Ultratrace determination of cadmium by cold vapor atomic absorption spectrometry after preconcentration with a simplified cloud point extraction methodology

A simplified micelle-mediated extraction methodology for the preconcentration of ultratrace levels of cadmium as a prior step to its determination by cold vapor atomic absorption spectrometry (CV-AAS) has been developed. The methodology is based on the cloud point extraction (CPE) of cadmium at pH 8 by using the non-ionic surfactant polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) without adding any chelating agent. Cadmium cold vapor was generated from 2 ml of the extracted surfactant-rich phase by means of sodium tetrahydroborate (3%, w/v) as a reducing agent and hydrochloric acid (0.2 mol l⁻¹) as a carrier solution. Several important variables that affect the cloud point extraction and cold vapor cadmium generation efficiency were investigated and optimized. The preconcentration of only 50 ml of solution in the presence of 0.06% (v/v) PONPE 7.5 gives an enhancement factor of 62. The calibration graph using the preconcentration system was linear in the range of 4-100 ng l⁻¹ with a correlation coefficient of 0.9992. Detection limit (3 s) obtained in the optimal conditions was 0.56 ng l⁻¹. The relative standard deviation (R.S.D.) for six replicate determinations at 20 ng l⁻¹ Cd level was 3.2%. The proposed method was successfully applied to the ultratrace determination of cadmium in water samples.     

Speciation of chromium(III) and chromium(VI) by in situ separation and sequential determination with electrothermal vaporization inductively coupled plasma atomic emission spectrometry

A novel method for the speciation of chromium(III) and chromium(VI) by in situ separation and sequential determination with electrothermal vaporization-inductively coupled plasma-atomic emission spectrometry (ETV-ICP-AES) was developed. The reaction conditions between Cr(III) and 8-hydroxyquinoline (8-Ox) and the vaporization behavior of the chelate formed were investigated in detail. It was found that the Cr(III)-8-Ox chelate could be formed at room temperature and vaporized from graphite furnace under controlled experimental conditions, therefore, an in situ separation of Cr(III) from Cr(VI) was achieved. The retained Cr(VI) in graphite tube was then determined by using fluorination vaporization ETV-ICP-AES with PTFE slurry as chemical modifier. Under optimum experimental conditions, the detection limits for Cr(III) and Cr(VI) are 8.6 ng/ml and 11.3 ng/ml, and the relative standard deviations (R.S.D.s) are 3.8% and 4.1% (c=0.1 μg/ml, n=6), respectively. The linear ranges of the calibration curve for both Cr(III) and Cr(VI) covered three orders of magnitude. The proposed method has been applied to the speciation of Cr(III) and Cr(VI) in water samples with the satisfactory results.     

Electrothermal vaporization on a tungsten filament for the determination of arsenic in chloride solutions by low-pressure helium ICP-MS.

A combined method of electrothermal vaporization and low-pressure helium ICP-MS was developed for the determination of traces of arsenic in chloride solutions, because serious spectral interference occurred in conventional argon ICP-MS. On a tungsten filament was placed 5 microl of a sample and heated electrothermally to remove the solvent. The resulting residue on the filament was covered with a vaporization chamber, and after reducing the pressure to ca. 5 Torr, it was rapidly heated by discharging a high-capacity condenser (0.22 F). The vapor of arsenic was transferred to a helium plasma with a stream of carrier gas for the determination. The background was not observed at m/z of 75, which allowed the determination of arsenic at ng/ml levels in chloride solutions. Sodium chloride significantly enhanced the intensity of the arsenic signal, whereas other chlorides, including KCl, MgCl2, CaCl2 and NH4Cl, suppressed the analytical signals. This enhancement due to sodium ions seems to be a peculiar phenomenon to the helium ICP. The proposed method can be applied to direct determinations of as low as 0.9 ng/ml of arsenic in seawater.     

Direct determination of mercury in cosmetic samples by isotope dilution inductively coupled plasma mass spectrometry after dissolution with formic acid

A new method was proposed for the accurate determination of mercury in cosmetic samples based on isotopic dilution (ID)-photochemical vapor generation (PVG)-inductively coupled plasma mass spectrometry (ICP MS) measurement. Cosmetic samples were directly dissolved in formic acid solution and subsequently subjected to PVG for the reduction of mercury into vapor species following by ICP MS detection. Therefore, the risks of analyte contamination and loss were avoided. Highly enriched ²⁰¹Hg isotopic spike is added to cosmetics and the isotope ratios of ²⁰¹Hg/²⁰²Hg were measured for the quantitation of mercury. With ID calibration, the influences originating from sample matrixes for the determination of mercury in cosmetic samples have been efficiently eliminated. The effects of several experimental parameters, such as the concentration of the formic acid, and the flow rates of carrier gas and sample were investigated. The method provided good reproducibility and the detection limits were found to be 0.6 pg mL⁻¹. Finally, the developed method was successfully applied for the determination of mercury in six cosmetic samples and a spike test was performed to verify the accuracy of the method.     

Application of low temperature electrothermal vaporization ICP-AES for determination of refractory yttrium with 1-(2-pyridylazo)-2-naphthol as chemical modifier

A low temperature electrothermal vaporization inductively coupled plasma atomic emission spectrometry (ETV-ICP-AES) method was developed for the determination of the refractory yttrium, using 1-(2-pyridylazo)-2-naphthol (PAN) as chemical modifier. The trace yttrium was vaporized as PAN complex into plasma from a graphite furnace at a comparatively low temperature of 1200 °C. The operation conditions were optimized, and the vaporization behavior of Y-PAN chelate and the main factors affecting the determination were investigated in detail. Under the optimized conditions, the detection limit of Y was 0.7 ng ml⁻¹, and the relative standard deviation (R.S.D.) for 0.1 μg ml⁻¹ Y was 4.5% (n=9, v=10 μl). The linear range of calibration curve covered three orders of magnitude. The recommended approach has been applied for analysis of three biological samples with satisfactory results. The accuracy of the method was demonstrated by analyzing two standard reference materials.     

Improved liquid chromatographic method with pulsed electrochemical detection for the analysis of kanamycin

This work describes the separation of the main component kanamycin A from its related substances using an improved liquid chromatographic method with pulsed electrochemical detection (LC-PED). Two methods, one using volatile ion pairing agents and the other using non-volatile ones were developed. Using volatile additives, the total run time was rather long with no possibility of developing gradient elution. The non-volatile method was found to be more performant and hence was selected for further quantitative work. This method employed gradient elution in order to reduce the analysis time and to improve the sensitivity of the late eluting peaks. Mobile phase A consisted of sodium sulphate (5.0 g/l), sodium octanesulphonate (0.5 g/l) and 0.2 M phosphate buffer pH 3.0 (50.0 ml/l). Mobile phase B was the same as A except for the amount of sodium sulphate which was increased to 15 g/l. Using a Platinum EPS column (150 mm × 4.6 mm ID, 3 μm) kept at 45 °C, 22 components could be separated within 45 min indicating that this method is much more selective than other already published ones. Robustness of the method was examined by means of an experimental design. The limit of detection and limit of quantitation were found to be 1.7 and 5 ng, respectively. The method was found to be linear in the range LOQ–600 ng injected with a coefficient of determination equal to 0.999.     

Importance of control of enzymatic degradation for determination of bisphenol A from fruits and vegetables

The purpose of this study was to develop an analytical method for determination of bisphenol A (BPA) from fruits and vegetables. The present method developed for extraction of BPA from samples was based on solid-phase extraction (SPE) method and solvent extraction. Recovery results in the samples spiked with a 10 ng/ml BPA [no detection (<1 ng/g) to 77%] were lower than those in the samples with a 50 ng/ml BPA (26-96%). The fact that the low recovery results were caused by BPA degradation by enzymes is found. These problems were proved by the pH (pH ≤3) and the heating treatment (at ≥80 °C for 5 min). However, because the heating treatment at temperatures of ≥80 °C for 5 min is more difficult and time-consuming method than the pH control, we suggest that the pH control is useful to prevent BPA degradation. Good recovery results (82-101%) were obtained from all fruit and vegetable samples after pH treatment (pH ≤3). Effective elimination of impurities and a good detection limit (1 ng/g) were obtained with a method involving two SPE cartridges (OASIS HLB and Sep-Pak Florisil cartridge).     

Determination of cadmium in polyethylene by analytical atomic spectrometry with gas-phase sample introduction technique

Cadmium in polyethylene was determined by both inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectrometry (AAS) with continuous-flow gas-phase sample introduction in a reaction medium of ascorbic acid. In the presence of mixture of cobalt and thiourea in the ascorbic acid solution, the sensitivities by both ICP-AES and AAS for cadmium were greatly enhanced. The gaseous cadmium species was phase-separated in a gas–liquid separator and directed via a stream of argon carrier gas to an inductively coupled plasma and an electrically heated quartz tube atomizer (QTA) for atomic spectrometry. Under the optimized experimental conditions, the best attainable detection limits at Cd I 228.802 nm line were 1.3 and 0.017 ng/ml with linear dynamic ranges of 10–500 ng/ml and 0.1–1 ng/ml in concentrations by ICP-AES and QTA-AAS, respectively. The instrumental precisions expressed as the relative standard deviation (R.S.D.) from ten replicate measurements of 50 and 1 ng/ml cadmium by ICP-AES and QTA-AAS were 5.6% and 3.2%, respectively. With the use of ICP-AES and QTA-AAS with gas-phase sample introduction method, six- and 200-fold improvements in detection limits for cadmium were obtained in comparison with their conventional solution nebulization methods, respectively. After the effects of several diverse elements on the determination of cadmium by ICP-AES and QTA-AAS with the present gas-phase sample introduction systems were examined, these methods were applied to the determination of low concentrations of cadmium in polyethylene. The results obtained by the present method were in good agreement with the certified values.     

Determination of benzoic acid in soft drinks by gas chromatography with on-line pyrolytic methylation technique

A new application of pyrolytic methylation was developed to determine benzoic acid in soft drinks by gas chromatography (GC) without using any pretreatment procedures and special pyrolyzer. With the on-line pyrolytic methylation by tetramethylammonium hydroxide (TMAH), benzoic acid was converted into its corresponding methyl ester in the injector at 280 °C. Thus, samples containing benzoic acid could be well determined by direct-injection in GC on the medium polar stationary phase column. To obtain optimum methylation conditions, important factors were investigated and then applied to the following experiments. The results were obtained as following: 280 °C as reaction temperature, 2:1 as the proportion of TMAH to benzoic acid. The storage time of mixed solution had no obvious effect on the area of benzoic acid methyl ester peak. With the p-xylene as an inter-standard, GC behaviors were investigated under these optimum conditions. The linear range achieved for benzoic acid was 1-10,000 mg/l with the correlation coefficient of 0.9985. The precision was quite high with the R.S.D. of 2.8% and the limit of detection reached 0.1 mg/l. The potential of the proposed method was assessed by applying it to the determination of benzoic acid in soft drinks. The results obtained coincided with the statement on the labels and all of the detected data were below the maximum permitted concentration of the European Union Legislation. This on-line pyrolytic methylation technique was proved to be simple to implement, sensitive and selective.     

Synthesis and LPG sensing properties of nano-sized cadmium oxide

This paper reports the synthesis and liquid petroleum gas (LPG) sensing properties of nano-sized cadmium oxide (CdO). The nano-sized CdO powder was successfully synthesized by using a chemical co-precipitation method using cadmium acetate and the ammonium hydroxide, as starting materials and water as a carrier. The resulting nano-sized powder was characterized by X-ray diffraction (XRD) measurements and the transmission electron microscopy (TEM). The LPG sensing properties of the synthesized nano-sized CdO were investigated at different operating temperatures and LPG concentrations. It was found that the calcination temperature and the operating temperature significantly affect the sensitivity of the nano-sized CdO powder to the LPG. The sensitivity is found to be maximum when the calcination temperature was 400 °C. The sensitivity to 75 ppm of LPG is maximum at an operating temperature 450 °C and it was found to be ∼341%. The response and recovery times were found to be nearly 3-5 s and 8-10 s, respectively. The synthesized nano-sized CdO powder is able to detect up to 25 ppm for LPG with reasonable sensitivity at an operating temperature 450 °C and it can be reliably used to monitor the concentration of LPG over the range (25-75 ppm). The experimental results of the LPG sensing studies reveal that the nano-sized CdO powder synthesized by a simple co-precipitation method is a suitable material for the fabrication of the LPG sensor.     

Cadmium and lead determination in foods by beam injection flame furnace atomic absorption spectrometry after ultrasound-assisted sample preparation

A simple method for cadmium and lead determination in foods by beam injection flame furnace atomic absorption spectrometry (BIFF-AAS) was proposed. Food slurries were prepared by transferring an exact amount of cryogenic-ground homogenized material (50-100 mg) to centrifuge tubes, followed by addition of 5 ml (up to 2.8 mol l⁻¹) nitric acid solution and sonication in an ultrasonic bath during 5-10 min. Thereafter, slurries were diluted with water to 10 ml, centrifuged during 5 min at 5400 rpm and 400 μl aliquot of the supernatant was analyzed by BIFF-AAS. The detection limits based on peak height measurements were 0.03 μg g⁻¹ Cd and 1.6 μg g⁻¹ Pb for 2% (m/v) slurry (200 mg/10 ml). For method validation, the certified reference materials Pig Kidney (BCR 186) and Rice Flour (NIES 10) were used. Quantitative cadmium and lead recoveries were obtained and no statistical differences were found at 95% level by applying the t-test.     

Organic,inorganic and total mercury determination in fish by chemical vapor generation with collection on a gold gauze and electrothermal atomic absorption spectrometry

A method for organic, inorganic and total mercury determination in fish tissue has been developed using chemical vapor generation and collection of mercury vapor on a gold gauze inside a graphite tube and further atomization by electrothermal atomic absorption spectrometry. After drying and cryogenic grinding, potassium bromide and hydrochloric acid solution (1 mol L^− 1 KBr in 6 mol L^− 1 HCl) was added to the samples. After centrifugation, total mercury was determined in the supernatant. Organomercury compounds were selectively extracted from KBr solution using chloroform and the resultant solution was back extracted with 1% m/v L-cysteine. This solution was used for organic Hg determination. Inorganic Hg remaining in KBr solution was directly determined by chemical vapor generation electrothermal atomic absorption spectrometry. Mercury vapor generation from extracts was performed using 1 mol L^− 1 HCl and 2.5% m/v NaBH₄ solutions and a batch chemical vapor generation system. Mercury vapor was collected on the gold gauze heated resistively at 80 °C and the atomization temperature was set at 650 °C. The selectivity of extraction was evaluated using liquid chromatography coupled to chemical vapor generation and determination by inductively coupled plasma mass spectrometry. The proposed method was applied for mercury analysis in shark, croaker and tuna fish tissues. Certified reference materials were used to check accuracy and the agreement was better than 95%. The characteristic mass was 60 pg and method limits of detection were 5, 1 and 1 ng g^− 1 for organic, inorganic and total mercury, respectively. With the proposed method it was possible to analyze up to 2, 2 and 6 samples per hour for organic, inorganic and total Hg determination, respectively.     

悬浮体制样/氟化电热蒸发-电感耦合等离子体原子发射光谱直接测定粉煤标样中的微量钒和钛

本文提出了悬浮体制样氟化ETV-ICP-AES直接测定粉煤中微量钒和钛的新方法。采用聚四氟乙烯为氟化剂;促进V、Ti的蒸发,检出限分别为1.5和0.8ng/ml,RSD分别为2.8％和1.9％,线性范围达三个数量级,该法用于NIST SRM 1635粉煤标样中V和Ti的测定,结果与参考值吻合很好。     

Rapid and direct speciation of methyltins in seawater by an on-line coupled high performance liquid chromatography-hydride generation-ICP/MS system

A novel on-line coupled HPLC-hydride generation (HG)-ICP/MS system was developed for rapid, direct and sensitive speciation of methyltins in seawater without any pretreatment step. Methyltin compounds were separated by reversed phase HPLC, and then on-line reacted with potassium borohydride and acetic acid to generate volatile hydride products. The volatile derivatization products were separated in the spray chamber of ICP/MS and then introduced into ICP/MS by argon gas for detection. Monomethyltin (MMT), dimethyltin (DMT) and trimethyltin (TMT) were baseline separated in less than 15 min by reversed phase HPLC. The influence of KBH₄ concentration and type of acid on the system performance was investigated and optimized. Calibration curves, based on peak heights against concentration, were linear in the range of 0.5-50 ng (Sn) mL⁻¹ of methyltins with correlation coefficients of 0.9990, 0.9990 and 0.9996 for MMT, DMT and TMT, respectively. The relative standard deviations measured at 10 ng (Sn) mL⁻¹ for these three methyltins were in the range of 0.6-1.4% (n = 5), and the calculated detection limits (S/N = 3) for MMT, DMT and TMT were 0.266, 0.095 and 0.039 ng (Sn) mL⁻¹, respectively. This method was successfully applied to the speciation of methyltins in seawater with spiked recovery in the range of 95.4-106.9%. MMT and DMT were detected in all the seawater samples with concentrations in the range of 1.0-1.5 and 0.30-0.57 ng (Sn) mL⁻¹ for MMT and DMT, respectively.     

Solid phase extraction for analysis of biogenic carbonates by electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS): an investigation of rare earth element signatures in otolith microchemistry

Uptake of trace elements into fish otoliths is governed by several factors such as life histories and environment in addition to stock and species differences. In an attempt to elucidate the elemental signatures of rare earth elements (REEs) in otoliths, a solid phase extraction (SPE) protocol was used in combination with electrothermal vaporization (ETV) as a sample introduction procedure for the determinations by inductively coupled plasma quadrupole mass spectrometry (ICP-MS). Effects of various parameters, such as carrier gas flow rate, atomization temperature and chemical modification, were examined for optimization of the conditions by ETV-ICP-MS. Atomization was achieved at 2800 °C. Lower temperatures (i.e. 2600 °C) resulted in severe memory problems due to incomplete atomization. Palladium was used as a chemical modifier. It was found that an increase in Pd concentration up to 0.5 μg in the injection volume (70 μl) led up to four-fold enhancement in the integrated signals. This phenomenon is attributed to the carrier effect of Pd rather than the stabilization since no significant losses were observed for high temperature drying around 700 °C even in the absence of Pd. Preconcentration was performed on-line at pH 5 by using a mini-column of Toyopearl AF-Chelate 650M chelating resin, which also eliminated the calcium matrix of otolith solutions. After preconcentration of 6.4 ml of solution, the concentrate was collected in 0.65 ml of 0.5% (v/v) HNO₃ in autosampler cups, and then analyzed by ETV-ICP-MS. The method was validated with the analysis of a fish otolith certified reference material (CRM) of emperor snapper, and then applied to samples. Results obtained from otoliths of fish captured in the same habitat indicated that otolith rare earth element concentrations are more dependent on environmental conditions of the habitat than on species differences.     

Simultaneous determination of bromine and chlorine in coal using electrothermal vaporization inductively coupled plasma mass spectrometry and direct solid sample analysis

A new method for the direct analysis of coal using electrothermal vaporization inductively coupled plasma mass spectrometry and direct solid sample analysis was developed, aiming at the determination of Br and Cl. The procedure does not require any significant sample pretreatment and allows simultaneous determination of both elements to be carried out, requiring small mass aliquots of sample (about 0.5 mg). All operating parameters, including carrier gas flow-rate and RF power, were optimized for maximum sensitivity. The use of modifiers/aerosol carriers (Pd, Pd + Al and Pd + Ca) was evaluated, and the mixture of Pd and Ca was chosen, allowing pyrolysis and vaporization temperatures of 700 °C and 1900 °C, respectively. Chlorine was accurately determined using calibration against solid standards, whereas Br could also be determined using calibration against aqueous standard solutions. The limits of quantification were 0.03 μg g⁻¹ for Br and 7 μg g⁻¹ for Cl, and no spectral interferences were observed.     

Evaluation of a new electrolytic cold vapor generation system for mercury determination by AFS

In this study we firstly report a new electrolytic cold vapor generation system for mercury determination on Pt/Ti cathode in the presence of organic acid catholyte. Comparing with the traditional inorganic acid, formic acid increased the signal intensity of Hg vapor from electrolytic generation on Pt cathode and reduced the impact of cathode erosion on the stability of signal intensity. Moreover, formic acid has better interference tolerance. The introduction location for carrier gas is probably the most important factor that influences the signal intensity of Hg from electrolytic vapor generation. The effects of the electrolytic conditions and interference ions on the ECVG have been studied. Under the optimized conditions, the detection limit (3σ) of Hg (II) in aqueous solutions is 1.4 ng L⁻¹; a relative standard deviation of 2.3% for 1 μg L⁻¹ Hg was obtained. The accuracy of this method was verified by the determination of mercury in the certified reference materials. This system has been applied satisfactorily to the determination of Hg in Traditional Chinese Medicines samples.     

Silicon determination by inductively coupled plasma atomic emission spectrometry after generation of volatile silicon tetrafluoride

A method for the determination of silicon by inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. The procedure is based on a discontinuous generation of volatile silicon tetrafluoride in concentrated sulphuric acid medium after injecting 125 μl of 0.1%, w/v sodium fluoride solution into 100 μl of the sample. The gaseous silicon tetrafluoride is fed directly into the ICP torch by a flow of 250 ml min⁻¹ Ar carrier gas. The calibration curve was linear up to at least 100 μg ml⁻¹ of Si(IV) and the absolute detection limit was 9.8 ng working with a solution volume of 100 μl. The relative standard deviation for six measurements of 10 μg ml⁻¹ of Si(IV) was 2.32%. The method was applied to the determination of silicon in water and iron ores.     

Hyphenated technique for the extraction and determination of isoflavones in algae: Ultrasound-assisted supercritical fluid extraction followed by fast chromatography with tandem mass spectrometry

New hyphenated technique for the extraction and determination of isoflavones in sea and freshwater algae and cyanobacteria was developed. The method consists of sonication sample pretreatment, extraction by supercritical CO₂ modified by 3% (v/v) of MeOH/H₂O mixture (9:1, v/v) at 35 MPa and 40 °C for 60 min, fast chromatography analysis by the means of Agilent 1200 Series Rapid Resolution and MS/MS determination. Agilent 1200 Series RRLC was used with Zorbax SB-CN chromatographic column (100 mm × 2.1 mm, particle size 3.5 μm), 3 μl injection volume, mobile phase consisting of 0.2% (v/v) acetic acid in water (solvent A) and acetonitrile (solvent B) and used with linear gradient (30% B at 0 min, from 0 min to 3 min up to 50% B, from 3 to 6 min up to 80% B and from 6 to 10 min down to 30% B). The flow-rate was 0.4 mL/min, column oven temperature 35 °C. MS detector Agilent Technologies 6460 Triple quadrupole LC/MS with Agilent Jet Stream was used in a negative ESI mode under following conditions: gas temperature 350 °C, gas flow 13 L/min, nebulizer gas pressure 50 psi, sheath gas temperature 400 °C, sheath gas flow 12 L/min, capillary voltage was 4 kV. Samples were analysed in the multiple reaction monitoring (MRM) mode. Eight isoflavone compounds were found for the first time in seven real samples of sea algae and in three control samples of freshwater algae and cyanobacteria. Usual optimisation study of extraction parameters was performed. Pressure and temperature optima for algae matrix are different from those obtained sooner for other matrices for most of the analytes, but the results of modifier optimisation study are in good accordance with those obtained sooner for spiked samples and red clover matrix. It seems that matrix has very small or no effect on the modifier selection. Two different approaches of sonication pretreatment were tested: sonication bath and the thorn instrument. In longer extraction time experiments, thorn sonication was more efficient and recovery of following supercritical fluid extraction was higher.     

Rapid determination of ethanol in fermentation liquor by full evaporation headspace gas chromatography

This paper reports a full evaporation (FE) headspace gas chromatographic (GC) method for rapid determination of ethanol in fermentation liquor. The data show that ethanol in the fermentation liquor was transferred to the vapor phase (headspace) almost completely within 3 min at a temperature of 105 °C when a very small volume (<50 μL) of sample was directly added to a sealed headspace sample vial (20 mL). The ethanol in the vapor phase was then measured by headspace GC using a flame ionization detector. The results show that the present method has an excellent measurement precision (RSD = 1.62%) and accuracy (recovery = 98.1 (±1.76%)) for the ethanol quantification in fermentation liquors. The method requires no sample pretreatment and is very simple and rapid.