Acid-base equilibria of phthalic acid in saline media: ion association from Pitzer equations

The protonation constants of 1,2-benzenedicarboxylic acid (phthalic acid) at 25 °C in NaCl and CaCl₂ (ionic strengths ranging from 0.1 to 2 mol kg⁻¹) were determined potentiometrically, and the results were analyzed by means of Pitzer equations. The values of the logarithm of the first and second dissociation constants ranged from 2.730 and 4.948 (in 0.101 mol kg⁻¹ NaCl) to 2.449 and 3.984 (in 0.624 mol kg⁻¹ CaCl₂), respectively. Tabulated interaction parameters for the inorganic species involved along with salting coefficients estimated from literature allowed the calculation of new interaction parameters for the phthalate-Na⁺/Ca²⁺ systems. The specific ion interaction model considered seems to account for the influence of the formation of weak complexes of phthalate with calcium ions on the equilibrium constants.     

Fluorimetric determination of phytic acid in urine based on replacement reaction

A sensitive fluorimetric method for determination of phytic acid in human urine samples was described. The method was based on a fluorimetric replacement reaction, in which the added phytic acid replaced the Cu²⁺ ion from Cu²⁺-gelatin complex, liberating the fluorescent gelatin molecule. The fluorescence of the solution was accordingly recovered proportionally to the amount of the foreign phytic acid. The excitation wavelength was 273.5 nm and the characteristic emission wavelength was 305.0 nm, respectively. The calibration graph was obtained by plotting the recovered fluorescent intensity at maximum 305.0 nm against the added standard phytic acid, and was divided into two sections. One section was linear over the range of 0.40-2.40 mg L⁻¹ with a linear regression equation of I_f = −0.895 + 15.146c (R² > 0.9993), and the other over the range of 2.40-9.20 mg L⁻¹ with a linear regression equation of I_f = −29.526 + 26.113c (R² > 0.9996), respectively. The relative standard deviation (R.S.D.) at 95% confidence degree for a 2.0 mg L⁻¹ of standard phytic acid within 1 month was less than 1.26% (n = 5), indicating the procedure is reproducible. The detection and the quantification limits of phytic acid were estimated to be 0.23 and 0.40 mg L⁻¹, respectively. The proposed method was applied to the determination of phytic acid in urine samples and the found concentrations of phytic acid in urine were in the range of 0.49-0.75 mg L⁻¹ with recoveries of 96.2-108.8%. Comparison of the obtained results with the reported HPLC was performed, indicating the proposed method was reliable.     

A sequential injection system for indirect spectrophotometric determination of lactic acid in yogurt and fermented mash samples

A suitable non-enzymatic method is presented as an alternative to the lactic acid determination in yogurt and fermented mash samples. The oxidative conversion of lactic acid by Ce⁴⁺ to CO₂ was performed in a sequential injection system with a heating coil set at 45 °C. A gas diffusion unit was coupled to the flow system for promoting the permeation of CO₂, which was collected into a bromothymol blue solution (pH 8.4), used as indicator solution for the spectrophotometric determination (619 nm). Simplicity in operation, low reagent consumption, low cost and ruggedness are some remarkable characteristics of the proposed system. Base line drift was < 0.005 h^− 1. A linear range from 20.0 to 100.0 mg L^− 1 lactic acid was obtained (r² = 0.998), and the detection and quantification limits were estimated as 0.158 mg L^− 1 and 1.6 mg L^− 1, respectively. The sampling rate was 22 h^− 1, with a consumption of 0.04 g Ce⁴⁺ per determination. Interferences of matrix components were not detected. Samples of yogurt and sugar cane fermented mash products were analyzed, and no significant difference at 95% confidence level was observed when comparing the proposed method with HPLC analysis.     

Rosmarinic acid determination using biomimetic sensor based on purple acid phosphatase mimetic

A new heterodinuclear Fe(III)Zn(II) complex which mimics the active site of the hydrolytic enzyme red kidney bean purple acid phosphatase was synthesized and characterized by IR, CHN and X-ray crystallographic analyses. This complex, [Fe^IIIZn^II(μ-OH)bpbpmp-CH₃](ClO₄)₂, containing the ligand (H₂bpbpmp-CH₃ = {2-[bis(2-pyridylmethyl)aminomethyl]-6-[(2-hydroxy-5-methylbenzyl) (2-pyridyl-methyl) aminomethyl]-4-methyl-phenol}) was employed in the construction of a biomimetic sensor and used in the determination of rosmarinic acid in plant extract samples. The response parameters and optimization of the biomimetic sensor design were evaluated. The best performance of this sensor was obtained for 75:15:10% (w/w/w) of the graphite powder:nujol:Fe(III)Zn(II) complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 7.5), 1.19 × 10⁻⁴ mol L⁻¹ hydrogen peroxide with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 0.6 mV, respectively. The rosmarinic acid concentration was linear in the range of 2.98 × 10⁻⁵ to 3.83 × 10⁻⁴ mol L⁻¹ (r = 0.9991) with a detection limit of 2.30 × 10⁻⁶ mol L⁻¹. This biomimetic sensor demonstrated long-term stability (300 days; 900 determinations) and reproducibility, with a relative standard deviation of 12.0%. The recovery study of rosmarinic acid in plant extract samples gave values from 90.3 to 98.3% and the concentrations determined showed agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level.     

Raman spectra and O NMR study effects of CaCl2 and MgCl2 on water structure

With various concentrations of CaCl₂ and MgCl₂ aqueous solution below 1.0 mol/l, Raman spectra of water in the OH stretch region of 2500-4000 cm⁻¹ and ¹⁷O NMR chemical shift of water are measured and the Raman spectra are deconvoluted. Both Raman spectra and ¹⁷O NMR of water show that the effect of Ca²⁺ on water structure is stronger than that of Mg²⁺. CaCl₂ and MgCl₂ destroy four hydrogen bonded water structure, but promote median water cluster size.     

Direct determination of kanamycin in raw materials, veterinary formulation and culture media using a novel liquid chromatography-evaporative light scattering method

A novel method for the direct determination of kanamycin A and its minor component kanamycin B was developed and validated based on reversed phase liquid chromatography with evaporative light scattering detector (ELSD). ELSD response to kanamycins was found to be enhanced by: (a) decrease of peak width and asymmetry (obtained by controlling the mobile phase acidity or ratio of organic solvent to water), (b) use of ion-pairing acidic reagents of increased molecular mass, and (c) increase of mobile phase volatility. Utilizing an Spherisorb ODS-2 C₁₈ column, the selected optimized mobile phase was water-acetonitrile (60:40, v/v), containing 11.6 mM heptafluorobutyric acid (isocratic elution with flow rate of 1.0 ml min⁻¹). Kanamycin A was eluted at 3.9 min and kanamycin B at 5.0 min with a resolution of 2.7. Logarithmic calibration curves were obtained from 0.6 to 28 μg ml⁻¹ (r > 0.9998) for kanamycin A and 4-36 μg ml⁻¹ (r > 0.9994) for kanamycin B, with a LOD equal to 0.20 and 1.4 μg ml⁻¹, respectively.In kanamycin acid sulfate pharmaceutical raw materials, the simultaneous determination of sulfate (t_R = 2.1 min, LOD = 2.3 μg ml⁻¹, %R.S.D. = 1.7, r > 0.9998) and kanamycins was feasible. No significant difference (t-test) was found between the results of the developed LC-ELSD method and those of reference methods, while recovery from kanamycin B spiked samples ranged from 95 to 105%. The developed method was also applied with very good accuracy for the determination of kanamycin A in veterinary formulation (%recovery 95-103, %R.S.D. < 1.4, n = 3) and for the determination of kanamycins A and B in bacteria culture media (%recovery 102 and 99, respectively).     

Simultaneous determination of Mn(II), Cu(II) and Fe(III) as 2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol complexes by adsorptive cathodic stripping voltammetry at a carbon paste electrode

A simple and precise square-wave adsorptive cathodic stripping voltammetry (SW-AdCSV) method has been described for simultaneous determination of Mn(II), Cu(II) and Fe(III) in water samples using a carbon paste electrode. In 0.1 mol L⁻¹ acetate buffer (pH 5) containing 50 μmol L⁻¹ of 2-(5′-bromo-2′-pyridylazo)-5-diethylaminophenol (5-Br-PADAP), Mn(II), Cu(II) and Fe(III) were simultaneously determined as metal-complexes with 5-Br-PADAP following preconcentration onto the carbon paste electrode by adsorptive accumulation at +1.0 V (vs. Ag/AgCl/3 M KCl). Insignificant interference from various cations (K⁺, Na⁺, Mg²⁺, Ca²⁺, Al³⁺, Bi³⁺, Sb³⁺, Se⁴⁺, Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Pb²⁺, V⁵⁺, Ti⁴⁺ and NH₄⁺), anions (HCO₃⁻, Cl⁻, NO³⁻, SO₄²⁻ and PO₄³⁻) and ascorbic acid was noticed. Limits of detection of 0.066, 0.108 and 0.093 μg L⁻¹ and limits of quantitation of 0.22, 0.36 and 0.31 μg L⁻¹ Mn(II), Cu(II) and Fe(III), respectively, were achieved by the described method. The described stripping voltammetry method was successfully applied for simultaneous determination of Mn(II), Cu(II) and Fe(III) in ground, tap and bottled natural water samples.     

Disposable biosensor based on cathodic electrochemiluminescence of tris(2,2-bipyridine)ruthenium(II) for uric acid determination

A new method for uric acid (UA) determination based on the quenching of the cathodic ECL of the tris(2,2-bipyridine)ruthenium(II)–uricase system is described. The biosensor is based on a double-layer design containing first tris(2,2-bipyridine)ruthenium(II) (Ru(bpy)₃²⁺) electrochemically immobilized on graphite screen-printed cells and uricase in chitosan as a second layer. The uric acid biosensing is based on the ECL quenching produced by uric acid over the cathodic ECL caused by immobilized Ru(bpy)₃²⁺ in the presence of uricase. The use of a −1.1 V pulse for 1 s with a dwelling time of 10 s makes it possible to estimate the initial enzymatic rate, which is used as the analytical signal. The Stern–Volmer type calibration function shows a dynamic range from 1.0 × 10⁻⁵ to 1.0 × 10⁻³ M with a limit of detection of 3.1 × 10⁻⁶ M and an accuracy of 13.6% (1.0 × 10⁻⁴ M, n = 5) as relative standard deviation. Satisfactory results were obtained for urine samples, creating an affordable alternative for uric acid determination.     

Determination of chlorogenic acid in coffee using a biomimetic sensor based on a new tetranuclear copper(II) complex

A new tetranuclear copper(II) complex which mimics the active site of catechol oxidase was synthesized and characterized by IR, CHN, electronic spectroscopic and ¹H NMR methods. The title complex [Cu₂(μ-OH)(bpbpmp-NO₂)]₂[ClO₄]₂ was employed in the construction of a novel biomimetic sensor and used in the determination of chlorogenic acid by square wave voltammetry. The performance and optimization of the resulting biomimetic sensor were studied in detail. The best response of this sensor was obtained for 75:15:10% (w/w/w) ratio of the graphite powder:nujol:Cu(II) complex, 0.1 mol L⁻¹ phosphate buffer solution (pH 7.0), with frequency, pulse amplitude, and scan increment at 30 Hz, 100 mV, and 3.0 mV, respectively. The chlorogenic acid concentration was linear in the range of 5.0 × 10⁻⁶ to 1.45 × 10⁻⁴ mol L⁻¹ (r = 0.9985) with a detection limit of 8.0 × 10⁻⁷ mol L⁻¹. This biomimetic sensor demonstrated long-term stability (250 days; 640 determinations) and reproducibility, with a relative standard deviation of 10.0%. The recovery study of chlorogenic acid in coffee samples gave values from 93.2% to 106.1% and the concentrations determined showed good agreement when compared with those obtained using capillary electrophoresis at the 95% confidence level.     

Factorial design for optimization of experimental variables in preconcentration of copper by a chromotropic acid loaded Q-Sepharose adsorbent

An agarose-based anion exchanger (Q-Sepharose) was loaded with chromotropic acid (CTA) and used for column preconcentration and determination of copper by flame AAS. Preliminary experiments indicated that a sample pH of 5.7-6.5 is best suited for accumulation of copper and a 2.5 ml portion of a 0.02 mol l⁻¹ HCl solution can efficiently desorb the analyte from the column. An incomplete factorial design was used for optimization of five different variables that affect recovery of copper. The results indicated that ionic strength, pH and sample volume variables are the most important effects, respectively. Hence, these variables and their possible interactions were studied more carefully. In optimized conditions, the column could tolerate up to 0.18 mol l⁻¹ sodium nitrate in the matrix. A 5 ml portion of a 0.02 mol l⁻¹ CTA was sufficient for loading of a 0.5 ml column prior to preconcentration of copper from a 150 ml sample solution. Matrix ions of Ca²⁺, Mg²⁺, Na⁺ and K⁺ and potentially interfering ions of Pb²⁺, Ni²⁺, Cd²⁺, Co²⁺, Zn²⁺ and Mn²⁺ with relatively high concentrations did not have any significant effect on the recovery of the analyte. A preconcentration factor of 60 and a detection limit of 1.0 μg l⁻¹ was obtained for the determination of copper by the flame AAS method. A precision better than 2.5%, expressed as R.S.D., was also achieved. Application of the method to tap water and two different river water samples resulted in values well confirmed by direct determinations with ET-AAS.     

Sensitive and robotic determination of bromate in sea water and drinking deep-sea water by headspace solid-phase micro extraction and gas chromatography–mass spectrometry

A robotic method has been established for the determination of bromate in sea water and drinking deep-sea water. Bromate in water was converted into volatile derivative, which was measured with headspace solid-phase micro extraction and gas chromatography–mass spectrometry (HS-SPME GC–MS). Derivatization reagent and the HS-SPME parameters (selection of fibre, extraction/derivatization temperature, heating time and; the morality of HCl) were optimized and selected. Under the established conditions, the detection and the quantification limits were 0.016 μg L⁻¹ and 0.051 μg L⁻¹, respectively, and the intra- and inter-day relative standard deviation was less than 7% at concentrations of 1.0 and 10.0 μg L⁻¹. The calibration curve showed good linearity with r² = 0.9998. The common ions Cl⁻, NO₃⁻, SO₄²⁻, HPO₄²⁻, H₂PO₄⁻, K⁺, Na⁺, NH₄⁺, Ca²⁺, Mg²⁺, Ba²⁺, Mn⁴⁺, Mn²⁺, Fe³⁺ and Fe²⁺ did not interfere even when present in 1000-fold excess over the active species. The method was successfully applied to the determination of bromate in sea water and drinking deep-sea water.     

Determination of palladium in various samples by atomic absorption spectrometry after preconcentration with dimethylglyoxime on silica gel

A preconcentration method based on the adsorption of palladium-dimethylglyoxime (DMG) complex on silica gel for the determination of palladium at trace levels by atomic absorption spectrometry (AAS) has been developed. The retained palladium as Pd(DMG)₂ complex was eluted with 1 mol l⁻¹ HCl in acetone. The effect of some analytical parameters such as pH, amount of reagent and the sample volume on the recovery of palladium was examined in synthetic solutions containing street dust matrix. The influence of some matrix ions on the recovery of palladium was investigated by using the developed method when the elements were present both individually and together. The results showed that 2500 μg ml⁻¹ Na⁺, K⁺, Mg²⁺, Al³⁺ and Fe³⁺; 5000 μg ml⁻¹ Ca²⁺ ; 500 μg ml⁻¹ Pb²⁺; 125 μg ml⁻¹ Zn²⁺; 50 μg ml⁻¹ Cu²⁺ and 25 μg ml⁻¹ Ni²⁺ did not interfere with the palladium signal. At the optimum conditions determined experimentally, the recovery for palladium was found to be 95.3±1.2% at the 95% confidence level. The relative standard deviation and limit of detection (3s/b) of the method were found to be 1.7% and 1.2 μg l⁻¹, respectively. In order to determine the adsorption behaviour of silica gel, the adsorption isotherm of palladium was studied and the binding equilibrium constant and adsorption capacity were calculated to be 0.38 l mg⁻¹ and 4.06 mg g⁻¹, respectively. The determination of palladium in various samples was performed by using both flame AAS and graphite furnace AAS. The proposed method was successfully applied for the determination of palladium in the street dust, anode slime, rock and catalytic converter samples.     

Biosensor for chlorogenic acid based on an ionic liquid containing iridium nanoparticles and polyphenol oxidase

A biosensor based on the ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate containing dispersed iridium nanoparticles (Ir-BMI.PF₆) and polyphenol oxidase was constructed. This enzyme was obtained from the sugar apple (Annona squamosa), immobilized in chitosan ionically crosslinked with oxalate. The biosensor was used for determination of chlorogenic acid by square wave voltammetry. The polyphenol oxidase catalyzes the oxidation of chlorogenic acid to the corresponding o-quinone, which is electrochemically reduced back to this substance at +0.25 V vs. Ag/AgCl. Under optimized operational conditions the chlorogenic acid concentration was linear in the range of 3.48 × 10⁻⁶ to 4.95 × 10⁻⁵ mol L⁻¹ with a detection limit of 9.15 × 10⁻⁷ mol L⁻¹. The biosensor was applied in the determination of chlorogenic acid in organic and decaffeinated coffee and the results compared with those obtained using the capillary electrophoresis method. The recovery study for chlorogenic acid in these samples gave values of 93.2-105.7%.     

Kinetic method for determination of nanogram amounts of copper(II) by its catalytic effect on hexacynoferrate(III)-citric acid indicator reaction

This paper describes a highly sensitive, selective catalytic-kinetic-spectrophotometric method for the determination of copper(II) concentration as low as 6 ng ml⁻¹. The method is based on the catalytic effect of copper(II) on the oxidation of citric acid by alkaline hexacyanoferrate(III). The reaction was followed by measuring the decrease in absorbance of hexacyanoferrate(III) at 420 nm (λ_max of [Fe(CN)₆]³⁻, ∈ = 1020 dm³ mol⁻¹ cm⁻¹). The dependence of rate of the indicator reaction on the reaction variables has been studied and discussed to propose a suitable mechanism to get a relation between the reaction rate and [Cu²⁺]. A fixed time procedure has been used to obtain a linear calibration curve between the initial rate and lower [Cu²⁺] or log[Cu²⁺] in the range 1 × 10⁻⁷ to 4 × 10⁻⁴ mol l⁻¹ (6.35-25,400 ng ml⁻¹). The detection limit has been calculated to be 4 ng ml⁻¹. The maximum average error is 3.5%. The effect of the presence of various cations, commonly associated with copper(II) and some anions has also been investigated and discussed. The proposed method is sensitive, accurate, rapid and inexpensive compared to other techniques available for determination of copper(II) in such a large range of concentration. The new method has been successfully applied for the determination of copper(II) in various samples.     

Microflow injection chemiluminescence system with spiral microchannel for the determination of cisplatin in human serum

A new microflow injection chemiluminescence (μFI-CL) system was described for the determination of cisplatin in human serum. By using the microchip with double spiral channel configuration, the sensitivity was greatly enhanced due to more efficient mixing of the analyte and reagent solutions. Experimental results revealed that common ions in human serum, such as Mn²⁺, Co²⁺, Fe³⁺, Cu²⁺, Zn²⁺, Ni²⁺, Na⁺, K⁺, Ca²⁺, Cl⁻, NO₃⁻, Ac⁻, CO₃²⁻, PO₄³⁻, SO₄²⁻ did not cause interference with the detection of Pt(II) by using 1,10-phenanthroline as the masking agent. Under the optimized conditions, a linear calibration curve (R² = 0.998) over the range 2.0 × 10⁻⁸ to 2.0 × 10⁻⁶ mol L⁻¹ was obtained with the detection limit of 1.24 × 10⁻⁹ mol L⁻¹. The relative standard deviation was found to be 3.46% (n = 12) for 2.0 × 10⁻⁷ mol L⁻¹. The sample consumption was only 2 μL with the sample throughput of 72 h⁻¹. It had been used for trace platinum determination in cisplatin injection and human serum samples after the dosage of cisplatin. The recovery varied from 97.6 to 103.9%. The results proved that the proposed μFI-CL system had the advantages of high sensitivity and precision, low sample and reagents consumption, and high analytical throughput.     

Analysis of salicylic acid based on the fluorescence enhancement of the As(III)-salicylic acid system

A new, simple and sensitive spectrofluorimetric method for the determination of salicylic acid (λ_ex = 315 nm, λ_em = 408 nm) using As(III) as a sensitizing reagent has been investigated by measuring the increase of fluorescence intensity of salicylic acid due to the complexation of As(III)-salicylic acid in presence of sodium dodecyl sulfate (SDS) 10⁻³ M. Under optimum conditions, a significant relationship was obtained between the fluorescence intensity and salicylic acid concentration. A linear calibration curve was obtained in the range 13.8-13812 μg l⁻¹ with product-moment correlation coefficient (R) 0.99985 and detection limit 4.2 μg l⁻¹. The R.S.D. is 2.35% (n = 5).The method was applied successfully to the determination of salicylic acid in human serum.     

Thermodynamic properties on quaternary aqueous solutions of chlorides charge-type 1-1*2-1*2-1: XCl + MgCl2 + CaCl2 + H2O with (X ≡ Na; NH4)

In this investigation, the quaternary aqueous solutions of chlorides charge-type 1-1*2-1*2-1 with a cation (Na⁺; NH₄⁺; Mg²⁺; Ca²⁺) have been studied using the hygrometric method at 298.15 K. The water activities of the systems NH₄Cl + MgCl₂ + CaCl₂ + H₂O and NaCl + MgCl₂ + CaCl₂ + H₂O are measured at total molalities from 0.60 mol kg⁻¹ to saturation for different ionic-strength fractions NH₄Cl or NaCl, y = 0.20, 0.50, 0.80, and z ratio ionic-strength for other solutes, with z = 0.20, 0.50 and 0.80 for each y. The obtained data allow the deduction of osmotic coefficients.     

Assessment of single extractions for the determination of mobile forms of metals in highly polluted soils and sediments--analytical and thermodynamic approaches

Highly polluted forest/tilled soils and stream sediments from a mining and smelting area were subjected to single-extraction procedures to determine the extractable contents of Cd, Cu, Pb, and Zn. The results obtained from four widely used operationally defined single extraction tests were compared: deionised water, 0.01 mol L⁻¹ CaCl₂, 1 mol L⁻¹ NH₄NO₃ and 0.005 mol L⁻¹ DTPA. The analytical data were coupled with measurement of the pH and Eh in extracts, mineralogical investigations and thermodynamic modelling using the PHREEQC-2 code. The changes in the pH of the equilibrated suspensions significantly influenced the metal extractabilities, with higher values in the lower pH regions. Although the DTPA procedure generally extracted the highest amounts of metals, it was found to be unsuitable for highly organic acidic forest soils, where anionic metal-DTPA complexes are assumed to be re-adsorbed on the positively charged surfaces of soil organic matter and oxides. The NH₄NO₃ extraction was also unsuitable due to the high ionic strength (1 mol L⁻¹), limiting the use of the thermodynamic speciation model and the formation of the Cu(NH₃)²⁺ complex, leading to acidification of the suspension. 0.01 mol L⁻¹ CaCl₂ can be proposed as the most appropriate extraction medium, suitable for speciation modelling and analytical determinations using ICP-techniques and having an ionic strength similar to that of the soil solution. The metals are present in free ionic forms or chlorocomplexes in the CaCl₂ extracts, preventing their re-adsorption on the positively charged surfaces of soil solids (organic matter, Fe- and Mn-oxides) in acidic and circum-neutral conditions.     

Determination of indole-3-acetic acid and indole-3-butyric acid in mung bean sprouts using high performance liquid chromatography with immobilized Ru(bpy)3-KMnO4 chemiluminescence detection

A novel method for determination of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) in an extract from mung bean sprouts using high performance liquid chromatography (HPLC) with chemiluminescence (CL) detection is described. The method is based on the CL reaction of auxin (indole-3-acetic acid and indole-3-butyric acid) with acidic potassium permanganate (KMnO₄) and tris(2,2′-bipyridyl)ruthenium(II), which was immobilized on the cationic ion-exchange resin. The chromatographic separation was performed on a Nucleosil RP-C18 column (i.d.: 250 mm × 4.6 mm, particle size: 5 μm, pore size: 100) with an isocratic mobile phase consisting of methanol-water-acetic acid (45:55:1, v/v/v). At a flow rate of 1.0 mL min⁻¹, the total run time was 20 min. Under the optimal conditions, the linear ranges were 5.0 × 10⁻⁸ to 5.0 × 10⁻⁶ g mL⁻¹ and 5.0 × 10⁻⁷ to 1.0 × 10⁻⁵ g mL⁻¹ for IAA and IBA, respectively. The detection limits were 2.0 × 10⁻⁸ g mL⁻¹ and 2.0 × 10⁻⁷ g mL⁻¹ for IAA and IBA, respectively. The relative standard deviation (RSD) of intra-day were 3.1% and 2.3% (n = 11) for 2 × 10⁻⁶ g mL⁻¹ IAA and 2 × 10⁻⁶ g mL⁻¹ IBA; The relative standard deviations of inter-day precision were 6.9% and 4.9% for 2 × 10⁻⁶ g mL⁻¹ IAA and 2 × 10⁻⁶ g mL⁻¹ IBA. The proposed method had been successfully applied to the determination of auxin in mung bean sprouts.     

Sensitive determination of cadmium in water samples by room temperature ionic liquid-based preconcentration and electrothermal atomic absorption spectrometry

A sensitive preconcentration methodology for Cd determination at trace levels in water samples was developed in this work. 1-Butyl-3-methylimidazolium hexafluorophosphate ([C₄MIM][PF₆]) room temperature ionic liquid (RTIL) was successfully used for Cd preconcentration, as cadmium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex [Cd-5-Br-PADAP]. Subsequently, Cd was back-extracted from the RTIL phase with 500 μL of 0.5 mol L⁻¹ nitric acid and determined by electrothermal atomic absorption spectrometry (ETAAS). A preconcentration factor of 40 was achieved with 20 mL of sample. The limit of detection (LOD) obtained under optimum conditions was 3 ng L⁻¹ and the relative standard deviation (R.S.D.) for 10 replicates at 1 μg L⁻¹ Cd²⁺ concentration level was 3.5%, calculated at peak heights. The calibration graph was linear from concentration levels near the detection limits up to at least 5 μg L⁻¹. A correlation coefficient of 0.9997 was achieved. Validation of the methodology was performed by standard addition method and analysis of certified reference material (CRM). The method was successfully applied to the determination of Cd in river and tap water samples.