On-line separation and preconcentration of inorganic arsenic and selenium species in natural water samples with CTAB-modified alkyl silica microcolumn and determination by inductively coupled plasma-optical emission spectrometry

A new, simple, and selective method has been presented for the separation and preconcentration of inorganic arsenic (As(III)/As(V)) and selenium (Se(IV)/Se(VI)) species by a microcolumn on-line coupled with inductively coupled plasma-optical emission spectrometry (ICP-OES). Trace amounts of As(V) and Se(VI) species were separated and preconcentrated from total As and Se at desired pH values by a conical microcolumn packed with cetyltrimethylammonium bromide (CTAB)-modified alkyl silica sorbent in the absence of chelating reagent. The species adsorbed by CTAB-modified alkyl silica sorbent were quantitatively desorbed with 0.10 ml of 1.0 mol l⁻¹ HNO₃. Total inorganic arsenic and selenium were similarly extracted after oxidation of As(III) and Se(IV) to As(V) and Se(VI) with KMnO₄ (50.0 μmol l⁻¹). The assay of As(III) and Se(IV) were based on subtracting As(V) and Se(VI) from total As and total Se, respectively. All parameters affecting the separation/preconcentration of As(V) and Se(VI) including pH, sample flow rate and volume, eluent solution and volume have been studied. With a sample volume of 3.0 ml, the sample throughput was 24 h⁻¹ and the enrichment factors for As(V) and Se(VI) were 26.7 and 27.6, respectively. The limits of detection (LODs) were 0.15 μg l⁻¹ for As(V) and 0.10 μg l⁻¹ for Se(VI). The relative standard deviations (RSDs) for nine replicate determinations at 5.0 μg l⁻¹ level of As(V) and Se(VI) were 4.0% and 3.6%, respectively. The calibration graphs of the method for As(V) and Se(VI) were linear in the range of 0.5–1000.0 μg l⁻¹ with a correlation coefficient of 0.9936 and 0.9992, respectively. The developed method was successfully applied to the speciation analysis of inorganic arsenic and selenium in natural water samples with satisfactory results.     

Determination of linuron in water samples by high performance liquid chromatography after preconcentration with octadecyl silanized magnetite

A sensitive and selective batch adsorption method is proposed for the preconcentration and determination of linuron. Linuron was preconcentrated on octadecyl silanized (ODS) magnetite as an adsorbent and then determined by high performance liquid chromatography (HPLC). Several parameters on the recovery of the analyte were investigated. The experimental results showed that it was possible to obtain sufficient preconcentration efficiency when the solution pH was 6 using 100 mL of sample solution containing 1.0 μg of linuron and 3 mL of ethanol as a desorption solution. Recovery of linuron was 50.7 ± 1.9% with a relative standard deviation for five determinations of 3.0% under optimum conditions. The calibration curve of linuron was linear up to 200 ng mL^− 1 with a correlation coefficient of 0.998 and the detection limit (3S/N) was 1.0 ng mL^− 1. The capacity of the adsorbent was also examined and found to be 0.15 mg g^− 1 for linuron. ODS-magnetite is suitable for repeated use without decreasing recovery at least 4 adsorption–desorption cycles. The proposed method was successfully applied to the determination of linuron in river water with high precision and accuracy.     

Determination of ultra trace amounts of protein by 4-chlorosulfo-(2′-hyaroxylphenylazo)-rhodanine-Ti(IV) complex [ClSARP-Ti(IV)] as the fluorescence spectral probe in AOT microemulsion

Experiments indicated that protein can enhance the fluorescence of the 4-chlorosulfo-(2′-hydroxylophenylazo)-rhodanine-Ti(IV) complex [ClSARP-Ti(IV)] in the presence of bis(2-ethylhexyl)sulfosuccinate sodium salt (AOT) microemulsion. Based on this, a sensitive and reproducible fluorometric method for the determination of micro amount protein was developed. The calibration curves of four proteins were given. Under the optimum experimental conditions, the enhanced fluorescence intensity of the system was in proportional to the concentration of protein in the range of 0.1–11 μg mL⁻¹ for bovine serum albumin (BSA), 1.0–10 μg mL⁻¹ for human serum albumin (HSA), 1.0–50 μg mL⁻¹ for ovalbumin (Ova) and 2.5–18 μg mL⁻¹ for γ-globulins (γ-G). Their detection limits were 0.070, 0.071, 0.33 and 0.22 μg mL⁻¹, respectively. The ClSARP-Ti(IV) complex as a spectral probe can be used to the determination of protein in milk powder and oatmeal yielding with satisfactory results. Therefore, the proposed method is one of the most sensitive methods available. In addition, the interaction mechanism of this system is studied by multi-techniques.     

Combined use of Pd and HF as chemical modifiers for the determination of total chromium in produced waters from petroleum exploration by ET AAS

This work reports the evaluation of the combined use of Pd and HF as chemical modifiers for the direct determination of total chromium in waters derived from petroleum exploration employing electrothermal atomic absorption spectrometry (ET AAS). Such waters, usually called as produced waters, have complex composition presenting a number of organic and inorganic substances. When obtained from offshore operations they also present high salinity. In order establish conditions for chromium measurement pyrolysis and atomization curves were built up in different media and employing Pd and HF as chemical modifiers. Also, a detailed study about calibration strategy was performed. At best conditions, pyrolysis and atomization temperatures were 1200 °C and 2600 °C, respectively, and 10 μL of a 500 mg L^− 1 Pd solution was added together with 10 μL of a 50% (v/v) HF solution on 20 μL of sample. Obtained results indicate that, in this kind of sample, chromium can be determined by standard addition method or employing external calibration with standard solutions prepared in 0.8 mol L^− 1 NaCl medium. In order to evaluate the accuracy of the procedure, a recovery test was performed with seven spiked samples of produced waters. The detection limit, quantification limit and the relative standard deviation in 0.8 mol L^− 1 NaCl were also calculated and the values found were 0.45 μg L^− 1, 1.5 μg L^− 1 and 6.0% (at 2.5 μg L^− 1 level), respectively.     

Use of high resolution continuum source atomic absorption spectrometry as a detector for chemically generated noble and transition metal vapors

Vapor generation and atomization conditions in a heated quartz tube to detect Ag, Cd, Co, Cu, Ni and Zn using High Resolution Continuum Source AAS (HRCSAAS), were optimized. Vapors were generated after mixing acidified solutions containing 8-hydroxiquinoline (oxine) with sodium tetrahydroborate. Afterwards, they were swept to the heated quartz cell by an argon flow.Reaction loop size and temperature of the quartz cell were optimized for each element. A temperature of 960 °C was selected as a compromise value to detect most of the metals. Afterwards, a Plackett–Burmann design was proposed to select which parameters were most important. Type of acid and its concentration were the most statistical significant variables. Optimum conditions for sequential detection of Cd, Cu, Ni and Zn were: 1 mg L^− 1 Co as catalyst, 250 mg L^− 1 oxine, 0.6 M nitric acid, 1.75% (w/w) sodium tetrahydroborate (prepared in 0.4 (w/v)% NaOH), a reaction loop of 250 µL, and a 25 L h^− 1 carrier Ar flow. Ag and Co were each detected in their own optimized conditions. Analytical performance of the system was evaluated in connection with a selected pixel number, and spectral correction was used to eliminate NO absorption bands interference in Zn detection. Detection limits were in the range of 1.5–18 μg L^− 1 for Ag, Cu, Cd and Zn, whereas sensitivity was worst for Co (169 μg L^− 1) and Ni (586 μg L^− 1). Atomization in a quartz cell of Co and Ni volatile species, generated by an addition of sodium tetrahydroborate to an acidified solution of the analytes, was reported for the first time in this paper. Precision expressed as RSD(%) had values lower than 10% except for Ni.     

Use of a graphite–polyurethane composite electrode for electroanalytical determination of indole-3-acetic acid in soil samples

A new electroanalytical methodology was developed for the quantification of the phytohormone indole-3-acetic acid (IAA), using a graphite–polyurethane composite electrode (GPU) and the square wave voltammetry (SWV), in 0.1 mol L^− 1 phosphoric acid solution (pH 1.6). Analytical curves were constructed under optimized conditions (f = 100 s^− 1, a = 50 mV, E_i = 5 mV) and the reached detection and quantification limits were 26 μg L^− 1 and 0.2 mg L^− 1, respectively. The developed methodology is simple and accurate for the routine determination of IAA. In order to verify the application of the electroanalytical methodology in fortified soil samples without previous treatment, an IAA assay was performed without serious interferences of the soil constituents.     

On-line molecularly imprinted solid phase extraction for the selective spectrophotometric determination of catechol

A molecularly imprinted polymer has been synthesized for a selective on-line catechol extraction, followed by its spectrophotometric determination in guarana powder, mate tea and tap water samples. A clean-up column, containing a methacrylic polymer + C₁₈ solid phase, was also used in order to enhance selectivity. The imprinted polymer was prepared by bulk polymerization using catechol as template and 4-vinylpyridine as the functional monomer. Permanganate solution was used as spectrophotometric reagent, where Mn(VII) was reduced to Mn(II) by catechol in an acid medium, causing color loss, which was monitored at 528 nm. Physical (extraction flow rate, elution flow rate, coil length) and chemical (nature and concentration of the eluent, potassium permanganate concentration) variables were optimized, and the selectivity was appraised using three molecules (4-chloro-2-methylphenol, 2-cresol, 2-methoxyphenol) similar to catechol. These molecules did not present interference in 1:8, 1:10 and 1:10 (catechol/concomitant) proportions, respectively. The analytical calibration curve ranged from 3.0 up to 100 μmol L^− 1 (r > 0.999; seven concentrations levels, n = 3) and the limits of detection (LOD) and quantification (LOQ) were 0.8 and 2.7 μmol L^− 1, respectively. Precision, expressed as RSD, was of 3.0% (20 μmol L^− 1, n = 10), and the analytical frequency was 15 h^− 1. Accuracy was checked by the HPLC technique and the results did not present significant difference at 95% confidence levels according to the t test.     

Speciation analysis of selenium in rice samples by using capillary electrophoresis-inductively coupled plasma mass spectrometry

An enzyme-assisted extraction used to extract all species of selenium in rice sample and a sensitive analytical method for the determination of ultratrace Se(VI), Se(IV), SeCys₂ (selenocystine) and SeMet (selenomethionine) with capillary electrophoresis-inductively coupled plasma mass spectrometry were firstly described in this study. The extraction method is simple, effective and can be used to extract trace selenium compounds in rice with high extraction efficiency and no altering its species. The analytical method has a detection limit of 0.1-0.9 ng Se/mL, and can be used to determine trace Se(VI), Se(IV), SeCys₂ and SeMet in rice directly without any derivatization and pre-concentration. With the help of above methods, we have successfully determined Se(VI), Se(IV), SeCys₂ and SeMet in selenium-enriched rice within 18 min with a recovery of 90-103% and a RSD (relative standard deviation, n = 6) of 3-7%. Our results indicated that selenium-enriched rice contained only one species of selenium, SeMet, and its concentration is in range of 0.136-0.143 μg Se/g dried weight. The proposed method providing a realistic approach for the nutritional and toxical evaluation of different selenium compounds in nutritional supplements.     

Flow injection-hydride generation atomic absorption spectrometric determination of selenium, arsenic and bismuth

A simple and robust flow injection system which permits low sample and reagent consumption is described for rapid and reliable hydride generation atomic absorption spectrometric determination of selenium, arsenic and bismuth. The system, which composed of one peristaltic pump and one four channel solenoid valve, used water as the carrier streams for both sample and NaBH₄ solution. Rapid off-line pre-reduction of the analytes was achieved by using hydroxylamine hydrochloride for selenium and a mixture of potassium iodide and ascorbic acid for arsenic and bismuth. Transition metal interference was eliminated with the addition of thiourea and EDTA into the NaBH₄ solution and significant sensitivity enhancement was observed for selenium in the presence of thiourea in the reductant solution. Under optimised conditions, the method achieved detection limits of 0.2 ng mL⁻¹ for Se, 0.5 ng mL⁻¹ for As and 0.3 ng mL⁻¹ for Bi. The method was very reproducible, achieving relative standard deviations of 6.3% for Se, 3.6% for As and 4.7% for Bi, and has a sample throughput of 360 h⁻¹. Successful application of the method to the quantification of selenium, arsenic and bismuth in a certified reference river sediment sample is reported.     

Determination of zinc and copper in human hair by slurry sampling employing sequential multi-element flame atomic absorption spectrometry

The present work proposes a direct method based on slurry sampling for the determination of zinc and copper in human hair samples by multi-element sequential flame atomic absorption spectrometry. The slurries were prepared by cryogenic grinding and sonication of the samples. The optimization step was performed using univariate methodology and the factors studied were: nature and concentration of the acid solution, amount sample/slurry volume, sonication time, and particle size. The established experimental conditions are the use of a sample mass of 50 mg, 2 mol L^− 1 nitric acid solution, sonication time of 20 min and slurry volume of 10 mL. Adopting the optimized conditions, this method allows the determination of zinc and copper with detection limits of 88.3 and 53.3 ng g^− 1, respectively, and precision expressed as relative standard deviation (RSD) of 1.7% and 1.6% (both, n = 10) for contents of zinc and copper of 100.0 and 33.3 μg g^− 1, respectively. The accuracy was checked and confirmed by analysis of two certified reference materials of human hair. The procedure was applied for the determination of zinc and copper in two human hair samples. The zinc and copper contents varied from 100.0 to 175.6 and from 3.2 to 32.8 μg g^− 1, respectively. These samples were also analyzed after complete digestion in a closed system and determination by FAAS. The statistical comparison by t-test (95% confidence level) showed no significant difference between these results.     

Simultaneous determination of pethidine and methadone by capillary electrophoresis with electrochemiluminescence detection of tris(2,2′-bipyridyl)ruthenium(II)

In this paper, we described a simple and rapid method, capillary electrophoresis with electrochemiluminescence (CE–ECL) detection using tris(2,2′-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺), to simultaneously detect pethidine and methadone. Analytes were injected to separation capillary of 67.5 cm length (25 μm i.d., 360 μm o.d.) by electrokinetic injection for 10 s at 10 kV. Under the optimized conditions: ECL detection at 1.20 V, 30 mM sodium phosphate (pH 6.0) as running buffer, separation voltage at 14.0 kV, 5 mM Ru(bpy)₃²⁺ with 50 mM sodium phosphate (pH 6.5) in the detection cell, the linear range from 2.0 × 10^− 6 to 2.0 × 10^− 5 M for pethidine and 5.0 × 10^− 6 to 2.0 × 10^− 4 M for methadone and detection limits of 0.5 μM for both of them were achieved (S/N = 3). Relative standard derivations of the ECL intensity were 2.09% and 6.59% for pethidine and methadone, respectively.     

Voltammetric determination of quercetin at a multi-walled carbon nanotubes paste electrode

Quercetin can effectively accumulate at multi-walled carbon nanotubes-paraffin oil paste electrodes (CNTPE) and cause a sensitive anodic peak at around 0.32 V (vs. SCE) in a 0.10 M phosphate buffer solution (pH = 4.0). Under optimized conditions, the anodic peak current is linear to quercetin concentration in the ranges of 2.0 × 10^− 9−1.0 × 10^− 7 M and 1.0 × 10^− 7−2.0 × 10^− 5 M, and the regression equations are i_p (μA) = 0.0017 + 0.928c (μM, r = 0.999) and i_p (μA) = 0.183 + 0.0731c (μM, r = 0.995), respectively. This paste electrode can be regenerated by repetitively cycling in a blank solution for about 2 min. A 1.0 × 10^− 6 M quercetin solution is measured for 10 times using the same electrode regenerated after every determination, and the relative standard deviation of the peak current is 1.7%. The method has been applied to the determination of quercetin in hydrolysate product of rutin and the recovery is 99.2–102.6%. In comparison with graphite paste electrode, carbon nanotubes-nujol paste electrode and carbon nanotubes casting film modified glassy carbon electrode, the CNTPE gives higher ratio of signal to background current and better defined voltammetric peak.     

Real-time monitoring of metal deposition and segregation phenomena during preparation of PdCu membranes

The N₂ and H₂ evolution, respectively, were monitored during deposition of Pd and Cu from electroless plating baths to obtain in-process control of the composition during preparation of 3–7 μm thick PdCu membranes on tubular ceramic substrates. Compositions estimated by gas evolution compare favorably to those measured in post-mortem XRD and EDS analyses, mostly differing by not more than 1 at.%. This result suggests that use of gas evolution measurements to enable in-process control of composition to within 1 at.% is feasible. Annealing experiments in an H₂ atmosphere demonstrated that, at 893 K, only 48 h are needed to form a stoichiometrically homogeneous, 9.5 μm thick, face centered cubic (fcc) Pd₆₃Cu₃₇ membrane from sequentially deposited layers; at 723 K, the same transformation requires over 2 weeks. The appearance of transient body centered cubic (bcc) and fcc phases with lower Pd contents signaled compositional segregation in the initial stages of alloy formation at 723 and 773 K and could be a source of persistent stoichiometric heterogeneity particularly in bcc PdCu membranes. The H₂ fluxes of fcc Pd₅₈Cu₄₂ and Pd₇₀Cu₃₀ membranes were J_H2=(1.6±1.1) mol m⁻² s⁻¹ exp[(−24.8±0.4)kJ mol⁻¹/RT] and J_H2=(3.7±0.6) mol m⁻² s⁻¹ exp[(−21.3±1.0)kJ mol⁻¹/RT], respectively, at 100 kPa H₂ pressure difference.     

Analysis of steroids in yeast-mediated cell culture by on-line solid-phase extraction coupled high-performance liquid chromatography electrospray-ionization/mass spectrometry and novel continuous postcolumn infusion of internal standard technique

The reduction of 17-ketosteroid estrone or androstenedione to corresponding 17α- and 17β-estradiol or testosterone and epitestosterone has been performed with Saccharomyces cerevisiae. In the analysis of the cell culture, the solid-phase extraction (SPE) method was on-line coupled to high-performance liquid chromatography electrospray-ionization/mass spectrometry (HPLC-ESI/MS) for sample pretreatment to eliminate the complicated matrix interference and preconcentrate of the analytes before chromatographic separation. A novel quantification method with the continuous postcolumn infusion of internal standard was developed for the determination of substrate and products. This novel quantitative method can stabilize and enhance the ionization of all analytes during analysis. The HPLC-ESI/MS analysis of estrone, 17α-, and 17β-estradiol was operated with a negative ion mode and the analysis of androstenedione, testosterone, and epitestosterone was operated with a positive ion mode. The optimal concentration of the internal standard progesterone with the continuous postcolumn infusion technique was 3 μg mL⁻¹ for estrogen analysis and 1 ng mL⁻¹ for androgen analysis and both were at a constant infusion rate of 0.5 μL min⁻¹. All of the linear correlation coefficients of the standard calibration curves were over 0.99 and had a linear range from 0 to 50 ng mL⁻¹. The limit of detections (LODs) and the limit of quantitations (LOQs) for steroids analyzed were from 0.12 to 0.36 ng mL⁻¹ and from 0.4 to 1.2 ng mL⁻¹, respectively. The analysis accuracies and precisions were better than 94% and lower than 8.8% R.S.D., respectively. The developed method for the analysis of steroids in the cell culture was successful.     

Determination of photoirradiated high polar benzoylureas in tomato by HPLC with luminol chemiluminescence detection

This study reports the first analytical application of luminol chemiluminescence reaction for the sensitive detection of two benzoylurea insecticides (diflubenzuron and triflumuron). Off-line experiments demonstrated that previously irradiated traces of these benzoylurea insecticides largely enhanced the chemiluminescence emission yielded from the oxidation of luminol in methanol:water mixtures, by potassium permanganate in alkaline medium, the enhancement being proportional to the concentration of both pesticides. The two benzoylureas were determined in tomato samples by coupling liquid chromatography with post-column photoderivatization and detection based on this chemiluminescence reaction. Tomato samples were extracted using the QuEChERS method based on extraction with acetonitrile and dispersive solid-phase clean-up using primary and secondary amine (PSA). Interferences due to matrix effect were overcome by using matrix-matched standards. The optimised method was validated with respect to linearity, limits of detection and quantification, precision and accuracy. Under the optimised conditions, calibrations graphs were linear between 0.05 and 0.50 μg mL⁻¹ for diflubenzuron and between 0.10 and 1.00 μg mL⁻¹ for triflumuron. Method detection limits were 0.0025 and 0.0131 μg mL⁻¹ (equivalent to 0.0005 and 0.0026 mg kg⁻¹) and quantification limits were 0.05 and 0.10 μg mL⁻¹ (equivalent to 0.01 and 0.02 mg kg⁻¹) for diflubenzuron and triflumuron, respectively. In both cases, quantification limits were lower than the maximum residue levels (MRLs) established by the European legislation. The relative standard deviation of intra-day precision was below 10% and recoveries were between 79.7% and 94.2% for both pesticides.     

Analysis of BTEX, PAHs and metals in the oilfield produced water in the State of Sergipe, Brazil

During oil and gas exploitation, large amounts of produced water are generated. This water has to be analyzed with relation to the chemical composition to deduce the environmental impact of its discharge after a treatment process. Therefore, a study was carried out to evaluate preliminarily the BTEX (benzene, toluene, ethylbenzene and xylenes), polycyclic aromatic hydrocarbons (PAHs) and metals contents in produced water samples taken from effluents of the Bonsucesso treatment plant located in the city of Carmópolis, the most important oil and gas producer in the State of Sergipe, North-east of Brazil. Three methods were optimized to determine the target compounds. Polycyclic aromatic hydrocarbons were determined by gas chromatography with mass spectrometric detection (GC/MS), volatile aromatic hydrocarbons (BTEX) by gas chromatography with photoionization detector (GC/PID) and metals were analyzed by flame atomic absorption spectrometry (FAAS). The results showed that concentrations of the target compounds in these samples ranged from 96.7 to 1397 μg L^− 1 for BTEX, from 0.9 to 10.3 μg L^− 1 for PAHs and from 0.003 to 4540 mg L^− 1 for metals.     

Selenium speciation in cow milk obtained after supplementation with different selenium forms to the cow feed using liquid chromatography coupled with hydride generation-atomic fluorescence spectrometry

The purpose of this paper is to develop an easy and quick on-line selenium speciation method (LC-UV-HG-AFS) in cow milk obtained after different supplementation to cow feed. This study focuses on selenium speciation in cow milk after the use of different selenium species (organic selenium as selenised yeast and inorganic selenium as sodium selenite) in the supplementation of forages. Separation was carried out on a μBondapack C₁₈ column with the positively charged ion-pairing agent tetraethylammonium chloride in the mobile phase. The optimization of pre-reduction conditions was carried out; this step was done with UV irradiation and a heating block to improve the reduction of the different Se-compounds. Variables such as exposure time, hydrochloric acid concentration and temperature were studied. The detection limits for SeCyst₂, Se(IV), SeMet and Se(VI) were 0.4, 0.5, 0.9 and 1.0 μg l⁻¹, respectively. The proposed method was applied to cow milk samples. The milk samples obtained after an organic supplementation of feeding as selenised yeast present three species of selenium, SeCyst2, Se(IV) and SeMet, while only SeCyst2 and Se(IV) are present in milk samples obtained after an inorganic supplementation of feeding.     

Precipitate flotation-separation, speciation and hydride generation atomic absorption spectrometric determination of selenium(IV) in food stuffs

A method for flotation and determination of selenium(IV) in foodstuffs using p-chlorophenylthiosemicarbazide (HCPT) was investigated. At pH  2, selenium(IV) forms a 1:1 reddish-brown precipitate with HCPT easily floated using oleic acid (HOL) surfactant. The separated complex was dissolved in 4 M HCl and diluted in 10-ml double-distilled water (DDW). Selenium(IV) content in the eluate was determined by hydride generation atomic absorption spectrometry (HG-AAS) at 196.4 nm using sodium borohydride. The HCPT–Se(IV) complexes formed in absence and presence of oleic acid were characterized by elemental analysis, mass and infrared spectral studies. The mode of chelation between Se(IV) and HCPT is proposed to be through S and N coordination. Interferences, on the flotation process, from various foreign ions were avoided by adding excess HCPT. The proposed flotation methodology was successfully applied to the analysis of selenium in real foodstuffs and natural water spiked with known amounts of Se(IV) with a preconcentration factor of 100 and a detection limit of 20 pg. Application was also extended to separate Se(IV) successfully from Se(VI) in their synthetic mixtures. The separation mechanism is proposed to be due to hydrogen bond formation between the COOH group of HOL and –NH of the HCPT–Se(IV) complex.     

Simultaneous determination of gibberellic acid, indole-3-acetic acid and abscisic acid in wheat extracts by solid-phase extraction and liquid chromatography-electrospray tandem mass spectrometry

A liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed for simultaneous determination of three representative phytohormones in plant samples: gibberellic acid (GA₃), indole-3-acetic acid (IAA) and abscisic acid (ABA). A solid-phase extraction (SPE) pretreatment method was used to concentrate and purify the three phytohormones of different groups from plant samples. The separation was carried out on a C₁₈ reversed-phase column, using methanol/water containing 0.2% formic acid (50:50, v/v) as the isocratic mobile phase at the flow-rate of 1.0 mL min⁻¹, and the three phytohormones were eluted within 7 min. A linear ion trap mass spectrometer equipped with electrospray ionization source was operated in negative ion mode. Selective reaction monitoring (SRM) was employed for quantitative measurement. The SRM transitions monitored were as 345 → 239, 301 for GA₃, 174 → 130 for IAA and 263 → 153, 219 for ABA. Good linearities were found within the ranges of 5–200 μg mL⁻¹ for IAA and 0.005–10 μg mL⁻¹ for ABA and GA₃. Their detection limits based on a signal-to-noise ratio of three were 0.005 μg mL⁻¹, 2.2 μg mL⁻¹ and 0.003 μg mL⁻¹ for GA₃, IAA and ABA, respectively. Good recoveries from 95.5% to 102.4% for the three phytohormones were obtained. The results demonstrated that the SPE-LC–MS/MS method developed is highly effective for analyzing trace amounts of the three phytohormones in plant samples.     

Development and critical comparison of greener flow procedures for nitrite determination in natural waters

Two greener procedures for flow-injection spectrophotometric determination of nitrite in natural waters were developed and critically compared. Replacement of toxic reagents, waste minimization and treatment were exploited to attend the standards of clean chemistry. The flow system was designed with solenoid micro-pumps in order to minimize reagent consumption and waste generation. The first procedure is based on the Griess diazo-coupling reaction with sulfanilamide and N-(1-naphthyl)ethylenediamine (NED) yielding an azo dye, followed by photodegradation of the low amount of waste generated based on the photo-Fenton reaction. The second procedure is based on the formation of iodine from nitrite and iodide in acid medium in order to avoid the use of toxic reagents. For Griess method, linear response was achieved up to 1.0 mg L^− 1, described by the equation A = − 0.007 + 0.460C (mg L^− 1), r = 0.999. The detection limit was estimated as 8 μg L^− 1 at the 99.7% confidence level and the coefficient of variation was 0.8% (n = 20). The sampling rate was estimated as 108 determinations per hour. The consumption of the most toxic reagent (NED) is reduced 55-fold and 20-fold in comparison to batch method and flow injection with continuous reagent addition, respectively. A colorless residue was obtained by in-line photodegradation with reduction of 87% of the total organic carbon content. The results obtained for natural water samples were in agreement with those achieved by the reference method at the 95% confidence level. For the nitrite–iodide method, linear response was observed up to 2.0 mg L^− 1, described by the equation A = − 0.024 + 0.148C (mg L^− 1), r = 0.999. The detection limit was estimated as 25 μg L^− 1 at the 99.7% confidence level and the coefficient of variation was 0.6% (n = 20). The sampling rate was estimated as 44 determinations per hour. Despite avoiding the use of toxic reagents, the nitrite–iodide method presented worst performance in terms of selectivity and sensitivity.