Determination of lead traces in water and liqueurs by derivative atom trapping flame atomic absorption spectrometry

 A new method for the direct determination of lead traces using derivative atom trapping flame atomic absorption spectrometry (DAT-FAAS) with an improved water-cooled stainless steel trapping equipment in an air-acetylene flame was investigated. The optimum conditions concerning the sensitivity were studied. For a 1 min collection, the characteristic concentration (given as derivative absorbance of 0.0044) and the detection limit (3s) were 1.4 ng/mL and 0.27 ng/mL, respectively. This is 361 and 74-fold better than those of the conventional flame atomic absorption spectrometry (FAAS) and comparable to those of graphite furnace atomic absorption spectrometry (GFAAS). The detection limit and sensitivity of DAT-FAAS for a 3 min collection time were 2 and 3 orders of magnitude higher than those of conventional FAAS. The present method was applied to the determination of lead in water and liqueur samples with a recovery range of 94–108% and a relative standard deviation of 3.5–5.6%. Received: 10 January 1996/Revised: 9 December 1996/Accepted: 20 December 1996     

原子捕集-导数火焰原子吸收光谱法测定中草药中的微量锌

提出了原子捕集－导数火焰原子吸收光谱法，考察了捕集管位置，火焰状态、冷却水流量、捕集时间、导数测量系统灵敏度档等实验条件对灵敏度的影响。在测量系统20mV/min灵敏度档下，捕集5min，特征浓度为0．037ng/mL，较常规火焰原子吸收光谱法提高了1243倍。     

Derivative hydride generation atomic absorption spectrometry and determination of lead traces in waters

Fundamentals of derivative hydride-generation atomic absorption spectrometry (DHGAAS) are described. A linear relationship was obtained between the derivative absorbance and the concentration of analysis in a sample. The new DHGAAS method was applied to the determination of traces of lead in water. The conditions affecting the derivative absorbance of lead were evaluated and optimized. The detection limit and sensitivity of the proposed method were 26 times and 8.8 times better, respectively, than those of conventional hydride-genera-tion atomic absorption spectrometry. The characteristic concentration (for a derivative absorbance of 0.0044) and detection limit (3sigma) for lead were 0.017 and 0.096 ng mL(-1), respectively, for a 2 mV min(-1) sensitivity range setting. The recovery range was 92.5-103%.     

Determination of trace lead in chinese herbs by derivative flame atomic absorption spectrometry using an atom-trapping technique.

A simple and sensitive method is described for the determination of trace lead in Chinese herbs by derivative atom trapping flame atomic absorption spectrometry (D-AT-FAAS) with a modified water-cooled quartz atom-trapping tube. The effects that influence the sensitivity of the derivative method, such as the trap position, the flame conditions and the collection time, were studied. The characteristics of the derivative atom trapping-atomic absorption signal and the linear nature of the working curve were investigated. The sensitivity of the derivative method is 2 or 3 orders of magnitude higher than that of FAAS, and the detection limit improved by 1 or 2 orders of magnitude. Satisfactory recoveries of 93.0-108.0% for lead were obtained by determining several Chinese herbs with a relative standard derivation range of 2.9 to 4.2%.     

Derivative flame atomic absorption spectrometry and its application in trace analysis

Flame atomic absorption spectrometry (FAAS) is an accepted and widely used method for the determination of trace elements in a great variety of samples. But its sensitivity doesn’t meet the demands of trace and ultra-trace analysis for some samples. The derivative signal processing technique, with a very high capability for enhancing sensitivity, was developed for FAAS. The signal models of conventional FAAS are described. The equations of derivative signals are established for FAAS, flow injection atomic absorption spectrometry (FI-FAAS) and atom trapping flame atomic absorption spectrometry (AT-FAAS). The principle and performance of the derivative atomic absorption spectrometry are evaluated. The derivative technique based on determination of variation rate of signal intensity with time (dI/dt) is different from the derivative spectrophotometry (DS) based on determination of variation rate of signal intensity with wavelength (dI/dλ). Derivative flame atomic absorption spectrometry (DFAAS) has higher sensitivity, lower detection limits and better accuracy. It has been applied to the direct determination of trace elements without preconcentration. If the derivative technique was combined with several preconcentration techniques, the sensitivity would be enhanced further for ultra-trace analysis with good linearity. The applications of DFAAS are reviewed for trace element analysis in biological, pharmaceutical, environmental and food samples.     

Field preconcentration of cadmium from seawater by using a minicolumn packed with Amberlite XAD-4/4-(2-pyridylazo) resorcinol and its flow-injection-flame atomic absorption spectrometric determination at the ng L(-1) Level

A flow injection analysis-flame atomic absorption spectrometric method for the determination of cadmium in seawater was developed with the aim of yielding a sensitive assay with a low detection limit. The method employs a field flow preconcentration technique involving a minicolumn containing Amberlite XAD-4 impregnated with the complexing agent 4-(2-pyridylazo) resorcinol. A Plackett-Burman 2(7)x3/32 design for seven factors (sample pH, sample flow rate, eluent volume, eluent concentration, eluent flow rate, ethanol percentage in the eluent and minicolumn diameter) was carried out in order to find the significant variables affecting the field continuous preconcentration system (FCPS) and the flow injection elution manifold for cadmium determination in seawater samples by flame atomic absorption spectrometry. Cadmium can be preconcentrated with an enrichment factor of 1053 for a sample volume of 200 mL and a preconcentration time of 57 min. In these experimental conditions, the method provides a linear relationship between absorbance and cadmium concentration in the range from 22-1900 ng L(-1), with a detection limit (3SD) of 6 ng L(-1). The precision (expressed as relative standard deviation) for eleven independent determinations reached values of 8.9-0.8% in cadmium solutions of 50-700 ng L(-1). Analysis of certified reference materials (SLEW-3 and NASS-5) showed good agreement with the certified value. This procedure was applied to the determination of cadmium in seawater from Galicia (Spain).     

Synthesis and application of amberlite XAD-2 functionalized with dithizone for field preconcentration and separation of trace cadmium in seawater.

A chelating resin coupling Amberlite XAD-2 functionalized with dithizone is synthesized and characterized. Dissolved cadmium is field-preconcentrated using a minicolumn packed with the synthesized resin and determined by flame atomic absorption spectrometry. Five experimental variables are evaluated. The enrichment factor of 416 is obtained for 50 mL of sampling volume, and the detection limit (3 sigma) of the procedure is 6.7 ng L(-1). The precision (RSD) for 11 independent determinations is 1.97%. This method has been successfully applied to the determination of cadmium in natural seawater samples.     

Use of paper capsules for cadmium determination in biological samples by solid sampling flame atomic absorption spectrometry

In this study, a new device was applied for direct solid sampling flame atomic absorption spectrometry. It was used for trace determination of cadmium in biological samples (bovine and chicken liver). Test samples (0.5 to 7 mg) were weighed into small paper capsules, which were introduced into a quartz cell heated by an air-acetylene flame. Operational conditions for the proposed system were evaluated. There was no significant difference between the results obtained with the proposed system and those obtained after digestion and determination by conventional graphite furnace atomic absorption spectrometry. Good agreement was also obtained with the certified values of two reference materials. Background signals were always low. The characteristic mass was 0.34 ng and relative standard deviation was less than 8%. The limit of detection for the proposed procedure was 1.6 ng or 0.23 μg g^− 1 if a sample mass of 7 mg was used. Excluding the steps for sample preparation (drying, milling and weighing), the proposed system allows the determination of 40 test samples per hour and it can be easily adapted to conventional flame atomic absorption spectrometers.     

开缝石英管原子化技术的改进

近年来,为提高火焰原子吸收光谱法的灵敏度,先后研究过水冷石英管和开缝石英管(简称缝管)原子化技术.前者使灵敏度提高1～2个数量级^[1～3],后者只提高几倍^[4～6].缝管技术比水冷石英管技术的装置简单,操作方便快速,但因其灵敏度不高,应用受到限制.本文以镉为例,探讨了提高缝管技术灵敏度的途径.     

Determination of selenium, zinc and cadmium in antidandruff shampoos by atomic spectrometry after microwave assisted sample digestion

Microwave assisted pre-treatments for atomic spectrometric determination (inductive coupled plasma-optical emission spectrometry, ICP-OES or flame atomic absorption spectrometry, FAAS) of metallic elements, usually present in antidandruff shampoos, are proposed. They are based on the digestion of the sample with HNO₃ into a closed reactor, which is irradiated at 800 W for a few minutes. Selenium was determined by ICP-OES. The limit of detection was 0.11 mg l⁻¹; the relative standard deviation (R.S.D.) for the selenium content in the samples was in the 0.6–3.6% range. The results obtained were in agreement with the label contents and the recovery of the proposed method was in the 100–106% range. Zinc and cadmium were determined by FAAS. The limit of detection for zinc determination was 0.078 mg l⁻¹; the R.S.D. for zinc contents was in the 0.8–8.6% range. A limit of detection of 0.09 mg l⁻¹ was obtained for cadmium determination; the R.S.D. for cadmium contents was in the 0.7–2.7% range. The determinations were performed after two different sample mineralization pre-treatments — dry ashing (in an electric furnace) and wet mineralization (in a microwave oven). Both methodologies provided comparable results for zinc and cadmium determination in shampoos. The proposed microwave assisted digestion procedures allow a precise and accurate determination of selenium, zinc and cadmium in commercial antidandruff shampoos, and the sample pre-treatment is less time-consuming than the classic methods.     

Atomic absorption spectrometric determination of trace tellurium after hydride trapping on platinum-coated tungsten coil

In this work, a sensitive and simple method for the determination of tellurium was developed by hyphenation of electrically heated quartz tube atomic absorption spectrometry and tellurium hydride trapping on platinum-coated tungsten coil. With a mixture of Ar and H₂, tellurium hydride was transported to tungsten coil for trapping at 390 °C and releasing at 1200 °C. A limit of detection (LOD, 3σ) of 0.08 ng mL^{− 1} was obtained with 1 min trapping (1.5 mL sampling volume), and enhancement factor was 28 compared to conventional hydride generation atomic absorption spectrometry. The LOD was better or at least comparable to literature levels involving on-line trapping and some other sophisticated instrumental method such as graphite furnace atomic absorption spectrometry (GF-AAS) and inductively coupled plasma mass spectrometry (ICP-MS), and it can be further lowered down to 0.03 ng mL^{− 1} by increasing the trapping time to 4 min. The platinum coating was stable for 300 firings without sensitivity loss. Interference and its alleviation were studied in detail. The proposed method was applied to the determination of tellurium in several geological standard reference materials, and the results were found in good agreement with the certified values.     

Precision and Accuracy Studies of Impaction-Electrothermal Atomization Atomic Spectrometry

Abstract

The precision of aqueous solutions of cadmium, copper, and manganese introduced as an aerosol by an pneumatic nebulizer and electrothermal vaporizer to an impaction-electrothermal atomization atomic absorption spectrometeric system was in the range of 1–3% which was similar to that obtained by manual introduction of similar concentrations of aqueous solutions of cadmium, copper, and manganese to the electrothermal atomizer and atomic absorption spectrometry. The precision of a laboratory air sample was 7.6–9.9%. Accuracy was assessed by comparison to conventional methods of sampling air by collection on a filter followed by digestion of the filter and analysis by flame atomic absorption spectrometry The levels were found to be 59–69% compared to the conventional method.     

Determination of heavy metal ions in environmental samples employing preconcentration on novel resins of polyurethane foam linked with o-Aminophenol or o-Hydroxyphenylazonaphthol

o-Aminophenol (AP) and its azo derivative with ß-Naphthol(Naph) is bonded to polyurethane foam (BPUF) and used as solid phase extractor of nickel, cadmium and zinc ions in aqueous solutions prior to their atomic absorption spectrometric determinations. The novel resins of polyurethane foam were characterised by density, elemental analysis, IR spectra and chemical stability. The parameters including pH, sample volume, matrix effects were investigated. The relative standard deviation (RSD) of the combined method of sample treatment, preconcentration and determination with atomic absorption spectrometry is generally lower than 10%. The limit of detection was found between 0.06 and 0.22?µg?L^?1. The procedure was used for determination of analyte ions in natural water samples, apple leaves and fish liver.     

Eine mikromethode der flammen-atomabsorptions- und emissions-spektrometrie (platinschlaufen-methode)—I. Die grundlagen der methode—anwendung auf die bestimmung von blei und cadmium in trinkwasser

The paper describes a microanalytical method using flame atomic absorption spectrometry (AAS). The sample is introduced on an electrically heated platinum loop into the flame. This way of sample introduction avoids a nebulizer with its inherent low efficiency; therefore the detection limits of volatile elements are substantially lower than those attained with the conventional flame-AAS method. The determinations of lead and cadmium in drinking water serve as examples which demonstrate that trace analysis with fair precision is feasible in the lower μg/1 range. This range is otherwise accessible only with the graphite tube technique, which is both circumstantial and prone to interferences. The high chemical resistivity of platinum permits several thousand analyses of even strongly acid solutions without perceptible changes of the platinum loop.     

Determination of chromium(III) and total chromium in water by derivative atomic absorption spectrometry using flow injection on-line preconcentration with a double microcolumn.

A rapid and sensitive method has been proposed for the sequential determination of chromium(III) and total chromium in water samples by flame atomic absorption spectrometry combined with a flow injection on-line preconcentration on a double-microcolumn. The chromium(III) and total chromium in samples were retained on a double-microcolumn with a cation exchange resin, respectively, and eluted directly into a nebulizer by 3 mol L(-1) HNO3. The characteristic concentration (gives a derivative absorbance of 0.0044) and the detection limit (3sigma) for chromium were 0.512 microg L(-1) and 0.647 microg L(-1) for a preconcentration time of 1 min, respectively. This is an improvement of 20 and 14-times than those of conventional FI-FAAS. The proposed method allows the determination of chromium in the range of 0-90 microg L(-1) with a relative standard deviation of 3.63% at the 10 microg L(-1) level. The method has been applied for the analysis of chromium in reference water of National Research Center for Certified Reference Materials (GBW08607) and other water samples with satisfactory results.     

Determination of cadmium and lead at low levels by using preconcentration at fullerene coupled to thermospray flame furnace atomic absorption spectrometry

A new and sensitive method for Cd and Pb determinations, based on the coupling of thermospray flame furnace atomic absorption spectrometry and a preconcentrator system, was developed. The procedure comprised the chelating of Cd and Pb with ammonium pyrrolidinedithiocarbamate with posterior adsorption of the chelates on a mixture (40 mg) of C₆₀ and C₇₀ at a flow rate of 2.0 ml min⁻¹. These chelates were eluted from the adsorbent by passing a continuous flow of ethanol (80% v/v) at 0.9 ml min⁻¹ to a nickel tube placed in an air/acetylene flame. After sample introduction into the tube by using a ceramic capillary (0.5 mm i.d.), the analytical signals were registered as peak height. Under these conditions, improvement factors in detectability of 675 and 200 were obtained for Cd and Pb, respectively, when compared to conventional flame atomic absorption spectrometry. Spiked samples (mineral and tap waters) and drinking water containing natural concentrations of Cd were employed for evaluating accuracy by comparing the results obtained from the proposed methodology with those using electrothermal atomic absorption spectrometry. In addition, certified reference materials (rye grass, CRM 281 and pig kidney, CRM 186) were also adopted for the accuracy tests. Due to the good linearity ranges for Cd (0.5–5.0 μg l⁻¹) and Pb (10–250 μg l⁻¹), samples with different concentrations could be analyzed. Detection limits of 0.1 and 2.4 μg l⁻¹ were obtained for Cd and Pb, respectively, and RSD values <4.5% were observed (n=10). Finally, a sample throughput of 24 determinations per hour was possible.     

Comparison of dissolution procedures for the determination of cadmium and lead in plastics

Summary A microwave digestion procedure and an oxygen flask combustion procedure were developed for the determination of cadmium and lead in plastic materials. A comparison with conventional wet ashing shows acceptable agreement. Different types of plastics such as polyvinylchloride, polypropylene, polyethylene, polystyrene, polyamide, and polyethyleneterephthalate were investigated. The precision of microwave digestion was determined within a series and from day to day. The results obtained by flame atomic absorption spectrometry were verified by measurement with inverse voltammetry. Overall, microwave digestion as well as oxygen flask combustion are time saving and cost-effective dissolution procedures to supervise the legal cadmium limit in plastics.Abbreviations FAAS Flame atomic absorption spectrometry - GFAAS Graphite furnace atomic absorption spectometry - ICPMS Inductively coupled plasma mass spectrometry - PVC Polyvinylchloride - PP Polypropylene - PE Polyethylene - PS Polystyrene - PET Polyethyleneterephthalate - PA Polyamide 6.6 - PTFE-TFM Polytetrafluoroethylene-tetrafluoromethoxylate - HMDE Hanging mercury drop electrode - MS Mass spectrometry - OFC Oxygen flask combustion - MWD Microwave digestion - CWA Conventional wet ashing - DL Detection limit - QL Quantification limit     

火焰原子吸收光谱法测定镍基高温合金中的镉

采用火焰原子吸收光谱法测定镍基高温合金中的镉,样品以硝酸-氢氟酸-水混合溶液(1+1+1)前处理,选择Cd 228.8nm为分析线进行测定,并通过标准加入法校正基体效应。考察了消解酸的选择,仪器工作参数的调整,基体和共存离子对镉测定的影响。结果表明,镍基高温合金中镉的检出限为0.088μg/g。加标回收率为94.1%～109%,结果的相对标准偏差(RSD,n=8)在0.54%～1.6%。方法操作简便、分析速度快、准确度好,适用于镉含量在0.0001%～0.001%的镍基高温合金中的测定。     

火焰原子吸收光谱法测定镍基高温合金中的镉

采用火焰原子吸收光谱法测定镍基高温合金中的镉,样品以硝酸-氢氟酸-水混合溶液(1+1+1)前处理,选择Cd 228.8 nm为分析线进行测定,并通过标准加入法校正基体效应。考察了消解酸的选择,仪器工作参数的调整,基体和共存离子对镉测定的影响。结果表明,镍基高温合金中镉的检出限为0.088μg/g。加标回收率为94.1%~109%,结果的相对标准偏差(RSD,n=8)在0.54%~1.6%。方法操作简便、分析速度快、准确度好,适用于镉含量在0.0001%~0.001%的镍基高温合金中的测定。     

Combination of flow-injection techniques with atomic spectrometry in agricultural and environmental analysis

Combinations of flow-injection techniques with flame atomic absorption spectrometry (a.a.s.) and inductively-coupled plasma/atomic emission spectrometry (i.c.p./a.e.s.) are reviewed in the general context of agricultural and environmental analysis. The flow-injection systems are valuable for sample introduction; appropriate dispersion control allows the analysis of solutions containing as much as 40% (w/v) urea or phosphate in fertilizers. A study on the determination of cadmium in soil extracts by on-line ion-exchange preconcentration and flame a.a.s. detection is described. The interpolative standard-addition method with i.c.p./a.e.s. detection is outlined. Improvements in the determinations of selenium in environmental samples by hydride-generation a.a.s. and of mercury by cold-vapour a.a.s. are reported.