Immersed single-drop microextraction interfaced with sequential injection analysis for determination of Cr(VI) in natural waters by electrothermal-atomic absorption spectrometry

Single-drop microextraction (SDME) and sequential injection analysis have been hyphenated for ultratrace metal determination by Electrothermal-Atomic Absorption Spectrometry (ETAAS). The novel method was targeted on extraction of the Cr(VI)-APDC chelate and encompasses the potential of SDME as a miniaturized and virtually solvent-free preconcentration technique, the ability of sequential injection analysis to handle samples and the versatility of furnace autosamplers for introducing microliter samples in ETAAS.     

Determination of antimony(III) and total antimony by single-drop microextraction combined with electrothermal atomic absorption spectrometry

A simple and sensitive method for using electrothermal atomic absorption spectrometry (ET AAS) with Rh as permanent modifier determination of Sb(III) and total Sb after separation and preconcentration by N-benzoyl-N-phenylhydroxylamine (BPHA)-chloroform single drop has been developed. Parameters, such as pyrolysis and atomization temperature, solvent type, pH, BPHA concentration, extraction time, drop size, stirring rate and sample volume were investigated. Under the optimized experimental conditions, the detection limits (3σ) were 8.0 ng L⁻¹ for Sb(III) and 9.2 ng L⁻¹ for total Sb, respectively. The relative standard deviations (R.S.Ds.) were 6.6% for Sb(III) and 7.1% for total Sb (c = 0.2 ng mL⁻¹, n = 7), respectively. The enrichment factor was 96. The developed method has been applied successfully to the determination of Sb(III) and total Sb in natural water samples.     

Green method for ultrasensitive determination of Hg in natural waters by electrothermal-atomic absorption spectrometry following sono-induced cold vapor generation and ‘in-atomizer trapping’

Sono-induced cold vapor generation (SI-CVG) has been used for the first time in combination with a graphite furnace atomizer for determination of Hg in natural waters by electrothermal-atomic absorption spectrometry after in situ trapping onto a noble metal-pretreated platform (Pd, Pt or Rh) inserted into a graphite tube. The system allows ‘in-atomizer trapping’ of Hg without the use of conventional reduction reactions based on sodium borohydride or tin chloride in acid medium for cold vapor generation. The sono-induced reaction is accomplished by applying ultrasound irradiation to the sample solution containing Hg(II) in the presence of an organic compound such as formic acid. As this organic acid is partly degraded upon ultrasound irradiation to yield CO, CO₂, H₂ and H₂O, the amount of lab wastes is minimized and a green methodology is achieved.     

单滴微萃取-气相色谱-质谱联用测定水中的硝基咪唑类药物

建立了单滴液相微萃取(SDME)与气相色谱-质谱(GC-MS)联用技术快速检测水中的硝基咪唑类药物,对影响萃取的因素(溶剂的种类及用量、萃取时间、萃取温度及搅拌子的搅拌速度)进行优化。优化的萃取条件为:溶剂为2.5μL正辛醇,温度为50℃,搅拌速度为600 r/min,时间为20 min。萃取后,微液滴转移至衍生化试管,于70℃水浴中衍生45 min,进样分析。该方法在水中的线性范围为0.5~400μg/L,线性相关系数良好(r0.998),检测限为0.16~0.57μg/L。加标自来水和湖水中的相对平均回收率为80.9%~103.6%,相对标准偏差为1.7%~9.0%。     

Fast determination of Z-ligustilide in plasma by gas chromatography/mass spectrometry following headspace single-drop microextraction

Angelica sinensis (danggui in Chinese) is a common traditional Chinese medicine (TCM), and its essential oil has been used for the treatment of many diseases such as hepatic fibrosis. Z-Ligustilide has been found to be an important active component in the TCM essential oil. In this work, for the first time, headspace single-drop microextraction (HS-SDME) followed by gas chromatography-mass spectrometry (GC-MS) was developed for the determination of Z-ligustilide in rabbit plasma after oral administration of essential oil of danggui. The extraction parameters of solvent selection, solvent volume, sample temperature, extraction time, stirring rate, and ion strength were systemically optimized. Furthermore, the method linearity, detection limit, and precision were also investigated. It was shown that the proposed method provided good linearity (0.02-20 microg/mL, R2 = 0.997), low detection limit (10 ng/mL), and good precision (RSD value less than 9%). Finally, HS-SDME followed by GC/MS was used for fast determination of Z-ligustilide in rabbit plasma at different time intervals after oral administration of danggui essential oil. The experimental results suggest that HS-SDME followed by GC/MS is a simple, sensitive, and low-cost method for the determination of Z-ligustilide in plasma, and a low-cost approach to pharmacokinetics studies of active components in TCMs.     

Ion chromatography for rapid and sensitive determination of fluoride in milk after headspace single-drop microextraction with in situ generation of volatile hydrogen fluoride

In this article, we report a new method that involves headspace single-drop microextraction and ion chromatography for the preconcentration and determination of fluoride. The method lies in the in situ hydrogen fluoride generation and subsequent sequestration into an alkaline microdrop (15 μL) exposed to the headspace above the stirred aqueous sample. The NaF formed in the drop was then determined by ion chromatography. The influences of some crucial single-drop microextraction parameters such as the extraction temperature, extraction time, sample stirring speed, sulphuric acid concentration and ionic strength of the sample, on extraction efficiency were investigated. In the optimal condition, an enrichment factor of 97 was achieved in 15 min. The calibration working range was from 10 μg L⁻¹ to 2000 μg L⁻¹ (R² = 0.998), and the limit of detection (signal to noise ratio of 3) was 3.8 μg L⁻¹ of fluoride. Finally, the proposed method was successfully applied to the determination of fluoride in different milk samples. The recoveries of fluoride (at spiked concentrations of 200 μg L⁻¹ and 600 μg L⁻¹ into milk) in real samples ranged from 96.9% to 107.7%. Intra-day precision (N = 3) in terms of peak area, expressed as relative standard deviation, was found to be within the range of 0.24-1.02%.     

Dispersive liquid-liquid microextraction versus single-drop microextraction for the determination of several endocrine-disrupting phenols from seawaters

Two liquid-phase microextraction procedures: single-drop microextraction (SDME) and dispersive liquid-liquid microextraction (DLLME), have been developed for the determination of several endocrine-disrupting phenols (EDPs) in seawaters, in combination with high-performance liquid chromatography (HPLC) with UV detection. The EDPs studied were bisphenol-A, 4-cumylphenol, 4-tertbutylphenol, 4-octylphenol and 4-n-nonylphenol. The optimized SDME method used 2.5 μL of decanol suspended at the tip of a micro-syringe immersed in 5 mL of seawater sample, and 60 min for the extraction time. The performance of the SDME is characterized for average relative recoveries of 102 ± 11%, precision values (RSD) < 9.4% (spiked level of 50 ng mL⁻¹), and detection limits between 4 and 9 ng mL⁻¹. The optimized DLLME method used 150 μL of a mixture acetonitrile:decanol (ratio 15.7, v/v), which is quickly added to 5 mL of seawater sample, then subjected to vortex during 4 min and centrifuged at 2000 rpm for another 5 min. The performance of the DLLME is characterized for average relative recoveries of 98.7 ± 3.7%, precision values (RSD) < 7.2% (spiked level of 20 ng mL⁻¹), and detection limits between 0.2 and 1.6 ng mL⁻¹. The efficiencies of both methods have also been compared with spiked real seawater samples. The DLLME method has shown to be a more efficient approach for the determination of EDPs in seawater matrices, presenting enrichment factors ranging from 123 to 275, average relative recoveries of 110 ± 11%, and precision values (RSD) < 14%, when using a real seawaters (spiked level of 3.5 ng mL⁻¹).     

Microvolume turbidimetry for rapid and sensitive determination of the acid labile sulfide fraction in waters after headspace single-drop microextraction with in situ generation of volatile hydrogen sulfide

In this work, we demonstrate the feasibility of applying headspace single-drop microextraction with in-drop precipitation for the quantitative determination of the acid labile sulfide fraction (H₂S, HS⁻, and S²⁻ (free sulfide), amorphous FeS and some metal sulfide complexes-clusters as ZnS) in aqueous samples by microvolume turbidimetry. The methodology lies in the in situ hydrogen sulfide generation and subsequent sequestration into an alkaline microdrop containing ZnO₂²⁻ and exposed to the headspace above the stirred aqueous sample. The ZnS formed in the drop was then determined by microvolume turbidimetry. The optimum experimental conditions of the proposed method were: 2 μL of a microdrop containing 750 mg L⁻¹ Zn(II) in 1 mol L⁻¹ NaOH exposed to the headspace of a 20-mL aqueous sample stirred at 1600 rpm during 80 s after derivatization with 1 mL of 6 mol L⁻¹ HCl. An enrichment factor of 1710 was achieved in only 80 s. The calibration graph was linear in the range of 5-100 μg L⁻¹ with a detection limit of 0.5 μg L⁻¹. The repeatability, expressed as relative standard deviation, was 5.8% (N = 9). Finally, the proposed methodology was successfully applied to the determination of the acid labile sulfide fraction in different natural water samples.     

Investigation of ultraviolet photolysis vapor generation with in-atomizer trapping graphite furnace atomic absorption spectrometry for the determination of mercury

Generation of mercury vapor by ultraviolet irradiation of mercury solutions in low molecular weight organic acid solutions prior to measurement by Atomic Absorption Spectrometry is a cheap, simple and green method for determination of trace concentrations of mercury. In this work mercury vapor generated by ultraviolet photolysis was trapped onto a palladium coated graphite furnace significantly improving the detection limit of the method. The system was optimized and a detection limit of 0.12 µg L^− 1 (compared to 2.1 µg L^− 1 for a previously reported system in the absence of trapping) with a precision of 11% for a 10 µg L^− 1 mercury standard (RSD, N = 5).     

Germanium determination by flame atomic absorption spectrometry: an increased vapor pressure-chloride generation system

A new chloride generation system was designed for the direct, sensitive, rapid and accurate determination of the total germanium in complex matrices. It was aimed to improve the detection limit of chloride generation technique by increasing the vapor pressure of germanium tetrachloride (GeCl₄). In order to do so, a novel joint vapor production and gas-liquid separation unit equipped with a home-made oven was incorporated to an ordinary nitrous oxide-acetylene flame atomic absorption spectrometer. Several variables such as reaction time, temperature and acid concentration have been investigated. The linear range for germanium determination was 0.1-10 ng mL⁻¹ for 1 mL sampling volume with a detection limit (3 s) of 0.01 ng mL⁻¹. The relative standard deviation (RSD) was 2.4% for nine replicates of a 1 ng mL⁻¹ germanium solution. The method was validated by the analysis of one non-certified and two certified geochemical reference materials, respectively, CRM GSJ-JR-2 (Rhyolite), and GSJ-JR-1 (Rhyolite), and GBW 07107 (Chinese Rock). Selectivity of the method was investigated for Cd²⁺, Co²⁺, Cu²⁺, Fe³⁺, Ga³⁺, Hg²⁺, Ni²⁺, Pb²⁺, Sn²⁺, and Zn²⁺ ions and ionic species of As(III), Sb(III), Te(IV), and Se(IV).     

A highly sensitive method for the determination of mercury using vapor generation gold wire microextraction and electrothermal atomic absorption spectrometry

The study introduces a new simple and highly sensitive method for headspace solid phase microextraction (HS-SPME) coupled with electrothermal atomic absorption spectrometric determination of mercury. In the proposed method, a gold wire, mounted in the headspace of a sample solution in a sealed bottle, is used for collection of mercury vapor generated by addition of sodium tetrahydroborate. The gold wire is then simply inserted in the sample introduction hole of a graphite furnace of an electrothermal atomic absorption spectrometry instrument. By applying an atomization temperature of 600 °C, mercury is rapidly desorbed from the wire and determined with high sensitivity.     

Photochemical vapor generation of carbonyl for ultrasensitive atomic fluorescence spectrometric determination of cobalt

UV photochemical vapor generation (photo-CVG) as sample introduction was first adapted for determination of ultratrace cobalt by atomic fluorescence spectrometry (AFS). Cobalt volatile species can be generated when the buffer system of formic acid and formate containing Co (II) is exposed to UV radiation. The generated gaseous products were separated from liquid phase within a gas–liquid separator and then transported to AFS for determination of cobalt. Factors affecting the efficiency of photo-CVG were investigated in detail, including type and concentration of low molecular weight (LMW) organic acid, buffer system, UV irradiation time, reaction temperature, carrier gas flow rate and hydrogen flow rate. With 4% (v/v) HCOOH and 0.4 mol L^{− 1} HCOONa buffer solution, 150 s irradiation time and 15 W low pressure mercury lamp, a generation efficiency of 23–25% was achieved. A limit of detection (LOD) of 0.08 ng mL^{− 1} without any pre-concentration procedure and a precision of 2.2% (RSD, n = 11) at 20 ng mL^{− 1} were obtained under the optimized conditions. The proposed method was successfully applied in the analysis of several simple matrix real water samples.     

蒸气发生火焰原子吸收法测定面粉中的铜

用自制的蒸气发生装置,在强还原剂存在下,对铜蒸气的生成进行了详细研究,并通过该装置测定非蒸气发生元素镁和在络合剂掩蔽下测铜两种不同的方法进行了验证。对酸的种类及浓度、NaBH4溶液流速及浓度、反应管道长度的影响等实验参数和干扰情况进行了研究。用该方法测定了面粉中铜的质量分数,检出限为6μg L。     

Headspace single-drop microextraction with in situ stibine generation for the determination of antimony (III) and total antimony by electrothermal-atomic absorption spectrometry

A headspace-single drop microextraction method combined with electrothermal atomic absorption spectrometry (ETAAS) is developed for the extraction and preconcentration of antimony(III) and total antimony into a Pd(II)-containing aqueous drop after hydride generation. Experimental variables such as hydrochloric acid and sodium tetrahydroborate concentrations, sample volume, Pd(II) concentration in the acceptor phase and microextraction time were optimized. A 2^6-2 _IV factorial fractional design was initially used for screening the effect of the variables, followed by an univariate approach. The method showed a great freedom from interferences caused by hydride-forming elements and transition metals. The detection limit of Sb(III) was 25 pg mL^?1. A preconcentration factor of 176 is achieved in 3 min. The repeatability, expressed as relative standard deviation, was 4.7%. The method was validated against two certified reference materials (NWRI-TM 27.2 and NIST 2711) and applied to the determination of Sb(III) and total Sb in waters.     

Hollow fiber based liquid-phase microextraction for the determination of mercury traces in water samples by electrothermal atomic absorption spectrometry

A three-phase liquid microextraction procedure for the determination of mercury at low concentrations is discussed. To the aqueous sample placed at pH 7 by means of a phosphate buffer, 0.002% (m/v) 1-(2-pyridylazo)-2-naphthol (PAN) is incorporated, and the mixture submitted to microextraction with a hollow-fiber impregnated with toluene and whose lumen contains a 0.05 mol L⁻¹ ammonium iodide solution. The final measurement of the extract is carried out by electrothermal atomic absorption spectrometry (300 °C and 1100 °C for the calcination and atomization temperatures, respectively). The pyrolytic graphite atomizer is coated electrolytically with palladium. An enrichment factor of 270, which results in a 0.06 μg L⁻¹ mercury for the detection limit is obtained. The relative standard deviation at the 1 μg L⁻¹ mercury level is 3.2% (n = 5). The reliability of the procedure is verified by analyzing waters as well as six certified reference materials.     

Electrochemical hydride generation atomic absorption spectrometry for determination of cadmium

An electrolytic hydride generation system for determination of another hydride forming element, cadmium, by catholyte variation electrochemical hydride generation (EcHG) atomic absorption spectrometry is described. A laboratory-made electrolytic cell with lead-tin alloy as cathode material is designed as electrolytic generator of molecular hydride. The influences of several parameters on the analytical signal have been evaluated using a Plackett-Burman experimental design. The significant parameters such as cathode surface area, electrolytic current, carrier gas flow rate and catholyte concentration have been optimized using univariate method. The analytical figures of merit of procedure developed were determined. The calibration curve was linear up to 20 ng ml⁻¹of cadmium. The concentration detection limit (3σ, n = 8) of 0.2 ng ml⁻¹ and repeatability (relative standard deviation, n = 7) of 3.1% were achieved at 10.0 ng ml⁻¹. It was shown that interferences from major constituents at high concentrations were significant. The accuracy of method was verified using a real sample (spiked tap water) by standard addition calibration technique. Recovery of 104% was achieved for Cd in the spiked tap water sample.     

Ultrasound-assisted extraction of gold and silver from environmental samples using different extractants followed by electrothermal-atomic absorption spectrometry

Ultrasound-assisted extraction combined with electrothermal-atomic absorption spectrometry has been applied to the determination of silver and gold at μg g^{− 1} levels in different environmental samples such as soil, sediment, fly ash and industrial sludge. Two different extraction systems have been tried, i.e. acid mixtures (HCl, HF, and HNO₃) and thiourea in diluted H₂SO₄ medium. In both cases, an efficient cup-horn sonoreactor was used as ultrasonic device to accelerate the extraction process. This ultrasonic processor allows the use of any extractant including HF and simultaneous treatment of up to six samples. Recovery ranged from 81% to 107% for silver, and from 91% to 105% for gold. Optimal acid mixtures were 25% v/v HNO₃ + 25% v/v HF for Ag and 25% v/v HNO₃ + 25% v/v HCl for Au. The thiourea method required 0.6% m/v thiourea + 2% v/v H₂SO₄. The latter method was considered advantageous since efficient Au and Ag extractions were obtained in a short time, and moreover, wastes generated were less harmful to the environment. Limits of detection for Ag and Au were 0.012 and 0.050 μg g^{− 1}, respectively. Repeatability expressed as relative standard deviation ranged from 2 to 10% for both metals. Both extraction methods were applied to the determination of Au and Ag in sediments and soils located at different sampling points from Galicia (Spain).     

Determination of organochlorine pesticides in complex matrices by single-drop microextraction coupled to gas chromatography-mass spectrometry

A rapid and simple single-drop microextraction method (SDME) has been used to preconcentrate eighteen organochlorine pesticides (OCPs) from water samples with a complex matrix. Exposing two microlitre toluene drop to an aqueous sample contaminated with OCPs proved an excellent preconcentration method prior to analysis by gas chromatography-mass spectrometry (GC-MS). A Plackett-Burman design was used for screening and a central composite design for optimizing the significant variables in order to evaluate several possibly influential and/or interacting factors. The studied variables were drop volume, aqueous sample volume, agitation speed, ionic strength and extraction time. The optimum experimental conditions of the proposed SDME method were: 2 μL toluene microdrop exposed for 37 min to 10 mL of the aqueous sample containing 0% w/v NaCl and stirred at 380 rpm.The calculated calibration curves gave high-level linearity for all target analytes with correlation coefficients ranging between 0.9991 and 0.9999. The repeatability of the proposed method, expressed as relative standard deviation, varied between 5.9 and 9.9% (n = 8). The detection limits were in the range of 0.022-0.101 μg L⁻¹ using GC-MS with selective ion monitoring. The LOD values obtained are able to detect these OCPs in aqueous matrices as required by EPA Method 625. Analysis of spiked effluent wastewater samples revealed that the matrix had no effect on extraction for eleven of the analytes but exerted notable effect for the other analytes.     

Mercury determination by cold vapor atomic absorption spectrometry utilizing UV photoreduction

A method for the determination of mercury via UV photoreduction has been investigated. Mercury vapor was generated by the reduction of mercury species in an acetic acid solution using UV radiation. Detection of the volatile mercury was accomplished by atomic absorption spectrometry. An optimized system was found to provide a detection limit (defined as the concentration giving a signal equal to three times the standard deviation of the blank) of 2.1 μg L⁻¹ with a precision of 2.9% relative standard deviation (n = 8) for a 500 μg L⁻¹ mercury standard. The effect of various metal ions on the mercury signal was investigated and the method validated with a NRCC certified dogfish liver material (DOLT-3) using the method of standard additions. A reaction pathway is hypothesized for UV photoreduction.     

Optimization of a single-drop microextraction method for multielemental determination by electrothermal vaporization inductively coupled plasma mass spectrometry following in situ vapor generation

A headspace single-drop microextraction (HS-SDME) method has been developed in combination with electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) for the simultaneous determination of As, Sb, Bi, Pb, Sn and Hg in aqueous solutions. Vapor generation is carried out in a 40 mL volume closed-vial containing a solution with the target analytes in hydrochloric acid and potassium ferricyanide medium. Hydrides (As, Sb, Bi, Pb, Sn) and Hg vapor are trapped onto an aqueous single drop (3 µL volume) containing Pd(II), followed by the subsequent injection in the ETV. Experimental variables such as medium composition, sodium tetrahydroborate (III) volume and concentration, stirring rate, extraction time, sample volume, ascorbic acid concentration and palladium amount in the drop were fully optimized. The limits of detection (LOD) (3σ criterion) of the proposed method for As, Sb, Bi, Pb, Sn and Hg were 0.2, 0.04, 0.01, 0.07, 0.09 and 0.8 µg/L, respectively. Enrichment factors of 9, 85, 138, 130, 37 and 72 for As, Sb, Bi, Pb, Sn and Hg, respectively, were achieved in 210 s. The relative standard deviations (N = 5) ranged from 4 to 8%. The proposed HS-SDME-ETV-ICP-MS method has been applied for the determination of As, Sb, Bi, Pb, Sn and Hg in NWRI TM-28.3 certified reference material.