Response of Surface‐Plasmon Resonance Sensor Based on Gold Surfaces Modified by Self‐Assembled Monolayer to Nonionic Surfactants

Abstract

A chemical sensor for the determination of nonionic surfactants (NISs) based on surface‐plasmon resonance (SPR) phenomenon was fabricated using a gold thin film, the surface of which was modified with a self‐assembled monolayer (SAM). Stearylmercaptan was used for the SAM constituent. The magnitude of the angle shift of SPR sensor to NISs increases in this order: Triton X‐100<heptaethyleneglycol dodecyl ether (HEEG)<hexaethyleneglycol dodecyl ether (HEG)<pentaethyleneglycol dodecyl ether (PEG). This order of magnitude of angle shift is in accord with the sequence of the hydrophobicity of the NISs. The linear relationships between Δθ (the change in the resonance angle relative to the baseline value) and the concentration of NISs were obtained in the concentration range from 2×10^?6 M to 1×10^?5 M. The coexistence of common inorganic cations and anions at 100 times excess to the Triton X‐100 gives only a positive error less than ca. +5%. The coexistence of an anionic surfactant (sodium dodecylbenzene sulfonate) at 10 times excess to the Triton X‐100 gives a very serious positive error of ca. +320%. This serious positive error was completely eliminated by using the flow system with an anion‐exchange resin column.     

A rapid and precise heterometric method for the determination of traces of phosphoric or arsenic acid with nitron and molybdate

The precipitation of phosphomolybdate or arsenomolybdate with nitron was studied by heterometry at various acidities. A rapid and precise heterometric method is presented for the determination of 0.03–0.08 mg of phosphorus (or 0.06–0.16 mg of arsenic). Foreign salts can be tolerated often in 100–200-fold molar amounts. No interference is caused by Ca, Ba, Mg, Zn, Cr³⁺, Fe, Mn, Co, Ni, Al, U(VI), Cd, Cu, Pb, Hg²⁺, Ag, Zr or Th. Iodide, silicic acid, tartrate or pyrophosphate can also be tolerated.The titration time is 10–15 min and the error is usually less than 1%.     

Non-linear Compensated Dwell Time for Efficient Fused Silica Surface Figuring Using Inductively Coupled Plasma

Atmospheric plasma etching has been increasingly applied in the fabrication of optical elements for high efficiency and near-zero damage to optical surfaces. However, the non-linearity of material removal rate is inevitable because of the thermal effect of inductively coupled plasma (ICP) etching for fused silica. To apply ICP to figure fused silica surface, the time-varying non-linearity between material removal rate and dwell time is analyzed. An experimental model of removal function is established considering the time-varying non-linearity. According to this model, an algorithm based on nested pulsed iterative method is proposed for calculating and compensating this time-varying non-linearity by varying the dwell time. Simulation results show that this algorithm can calculate and adjust the dwell time accurately and remove surface errors with rapid convergence. Surface figuring experiments were set up on the fused silica planar work-pieces with a size of 100 mm (width) × 100 mm (length) × 10 mm (thickness). With the compensated dwell time, the surface error converges rapidly from 4.556 λ PV (peak-to-valley) to 0.839 λ PV within 13.2 min in one iterative figuring. The power spectral density analysis indicates that the spatial frequency errors between 0.01 and 0.04 mm^?1 are smoothed efficiently, and the spatial frequency errors between 0.04 and 0.972 mm^?1 are also corrected. Experimental results demonstrate that the ICP surface figuring can achieve high convergence for surface error reduction using the compensated dwell time. Therefore, the ICP surface figuring can greatly improve surface quality and machining efficiency for fused silica optical elements.     

An improved nephelometric method for the determination of small amounts of thiosulfate in aqueous samples

The procedure is based on decomposition of thiosulfate, with formation of sulfur, in the presence of 0.5 mol l^?1 nitric acid. Thiosulfate is determined in the range 15–100 mg l^?1, with a relative standard deviation of 5.4% and a mean relative error of 3.2%. These data are of the same order of magnitude as those obtained for the earlier silver/1,10-phenanthroline method. The present method has the advantage of being almost completely free from interferences; the only interference observed (sulfide) is easily eliminated.     

Direct flame-photometric determination of calcium in soil and plant extracts,water and serum with special reference to sodium,potassium and phosphate interference

An investigation of the possibilities for the direct determination of calcium with a single-cell filter flame photometer, without preliminary separation as oxalate, led to the following conclusions:Calibration curves for 100 p.p.m. of calcium are rectilinear.Sodium causes an appreciable positive error.The error due to potassium interference is relatively much smaller than that due to sodium. Up to a certain concentration it is positive and increases with the concentration, then the emission seems to be gradually depressed and the error finally becomes negative.Phosphates cause a very significant negative error, which tends to be asymptotic. The “radiation buffer” method of correction is not practical here because the max. error is too high (—92.5%).Except for extreme cases, calcium can be determined by direct spraying, without preliminary separation as oxalate: (a) in drinking and irrigation water, correction being necessary only for sodium interference, (b) in soil extracts, correcting only for phosphate effects, (c) in normal blood sera, without clinically significant corrections at 1+3 dilution.Owing to the large variations in the contents of Na, K and PO₄^-3 in plants, calcium cannot be determined in plant-ash extracts without preliminary separation as oxalate. This applies also to abnormal sera, although there the variations in Na and PO₄^-3 content are not so large.     

Determination of silicon in aluminium by 14 MeV neutron activation analysis

A method has been developed for determining silicon in aluminium by fast neutron activation. It is based on the separation of two gamma lines by a Ge(Li) detector: the 1.73 MeV line from the product of²⁷Al(n, α)²⁴Na and the 1.78 MeV line from the²⁸Si(n, p)²⁸Al reaction. In the case of aluminium-silicon alloys 100 μg silicon can be determined, with an error of 10% in an aluminium sample of 1 g. This work was supported in part by the International Atomic Energy Agency.     

Near-infrared diffuse reflectance spectroscopy and neural networks for measuring nutritional parameters in chocolate samples

A rapid and non-destructive method has been developed for the characterization of chocolate samples based on diffuse reflectance near-infrared Fourier transform spectroscopy (DRIFTS) and artificial neural networks (ANNs). This methodology provides a potentially useful alternative to time-consuming chemical methods of analysis. To assess its utility, 36 chocolate samples purchased from the Spanish market were analyzed for the determination of the main nutritional parameters like carbohydrates, fat, proteins, energetic value and cocoa content.Direct triplicate measurements of each sample were carried out by DRIFTS. Cluster hierarchical analysis was used for selecting calibration and validation data sets, resulting in a calibration set comprised of 19 samples and a validation data set of 17 samples. As it is common the presence of non-linear effect in reflectance spectroscopy, ANNs was chosen for data pretreatment. The root-mean-square error of prediction (RMSEP) values obtained for carbohydrates, fat, energetic value and cocoa were 1.0% (w/w), 1.0% (w/w), 50 kJ (100 g)⁻¹ and 1.4%, respectively. The mean difference (d_x-y) and standard deviation of mean differences (s_x-y) of the carbohydrates, fat, proteins content, energetic value and cocoa content were 0.9 and 2.4% (w/w), 0.2 and 1.0% (w/w), 9.1 and 50 kJ (100 g)⁻¹, and −0.5 and 1.4%, respectively. The maximum relative error for the prediction (QC) of any of these parameters for a new sample did not exceed 5.2%.     

Preconcentration and separation of <Superscript>99</Superscript>Tc in groundwater by using TEVA resin

An effort has been made to optimize the counting time for low-level measurement of naturally occurring radioactive material (NORM) by considering the standard deviation between the activity values of different photopeaks and counting error. It is observed that at lower counting time, relative standard deviation (RSD) varies randomly, but attains a gradual trend with increasing time and also comes closure to the counting error. Therefore minimum counting time for low-level NORM measurement of ²³⁸U and ²³²Th would be the time required to stabilize the RSD values.     

Representation of cupric chloride solutions with Pitzer's model: Application to the extraction equilibrium of copper (II) by LIX 65N

A model combining formation of cupric chlorocomplexes and deviations to ideality in electrolyte solutions is proposed for the representation of ther-modynamic properties of concentrated cupric chloride solutions at 25°C in the presence of other ions (Na⁺, Li⁺, Mg²⁺, H⁺ or SO ₄ ^2– ). A set of equilibrium constants for the formation of cupric chlorocomplexes is obtained. The equation for the calculation of activity coefficients, using a modified Pitzer expression, yields not only the composition of CuCl₂ solutions at various experimental conditions, but also the activities for each species. The model represents, with a mean accuracy of 1.2%, a large number of spectrophotometric, as well as osmotic data. It was applied to the extraction of Copper (II) from chloride aqueous solutions by LIX 65N in ESCAID 100 solvent. In this case, the accuracy of the representation (4%) is consistent with the estimated experimental error.     

An atomic absorption spectrometric method for the determination of non-ionic surfactants

A method is described for the determination of non-ionic surfactants in the concentration range 0.05–2 mg l^-1.Surfactant molecules are extracted into 1,2-dichlorobenzene as a neutral adduct with potassium tetrathiocyanatozincate(II) and the determination is completed by atomic absorption spectrometry. With a 150-ml water sample, the limit of detection is 0.03 mg l^-1(as Triton X-100).The method requires a single phase separation step, is applicable, without modification, to fresh, estuarine and sea-water samples and is relatively free from interference by anionic surfactants; the presence of up to 5 mg l^-1 of anionic surfactant (as LAS) introduces an error of no more than 0.07 mg l^-1 (as Triton X-100) in the apparent non-ionic surfactant concentration.     

Polymerization processes at conditions of moderately short kinetic chains by calorimetry

A method has been developed for the determination of the heat of the acts of chain growth q_g and of the summary heats of the acts of chain initiation and termination q^** for the radical polymerization of vinyl monomers at the conditions of moderately short kinetic chains, when the length of the kinetic chain v < 100, but the degree of polymerization is ¯P > 20. The analysis of the experimental data, obtained by investigating the kinetics of polymerization of vinyl monomers in solution by calorimetry has led to the conclusion, that at v > 100 an approximation of the long material chains can be used (when the contribution of q^** is negligibly small) with a permissible experimental error; however, in the region of moderately short chains a correction for q^** must be introduced, in order to obtain the correct kinetics of the process.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 6, pp. 695–701, November–December, 1988.     

Isotope beating effects in the analysis of polymer distributions by Fourier transform mass spectrometry

For Fourier transform mass spectrometry analysis of high mass ions, the signals from closely spaced isotope peaks undergo periodic destructive interference, producing a beat pattern in the time-domain signal. The mass spectra that are obtained by sampling transient signals for less than two beat periods exhibit an error in the relative abundances that are measured. This effect is shown to cause significant errors in the measurement of the relative abundances of the components of polymer distributions, leading to errors in the derived average molecular weights for such samples. Computer simulations show that isotope beating causes this error to increase as the duration of an acquired transient becomes short compared to the beating period. This error becomes insignificant when the transient is acquired for longer than twice the beat period. Experimental data are presented for polymers in which an oligomeric distribution of monoisotopic peaks is produced by stored waveform inverse Fourier transform ejection of all ¹³C-containing isotope peaks. The data show that the isotope beating-induced abundance errors are eliminated when there are no isotope peaks present.     

Size effect and mechanochemical contraction of the Si(100) specimens

Variation of thickness of specimens of single crystalline silicon Si(100) prepared by scribing of the water of 100 mm diameter to parts of smaller size under atmospheric conditions is studied. It is shown that the thickness of specimens having small surface (∼1 cm²) decreases after scribing by 0.8–1.0% (with the error of measurements < 0.3%). The observed decrease in the thickness is explained by the effect of sorption of vapors of atmospheric moisture in micropores with the decrease in the external surface of specimens of Si(100) (the sorbostriction phenomenon).     

Adsorption of Zn2+ from Synthetic Wastewater Using Dried Watermelon Rind (D-WMR): An Overview of Nonlinear and Linear Regression and Error Analysis

Sustainable wastewater treatment is one of the biggest issues of the 21st century. Metals such as Zn²⁺ have been released into the environment due to rapid industrial development. In this study, dried watermelon rind (D-WMR) is used as a low-cost adsorption material to assess natural adsorbents’ ability to remove Zn²⁺ from synthetic wastewater. D-WMR was characterized using scanning electron microscope (SEM) and X-ray fluorescence (XRF). According to the results of the analysis, the D-WMR has two colours, white and black, and a significant concentration of mesoporous silica (83.70%). Moreover, after three hours of contact time in a synthetic solution with 400 mg/L Zn²⁺ concentration at pH 8 and 30 to 40 °C, the highest adsorption capacity of Zn²⁺ onto 1.5 g D-WMR adsorbent dose with 150 μm particle size was 25 mg/g. The experimental equilibrium data of Zn²⁺ onto D-WMR was utilized to compare nonlinear and linear isotherm and kinetics models for parameter determination. The best models for fitting equilibrium data were nonlinear Langmuir and pseudo-second models with lower error functions. Consequently, the potential use of D-WMR as a natural adsorbent for Zn²⁺ removal was highlighted, and error analysis indicated that nonlinear models best explain the adsorption data.     

Investigation of accuracy and precision for determination of the short-lived nuclides by INAA and the Mössbauer-effect

Different reference materials of environmental and geological origin, such as NBS 1633a (Coal Fly Ash, CFA), NBS 1645 (River Sediment, RS), GXR-2, and IAEA Soil-5, were investigated by short time activation analysis. The samples were analyzed in 5 replicates each between 100 to 150 mg, at neutron flux of 1.3 E 12 cm^–2 s^–1, using a high rate — high resolution gamma spectroscopy with a Loss Free Counting (LFC) System to correct the dead time and pile up to 500,000 cps. The results of the measurements indicate that the precision in determination of²⁸Al,^46mSc, and⁵²V is between 1 to 6%. Different evaluation programs (i.e. ALCHEM, AKTAN, and ND-PEAK) were used to calculate the peak areas. The results indicate that, at lower counts, the statistical error of peak area calculation becomes more significant. Finally, Mössbauer spectroscopy was used to investigate the main Fe compounds present in some reference materials.     

Field testing of collection and measurement of radioxenon for the Comprehensive Test Ban Treaty

Pacific Northwest National Laboratory, with guidance and support from the U.S. Department of Energy's NN-20 Comprehensive Test Ban Treaty (CTBT) Research and Development program, has developed and demonstrated a fully automatic sampler-analyzer (ARSA) for the collection and quantitative measurement of the four xenon radionuclides,^131mXe (11.9 d),^133mXe (2.19 d),¹³³Xe (5.24 d), and¹³⁵Xe (9.10 h), in the atmosphere. These radionuclides are important signatures in monitoring for compliance to a CTBT, and may have applications in stack monitoring and other areas where xenon radionuclides are present. The activity ratios between certain of these radionuclides permit discrimination between radioxenon originating from nuclear detonations and that from nuclear reactor operations, nuclear fuel reprocessing, or from medical isotope production and usage. With the ARSA system, xenon is continuously and automatically separated from the atmosphere at flow rates of about 100 lpm by sorption-bed techniques. Samples collected in 8 hours are automatically analyzed by electron-photon coincidence spectrometry to provide detection sensitivities as low as 100 μBq/m³ of air. This sensitivity is about 10-fold better than achieved with reported laboratory-based procedures¹ for the short time collection intervals of interest. Gamma-ray energy spectra and gas analysis data are automatically collected.     

Bipolar pulse conductometric monitoring of ion-selective electrodes: Part 1. Method development with a calcium-selective electrode and elucidation of the basic principles involved

The potential generated by a plastic-membrane calcium ion-selective electrode (i.s.e.) is shown to be indirectly measurable by a non-zero current method based on bipolar pulse conductance. Linear current—voltage curves are obtained using 0–5-V pulses; the current axis intercept is related to the i.s.e. potential. A simple electrical contact (e.g., platinum or stainless steel) can be used instead of a poised reference electrode as the counter electrode in this two-electrode system. Long-term exposure of the i.s.e. to calcium solutions causes an upward drift in the measured current. This drift is minimized by avoiding long exposure times to solution, rinsing the electrode between measurements, and constructing current—voltage curves for determination of the current axis intercepts. Voltage pulses lasting 100 μs are optimum for this method. Shorter pulses are subject to error from capacitive charging currents, and longer pulses yield poorer precision, and degrade the electrode through faradaic reactions. The measured signal is dependent upon Ca²⁺ concentration (rather than activity), making ionic strength adjustment unnecessary. The concentration dependence is induced by application of voltage pulses greater than ~ 15 mV in amplitude. Selectivities of the potentiometric and conductometric methods are shown to be comparable for a variety of interfering monovalent and divalent cations. The conductometric method yields a fast i.s.e. response because of induced migration of Ca²⁺ into the membrane. Response time decreases as the pulse height increases. Pulses greater than 2 V in magnitude yield response times limited by the solution mixing time rather than by the electrode.     

An Inexpensive Biosensor for Uric Acid Determination in Human Serum by Flow‐Injection Analysis

An inexpensive and easy to construct miniaturized biosensor is described for the determination of uric acid in biological fluids. The amperometric biosensor was prepared by using a carbon paste electrode prepared with uricase from Arthrobacter globiforms and tetracyanoquinodimethane as electron transfer mediator. When incorporated into a flow‐injection system it was enabled to perform 50 measurements/h of uric acid in the analytical range of 1–100 μmol dm^?3 with a relative standard deviation of 0.20% (n=14). The system was applied to human serum samples analysis providing good data correlation with those obtained by the reference spectrophotometric method. A linear relationship AM (μmol dm^?3)=1.02 (±0.05) SP (μmol dm^?3) ?0.12 (±0.13) was obtained evidencing the absence of significant error. The constructed biosensor was successfully used for at least four months (250 assays) with only a 13% of decrease in the enzymatic activity.