracy of the method was confirmed with an average recovery ranging between 85.2 and 107.3%. Under optimum conditions the detection limits ranged from 50 to 1000 mg/L.     

Analysis of anions in alkaline solutions by ion chromatography after solid-phase extraction

An Ion Chromatographic (IC) method for the determination of six organic acids and three inorganic anions in alkaline solutions was reported. Formic, acetic, propionic, oxalic, succinic, glutaric acid, F-, Cl-, and SO4(2-) were separated and determined in 33 min. The analytes were removed from Bayer liquor by using an ion-exchange resin column. The chromatographic separation was achieved with only one IonPac AS11-HC column thermostated at 30 degrees C. Organic acids and inorganic anions were detected with a suppressed conductance detector. The precision results' showed that the repeatability and reproducibility were < 2.94 and < 1.37%, respectively. The accuracy of the method was assessed by the recoveries ranging from 86.3 to 105.6%. Under optimum conditions the detection limits ranged from 0.008 to 0.053 mg/l.     

Application of co-electroosmotic capillary electrophoresis for the determination of inorganic anions and carboxylic acids in soil and plant extract with direct UV detection

Summary Indirect UV detection in capillary zone electrophoresis (CZE) is frequently used for the determination of inorganic anions and carboxylic acids. However, there are few reports on direct UV detection of these solutes in real samples. This paper describes the use of direct UV detection of inorganic anions and organic acids in environmental samples using co-electroosmotic capillary zone electrophoresis (co-CZE) at 185 nm. The best separation and detection of the solutes was achieved using a fused silica capillary with an electrolyte containing 25 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide (TTAB) and 15% acetonitrile (v/v) at pH 6.0. Four common inorganic anions (Cl⁻, NO₂ ⁻, NO₃ ⁻ and SO₄ ²⁻) and 11 organic acids (oxalic, formic, fumaric, tartaric, malonic, malic, citric, succinic, maleic, acetic, and lactic acid), were determined simultaneously in 15 min. Linear calibration plots for the test solutes were obtained in the range 0.02–0.5 mM with detection limits ranging from 1–9 μM depending on the analyte. The proposed method was successfully used to determine inorganic anions and carboxylic acids in soil and plant tissue extracts with direct injection of the sample.     

Determination of Organic Acids in Red Wine and Must on Only One RP-LC-Column Directly After Sample Dilution and Filtration

A new method for simultaneous determination of organic acids in red wine and must by liquid chromatography was studied. The determination of organic acids in wines can be achieved in less than 13 min, preceded only by a simple sample dilution and filtration step. With this method, the chromatographic separation of eight organic acids and interfering peaks present in red wine, required only one reversed phase column (Waters Atlantis dC18 column, 4.6 × 150 mm ID, 5 μm). As mobile phase, isocratic acetonitrile–0.01 mol L⁻¹ KH₂PO₄ at pH 2.7 5:95 (v/v) at a flow rate of 0.8 mL min⁻¹ was used. Detection wavelength was set at 210 nm except for ascorbic acid which was detected at 243 nm. Application to red wine and must confirmed good repeatability and showed a wide variation range for concentrations of organic acids.     

Chromatographic separation of uranium(VI) from other elements using L-valine and poly[dibenzo-18-crown-6]

A selective and effective column chromatographic separation method has been developed for uranium(VI) using poly[dibenzo-18-crown-6]. The separation was carried out in L-valine medium. The adsorption of uranium(VI) was quantitative from 1.0 × 10⁻⁴ to 1 × 10⁻¹ M of L-valine. Amongst various eluents 2.0–8.0 M hydrochloric acid, 1.0–4.0 M sulfuric acid, 1.0–5.0 M perchloric acid, 6.0–8.0 M hydrobromic acid and 5.0–6.0 M acetic acid were found to be efficient eluents for uranium(Vl). The capacity of poly[dibenzo-18-crown-6] for uranium(VI) was 0.25 ± 0.01 mmol/g of crown polymer. Uranium(VI) was separated from number of cations and anions in binary mixtures in which most of the cations and anions show a very high tolerance limit. The selective separation of uranium(VI) was carried out from multicomponent mixtures. The method was extended to determination of uranium(VI) in geological samples. The method is simple, rapid and selective with good reproducibility (approximately ∼2%).     

Determination of organic acids in air by capillary electrophoresis and ion-exclusion chromatography

Summary A capillary electrophoretic (CE) method for the determination of organic acids in the low ppm range is described. The buffer consisted of 5 mM 2,6-pyridinedicarboxylic acid and 0.5 mM cetyltrimethylammonium bromide, pH 5.6. The former served as background electrolyte for indirect UV detection at 200 nm, whereas the latter was used to reverse electroosmotic flow. In <5 min 8 low molecular mass organic acids (oxalic, formic, malonic, glutaric, glycolic, acetic, lactic and propanoic) and two inorganic acids (hydrochloric and sulphuric) were separated. Detection limits for anions tested were 0.04 mg L⁻¹ (lactic acid) to 0.6 mg L⁻¹ (malonic acid). The method was applied to the determination of organic acids in air samples. The CE results when compared with ion-exclusion chromatography (IEC) agreed well. The use of electrokinetic injection in CE proved beneficial for preconcentration of organic acids in real samples. Using electrokinetic injection, preconcentration factors ranging from 14 (hydrochloric acid) to 3 (propanoic acid) were obtained. Presented at Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Direct analysis of clomipramine in human plasma by microbore high performance liquid chromatography with column-switching

Summary An automated microbore, liquid chromatographic method with column-switching was developed for the determination of clomipramine from human plasma samples. After direct injection of samples (60 μL), plasma proteins and clomipramine were separated in size-exclusion mode using 20% acetonitrile in 20 mM phosphate buffer (pH 7.0) on Capcell Pak MF Ph-1 precolumn (10×4 mm I.D.). By valve switching, a fraction containing clomipramine was directed to an intermediate column for subsequent main separation on a microbore C₁₈ column (250×1.5 mm I.D.) using 50% acetonitrile in 20 mM phosphate buffer (pH 2.5) at 0.1 mL min⁻¹. The method was advantageous for rapidity (total analysis time: 15 min), reproducibility (C.V.<4.8%), and increased sensitivity (1 ng mL⁻¹). The linearity of response was good (r ²≥0.999) over the concentration range 1–250 ng mL⁻¹.     

HPLC of amino acids and oligopeptides by pre-column fluorescence derivatization with N-hydroxysuccinimidyl-α-(9-phenanthrene)-acetate

Summary A sensitive LC method for the detection of amino acids and oligopeptides with pre-column fluorescence derivatization has been developed. Glycine, glycylglycine, triglycine, glutathione, glutamic acid, and cysteine were separated on a reversed-phase C₁₈ column with methanol-water-triethylamine eluent, derivatization and chromatographic conditions were optimized. The six derivatives were eluted in 20 min with good reproducibility. The relative standard derviations (n=6) at an analytical concentration of 2×10⁻⁶ M are <5%. Detection limits (signal-to-noise ratio=3) for the six derivatives are 23–68 fmol.     

Determination of Pyrethroid Insecticide Deltamethrin by Micellar Liquid Chromatography with Spectrophotometric Detection

A simple micellar liquid chromatographic technique for deltamethrin determination was developed and validated. The method provided to be suitable for deltamethrin determination in pediculicide shampoo. Kromasil C18 column (150 mm×4.6 mm, 5 μm) and mobile phase −0.12 M sodium dodecyl sulfate with 9% (v/v) 1-butanol were used for deltamethrin separation. Detection wavelength was 265 nm. The retention time was about 15 min. Different validation parameters were evaluated. The specificity of the method was demonstrated. Linearity was established in the range 10–40 μg L⁻¹. The limits of detection and quantitation were 1.06 and 3.22 μg mL⁻¹, respectively. The method showed excellent accuracy (100.6%) and precision (repeatability) gave a relative standard deviation of less than 1%. The influence of the various method parameters (robustness study) was also studied.     

Reversed Capillary Electrochromatography: Investigation of Peak Symmetry for Eluting Curves of Solutes

Summary A clean method without use of organic solvents has been developed for isolation and high-performance liquid chromatographic (HPLC) determination of oxytetracycline (OTC) and sulphadimidine (SDD) in cow's milk. Isolation is rapid and simple—homogenization with an inorganic acid solution by means of a handy ultrasonic homogenizer, which is easy-to-use and portable, followed by centrifugation. Reversed-phase HPLC was performed on a C₄ column, with 1.25 mmol L⁻¹ succinic acid solution as mobile phase, and identification was by means of a photodiode-array detector. Separation of the analytes was achieved in less than 8 min. Significant linearity was established over the concentration range of 0.1–1.0 μg mL⁻¹ for both target compounds (r>0.99,P<0.01). Average recoveries of OTC and SDD (each spiked at 0.1–1.0 μg mL⁻¹) were ≥88.8, and inter- and intra-assay variability was ≤2.8%. The total time required for analysis of one sample was <20 min. The limits of quantitation of the method (μg mL⁻¹ in milk) were 0.044 for OTC and 0.023 for SDD. No organic solvent was used at any stage of the analysis.     

Properties of naproxen ion-selective electrodes

Naproxen membrane electrodes based on different plasticizers and the quaternary ammonium salts (QASs) dimethyldidecylammonium bromide, methyltrioctylammonium chloride, or tetraoctylammonium chloride, were prepared. The following basic parameters were investigated for the optimal electrode: measurement range (10⁻⁴ − 10⁻¹ mol L⁻¹), slope of the linear range of the calibration curve (−58.3 mV decade⁻¹), limit of detection (6.0 × 10⁻⁵ mol L⁻¹), lifetime (2.5 months), dependence of the electrode potential on pH (5.5 − 9.0), reproducibility of potential (1.2 mV) and selectivity coefficients in relation to selected organic and inorganic anions. The electrode was utilized for determination of naproxen in tablets by the calibration curve method and the standard addition method.      

Application of a trazodone-selective electrode to pharmaceutical quality control and urine analyses

A trazodone-selective electrode for application in pharmaceutical quality control and urine analysis was developed. The electrode is based on incorporation of a trazodone-tetraphenylborate ion exchanger in a poly(vinyl chloride) membrane. The electrode showed a fast, stable and Nernstian response over a wide trazodone concentration range (5 × 10⁻⁵−1 × 10⁻² M) with a mean slope of 59.3 ± 0.9 mV/dec of concentration, a mean detection limit of 1.8 × 10⁻⁵± 2.2 × 10⁻⁶ M, a wide working pH range (5–7.5) and a fast response time (less than 20 s). The electrode also showed good accuracy, repeatability, reproducibility and selectivity with respect to some inorganic and organic compounds, including the main trazodone metabolite. The electrode provided good analytical results in the determination of trazodone in pharmaceuticals and spiked urine samples; no extraction steps were necessary. Dissolution testing of trazodone tablets, in different conditions of pH and particle size, based on a direct potentiometric determination with the new selective electrode is presented as well.     

Potentiometric sensor arrays for the individual determination of penicillin class antibiotics using artificial neural networks

Arrays of potentiometric sensors with plasticized polymer membranes based on tetraalkylammonium organic ion exchanges with anions of penicillin class antibiotics (benzylpenicillin, ampicillin, oxacillin, and amoxicillin) have been proposed for the individual determination of antibiotics in model mixtures and pharmaceutical preparations. The following cross-sensitivity parameters of sensors have been estimated: the average slope of the electrode function (54 < S _av < 61), the nonselectivity factor (2.8 < F < 74.6), and the reproducibility factor (31.9 < K < 61.2). Artificial neural networks have been applied to the treatment of analytical signals from the multisensor system in the concentration range 2.5 × 10⁻⁴–1 × 10⁻¹ M. The average error of the individual determination of penicillin class antibiotics is 5–7%.     

Sensitive determination of inorganic anions at trace levels in samples of snow water from sierra nevada (Granada, Spain) by capillary ion electrophoresis using calix[4]arene as selective modifier

Summary A highly sensitive and selective capillary ion electrophoretic (CIE) method has been established to show the applicability of this separation technique to the determination of some of the anions usually found in water samples. The ions were monitored by UV spectrophotometry with diode-array detection in presence of sulfonated calixarene compounds as organic modifiers in the electrophoretic buffer medium. The instrumental variables affecting the sensitivity and resolution of the mixture were carefully optimized. Snow water samples were been selected for analytical determination of iodide, chloride, sulfate, nitrite, phosphate, and nitrate anions at ng mL⁻¹ levels. The repeatability and reproducibility were calculated and were in the range 2.1 to 5.4% for the analytes determined.     

Properties of ibuprofen ion-selective electrodes based on the ion pair complex of tetraoctylammonium cation

Ibuprofen membrane electrodes based on different plasticizers: diisobutyl phthalate (DIBP), o-nitrophenyloctyl ether (o-NPOE), dioctyl sebacate (DOS) and tetraoctylammonium 2-(4-isobutylphenyl)propionate were prepared. All electrodes show: a near Nernstian slope of characteristic (58.3–60.9 mV decade⁻¹) in the measurement range (10⁻⁴–10⁻¹ mol L⁻¹), limit of detection (5.0×10⁻⁵ mol L⁻¹), really long lifetime (12 months), dependence of the electrode potential on pH (5.5–9.0), reproducibility of potential (0.6–1.2 mV) and selectivity coefficients in relation to some organic and inorganic anions. The electrodes were applied for the determination of ibuprofen in tablets by the calibration curve method and the standard addition method.      

Simultaneous determination of oxalate, thiosulfate, and thiocyanate in urine by ion-exclusion chromatography with electrochemical detection

Summary A sensitive ion-exclusion chromatographic method has been developed for determination of oxalate, thiosulfate, and thiocyanate. The method is based on separation of these anions on a polymethacrylate-based, weakly acidic cation-exchange resin (TSKgel OApak-A) and detection by means of a glassy carbon (GC) electrode electrochemically modified with polyvinylpyridine (PVP), palladium, and iridium oxide (PVP/Pd/IrO₂). The electrochemical behavior of oxalate, thiosulfate, and thiocyanate at this chemically modified electrode (CME) have been investigated by cyclic voltammetry. The results indicated that electrocatalytic oxidation of these anions by the electrode was efficient and that the sensitivity, stability, and lifetime of the electrode were relatively high. Combined with ion-exclusion chromatography the PVP/Pd/IrO₂ electrode was used as the working electrode for amperometric detection of these anions. All linear ranges were over two orders of magnitude and detection limits, defined asS/N=3, were 9.0×10⁻⁷ mol L⁻¹ for oxalate, 6.7×10⁻⁷ mol L⁻¹ for thiosulfate, and 5.6×10⁻⁷ mol L⁻¹ for thiocyanate. Correlation coefficients were all>0.998. Coupled with microdialysis sampling the method has been successfully applied to the determination of oxalate, thiosulfate, and thiocyanate in urine.     

Determination of eight penicillins in serum from cattle and pigs by generic HPLC method

Summary An HPLC method was developed for determination of amoxicillin, penicillin G, penicillin V, ampicillin, oxacillin, cloxacillin, nafcillin and dicloxacillin in serum from pigs and cattle. Serum was cleaned up by solid-phase extraction (SPE), ultra-filtered and derivatised. The method was linear in the range tested up to 2000 ng mL⁻¹ of individual penicillins in serum. Limits of detection were 11–14 ng mL⁻¹. Mean recoveries were 90–103% in the range 20–2000 ng mL⁻¹. The relative repeatability, standard deviation was <10% at 20 ng mL⁻¹ level and <6% in the range 100–2000 ng mL⁻¹.     

Determination of Carbamazepine in Parenteral Nanoemulsions: Development and Validation of an HPLC Method

A high performance liquid chromatographic method was developed and validated for the quantitative determination of carbamazepine in intravenous nanoemulsions. The method validation yielded good results with respect to linearity, specificity, precision and accuracy. The method was carried out on a RP-18 column with a mobile phase composed of methanol–water (70:30 v/v) subjected to a gradient of acetonitrile after drug elution, and detection at 286 nm. The linearity in the range of 10.0–50.0 μg mL⁻¹ presented a determination coefficient (r ²) of 0.9996, calculated by least-squares regression; the RSD values for intra-day and inter-day precision for % recovered were <0.44 and <1.21%, respectively; and the recovery of carbamazepine from the sample matrix ranged from 94.3 to 104.9%.     

Determination of inorganic anions in mushrooms by ion chromatography with potentiometric detection

A simple method for determination of common inorganic anions in mushroom samples has been developed by using suppressed ion chromatography with a pH detection unit. The detection unit which was constructed in such a way that practically no additional dispersion occurred consisted of a flow-through quinhydrone pH sensor and a small reference electrode. Chromatographic separation was performed in the order F⁻, Cl⁻, NO₂⁻, Br⁻, PO₄³⁻, ClO₃⁻, NO₃⁻, and SO₄²⁻, at room temperature by using Ion Pac AS 9-HC anion exchange column. Anion extracts from dried mushroom samples at room temperature were homogenized and filtered before injection. Under optimized analytical conditions, the detection limits of the method were between 2 × 10⁻⁶ and 3 × 10⁻⁴ M, depending on the anion studied. The results showed that the concentrations of fluoride and bromide in all mushroom samples were below their limit of detection. Nitrite was found to be the lowest abundant ion, while the most abundant ion was sulfate in all the mushroom samples studied.     

Validation of a high-performance liquid chromatographic method for determination of isoflavonoids in soybeans. Study of the extraction procedure by experimental design

Summary An improved analytical method, reversed-phase high-performance liquid chromatography on a narrow-bore C₁₈ column, has been developed for the simultaneous determination of genistein, daidzein, formononetin, and biochanin A. The method was validated in terms of detection limits, quantitation limits (LOQ), linearity, and precision.LOQ in the 0.04–0.1 μg mL⁻¹ range were calculated, enabling determination of these compounds of nutritional concern at trace levels. Good linearity was demonstrated over three orders of magnitude of concentration for each analyte (r ²=0.998–1.000). The intra-day repeatability was evaluated in terms ofRSD (%) at two concentration levels for each analyte (RSD (%) <1.8%). Good inter-day reproducibility of data was proved by performing homoscedasticity and ANOVA tests (P>0.05 at the 95% confidence level). The method was applied to the determination of genistein and daidzein in yellow soybeans, after optimization of the method for extraction of isoflavonoid aglycones from soybeans by experimental design, i.e. central composite design. Extraction recoveries up to 87±4% were obtained when the corresponding glycosidic forms (genistin and daidzin) were added to soybean samples.