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1.
Bravo M Lespes G De Gregori I Pinochet H Gautier MP 《Analytical and bioanalytical chemistry》2005,383(7-8):1082-1089
A method based on Headspace solid-phase microextraction (HS-SPME, with a 100 μm PDMS-fiber) in combination with gas-chromatography
and pulsed flame-photometric detection (GC-PFPD) has been investigated for simultaneous determination of eight organotin compounds.
Monobutyltin (MBT), dibutyltin (DBT), tributyltin (TBT), monophenyltin (MPhT), and the semi-volatile diphenyltin (DPhT), triphenyltin
(TPhT), monooctyltin (MOcT), and dioctyltin (DOcT) were determined after derivatization with sodium tetraethylborate. The
conditions used for the extraction and preconcentration step were optimised by experimental design methodology. Tripropyltin
(TPrT) and diheptyltin (DHepT) were used as internal standards for quantification of volatile and semi-volatile organotin
compounds, respectively. The analytical precision (RSD) for ten successive injections of a standard mixture containing all
the organic tin compounds ranged between 2 and 11%. The limits of detection for all the organotin compounds were sub ng (Sn)
L−1 in water and close to ng (Sn) kg−1 in sediments. The accuracy of the method was evaluated by analysis of two certified reference material (CRM) sediment samples.
The HS-SPME–GC–PFPD was then applied to the analysis of three harbour sediment samples. The results showed that headspace
SPME is an attractive tool for analysis of organotin compounds in solid environmental matrices. 相似文献
2.
Summary Two procedures, based on large-volume injection with a programmed-temperature vaporizer (PTV), have been developed for the
determination of several triazine and organophosphorus pesticides. The use of PTV for injection in gas chromatography (GC)
has enabled the introduction of up to 200 μL sample extract into the GC, thus increasing the sensitivity of the method. PTV
injection has been combined off-line with two different microextraction procedures—liquid-liquid partition and solid-phase
extraction.
A simple and rapid off-line liquid-liquid microextraction procedure (5 mL water/1 mL methyltert-butyl ether) was applied to surface water samples spiked at levels between 0.01 and 5μg L−1. Recoveries of the overall procedure were >80% and the precision was better than 15%. Detection limits were <30 ngL−1 from 200-μL injections in GC-NPD analysis of triazines and GC-FPD analysis of organophosphorus pesticides. Off-line automated
solid-phase extraction with C18 cartridges has been applied to water samples (50 mL) spiked at 0.01, 0.1 and 1 μg L−1. The overall procedure was satisfactory (recoveries >80% and coefficients of variation <12%) and the limits of detection
ranged from 1 to 9 ng L−1.
Finally, several surface water samples were anlysed, and triazine herbicides were detected at concentrations of approx. 0.1–0.2
μg L−1. The results were similar to those obtained by conventional solvent extraction then GC-MSD after splitless injection of 2
μL. 相似文献
3.
de la Escosura-Muñiz A González-García MB Costa-García A 《Analytical and bioanalytical chemistry》2006,384(3):742-750
A new electroactive label has been used to monitor immunoassays in the determination of human serum albumin (HSA) using glassy-carbon
electrodes as supports for the immunological reactions. The label was a gold(I) complex, sodium aurothiomalate, which was
bound to rabbit IgG anti-human serum albumin (anti-HSA-Au). The HSA was adsorbed on the electrode surface and the immunological
reaction with gold-labelled anti-HSA was then performed for one hour by non-competitive or competitive procedures. The gold(I)
bound to the anti-HSA was electrodeposited in 0.1 mol L−1 HCl at −1.00 V for 5 min then oxidised in 0.1 mol L−1 H2SO4 solution at +1.40 V for 1 min. Silver electrodeposition at −0.14 V for 1 min followed by anodic stripping voltammetry were
then performed in aqueous 1.0 mol L−1 NH3–2.0×10−4 mol L−1 AgNO3. For both non-competitive and competitive formats, calibration plots in the ranges 5.0×10−10 to 1.0×10−8 mol L−1 and 1.0×10−10 to 1.0×10−9 mol L−1 HSA, respectively, with estimated detection limits of 1.5×10−10 mol L−1 (10 ng mL−1) and 1.0×10−10 mol L−1 (7 ng mL−1), respectively, were obtained. Levels of HSA in two healthy volunteer urine samples were also evaluated, using both immunoassay
formats. 相似文献
4.
A novel thiocyanate (SCN−)-selective PVC membrane electrode based on a zinc-phthalocyanine (ZnPc) complex as neutral carrier is described. The membrane electrode containing ZnPc with 5.1% (w/w) ionophore, 29.2% (w/w) PVC, and 65.7% (w/w) 2-nitrophenyl octyl ether (o-NPOE) as plasticizer displayed an anti-Hofmeister selectivity sequence , and exhibited near-Nernstian potential response to thiocyanate ranging from about 1.0×10−1 to 1.0×10−6 mol L−1 with a detection limit of 7.5×10−7 mol L−1 and a slope of 58.1±0.5 mV per decade in pH 3.0 phosphate buffer solution at 25 °C. This preferential response is believed to be associated with the unique coordination between the central metal of the carrier and thiocyanate.
相似文献
5.
Tripodal chelating ligand-based sensor for selective determination of Zn(II) in biological and environmental samples 总被引:1,自引:0,他引:1
Potassium hydrotris(N-tert-butyl-2-thioimidazolyl)borate [KTtt-Bu] and potassium hydrotris(3-tert-butyl-5-isopropyl-l-pyrazolyl)borate [KTpt-Bu,i-Pr] have been synthesized and evaluated as ionophores for preparation of a poly(vinyl chloride) (PVC) membrane sensor for Zn(II)
ions. The effect of different plasticizers, viz. benzyl acetate (BA), dioctyl phthalate (DOP), dibutyl phthalate (DBP), tributyl
phosphate (TBP), and o-nitrophenyl octyl ether (o-NPOE), and the anion excluders sodium tetraphenylborate (NaTPB), potassium tetrakis(p-chlorophenyl)borate (KTpClPB), and oleic acid (OA) were studied to improve the performance of the membrane sensor. The best
performance was obtained from a sensor with a of [KTtt-Bu] membrane of composition (mg): [KTtt-Bu] (15), PVC (150), DBP (275), and NaTPB (4). This sensor had a Nernstian response (slope, 29.4 ± 0.2 mV decade of activity)
for Zn2+ ions over a wide concentration range (1.4 × 10−7 to 1.0 × 10−1 mol L−1) with a limit of detection of 9.5 × 10−8 mol L−1. It had a relatively fast response time (12 s) and could be used for 3 months without substantial change of the potential.
The membrane sensor had very good selectivity for Zn2+ ions over a wide variety of other cations and could be used in a working pH range of 3.5–7.8. The sensor was also found to
work satisfactorily in partially non-aqueous media and could be successfully used for estimation of zinc at trace levels in
biological and environmental samples.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
6.
Joanna Lenik Cecylia Wardak Barbara Marczewska 《Central European Journal of Chemistry》2008,6(4):513-519
Naproxen membrane electrodes based on different plasticizers and the quaternary ammonium salts (QASs) dimethyldidecylammonium
bromide, methyltrioctylammonium chloride, or tetraoctylammonium chloride, were prepared. The following basic parameters were
investigated for the optimal electrode: measurement range (10−4 − 10−1 mol L−1), slope of the linear range of the calibration curve (−58.3 mV decade−1), limit of detection (6.0 × 10−5 mol L−1), lifetime (2.5 months), dependence of the electrode potential on pH (5.5 − 9.0), reproducibility of potential (1.2 mV) and
selectivity coefficients in relation to selected organic and inorganic anions. The electrode was utilized for determination
of naproxen in tablets by the calibration curve method and the standard addition method.
相似文献
7.
The sensitivity and precision of headspace solid-phase micro extraction (HS-SPME) at an analyte solution temperature (T
as) of +35 °C and a fiber temperature (T
fiber) of +5 °C were compared with those for HS-SPME at T
as and T
fiber of −20 °C for analysis of the volatile organic compounds benzene, 1,1,1-trichloroethane, trichloroethylene, toluene, o-xylene, ethylbenzene, m/p-xylene, and tetrachloroethylene in water samples. The effect of simultaneous fiber cooling and analyte solution freezing
during extraction was studied. The compounds are of different hydrophobicity, with octanol/water partition coefficients (Kow) ranging from 126 and 2511. During a first set of experiments the polydimethylsiloxane (PDMS) SPME fiber was cooled to
+5 °C with simultaneous heating of the aqueous analyte solution to +35 °C. During a second set of experiments, both SPME fiber
holder and samples were placed in a deep freezer maintained at −20 °C for a total extraction time of 30 min. After approximately
2 min the analyte solution in the vial began to freeze from the side inwards and from the bottom upwards. After approximately
30 min the solution was completely frozen. Analysis of VOC was performed by coupling HS-SPME to gas chromatography-mass spectrometry
(GC-MS). In general, i.e. except for tetrachloroethylene, the sensitivity of HS-SPME increased with increasing compound hydrophobicity
at both analyte solution and fiber temperatures. At T
as of +35 °C and T
fiber of +5 °C detection limits of HS-SPME were 0.5 μg L−1 for benzene, 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene, 0.125 μg L−1 for toluene, and 0.025 μg L−1 for ethylbenzene, m/p-xylene, and o-xylene. In the experiments with T
as and T
fiber of −20 °C, detection limits were reduced for compounds of low hydrophobicity (Kow<501), for example benzene, toluene, 1,1,1-trichloroethane, and trichloroethylene. In the concentration range 0.5–62.5 μg
L−1, the sensitivity of HS-SPME was enhanced by a factor of approximately two for all compounds by performing the extraction
at −20 °C. A possible explanation is that freezing of the water sample results in higher concentration of the target compounds
in the residual liquid phase and gas phase (freezing-out), combined with enhanced adsorption of the compounds by the cooled
fiber. The precision of HS-SPME, expressed as the relative standard deviation and the linearity of the regression lines, is
increased for more hydrophobic compounds (Kow>501) by simultaneous direct fiber cooling and freezing of analyte solution. Background contamination during analysis is
reduced significantly by avoiding the use of organic solvents. 相似文献
8.
A sensitive complex absorptive wave of Ca-ARS was obtained by using differential pulse voltammetry when a mercury film glass
carbon electrode was immersed in 0.1 mol L−1 KOH and 4.5×10−4 mol L−1 ARS solution. The peak potential obtained was −1.17 V (vs Ag-AgCl). The peak current was proportional to the concentration
of calcium in the range of 5.0×10−8−4.2×10−5 mol L−1. The detection limit was 2.0×10−8 mol L−1. This method was applied successfully to determining traces of calcium in blood serum. The electrochemical behavior of the
system was also studied by cyclic voltammetry, and the experiment results showed that the electrode process was an irreversible
absorptive with two electrons participating.
Translated from Journal of Beijing Normal University (Natural Science Edition), 2005, 41(2) (in Chinese) 相似文献
9.
Jinzhang Gao Dongyu Lv Wu Yang Xiaoxia Wei Jie Qu Hua Chen Hongxia Dai Jie Ren 《Central European Journal of Chemistry》2007,5(2):581-589
A convenient and sensitive method for determination of sulfanilamide (SNA) was described based on the Mn(II)-catalyzed oscillating
chemical reaction. Under optimum conditions, a linear relationship existed between the changes of oscillating period or amplitude
and the negative of logarithm of SNA concentration in the range of 4.27 × 10−8 mol ·L−1 ∼ 7.41 × 10−6 mol ·L−1 (RSD, 0.85%) and 9.33 × 10−8 mol ·L−1 ∼ 3.02 × 10−6 mol ·L−1 (RSD, 1.08%), respectively. The lower limit of detection was found to be 2.69 × 10−8 mol ·L−1 and 6.03 × 10−8 mol ·L−1, respectively.
相似文献
10.
Jiming Xu Yanping Wang Yuezhong Xian Hui Li Litong Jin K. Tanaka H. Haraguchi 《Chromatographia》2002,56(7-8):449-453
Summary A sensitive ion-exclusion chromatographic method has been developed for determination of oxalate, thiosulfate, and thiocyanate.
The method is based on separation of these anions on a polymethacrylate-based, weakly acidic cation-exchange resin (TSKgel
OApak-A) and detection by means of a glassy carbon (GC) electrode electrochemically modified with polyvinylpyridine (PVP),
palladium, and iridium oxide (PVP/Pd/IrO2). The electrochemical behavior of oxalate, thiosulfate, and thiocyanate at this chemically modified electrode (CME) have
been investigated by cyclic voltammetry. The results indicated that electrocatalytic oxidation of these anions by the electrode
was efficient and that the sensitivity, stability, and lifetime of the electrode were relatively high. Combined with ion-exclusion
chromatography the PVP/Pd/IrO2 electrode was used as the working electrode for amperometric detection of these anions. All linear ranges were over two orders
of magnitude and detection limits, defined asS/N=3, were 9.0×10−7 mol L−1 for oxalate, 6.7×10−7 mol L−1 for thiosulfate, and 5.6×10−7 mol L−1 for thiocyanate. Correlation coefficients were all>0.998. Coupled with microdialysis sampling the method has been successfully
applied to the determination of oxalate, thiosulfate, and thiocyanate in urine. 相似文献
11.
A novel fluorescence quenching method for the determination of cationic surfactants (CS), specifically cetyltrimethylammonium
bromide (CTAB), dodecyltrimethylammonium bromide (DTAB), and cetylpyridinium chloride (CPC), has been developed using water-soluble
luminescent CdTe quantum dots (QDs) modified with thioglycolic acid (TGA). The possible interference from heavy and transition
metals (HTM) has been efficiently eliminated through simple sample treatment with mercapto cotton made in-house. Under optimum
conditions, the extent of fluorescence quenching of CdTe QDs is linearly proportional to the concentration of CS from 2.0 × 10−7 to 7.0 × 10−6 mol L−1 with a detection limit of 5.0 × 10−8 mol L−1. The relative standard deviation for 1.0 × 10−6 mol L−1 CTAB is 2.5% (n = 6). The proposed method exhibits high sensitivity and selectivity and furthermore avoided the use of toxic organic solvents
and tedious solvent extraction procedures. It has been applied to the determination of trace CS in natural river water and
commodity samples with satisfactory results.
Potential interference from heavy and transition metals is eliminated during photoluminescence detection of CS through simple
sample pre-treatment with mercapto cotton 相似文献
12.
An electrochemical study of the doxazosin oxidative process at carbon paste electrodes using different voltammetric techniques
has been carried out. The process is irreversible and controlled by adsorption, giving rise to an oxidation wave around 1.0 V
in citric acid-citrate buffer (pH 3.0). A mechanism based on the oxidation of the amine group is postulated. Two methods based
on adsorptive stripping (AdS) of doxazosin at the C8-modified carbon paste electrode (C8-MCPE), before its voltammetric determination, are studied, using differential pulse voltammetry (DPV) and square wave voltammetry
(SWV) as redissolution techniques. By means of AdS-DPV and C8-MCPE, doxazosin can be determined over the 1.0 × 10−9 to 3.0 × 10−8 mol L−1 range with a variation coefficient of 2.2% (2.0 × 10−8 mol L−1) and a limit of detection of 7.4 ×10−10 mol L−1. If AdS-SWV is used, a linear range from 1.0 × 10−9 to 4.0 × 10−8 mol L−1 is obtained, the variation coefficient being 2.8% (2.0 × 10−8 mol L−1, and the limit of detection reached 7.7 × 10−10 mol L−1. The AdS-DPV procedure was applied to the determination of doxazosin in urine and formulations.
Received March 13, 1999. Revision December 23, 1999. 相似文献
13.
Dora Melucci Simona Montalbani Clinio Locatelli 《Central European Journal of Chemistry》2012,10(1):267-276
The present work reports the critical comparison about the employment of three different supporting electrolytes (0.1 mol
L−1 HClO4, 0.01 mol L−1 EDTA-Na2 + 0.06 mol L−1 NaCl + 2.0 mol L−1 HClO4 and 0.1 mol L−1 KSCN + 0.001 mol L−1 HClO4) and their instrumental and chemical optimisation for the simultaneous voltammetric determination of total mercury(II) and
copper(II) in sediments and sea water at gold electrode, especially discussing the reciprocal interference problems. 相似文献
14.
Santos EM Araújo AN Couto CM Montenegro MC 《Analytical and bioanalytical chemistry》2006,384(4):867-875
The construction and general performance of new valproate-selective electrodes based on manganese(III) tetraphenylporphyrin
[Mn(III)TPP-Cl], as an ionophore, are presented. The ionophore was incorporated into PVC and ceramic membranes (sol–gel) based
on methyltriethoxysilane. The influence of membrane composition and pH and the effect of lipophilic cationic and anionic additives
in PVC membranes were investigated concerning their influence on the slope, response time, selectivity and lifetime of the
electrodes. The PVC membrane without additive and the sol–gel membrane presented slopes and practical limits of detection
of −60.8 mV dec−1 and 5x10−6 mol l−1 and −60.3 mV dec−1 and 1×10−4 mol l−1, respectively. The sol–gel membranes displayed higher selectivity for valproate when compared with PVC membranes. These two
types of electrodes were coupled to a sequential-injection analysis (SIA) system for the direct determination of valproate
in pharmaceutical formulations. The association of Mn(III)TPP-Cl with the sol–gel support inserted in a SIA system provided
potentiometric sensors with an analytical range of 1x10−3–5x10−2 mol l−1, with a sample rate of 55 samples per hour and a sample and carrier consumption of 140 and 2,500 μl per determination, respectively. 相似文献
15.
A simple and reliable method has been established for determination of cis and trans-1,3-dichloropropene (1,3-DCP) in water by headspace solid-phase microextraction (HS-SPME) then GC–ECD. An experimental design
with two steps was performed to determine the best experimental conditions for extraction of the 1,3-DCP isomers. First, a
26−2 fractional factorial design was conducted to screen for significant conditions. Second, a central composite design (CCD)
was performed to optimise the variables. The best experimental extraction conditions were: polydimethylsiloxane–divinylbenzene
(PDMS–DVB)-coated fibre, 20-min extraction time, 12 °C extraction temperature, 300 g L−1 NaCl, and 20 mL headspace volume in 40-mL vial. Under these conditions the method detection limit (MDL) was 0.5 ng L−1 for cis-1,3-DCP and 1.0 ng L−1 for trans-1,3-DCP. The method quantification limit (MQL) was 1.2 ng L−1 for cis-1,3-DCP and 3.0 ng L−1 for trans-1,3-DCP. For both isomers the relative standard deviation (RSD) for analysis of 50 ng L−1 or 0.5 μg L−1 of the isomer mixture was less than 8%. When the proposed method was applied to surface (river) water and tapwater samples
from Gipuzkoa province (Spain) the target analytes were not detected. The method was also used to investigate the presence
of the isomers in leachates from agricultural soil. A mixed solution was added to samples of two different soils and 1,3-DCP
isomers were quantified in leachate obtained from the samples. 相似文献
16.
A sensitive adsorptive anodic stripping procedure for the determination of trace zirconium at a carbon paste electrode (CPE)
has been developed. The method is based on adsorptive accumulation of the Zr(IV)-alizarin red S(ARS) complex onto the surface
of the CPE, followed by oxidation of adsorbed species. The optimal experimental conditions include the use of 0.10 mol · L−1 ammonium acetate buffer (pH 4.3), ARS, an accumulation potential of 0.20 V (versus SCE), an accumulation time of 2 min, a
scan rate of 200 mV · s−1 and a second-order derivative linear scan mode. The oxidation peak for the complex appears at 0.69 V. The peak current is
proportional to the concentration of Zr(IV) over the range of 1.0 × 10−9–2.0 × 10−7 mol · L−1, and the detection limit is 3 × 10−10 mol · L−1 for a 2 min adsorption time. The relative standard deviations (n = 8) for 5.0 × 10−8 and 5.0 × 10−9 mol · L−1 Zr(IV) are 3.3 and 4.8%, respectively. The proposed method was applied to the determination of zirconium in ore samples with
satisfactory results. 相似文献
17.
It has been found that gold nanoparticles (nano-Au) enhance the chemiluminescence (CL) of the luminol–hydrogen peroxide system
and that estrogens inhibit these CL signals in alkaline solution. CL spectra, UV–visible spectra, X-ray photoelectron spectra
(XPS), and transmission electron microscopy (TEM) were used to investigate the mechanism of the CL enhancement. On the basis
of the inhibition, a flow-injection CL method has been established for determination of three natural estrogens. Under the
optimized conditions, the linear range for determination of the estrogens was 0.07 to 7.0 μmol L−1 for estrone, 0.04 to 10 μmol L−1 for estradiol, and 0.1 to 10 μmol L−1 for estriol. The detection limits were 3.2 nmol L−1 for estrone, 7.7 nmol L−1 for estradiol, and 49 nmol L−1 for estriol, with RSD of 2.9, 2.6, and 1.8%, respectively. This method has been used for analysis of estrogens in commercial
tablets and in urine samples from pregnant women. 相似文献
18.
A poly(caffeic acid) thin film was deposited on the surface of a glassy carbon electrode by potentiostatic technique in an
aqueous solution containing caffeic acid. The poly(caffeic acid)-modified electrode was used for the determination of ascorbic
acid (AA), dopamine (DA), and their mixture by cyclic voltammetry. This modified electrode exhibited a potent and persistent
electron-mediating behavior followed by well-separated oxidation peaks toward AA and DA at a scan rate of 10 mV s−1 with a potential difference of 135 mV, which was large enough to determine AA and DA individually and simultaneously. The
catalytic peak current obtained was linearly dependent on the AA and DA concentrations in the range of 2.0 × 10−5−1.2 × 10−3 and 1.0 × 10−6−4.0 × 10−5 mol L−1 in 0.15 mol L−1 phosphate buffer (pH 6.64). The detection limits for AA and DA were 9.0 × 10−6 and 4.0 × 10−7 mol L−1, respectively. The modified electrode shows good sensitivity, selectivity, and stability and has been applied to the determination
of DA and AA in real samples with satisfactory results. 相似文献
19.
A survey of contamination of surface and drinking waters around Lake Maggiore in Northern Italy with polar anthropogenic environmental
pollutants has been conducted. The target analytes were polar herbicides, pharmaceuticals (including antibiotics), steroid
estrogens, perfluorooctanesulfonate (PFOS), perfluoroalkyl carboxylates (including perfluorooctanoate PFOA), nonylphenol and
its carboxylates and ethoxylates (NPEO surfactants), and triclosan, a bactericide used in personal-care products. Analysis
of water samples was performed by solid-phase extraction (SPE) then liquid chromatography–triple-quadrupole (tandem) mass
spectrometry (LC–MS–MS). By extraction of 1-L water samples and concentration of the extract to 100 μL, method detection limits
(MDLs) as low as 0.05–0.1 ng L−1 were achieved for most compounds. Lake-water samples from seven different locations in the Southern part of Lake Maggiore
and eleven samples from different tributary rivers and creeks were investigated. Rain water was also analyzed to investigate
atmospheric input of the contaminants. Compounds regularly detected at very low concentrations in the lake water included:
caffeine (max. concentration 124 ng L−1), the herbicides terbutylazine (7 ng L−1), atrazine (5 ng L−1), simazine (16 ng L−1), diuron (11 ng L−1), and atrazine-desethyl (11 ng L−1), the pharmaceuticals carbamazepine (9 ng L−1), sulfamethoxazole (10 ng L−1), gemfibrozil (1.7 ng L−1), and benzafibrate (1.2 ng L−1), the surfactant metabolite nonylphenol (15 ng L−1), its carboxylates (NPE1C 120 ng L−1, NPE2C 7 ng L−1, NPE3C 15 ng L−1) and ethoxylates (NPE
n
Os, n = 3-17; 300 ng L−1), perfluorinated surfactants (PFOS 9 ng L−1, PFOA 3 ng L−1), and estrone (0.4 ng L−1). Levels of these compounds in drinking water produced from Lake Maggiore were almost identical with those found in the lake
itself, revealing the poor performance of sand filtration and chlorination applied by the local waterworks. 相似文献
20.
A Pt wire coated with a bentonite–carbon composite in a poly(vinyl chloride) membrane was used for detection of lead. The
sensor has a Nernstian slope of 29.42±0.50 mV per decade over a wide range of concentration, 1.0×10−7 to 1.0×10−3 mol L−1 Pb(NO3)2. The detection limit is 5.0×10−8 mol L−1 Pb(NO3)2 and the electrode is applicable in the pH range 3.0–6.7. It has a response time of approximately 10 s and can be used at
least for three months. The electrode has good selectivity relative to nineteen other metal ions. The practical analytical
utility of the electrode is demonstrated by measurement of Pb(II) in industrial waste and river water samples. 相似文献