Development and validation of a reversed-phase ion-pair high-performance liquid chromatographic method for the determination of risedronate in pharmaceutical preparations

A stability indicating, reversed-phase ion-pair high-performance liquid chromatographic method was developed and validated for the determination of risedronate in pharmaceutical dosage forms. The determination was performed on a BDS C₁₈ analytical column (250 mm × 4.6 mm i.d., 5 μm particle size); the mobile phase consisted of 0.005 M tetrabutylammonium hydroxide and 0.005 M pyrophosphate sodium (pH 7.0) mixed with acetonitrile in a ratio (78:22, v/v) and pumped at a flow rate 1.00 mL min⁻¹. The ultraviolet (UV) detector was operated at 262 nm. The retention times of magnesium ascorbyl phosphate, which was used as internal standard and risedronate were 4.94 and 5.95 min, respectively. The calibration graph was ranged from 2.50 to 20.00 μg mL⁻¹, while detection and quantitation limits were found to be 0.48 and 1.61 μg mL⁻¹, respectively. The intra- and inter-day percentage relative standard deviations, %R.S.D., were less than 5.9%, while the relative percentage error, %E_r, was less than 0.4%. The method was applied to the quality control of commercial tablets and content uniformity test and proved to be suitable for rapid and reliable quality control.     

Development and validation of a hydrophilic interaction liquid chromatographic method for determination of aromatic amines in environmental water

A simple, precise, and accurate hydrophilic interaction liquid chromatographic (HILIC) method has been developed for the determination of five aromatic amines in environmental water samples. Chromatography was carried out on a bare silica column, using a mixture of acetonitrile and a buffer of NaH₂PO₄–H₃PO₄ (pH 1.5, containing 10 mM NaH₂PO₄) (85:15, v/v) as a mobile phase at a flow rate of 1 mL min⁻¹. Aromatic amines were detected by UV absorbance at 254 nm. The linear range of amines was good (r² > 0.998) and limit of detection (LOD) within 0.02–0.2 mg L⁻¹ (S/N = 3). The retention mechanism for the analytes under the optimum conditions was determined to be a combination of adsorption, partition and ionic interactions. The proposed method was applied to the environmental water samples. Aromatic amines were isolated from aqueous samples using solid-phase extraction (SPE) with Oasis HLB cartridges. Recoveries of greater than 75% with precision (RSD) less than 12% were obtained at amine concentrations of 5–50 μg L⁻¹ from 100 mL river water and influents from a wastewater treatment plant (WWTP). The present HILIC technique proved to be a viable method for the analysis of aromatic amines in the environmental water samples.     

Determination of Pb in natural waters with 2-mercaptobenzimidazole-5-sulfonate (MBIS)chemically modified gold electrode

The preparation, characterization and analytical applications of gold electrodes modified with ω-mercapto alkyl/aryl sulfonates are described. The devices resulted effective for the determination of free and labile Pb(II) in water samples by anodic stripping voltammetry (E_dep = −600 mV) and in particular 2-mercaptobenzimidazole-5-sulfonate (MBIS) offered the best performances with detection limit of 0.4 μg L⁻¹.Quantitative stripping of Pb from the electrode surface during the anodic scan, is obtained using sodium citrate buffer (pH = 9.0) as supporting electrolyte. Natural waters were analysed by standard addition method with good recoveries (mean percentage = 97%); no fouling effects due to humic acids or other organic constituents were observed in the reported conditions.     

Simultaneous analysis of trans- and cis-isomers of 2-glucosyloxycinnamic acids and coumarin derivatives in Dendrobium thyrsiflorum by high-performance liquid chromatography (HPLC)-photodiode array detection (DAD)-electrospray ionization (ESI)-tandem mass spectrometry (MS)

A novel method has been developed for simultaneous analysis for three pairs of trans- and cis-isomers of 2-glucosyloxycinnamic acids, along with their biogenic metabolites (three coumarin derivatives including scopoletin, scoparone and ayapin) in a Chinese medicinal herb Dendrobium thyrsiflorum by using high-performance liquid chromatography (HPLC)-photodiode array detection (DAD)-electrospray ionization (ESI)-tandem mass spectrometry (MS). The method was carried out by using a Polaris C₁₈ column with a gradient solvent system of 0.5% acetic acid aqueous solution-acetonitrile. Seven target analytes including isodensifloside, isothyrsifloside, densifloside, thyrsifloside, scoparone, ayapin and scopoletin were exclusively identified by comparing their retention behaviors, UV and MS spectra with the authentic standards, and their contents in D. thyrsiflorum were simultaneous determined by employing UV detection at 342 nm. In addition, another pair of isomers of 2-glucosyloxycinnamic acids was putatively elucidated mainly based on the MS fragmentation. The method was validated and found to be satisfactorily linear, selective and robust. Recoveries ranged from 95.56 to 97.94% for all compounds at three different spiking levels. The limits of detection (LOD) and quantitation (LOQ) ranged, respectively, from 0.02 to 0.13 μg mL⁻¹ and 0.07 to 0.39 μg mL⁻¹ depending on various compounds. The established quality evaluation method was successfully used for evaluating the quality of D. thyrsiflorum samples of different organs and collections.     

Determination of lead in the presence of morin-5′-sulfonic acid and sodium dodecyl sulfate by adsorptive stripping voltammetry

A simple and sensitive electroanalytical method is developed for the determination of lead by adsorptive stripping voltammetry (AdSV) in the presence of morin-5′-sulfonic acid (MSA) and sodium dodecyl sulfate (SDS). The Pb-MSA complex accumulates on the surface of a hanging mercury drop electrode (HMDE) and peak current is measured by square wave voltammetry (SWV). The complex is reduced at −0.48 V and peak current increases when low concentrations of SDS are added to the sample solution. The experimental variables pH, MSA concentration (C_MSA); accumulation time (t_acc); accumulation potential (E_acc), and SDS concentration (C_SDS), as well as potential interferences, are investigated. Under the optimized conditions (pH 3.2; C_MSA: 0.5 μmol L⁻¹; t_acc: 60 s; E_acc: −0.35 V, and C_SDS: 20 μmol L⁻¹), peak current is proportional to the concentration of Pb(II) over the 0.1-32.0 μg L⁻¹ range, with a detection limit of 0.04 μg L⁻¹. The relative standard deviation for a solution containing 5.0 μg L⁻¹ of Pb(II) solution was 1.5% for seven successive assays. The method was validated by determining Pb(II) in synthetic sea water (ASTM D665) spiked with ICP multi-element standard solution and in certified reference water (GBW08607). Finally, the method was successfully applied to the determination of Pb(II) in tap water and sea water after UV digestion.     

A novel tris(2,2′-bipyridine)ruthenium(II)/tripropylamine cathodic electrochemiluminescence in acetonitrile for the indirect determination of hydrogen peroxide

A novel tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) cathodic electrochemiluminescence (ECL) was generated at −0.78 V at the Pt electrode in acetonitrile (ACN), which suggested that the cathodic ECL differed from conventional cathodic ECL. It was found that tripropylamine (TPrA) could enhance this cathodic ECL and the linear range (log-log plot) was 0.2 μM-0.2 mM. In addition, hydrogen peroxide (H₂O₂) could inhibit the cathodic ECL and was indirectly detected with the linear range of 27-540 μM. The RSD (n = 12) of the ECL intensity in the presence of 135 μM H₂O₂ was 0.87%. This method was also demonstrated for the fast determination of H₂O₂ in disinfectant sample and satisfactory results were obtained.     

Enzyme sensor for the electrochemical detection of the marine toxin okadaic acid

An enzyme sensor for the electrochemical detection of the marine toxin okadaic acid (OA) has been developed. The strategy was based on the inhibition of immobilised protein phosphatase (PP2A) by this toxin and the electrochemical measurement of the enzyme activity by the use of appropriate enzyme substrates, electrochemically active after dephosphorylation by the enzyme. Colorimetric inhibition assays have demonstrated the PP2A from human red blood cells to be more sensitive and to provide a wider linear range than the one produced by genetic engineering. Catechyl monophosphate (CMP) and p-aminophenyl phosphate (p-APP) have been tested as enzyme substrates, the former providing higher electrochemical currents at convenient working potentials (+450 mV vs. Ag/AgCl). Biosensors with 19.1 and 5.0 U of immobilised enzyme have been applied to the OA detection. Whereas the 19.1-U biosensor has provided higher electrochemical currents and more reliable determinations, the 5.0-U one has attained a lower 50% inhibition coefficient (IC₅₀) value (22.19 in front of 154.84 μg L⁻¹) and a larger working range (2.69-171.87 in front of 42.97-171.87 μg L⁻¹). The analysis of toxicogenic dinoflagellate extracts with both biosensors and the comparison with the colorimetric assay and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) have demonstrated the applicability of the developed electrochemical devices as screening biotools for the assessment of the toxicity of a sample.     

Pretreatment of plasma samples by a novel hollow fiber centrifugal ultrafiltrate device for the determination of cefaclor concentrations in human plasma

A simple sample preparation method was developed by using a centrifugal ultrafiltration (CF-UF) device with hollow fiber (HF) for the determination of cefaclor in plasma by HPLC. Samples were placed into a homemade device, which was consisted of a glass tube and a U-shaped hollow fiber. The filtrate was withdrawn from the hollow fiber into a syringe after centrifugation and 20 μL was directly injected into the HPLC for analysis. The HPLC method had a linear calibration curve in the concentration range of 6.00 × 10⁻²–30.7 μg mL⁻¹(r = 0.9996). The limit of detection (LOD) and limit of quantitation (LOQ) were 0.02 and 0.06 μg mL⁻¹, respectively. The intra and inter-day precisions (RSD) were 1.7%, 1.2%, 1.0% and 3.6%, 2.5%, 1.9%, respectively, for three concentrations. Assay accuracy was higher than 99.2% and the absolute recovery was 86.8–92.5%. It is feasible to use this novel and low cost device for sample pretreatment for the analysis of cefaclor in plasma.     

Poly(etheretherketone)-turnings a novel sorbent material for lead determination by flow injection flame atomic absorption spectrometry and factorial design optimization

A novel hydrophobic sorbent material for on-line column preconcentration and separation systems coupled with atomic spectrometry was developed. Poly(etheretherketone) (PEEK) in the form of turnings was used as packing material and evaluated for trace lead determination in environmental samples. Sample and ammonium diethyl-dithiophosphate (DDPA) reagent were mixed on-line and the Pb(II)-DDPA complex was retained effectively on PEEK-turnings. Isobutyl methyl ketone (IBMK) was adopted for efficient analyte complex elution and subsequently transportation into the nebulizer-burner system for atomization. The developed sorbent material has shown, excellent chemical and mechanical resistance, fast adsorption kinetics permitting the use of high sample flow rates without significant loss of retention efficiency. For 120 s sample preconcentration time the sampling frequency was 20 h⁻¹, the enhancement factor was 110, the detection limit (3 s) was c_L = 0.32 μg L⁻¹, and the relative standard deviation (RSD) was s_R = 2.2%, at the 50.0 μg L⁻¹ Pb(II) level. The accuracy of the developed method was evaluated by analyzing certified reference materials.     

Synthesis and solvent dependence of the photophysical properties of [60]fullerene-sugar conjugates

A method for the synthesis of optically pure C₆₀ derivatives containing one or two d-galactose or d-glucose units is described. It involves the synthesis of sugar-malonate derivatives followed by a cyclopropanation reaction with C₆₀. The solvent dependence of the photophysical properties of the methano[60]fullerene-sugar derivatives was studied using nanosecond laser flash photolysis coupled with kinetic UV-vis absorption spectroscopy and time-resolved singlet oxygen luminescence measurements. The triplet properties of these fullerenes, including transient absorption spectra, molar absorption coefficients and quantum yield for the photosensitised production of ¹O₂ were determined in toluene, benzonitrile and acetonitrile solutions. The transient absorption spectral profiles are solvent independent although small differences are observed in the transient absorption maximum: 720±5 nm for toluene, 710±5 nm for benzonitrile and 700±5 nm for acetonitrile. Triplet state molar absorption coefficients (ε_T) of C₆₀ derivatives vary from 9456±2090 M⁻¹ cm⁻¹, for compound 10 in toluene, and 15,272±4462 M⁻¹ cm⁻¹, for compound 6 in acetonitrile. Triplet state lifetimes (τ_T) for methano[60]fullerene-sugar derivatives, under our experimental conditions, are similar in toluene or benzonitrile solutions (47.5±1.1 μs≤τ_T≤51.4±2.0 μs) but are lower in acetonitrile solutions (31.8±0.6 μs≤τ_T≤43.0±1.1 μs). Toluene and benzonitrile solutions of C₆₀ derivatives have Φ_Δ close to unity.     

Determination of clarithromycin in rat plasma by HPLC-UV method with pre-column derivatization

A novel high-performance liquid chromatographic (HPLC) method using pre-column derivatization and UV detection at 275 nm for the determination of clarithromycin in rat plasma has been validated. Clarithromycin was extracted from plasma sample spiked with internal standard (erythromycin) under alkaline condition with ethyl ether and derivatizated with trimethylbromosilane. The analyses were run on a C₁₈ column, maintained at 40 °C during elution, using a mobile phase comprised of potassium dihydrogen phosphate (50 mM, pH 6.8, contained 0.7% triethylamine), acetonitrile, and methanol (30:45:25, v/v/v). The standard calibration curve for clarithromycin was linear (r² = 0.9998) over the concentration range of 0.1-10 μg ml⁻¹ in rat plasma. The limit of detection (LOD) and limit of quantitation (LOQ) was 30 ng ml⁻¹ and 0.1 μg ml⁻¹ respectively. The intra- and inter-day assay variability range was 2.6-7.4% and 3.3-8.5%, respectively. This method has been successfully applied to a pharmacokinetic study of clarithromycin in rats.     

Enzyme inhibition-based biosensor for the electrochemical detection of microcystins in natural blooms of cyanobacteria

An electrochemical biosensor for the detection of microcystin has been developed based on the inhibition of the protein phosphatase 2A (PP2A) by this cyanobacterial toxin. The enzyme has been immobilised by entrapment using a poly(vinyl alcohol) azide-unit pendant water-soluble photopolymer (PVA-AWP). Electrode supports and immobilisation conditions have been optimised by colorimetric assays, the highest immobilisation yields being obtained with screen-printed graphite electrodes and the 1:2 PP2A:PVA ratio. Catechyl monophosphate (CMP), α-naphthyl phosphate (α-NP) and 4-methylumbelliferyl phosphate (4-MUP) have been used as phosphorylated substrates to monitor the protein phosphatase activity by electrochemical methods, the former providing the highest chronoamperometric currents at appropriate working potentials (+450 mV versus Ag/AgCl). Incubation with standard microcystin solutions has demonstrated the inhibition of the immobilised enzyme, proportional to the toxin concentration. The standard inhibition curve has provided a 50% inhibition coefficient (IC₅₀) of 83 μg L⁻¹, a limit of detection (LOD; 35% inhibition) of 37 μg L⁻¹, and 100% inhibition at about 1000 μg L⁻¹. Real samples of cyanobacterial blooms from the Tarn River (Midi-Pyrénées, France) have been analysed using the developed amperometric biosensor and the toxin contents have been compared to those obtained by a conventional colorimetric protein phosphatase inhibition (PPI) assay and high-performance liquid chromatography (HPLC). The results clearly justify the use of the developed amperometric biosensor as screening method for microcystin detection.     

Comparative study on 2-amino-1,4-naphthoquinone derived ligands as indium (III) selective PVC-based sensors

The three different ligands (Q₂ to Q₄) based on 2-amino-1,4-naphthoquinone (Q₁), have been synthesized and explored as neutral ionophores for preparing polyvinyl chloride-based membrane sensors selective to indium (III). The addition of potassium tetrakis(4-chlorophenyl) borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 16 having membrane of ligand (Q₂) with composition (%, w/w) ionophore Q₂ (3.0%):PVC (30.0%):o-NPOE (63.0%):KTpClPB (4.0%). This sensor exhibits Nernstian response with slope 19.8 mV/decade of activity in the concentration range 2.5 × 10⁻⁷ to 1.0 × 10⁻² M indium (III), performs satisfactorily over wide pH range of (2.5-7.5) with a fast response time (10 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of acetonitrile, ethanol and methanol. The proposed sensor can be used over a period of 3.5 months without significant drift in potentials. The quantitative application of sensor was also evaluated by comparative analysis of artificially made sea water with AAS.     

Development of a rapid and sensitive method for determination of cysteine/cystine ratio in chemically defined media

Two rapid, sensitive and quantitative methods for the determination of the cysteine and cystine ratio in complex defined media feedstock using monolithic reversed-phase liquid chromatography (RPLC) and RPLC–MS are presented. Cysteine is pre-derivatised with purified 2-chloro-1-methylquinolinium tetrafluoroborate (CMQT) and separated from other derivatisation products on a narrow-bore 50 mm × 2 mm I.D. monolithic C₁₈ column with UV detection at 355 nm. For reversed-phase LC (RPLC) the separation is carried out isocratically using a mobile phase of 50 mM trichloroacetic acid (TCA) adjusted to pH 2.5 with lithium hydroxide (LiOH) and acetonitrile (83:14) pumped at 1.5 mL/min with an elevated column temperature. For RPLC–MS an ammonium acetate and acetonitrile gradient method was developed with a reduced flow rate of 0.3 mL/min. The treatment of the samples consisted of dividing them into two aliquots, the first aliquot is analysed for cysteine and the second aliquot is analysed for cystine after its quantitative reduction to cysteine using tris(2-carboxyethyl)phosphine (TCEP). Both methods are linear, with R² > 0.999 for 0.25–500 μM for cysteine and 0.25–250 μM for cystine using the LC–UV method, sensitive, with detection limit of 36 nM for cysteine, and precise, with ≤1.1% RSD for both retention time and peak area (n = 6). Samples (n = 31) of an industry standard and supplied chemically defined media feedstock were analysed, finding cysteine ranging from 1.56 to 2.26 μg/mL and cystine from 1062.02 to 1348.13 μg/mL.     

Rapid and sensitive liquid chromatography-tandem mass spectrometry for the quantitation of epirubicin and identification of metabolites in biological samples

A highly sensitive and selective liquid chromatography-mass spectrometry (LC-MS) method has been developed for the determination of epirubicin in serum and cell specimens using daunorubicin as an internal standard. Using atmospheric pressure chemical ionisation (APCI), the epirubicin metabolites were readily distinguishable by their fragmentation pattern in the mass spectrometer. Selected reaction monitoring (SRM) mode was employed for quantitation of epirubicin and the metabolites. Following extraction, chromatography was performed on a C18 column with a mobile phase consisting of water-acetonitrile-formic acid, pH 3.2, with a flow rate of 200 μl/min. The limit of detection (LOD) and the limit of quantitation (LOQ) of this method in serum were determined to be 1.0 and 2.5 ng/ml, respectively. Linearity of the method was verified over the concentration range of 2.5-2000 ng/ml, with a high correlation coefficient (R² ≥ 0.998). For the extraction procedure, an aliquot of 500 μl serum, spiked with internal standard, was extracted using a chloroform-2-isopropanol (2:1, v/v) mixture. The method has been applied to the analysis of epirubicin in cancer cell samples and the identification of known and unknown metabolites in clinical trial patient serum samples.     

High throughput method for the analysis of cetrizine hydrochloride in pharmaceutical formulations and in biological fluids using a tris(2,2'-bipyridyl)ruthenium(II)-peroxydisulphate chemiluminescence system in a two-chip device

A fast, economic and sensitive chemiluminescence (CL) method has been developed for the analysis of cetrizine hydrochloride (CET) in pharmaceutical formulations and in biological fluids. The CL method is based on the oxidation of tris(2,2′-bipyridyl)ruthenium(II) (Ru (bipy)₃²⁺) by peroxydisulphate in a two-chip device. Up to 180 samples can be analysed per hour, consuming only minute quantities of reagents. Three instrumental setups were tested to find the most economical, sensitive and high throughput setup. In the first setup, a continuous flow of sample and CL reagents was used, whereas in the second setup, a fixed volume (2 μL) of (Ru (bipy)₃²⁺) was introduced into a continuous infusion of peroxydisulphate and the sample. In the third design, a fixed volume of sample (2 μL) was injected while the CL reagents were continuously infused. Compared to the first setup, a 200% signal enhancement was observed in the third setup. Various parameters that influence the CL signal intensity, including pH, flow rates and reagent concentrations, were optimized. A linear response was observed over the range of 50 μg L⁻¹ to 6400 μg L⁻¹ (R² = 0.9959) with RSD values of 1.1% (n = 15) for 1000 μg L⁻¹. The detection limit was found to be 15 μg L⁻¹ (S/N = 3). The amount of consumed sample was only 2 μL, from which the detected amount of CET was found to be 6.5 × 10⁻¹⁴ mol. This procedure was successfully applied to the analysis of CET in pharmaceutical formulations and biological fluids.     

Ni(II) selective sensors based on Schiff bases membranes in poly(vinyl chloride)

The two nickel chelates of Schiff bases, 3-hydroxy-N-{2-[(3-hydroxy-N-phenylbutyrimidoyl)-amino]-phenyl}-N′-phenylbutyramidine (M₁) and bis-4-(ethyliminomethyl)naphthalene-1-ol (M₂), have been synthesized and explored as ionophores for preparing PVC-based membrane sensors selective to nickel ion. The influences of membrane compositions on the potentiometric response of the electrodes have been found to substantially improve the performance characteristics. The best performance was obtained with the electrode having a membrane composition (w/w; mg) of (M₁): PVC:NaTPB:CN in the ratio 5:150:5:150. The sensor shows a linear potential response for Ni²⁺ over a wide concentration range 1.6 × 10⁻⁷ to 1.0 × 10⁻² M with Nernstian compliance (30.0 ± 0.2 mV/decade of activity) within pH range 2.5-9.5 and a fast response time of 10 s. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol, and acetonitrile and could be used for a period of 4 months. The analytical usefulness of the proposed electrode has been evaluated by its application in the determination of nickel in real samples. The practical utility of the membrane electrode has also been observed in the presence of surfactants.     

Development and validation of a HPLC method for the determination of buprenorphine hydrochloride, naloxone hydrochloride and noroxymorphone in a tablet formulation

A simple isocratic reversed-phase high-performance liquid chromatographic method (RP-HPLC) was developed for the simultaneous determination of buprenorphine hydrochloride, naloxone hydrochloride dihydrate and its major impurity, noroxymorphone, in pharmaceutical tablets. The chromatographic separation was achieved with 10 mmol L⁻¹ potassium phosphate buffer adjusted to pH 6.0 with orthophosphoric acid and acetonitrile (17:83, v/v) as mobile phase, a C-18 column, Perfectsil Target ODS3 (150 mm × 4.6 mm i.d., 5 μm) kept at 35 °C and UV detection at 210 nm. The compounds were eluted isocratically at a flow rate of 1.0 mL min⁻¹. The average retention times for naloxone, noroxymorphone and buprenorphine were 2.4, 3.8 and 8.1 min, respectively. The method was validated according to the ICH guidelines. The validation characteristics included accuracy, precision, linearity, range, specificity, limit of quantitation and robustness. The calibration curves were linear (r > 0.996) over the concentration range 0.22-220 μg mL⁻¹ for buprenorphine hydrochloride and 0.1-100 μg mL⁻¹ for naloxone hydrochloride dihydrate and noroxymorphone. The recoveries for all three compounds were above 96%. No spectral or chromatographic interferences from the tablet excipients were found. This method is rapid and simple, does not require any sample preparation and is suitable for routine quality control analyses.     

Rapid and simultaneous analysis of dichlorvos, malathion, carbaryl, and 2,4-dichlorophenoxy acetic acid in citrus fruit by flow-injection ion spray ionization tandem mass spectrometry

A simple method for the rapid and simultaneous analysis of dichlorvos (DDVP), malathion, carbaryl, and 2,4-dichlorophenoxy acetic acid (2,4-D) in citrus fruit, which uses flow-injection ion spray ionization tandem mass spectrometry, has been developed for the first time. The method involves the combined use of stable isotopically labeled internal standards (DDVP-d₆, malathion-d₁₀, carbaryl-d₇, and 2,4-D-d₅) and a multiple reaction monitoring technique. The average recoveries for the pesticides at the same concentrations as their tolerance levels (DDVP: 0.1-0.2 μg g⁻¹; malathion: 0.5-4.0 μg g⁻¹; carbaryl: 1.0 μg g⁻¹; 2,4-D: 1.0-2.0 μg g⁻¹) ranged from 90 to 119% with the relative standard deviation (R.S.D.) ranging from 1.0 to 13.1% (n = 5). Analysis time, including sample preparation and determination, was only 15 min. The present method is effective for screening DDVP, malathion, carbaryl, and 2,4-D in citrus fruit.     

An in-tube SPME device for the selective determination of chlorophyll a in aquatic systems

We report a new device for the estimation of the content of chlorophyll a pigment in water samples as an indicator of water quality. The extraction of the pigment from water was also optimized. 10 mL of water was filtered through a nylon filter (45 μm pore size and 13 mm of diameter), after the chlorophylls were dissolved by immersing the filter in 1 mL of a low non-hazardous solvent as ethanol. An in-valve in-tube SPME device coupled to capillary liquid chromatography with diode array detection was designed. A capillary column of 70 cm in length (0.32 mm i.d. coated with 5% diphenyl-95% polydimethylsiloxane, 3 μm coating thickness) was used as the loop of the injection valve for preconcentration and a Zorbax SB C₁₈ (SiO₂-based) 150 mm × 0.5 mm i.d., 5 μm column (Agilent) was used as analytical column. The achieved detection limit was 0.05 μg L⁻¹ and the working range of concentrations was 0.1-1 μg L⁻¹. % RSD values between 2 and 11 were obtained. Chlorophyll a in several water matrices was determined with good results in presence of other pigments such as chlorophyll b, pheophytin a and pheophytin b.