Showing papers on "Detection limit published in 1989"

Fluorometric measurement of aqueous ammonium ion in a flow injection system

Abstract: An automated flow-injection method for NH/sub 3//NH/sub 4//sup +/ involving the ternary reaction of the analyte with o-phthaldialdehyde (OPA) and sulfite is described. The use of malodorous thiol compounds is avoided and the reaction provides much greater sensitivity by either fluorescence (detection limit 300 fmol or 20 nM NH/sub 4//sup +/) or absorption detection compared to the reaction involving 2-mercaptoethanol. The reaction shows considerable selectivity for ammonia over amino acids by a factor of 16 to > 500 for 11 common amino acids studied. The throughput rate is 25 samples/h.

Comparison of pulsed coulometric detection and potential-sweep pulsed coulometric detection for underivatized amino acids in liquid chromatography.

Abstract: Pulsed coulometric detection (PCD) and potential-sweep pulsed coulometric detection (PS-PCD) are applied to the direct detection of amino acids in protein hydrolyzates. The detection mechanisms are based upon surface-catalyzed oxidation of the amine functionalities activated by the transient formation of surface oxide on Au electrodes. PCD uses a triple-step potential waveform in which the integration of electrode current at a constant potential is followed by anodic and cathodic polarizations to clean and reactivate the electrode surface. PS-PCD incorporates a cyclic potential sweep into the triple-step waveform which proceeds through the formation and subsequent removal of the surface oxide with simultaneous current integration. Reactions catalyzed by the formation of the noble metal oxide can be monitored in PS-PCD with the automatic rejection of the surface oxide background. A significant decrease is obtained also in the fluctuation and drift in the base line resulting from gradient elution and variations of the electrode surface. PCD and PS-PCD following gradient elution chromatography are demonstrated to allow for the direct detection of 20 amino acids including secondary amino acids. Detection limits for lysine are ca. 220 ppb (11 ng, 75 pmol) by PCD and 60 ppb (3 ng, 19 pmol) by PS-PCD applied at gold electrodes.

Pulsed amperometric detection of glucose in biological fluids at a surface-modified gold electrode.

Abstract: A nonenzymatic glucose sensor that utilizes permselective membranes to achieve the selectivity required for screening glucose in biological fluids has been described. Interference from endogenous oxidizable substances such as amino acids, urea, ascorbic acid, and uric acid, as well as the effect of chloride and proteins on glucose response, is studied by using flow injection analysis. A set of membranes made of Naflin perfluorinated membrane and collagen, when arranged in front of the working electrode (gold), result in significant improvement in the system selectivity. Even at physiological pH, which is far from being the optimum pH for pulsed amperometric detection of carbohydrates, the sensor shows a good limit of detection (4-5 micrograms of glucose injected).

Speciation of arsenic in urine using high-performance liquid chromatography with inductively coupled plasma mass spectrometric detection

Abstract: High-performance liquid chromatography (HPLC) has been coupled with inductively coupled plasma mass spectrometry (ICP-MS) for the speciation of four arsenic compounds commonly found in urine. Arsenite (As3+), arsenate (As5+), dimethylarsinate (DMA) and monomethylarsonate (MMA) were separated via anion-exchange HPLC and detected on-line using ICP-MS. The absolute detection limits ranged from 20 to 91 pg of arsenic in aqueous media and 36–96 pg in urine. The four species were determined in two freeze-dried urine standards using the method of standard additions. The total of the four species was found to be within 13% of the average reported total arsenic concentration for both freeze-dried urine standards containing elevated levels of As5+. The relative standard deviation of peak-height measurements was less than 10% for each of the four species in urine. The determination of As3+ is complicated by the presence of an interfering peak, which is believed to arise from the co-elution of chlorine-containing species and subsequent formation of 40Ar35CI+ ions (m/z= 75).

Attomole amino acid determination by capillary zone electrophoresis with thermooptical absorbance detection.

Abstract: Attomole quantities of 4-(dimethylamino)azobenzene-4'-sulfonyl chloride derivatized amino acids are separated by using capillary zone electrophoresis in a mixed acetonitrile/aqueous buffer system. Detection is performed with an on-column thermooptical absorbance detection technique based on a 130-mW argon ion pump laser. Detection limits for the concentration of analyte injected onto the column range from 5 x 10(-8) M for methionine to 5 x 10(-7) M for aspartic acid. Only 37 amol of methionine and 450 amol of aspartic acid are contained within the subnanoliter injection volume. It is interesting to note that these limits are a factor of 4 superior to the best fluorescence detection limit reported for chromatographic separation of amino acids. A subnanoliter sample of derivatized human urine was analyzed with this technique; quantities of amino acids contained within the sample are 3 orders of magnitude greater than the detection limit.

Method and apparatus for conducting electrochemiluminescence measurements.

Abstract: A method and apparatus (10) for conducting electrochemiluminescence (ECL) measurements which control the initial conditions relating to the surface state of a triggering working electrode (54) by reproducibly creating and maintaining a favorable surface condition so as to enhance the precision and detection limit of the measurements. Assays are performed with ECL detection in a flow-through cell (12) environment and the precision and detection limit are enhanced by alternating initialization and measurement steps.

Inductively Coupled Plasma Mass Spectrometry and Atomic Emission Spectrometry Coupled to High-Performance Liquid Chromatography for Speciation and Detection of Organotin Compounds

Abstract: Inductively coupled plasma mass spectrometry (ICP/MS) is utilized as a detector for several organotin species separated by high-performance liquid chromatography. Detection limits obtained by ICP/MS are 3 orders of magnitude lower than those obtained with inductively coupled plasma atomic emission spectrometry (ICP/AES) detection under the same chromatographic conditions. Chromatographic detection limits are higher than conventional solution nebulization for the same compound by a factor of 20. Ion-exchange chromatography yields linear response over 3 orders of magnitude, while ion pair chromatography gives a linear response of only 2 orders of magnitude as a result of poor resolution. The relative standard deviation for the injection of 20 ng of tin compounds is less than 10%.

Determination of naphthalene-2,3-dicarboxaldehyde-labeled amino acids by open tubular liquid chromatography with electrochemical detection.

Abstract: Naphthalene-2,3-dicarboxaldehyde (NDA) has been investigated as a new derivatizing reagent for the electrochemical detection of tagged amino acids. Gradient elution allowed for the separation of 18 NDA-derivatized amino acids on an open tubular liquid chromatography column in less than 50 min. Gradient elution and electrochemical detection were found to be compatible. A detection limit of 36 amol was obtained for the asparagine-NDA derivative. The usefulness of this technique for quantitation was demonstrated by the analysis of the NDA-tagged hydrolysis products from bovine chymotrypsinogen.

Determination of iron species in wine by ion-exchange chromatography-flame atomic absorption spectrometry

Abstract: The direct coupling of ion-exchange chromatography to flame atomic absorption spectrometry (AAS) has been achieved by employing a Babington type nebuliser. The system enables all the processes on the column to be followed directly at flow-rates of between 1 and 5 ml min–1. The potential of the system was investigated for the determination of various iron species in synthetic samples containing iron(II) and iron(III) in ionic or chelated form by employing various ion-exchange (Dowex 50-X8, Dowex 1-X8) and sorptive (Amberlite XAD-2) resins, respectively. In some instances where direct coupling was impossible, owing to the physical properties of the effluent or eluent, conventional analyses of chromatographically separated iron species were performed by flame AAS. The optimum concentration range, limit of detection and reproducibility of measurement were also determined for a particular column capacity. When direct coupling was employed, the detection limit for the separated iron species was 15 µg with a relative standard deviation (RSD) of ±3% and, using the conventional method of analysis, 2–5 µg with an RSD of ±1%. On the basis of these results the system was applied to the determination of the ratio of iron(II) to iron(III) in wines.

Inductively coupled plasma mass spectrometric determination of trace elements in surface waters subject to acidic deposition

Abstract: More than 250 water samples from lakes in the Eastern US were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) for 49 elements. Standard calibrations were used for 21 elements, and surrogate standards were used for 28 elements. The system detection limits, evaluated by using field blanks carried through the entire sampling and pretreatment process, were less than 0.2 ..mu..g/L for most elements. Contamination during sampling and pretreatment was often the limiting factor. The accuracy of the determinations, as determined from the analysis of NBS SRM 1643b samples and by recoveries for spiked water samples, was typically better than /plus minus/ 10% for the elements determined by using standard calibration and better than /plus minus/ 25% for the elements determined by using surrogate standards. The long-term (12 months) precision was generally better than /plus minus/ 10%, expressed as relative standard deviation, for both methods of determination. The use of surrogate standards and interference corrections is discussed in detail.

Horseradish‐root‐modified carbon paste bioelectrode

Abstract: The incorporation of horseradish roots into the carbon paste matrix results in an effective bioelectrode for sensing hydrogen peroxide. The response is based on the hydrogen peroxidase activity in the tissue. Because of the intimate contact between the biocatalytic and sensing sites, a very fast response is observed, as desired for practical biosensing applications. The behavior of the new bioelectrode is characterized using a flow injection system. Response time (t95%) as low as 11 s has been determined. The limit of detection is 3 × 10−7 M (1 ng), the relative standard deviation is 1.4%, and the response is linear up to 1.2 × 10−4 M. Oxidizable biological compounds do not interfere in the determination of hydrogen peroxide. The response is characterized also with respect to paste composition, flow rate, applied potential, reducing-agent concentration, injection volume, and other variables. Rapid and sensitive flow-injection measurements of glucose are illustrated. The tissue-modified electrode possesses many of the features desirable for use as an amperometric sensor for oxidase substrates.

Electrocatalysis and determination of hydrazine compounds at glassy carbon electrodes coated with mixed‐valent ruthenium(III, II) cyanide films

Abstract: Chemically modified electrodes, which were constructed by anodizing glassy carbon electrodes in a RuCl3/K4Ru(CN)6 solution, are shown to catalyze the electrooxidation of hydrazine compounds in acidic and neutral media. The mixed-valent ruthenium cyanide film offers improved stability and a broader operational pH range compared to previously described phthalocyanine-catalytic surfaces. The catalytic response of hydrazine, methylhydrazine, and dimethylhydrazine is evaluated with respect to the film preparation conditions, solution pH, potential scan rate, concentration dependence, and other variables. Highly stable and sensitive flow injection measurements [with a relative standard deviation (RSD) of 1.4% (n = 30) and a detection limit of 0.13 ng] are described. A composite film prepared by the codeposition of polyaniline offers additional advantages.

Ionspray mass spectrometry/mass spectrometry: Quantitation of tributyltin in a sediment reference material for trace metals

Abstract: La limite minimale d'etain detectable est d'environ 0,2 μg/g de sediment. Le materiau reference analyse dans cette etude contient 1,29±0,07 μg de Sn par gramme de sediment

Surface-enhanced resonance Raman spectroscopy as an ancillary high-performance liquid chromatography detector for nitrophenol compounds.

Abstract: In this study, the potential application of surface-enhanced resonance Raman scattering (SERRS) spectroscopy as an off-line secondary detector for HPLC has been evaluated. Four nitrophenol compounds, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 4,6-dinitrocresol were separated by isocratic reverse-phase high-performance liquid chromatography (RP-HPLC) and monitored with a conventional UV detector. Resonance Raman (RR) and SERRS spectroscopy were next used to provide the required specificity for distinguishing the nitrophenol compounds. The SERRS detection limit for both 2-nitrophenol and 4-nitrophenol was calculated to be 14 ppb and that for 2,4-dinitrophenol and 4,6-dinitrocresol was estimated to lie near the parts-per-billion level as well. This detection limit is 2-3 orders of magnitude lower than that obtained by RR spectroscopy.

Inductively Coupled Plasma Mass Spectrometry as a Detector for Micellar Liquid Chromatography: Speciation of Alkyltin Compounds

Abstract: Inductively coupled plasma mass spectrometry has been used as a detector for several organotin compounds which were separated with the use of micellar liquid chromatography. Trimethyltin chloride, triethyltin bromide, and tripropyltin chloride were separated with a 0.1 M sodium dodecyl sulfate (SDS) micellar mobile phase and C-18 stationary phase. Detection limits for the three were 27, 51, and 111 picograms tin, respectively. A 0.02 M SDS mobile phase was used to separate mono-methyltin trichloride, dimethyltin dichloride, and trimethyltin chloride. Detection limits for these compounds were 46, 26, and 126 picograms tin, respectively. Preliminary separation of those five organotin compounds was obtained by gradient elution. Calibration curves were linear over 3.5 orders of magnitude. The relative standard deviation for ten 100-μL injections containing 4 ng tin ranged from 1.3 to 1.9% with a 0.1 M SDS mobile phase and from 3.4 to 4.8% with a 0.02 M SDS mobile phase.

Visible semiconductor laser fluorometry

Abstract: Un laser oscillant a 670 nm est utilise comme source d'excitation en spectrometrie de fluorescence. Une limite de detection de 4×10 −12 M a ete obtenue pour la rhodamine 800, legerement meilleure que celle obtenue avec un laser semiconducteur proche infrarouge

Pulmonary glucose transport in the fetal sheep.

Abstract: 1. In the chronically catheterized sheep fetus between 122 and 143 days gestation the concentration of D-glucose in lung liquid was very low (usually less than 0.01 mM, the lower limit of detection of the analytical method) whereas the mean plasma concentration was 0.19 mM (S.E.M. 0.4, n = 13). 2. When the lung liquid concentration of D-glucose was raised to 1.67-5.00 mM, rapid uptake was observed until the concentration had fallen to its preceding low level. The uptake showed saturation kinetics (Vmax = 2.29-8.78 mumol/min, increasing with gestation; mean Km = 0.14 +/- 0.02 mM, n = 11, no change with gestation). This active uptake of glucose was blocked by phloridzin (10(-4) M). It was associated with a decrease in lung liquid secretion rate from which a change in net sodium flux could be inferred of an order suggesting one-to-one glucose-sodium co-transport. 3. Radiolabelled 3-O-methyl-D-glucose (3-O-meG) - a monosaccharide which is transported but not metabolized - was taken up rapidly from lung liquid and this rapid uptake was inhibited by D-glucose with 50% inhibition at 0.35 mM (+/- 0.08, n = 9). It was also inhibited by phloridzin (10(-4) M). 4. Radiolabelled 2-deoxy-D-glucose - a monosaccharide which is not a substrate for sodium-coupled transport - was taken up only very slowly from lung liquid; the rate of uptake was appropriate for passive diffusional transport and it was unaffected by the addition of D-glucose or phloridzin to lung liquid. 5. Intravenous infusion of D-glucose caused no detectable increase in the concentration of glucose in lung liquid unless phloridzin was added, when a slow increase was observed. 6. In two experiments with active transport blocked by phloridzin in lung liquid (10(-4) M), the rate of entry of labelled 3-O-meG from plasma to lung liquid was measured during intravenous infusion of this tracer for 29 and 23 h. The rates of entry were similar to the rate of efflux of the tracer from lung liquid when uptake was blocked by phloridzin or D-glucose, and similar to the rate expected for a metabolically inert tracer (i.e. it was some two orders of magnitude less than efflux from lung liquid in the absence of an inhibitor).(ABSTRACT TRUNCATED AT 400 WORDS)