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Showing papers on "Detection limit published in 1996"


Journal ArticleDOI
TL;DR: A portable instrument based on laser-induced breakdown spectroscopy (LIBS) has been developed for the detection of metal contaminants on surfaces as mentioned in this paper, which consists of a sampling probe connected to the main analysis unit by electrical and optical cabling.
Abstract: A portable instrument, based on laser-induced breakdown spectroscopy (LIBS), has been developed for the detection of metal contaminants on surfaces. The instrument has a weight of 14.6 kg, fits completely into a small suitcase (46 x 33 x 24 em), and operates from 115 V ac. The instrument consists of a sampling probe connected to the main analysis unit by electrical and optical cabling. The hand-held probe contains a small laser to generate laser sparks on a surface and a fiber-optic cable to collect the spark light. The collected light is spectrally resolved and detected with the use of a compact spectrograph/CCD detector system. The instrument has been evaluated for the analysis of metals in the environment: Ba, Be, Pb, and Sr in soils; Pb in paint; and Be and Pb particles collected on filters. Detection limits in ppm for metals in soils were 265 (Ba), 9.3 (Be), 298 (Pb), and 42 (Sr). The detection limit for Pb in paint was 0.8% (8000 ppm), corresponding to 0.052 mg/cm2. The higher limit obtained for Pb in paint is attributed to the use of the 220.35-nm Pb(II) line instead of the stronger 405.78-nm Pb(I) line used for soils. Spectral interferences prevented use of the 405.78-nm line to determine Pb in paint. The surface detection limit for Be particles on filters was dependent on particle size and ranged from 21 to 63 ng/cm2. The detection limit for Pb particles on filters was 5.6 μg/cm2.

322 citations


Journal ArticleDOI
TL;DR: It is suggested that MALDI/TOF analysis may provide a rapid means to identify changes in carbohydrate composition in glycoproteins by offering improved sensitivity for detection of acidic glycopeptides over alpha-cyano-4-hydroxycinnamic acid.
Abstract: 2,5-Dihydroxybenzoic acid (DHB) is the most commonly used matrix for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI/TOF) of oligosaccharides. Because acidic, sialylated oligosaccharides are detected at only the low picomole level with DHB, alternative matrices were screened to identify a matrix with a lower limit of detection. Negative-ion spectra of pure mono-, di-, and trisialylated oligosaccharides were acquired with either 6-aza-2-thiothymine or 2‘,4‘,6‘-trihydroxyacetophenone (THAP) in the linear mode. Detection limits of less than 50 fmol with signal-to-noise ratios of better than 5:1 were achieved with both matrices. THAP was the preferred matrix because it provided a lower limit of detection and gave less prompt fragmentation. Incorporation of ammonium citrate into the matrix, along with vacuum drying of the sample, was required in order to obtain maximum sensitivity with THAP. No evidence of competition for ionization was found when a mixture of mono-, di-, an...

277 citations


Journal ArticleDOI
TL;DR: This extremely sensitive method enables, for the first time, determination of flavonols in body fluids after consumption of a normal diet.
Abstract: Flavonols are dietary antioxidants which may prevent coronary heart disease. To be able to study absorption of flavonols in humans, we developed a postcolumn derivatization with aluminum for HPLC with fluorescence detection. Variables governing postcolumn chelation, such as water content, buffer, organic modifier of the eluent, concentration of Al3+, presence of acetic acid in the postcolumn reagent, and temperature, were studied and optimized. Of the flavonoids, only flavonols that contain a free 3-hydroxyl and 4-keto oxygen binding site form fluorescent complexes with Al3+. The method has a detection limit of 0.15 ng/mL for quercetin, 0.05 ng/mL for kaempferol, 0.45 ng/mL for myricetin, and 0.05 mg/mL for isorhamnetin, thus improving detectability of quercetin 300-fold as compared to that possible with UV detection. The reproducibility relative standard deviation of the method is 1.4%. This extremely sensitive method enables, for the first time, determination of flavonols in body fluids after consumptio...

152 citations


Journal ArticleDOI
01 Jan 1996-Analyst
TL;DR: The results obtained by the proposed method and the certified values are in good agreement and represent the practical detection limit of this method.
Abstract: A method for determining iodine, bromine, chlorine and fluorine in geological and biological materials is described. In a quartz tube, solid material was heated to 1100 °C under a wet oxygen flow (pyrohydrolysis). By this process the halogens (I, Br, Cl, F) were separated from the matrix and then collected in a receiver solution. The chemical yield of iodine was determined by a radioactive tracer. ICP-MS and ion chromatographic measurements were used for the determination of the halogens. The method was optimized by investigating different experimental conditions. All four halogens can be trapped in the receiver solution from one combustion procedure. Precision and accuracy were evaluated by the analysis of environmental standard reference materials (rock, soil, milk, leaves, marine tissue). The concentrations in the materials analysed were in the ranges 0.006–50 mg kg–1 for I, 0.06–1300 mg kg–1 for Br, 50–1100 mg kg–1 for F and 400–1100 mg kg–1 for Cl. The lower values represent the practical detection limit of this method. The results obtained by the proposed method and the certified values are in good agreement.

134 citations


Journal ArticleDOI
TL;DR: A comparison of extraction efficiency between a new polymeric sorbent for solid-phase extraction (SPE) and classical RP-18 is described and a method is presented regarding the determination of carbendazim in water, using SPE on a mixed RP/polymer phase and high-performance liquid chromatography.

112 citations


Journal ArticleDOI
TL;DR: In this article, a rapid procedure for the simultaneous determination of mono-, di-and tributyltin in sediments and biological materials is described, which is much faster than previously reported methods.
Abstract: A rapid procedure for the simultaneous determination of mono-, di- and tributyltin in sediments and biological materials is described. The target compounds in sediments were subject to quantitative microwave-assisted leaching with acetic acid. Biomaterials were dissolved in a tetramethylammonium hydroxide solution under the action of a low-power microwave field in such a way that the organotin moiety remained intact. The leaching of the analytes from a sediment as well as the dissolution of a biomaterial in a focused microwave field took only 1–5 min, which is much faster than previously reported methods. It was also demonstrated that the leaching efficiency of monobutyltin from certified reference sediments was superior to that of most literature procedures. The butyltins were derivatized with sodium tetraethylborate (NaBEt4) in the aqueous phase, and simultaneously extracted into isooctane (5 min). The analysis was carried out by capillary gas chromatography (GC) with microwave-induced plasma atomic emission detection. The sample throughput was limited by the duration of the GC run (10 min). The detection limit was 2 ng g–1 for 0.2 g of sample (dry) without preconcentration; it could be improved by a factor 10 if preconcentration was applied. The developed method was applied to a variety of real samples and was validated by analysing three certified reference materials: PACS-1, CRM 462 and NIES 11.

110 citations


Journal ArticleDOI
TL;DR: In this paper, surface-enhanced Raman spectroscopy (SERS) is evaluated as a quantitative analytical tool for low concentrations of melamine and melamine derivatives in solution, and the results of multiple measurements using a hard cathodic cleaning step in between each adsorption experiment gave a relative standard deviation of 15%.
Abstract: Surface-enhanced Raman spectroscopy (SERS) is evaluated as a quantitative analytical tool for low concentrations of melamine and melamine derivatives in solution. Substantial variations in absolute and relative intensities of SERS bands were encountered using silver sols, which cannot be controlled. Alternatively, it was shown that SERS using a roughened silver electrode, while conditioning the applied potential, permits the acquisition of Raman spectra from electrode spots down to 1 μm in size, and the results of multiple measurements using a hard cathodic cleaning step in between each adsorption experiment gave a relative standard deviation of 15%. The high enhancement factor of the electrode micro-Raman scattering intensity creates a new trace analytical technique for obtaining high-resolution spectra of melamine from dilute aqueous solution (detection limit ∼ 10-7 mol L-1) in the opto-electrochemical cell. As an alternative for the hard cathodic cleaning step, we demonstrated that the cationic surfact...

108 citations


Journal ArticleDOI
TL;DR: The microwave assisted conventional HNO3-HF-H2O2-H3BO3 digestion system has been explored for direct ICP-MS analysis of total metals in silicon-containing solid samples as discussed by the authors.
Abstract: The microwave-assisted conventional HNO3–HF–H2O2–H3BO3 digestion system has been explored for direct ICP-MS analysis of total metals in silicon-containing solid samples. In closed Teflon PFA vessels under microwave heating with temperature/pressure regulation, a 0.25 g portion of sample containing ⩽ 33% silicon was digested in 1.5 ml of HF (48%), 5 ml of concentrated HNO3 and 2 ml of H2O2(30%), followed by a second digestion stage with 12 ml of 5% m/v boric acid. The amount of HF used was approximately twice the stoichiometric requirement for 33% silicon contained in the samples, assuming all silicon exists as silica. The amount of boric acid used was the stoichiometric requirement for the HF added. With a sample dilution factor of 2000 (v/m), the end solution contained ⩽ 0.17% total dissolved solids for ICP-MS analysis. The ICP-MS system was calibrated by the method of external standards prepared in reagent blank solutions with in as the internal standard. The sensitivity of the In signal in a 5–8 h operation was only decreased by 5–10%. Background interferences from the digestion reagents were studied and corrected. The method developed is simple and rugged and suitable for routine analysis of at least 25 elements: Al, Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Mo, Ni, Pb, Sb, Sn, Sr, Th, Ti, Tl, U, V and Zn. The recoveries for most of these elements in standard reference materials including coal fly ash, urban particulate matter, sediment and soil were within 90–110%, and the relative standard deviations were within 5%. The method cannot determine B and is not suitable for Hg determination. The detection limits for Be and Se determination are not adequate.

102 citations


Journal ArticleDOI
TL;DR: A stereospecific HPLC method for the quantitation of CGP 49309 in samples of its corresponding enantiomer valsartan has been developed and validated and both methods were found to be suitable for the analysis of the respective analytes.

100 citations


Journal ArticleDOI
TL;DR: A new method for the determination of tetraethyllead (TEL) and ionic lead in water by SPME has been developed and has been verified on spiked tap water samples.
Abstract: A new method for the determination of tetraethyllead (TEL) and ionic lead in water by SPME has been developed. TEL is extracted from the headspace over the sample. Inorganic lead is first derivatized with sodium tetraethylborate to form TEL, which is extracted in the same way as pure TEL samples. The analytical procedure was optimized with respect to pH, amount of derivatizing reagent added, stirring conditions, and extraction time. The detection limit obtained for TEL was found to be 100 ppt when using FID and 5 ppt when using ion trap MS (ITMS). The detection limit for Pb(2+), limited by the nonzero blank, was found to be 200 ppt. Linear calibration curves were obtained for both analytes when FID was used for detection. For lead they spanned over 4 orders of magnitude. ITMS offered excellent sensitivity and selectivity, but the calibration curves were nonlinear when the m/z = 295 ion was used for quantitation. The method has been verified on spiked tap water samples. An excellent agreement was found between the results obtained for standard solutions prepared using NANOpure water and spiked tap water samples.

99 citations


Journal ArticleDOI
TL;DR: An online sensor with a low detection limit for L- glutamate was developed in order to monitor the change in the extracellular L-glutamate concentration as a result of stimulated release from cultured nerve cells.
Abstract: An online sensor with a low detection limit for l-glutamate was developed in order to monitor the change in the extracellular l-glutamate concentration as a result of stimulated release from cultured nerve cells. The sensor consisted of a microdialysis (MD) probe fixed at the manipulator, a small-volume l-glutamate oxidase enzymatic reactor (0.75 mm i.d. and 2.5 cm long), and an electrochemical detector in a thin-layer radial flow cell with an active volume of 70−340 nL. Glassy carbon bulk or carbon film ring−disk electrodes were used as detectors by modifying them with Os poly(vinylpyridine) mediator containing horseradish peroxidase. The overall efficiency of l-glutamate detection with the sensor is 94% under optimum conditions, due to an efficient enzymatic reaction in the reactor and a high conversion efficiency in the radial flow cell. As a result, we achieved a sensitivity of 24.3 nA/μM and a detection limit of 7.2 nM (S/N = 3). The effect of interferents such as l-ascorbic acid can be minimized eff...

Journal ArticleDOI
TL;DR: A preconcentration procedure, using a short column filled with Amberlite XAD-8, is proposed for the Spectrophotometric determination of traces of molybdenum in steel as mentioned in this paper.

Journal ArticleDOI
TL;DR: Since 3-nitrotyrosine is a stable product of peroxynitrite, an oxidant formed by a reaction of nitric oxide and superoxide radicals, the measurement of its plasma concentration may be useful as a marker of nitrics oxide-dependent oxidative damage.

Journal ArticleDOI
TL;DR: In this article, a gas chromatographic/mass spectrometric (GC/MS) method for determining acetochlor in environmental water samples was developed. The method involves automated extraction of the herbicide from a filtered 1 L water sample through a C 18 solid-phase extraction column, elution from the column with hexane-isopropyl alcohol (3 + 1), and concentration of the extract with nitrogen gas.
Abstract: A sensitive and reliable gas chromatographic/mass spectrometric (GC/MS) method for determining acetochlor in environmental water samples was developed. The method involves automated extraction of the herbicide from a filtered 1 L water sample through a C 18 solid-phase extraction column, elution from the column with hexane-isopropyl alcohol (3 + 1), and concentration of the extract with nitrogen gas. The herbicide is quantitated by capillary/column GC/MS with selected-ion monitoring of 3 characteristic ions. The single-operator method detection limit for reagent water samples is 0.0015 μg/L. Mean recoveries ranged from about 92 to 115% for 3 water matrixes fortified at 0.05 and 0.5 μg/L. Average single-operator precision, over the course of 1 week, was better than 5%.

Journal ArticleDOI
TL;DR: In this paper, the separation and detection of eleven priority phenols using capillary zone electrophoresis with UV detection was described using a 70 cm x 75 μm I.D. capillary at 15 kV and an electrophoretic buffer of 20 mM sodium borate (pH 9.9 ± 0.1).

Journal ArticleDOI
TL;DR: The detection limits using UV absorbance detection were found to be too high to determine the concentration of isoproterenol in plasma for a sufficient time following administration to establish the pharmacokinetics.

Journal ArticleDOI
TL;DR: In this article, the authors used the chemiluminescence reagent luminol as a component of the separation electrolyte, thus preventing loss of the light signal where luminol and H2O2 are mixed in advance in conventional flow injection analysis or ion chromatography chemilumininescence detection.
Abstract: Highly sensitive chemiluminescence detection for capillary ion analysis has been developed. The new idea lies in using the chemiluminescence reagent luminol as a component of the separation electrolyte, thus preventing loss of the light signal where luminol and H2O2 are mixed in advance in conventional flow injection analysis or ion chromatography chemiluminescence detection. Signal enhancement is achieved by sample stacking injection in the electrophoresis process. The detection limit (S/N = 3) of 20 zmol (5 × 10-13 mol/L) for cobalt(II) is ∼2 orders of magnitude better than the most sensitive results (1.7 × 10-11 mol/L) reported so far. Detection limits are 2 amol, 80 amol, 740 amol, and 100 fmol for copper(II), nickel(II), iron(III), and manganese(II), respectively. The sensitivity is significantly better than that in the electrochemical detection and the commonly used UV detection in capillary ion analysis. The capillary electrophoresis−chemiluminescence detector has been used to separate five metal i...

Journal ArticleDOI
TL;DR: An HPLC method for the simultaneous determination of both caffeine and theophylline in human plasma is described, using a reversed-phase chromatography column heated by a thermostatic oven at 35 degrees C, with UV detection and isocratic elution.

Journal ArticleDOI
TL;DR: In this paper, three different analytical techniques, i.e., capillary electrophoresis (CE), ion chromatography (IC), and ion-selective electrode potentiometry (ISE), were used to determine the fluoride concentration in Dutch rain water.

Journal ArticleDOI
TL;DR: It is concluded that pre-column derivatization with FMOC-Cl substantially improves the analysis of gentamicin compared with present methods based on reaction with o-phthaldialdehyde.

Journal ArticleDOI
TL;DR: In this paper, a sample preparation method was developed for the determination of mercury in gasoline and other petroleum products, where organo-mercury compounds in the materials were oxidized, while being extracted into the aqueous phase using an oxidant/acid solution, BrCl HCl.

Journal ArticleDOI
TL;DR: It is shown that CZE-ES-MS, combined with solid-phase sample cleanup, can detect adducts at levels of fourAdducts in 10(7) unmodified bases or less, and the application of sample stacking significantly increases the concentration detection limit.
Abstract: Capillary zone electrophoresis (CZE) coupled with negative ion electrospray mass spectrometry (ES-MS) is used for the detection and identification of adducts formed from the reaction of DNA with (±)-anti-7,8,9,10-tetrahydrobenzo[a]pyrene-7,8-diol 9,10-epoxide (BPDE), an active metabolite of benzo[a]pyrene (BaP). Results presented in this paper demonstrate low nanogram detection limits (<10 ng or <15 pmol) for normal scan spectra and collision-induced dissociation spectra of the main nucleotide adduct formed from this reaction. (BPDE reacts predominantly with the exocyclic amino group of guanine.) Exploitation of selective reaction monitoring (SRM) produces detection limits in the low picogram range (<85 pg or <130 fmol). The application of sample stacking significantly increases the concentration detection limit (to approximately 10-8 M). Nucleotide adducts are negatively charged at most pHs and are therefore ideally suited to the stacking process used in this research. These techniques have been applied ...

Journal ArticleDOI
TL;DR: A flow-injection analysis with chemiluminescence detection is described for the determination of captopril based on the photochemical reaction with cerium(IV) in sulphuric acid medium yielding a strong chemilUMinescent signal which can be sensitized by some fluorescers.

Journal ArticleDOI
TL;DR: An on-line competitive immunoassay for insulin has been developed and applied to monitoring insulin concentration in a flowing stream and the insulin content of single islets of Langerhans was determined by flow injection analysis.
Abstract: An on-line competitive immunoassay for insulin has been developed and applied to monitoring insulin concentration in a flowing stream In the assay, solutions of fluorescein-labeled insulin (FITC-insulin), monoclonal anti-insulin, and sample containing insulin are pumped into a cross where they begin to mix The mixture flows through a fused silica reactor capillary to a flow-gated interface During transfer to the interface, insulin and FITC-insulin compete to form a complex with the antibody At the interface, a plug of the mixture is injected into a separation capillary, where the bound and free FITC-insulin are separated and detected by capillary electrophoresis with laser-induced fluorescence detection The amount of bound FITC-insulin, amount of free FITC-insulin, or bound/free ratio can be used to quantify insulin concentration Typical relative standard deviations of bound over free ratio are 5% The detection limit of the immunoassay in the on-line mode is <03 nM Each separation requires as lit

Journal ArticleDOI
01 Jan 1996-Analyst
TL;DR: In this paper, an on-line amalgamation trap was constructed for the collection of mercury species separated by capillary GC for detection by microwave-induced plasma atomic emission spectrometry, and the trap allowed the determination of dimethylmercury in condensate down to a detection limit of 0.24 µg l−1 and derivatized (butylated) monomethyl and inorganic mercury down to 0.56 µgl−1 in natural gas condensates.
Abstract: An on-line amalgamation trap was constructed for the collection of mercury species separated by capillary GC for detection by microwave-induced plasma atomic emission spectrometry. For direct measurement of the column eluate, the detection limits for mercury species in natural gas condensate are elevated because of background interference from carbon compounds passed to the plasma at the same time. Carbon compounds give rise to emission that spectrally interferes with the signal from the mercury detector and can overload the plasma discharge, reducing the excitation capability. With an amalgamation trap, mercury can be selectively collected from the column eluate and subsequently passed to the plasma in a flow of pure helium. By removing the carbon background emission, the trap allows the determination of dimethylmercury in condensate down to a detection limit of 0.24 µg l–1 and derivatized (butylated) monomethyl and inorganic mercury down to a detection limit of 0.56 µg l–1 in natural gas condensate. Use of the trap is compared with some existing determination methods for mercury species in condensate and other samples. Solid-phase micro-extraction is used for dimethylmercury, which gives a poorer detection limit of around 20 µg l–1 because the analyte mass collected is small compared with liquid sample injection. Following derivatization, samples are diluted for direct methylbutylmercury and dibutylmercury determination, corresponding to methylmercury and inorganic mercury. Dilution ensures a reasonably stable background for mercury signals. Again, poorer detection limits of 3.1 and 2.3 µg l–1, respectively, are obtained owing to the reduced analyte mass. The trap permits the injection of untreated condensate, or condensate reacted with butylmagnesium chloride, into the gas chromatograph without the need for dilution or sample clean-up.

Journal ArticleDOI
TL;DR: The protocol has been demonstrated to be suitable for the analysis of L-AA in Arabidopsis, parsley, and mushroom and has superior resolution to comparable HPLC separations, a comparable analysis time, but lower sensitivity because of the concentration limitations of the detection system.

Journal ArticleDOI
TL;DR: In this article, a simple flow-injection system with chemiluminescent detection for selective determination of sulphite is described, where the light accompanying the reaction between sodium carbonate and copper(II) mixture solution with sulphite was detected.

Journal ArticleDOI
TL;DR: Fluorescent whitening agents (FWAs) used in laundry detergents were determined in aqueous samples from sewage treatment plants and rivers using solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) with post-column UV irradiation and fluorescence detection as discussed by the authors.
Abstract: Fluorescent whitening agents (FWAs) used in laundry detergents were determined in aqueous samples from sewage treatment plants and rivers using solid-phase extraction (SPE) and high-performance liquid chromatography (HPLC) with post-column UV irradiation and fluorescence detection. FWAs were extracted from 10−200-mL water samples with C18 bonded- phase silica extraction disks and eluted with methanol-containing tetrabutylammonium ion-pairing reagent. No further sample cleanup steps were necessary due to the sensitive and selective fluorescence detection. Recovery of FWAs from raw sewage, primary effluent, secondary effluent, and river water ranged from 76 to 96%. The overall precision of the method, indicated by the relative standard deviation, ranged from 1 to 11%. The limit of quantification was less than 30 ng/L. The concentrations of the two most frequently used FWAs ranged from 7 to 21 μg/L in primary effluent, from 2.6 to 8.9 μg/L in secondary effluent, and from 0.04 to 0.57 μg/L in river water. FWA...

Journal ArticleDOI
TL;DR: In this paper, a rapid, sensitive method for the determination of paraquat and diquat in aqueous media using square wave voltammetry (SWV) is discussed on the basis of the analyte behavior in cyclic voltameters.

Journal ArticleDOI
TL;DR: In this paper, a flow injection analysis system and inductively coupled plasma mass spectrometric detection was used to detect uranium compounds in urine, with an analysis time of 60 s per sample and a lower limit of detection is 1.5ng l−1.