Development of a colorimetric microfluidic pH sensor for autonomous seawater measurements

High quality carbonate chemistry measurements are required in order to fully understand the dynamics of the oceanic carbonate system. Seawater pH data with good spatial and temporal coverage are particularly critical to apprehend ocean acidification phenomena and their consequences. There is a growing need for autonomous in situ instruments that measure pH on remote platforms. Our aim is to develop an accurate and precise autonomous in situ pH sensor for long term deployment on remote platforms. The widely used spectrophotometric pH technique is capable of the required high-quality measurements. We report a key step towards the miniaturization of a colorimetric pH sensor with the successful implementation of a simple microfluidic design with low reagent consumption. The system is particularly adapted to shipboard deployment: high quality data was obtained over a period of more than a month during a shipboard deployment in northwest European shelf waters, and less than 30 mL of indicator was consumed. The system featured a short term precision of 0.001 pH (n = 20) and an accuracy within the range of a certified Tris buffer (0.004 pH). The quality of the pH system measurements have been checked using various approaches: measurements of certified Tris buffer, measurement of certified seawater for DIC and TA, comparison of measured pH against calculated pH from pCO₂, DIC and TA during the cruise in northwest European shelf waters. All showed that our measurements were of high quality. The measurements were made close to in situ temperature (+0.2 ?C) in a sampling chamber which had a continuous flow of the ship’s underway seawater supply. The optical set up was robust and relatively small due to the use of an USB mini-spectrometer, a custom made polymeric flow cell and an LED light source. The use of a three wavelength LED with detection that integrated power across the whole of each LED output spectrum indicated that low wavelength resolution detectors can be used instead of the current USB mini spectrophotometer. Artefacts due to the polychromatic light source and inhomogeneity in the absorption cell are shown to have a negligible impact on the data quality. The next step in the miniaturization of the sensor will be the incorporation of a photodiode as detector to replace the spectrophotometer.     

A method for quick, low-cost automated confluency measurements

A culture's confluency is a fundamental measure in the field of biology, and routine quantification of confluence in cell culture protocols, biological assays and tissue engineering work is important. However, current techniques for obtaining confluency are either subjective, destructive, not simple enough, or time-consuming. We developed an image processing method for automated confluency measurement from a single microscope image without any chemical staining. To demonstrate utility we monitored the confluency of three cell types: NIH3T3 fibroblasts, C2C12 myoblasts, and 3T3L1 pre-adipocytes for 5 days, twice a day. The captured micrographs had different and uneven illumination, the cell types varied in cell-to-background contrast, and the confluency ranged between 10% and 100%. Despite these variable conditions, our method was shown to be practical, economic, and easy to implement, providing quantitative confluency measurements over time in each culture case. The method is hence suitable for routine automatic determination of confluency to standardize handling of cells, achieve reproducibility across trials, and improve accuracy in experimental outcome measures.     

A sensitive spectrophotometric method for lead determination by flow injection analysis with on-line preconcentration

A new flow injection (FI) system for the determination of Pb(II) at trace level with a preconcentration step and spectrophotometric detection is proposed. It is based on preconcentration of lead ions on chitosan and dithizone-lead complex formation in aqueous medium (pH 9). The chemicals and FIA variables influencing the performance of the system were optimized and applied to the determination of lead in natural, well, and drinking water samples. It is a simple, highly sensitive, and low cost alternative methodology. The method provided a linear rage between 25 and 250 μg l⁻¹, a detection limit of 5.0 ng ml⁻¹ and a sample throughput of 15 h⁻¹. The obtained results of spiked samples are in good agreement between the proposed method and ICP-AES.     

A clean analytical method for the spectrophotometric determination of formetanate incorporating an on-line microwave assisted hydrolysis step

A fast and completely automated procedure is proposed for the spectrophotometric determination of formetanate in waters by means of its reaction with p-aminophenol (PAP). The method involves the on-line alkaline hydrolysis of formetanate to m-aminophenol (MAP) and its reaction, in the presence of KIO₄ as oxidant agent, with the quinoneimine form of PAP, to form a blue indophenol dye which absorbs at 576 nm. The on-line hydrolysis can be carried out in a 6 m reaction coil located inside the cavity of a domestic microwave oven operated at 650 W, or in a 4 m reaction coil located inside the cavity of a Microdigest 301 microwave system operated at 60 W and allows us, in both cases, a complete hydrolysis of formetanate thus improving the complete automation of the analytical procedure. After the measurement step, the analytical waste is merged with a TiO₂ slurry and then detoxified by on-line UV-irradiation.     

A rapid method for the spectrophotometric determination of palladium(II) and osmium(VIII)

Propionyl promazine phosphate is proposed as a new reagent for the rapid spectrophotometric determination of microgram amounts of Pd(II) and Os(VII). PPP instantaneously forms an orange-red 1:1 complex with Pd(II) in sodium acetate-hydrochloric acid buffer of pH 0.8 to 4.0 at room temperature. The reagent also forms an orange-red radical cation with Os(VIII) in 0.5 to 2.0 M hydrochloric acid. The Pd-PPP complex exhibits an absorption maximum at 490–500 nm with molar absorptivity of 7.1 × 10³ liter mol^?1 cm^?1. The Os-PPP radical cation has an absorption maximum at 505–515 nm with molar absorptivity of 2.21 × 10⁴ liters mol^?1 cm^?1. The Sandell sensitivity is 0.022 μg/cm² (Pd) and 0.008 μg/ cm² (Os). Beer's law is valid over the concentration range 0.2 to 21 ppm (Pd) and 0.2 to 4.2 ppm (Os). The proposed method offers the advantages of simplicity, rapidity, and without the need for heating or extraction. The reagent is used for the determination of Pd in the synthetic mixtures corresponding to Pd alloys used in jewelery and Os in osmiridium alloy.     

A sensitive and selective spectrophotometric method for the determination of chromium (III)

Microchimica Acta - Chromium (III) forms a golden yellow colour with tropolone on heating on a boiling water-bath, and is extractable into chloroform. The complex absorbs maximum at 400 nm. The...     

Kinetic spectrophotometric method for gold(III) determination

The kinetic spectrophotometric method for Au(III) determination was developed and validated. It was based on the catalytic effect of gold on the oxidation of methylene blue B (3,7di-(dimethyl amino)-10-dehydro-phenotiazin chloride) by ammonium peroxo-disulfate in citric buffer solution. There was the linearity of the calibration curve in the concentration range from 0.09 to 2.90 μg ml⁻¹ Au(III). The relative standard deviation was 2.50% and correlation coefficient of 0.9999. The limit of detection was determined as signal to noise ratio (3:1) and it was 5.5 ng ml⁻¹. The limit of quantification, based on signal to noise ratio 10:1 was 19.25 ng ml⁻¹. The selectivity was tested on the basis of influence of known amounts of different ions in the reaction mixture, upon the reaction rate. Kinetic and thermodynamic parameters were reported for both catalytic and non-catalytic reactions. The method was verified by Au(III) determination in anti-rheumatic drug “Tauredon” and in human urine samples, using ICP-AES as the comparative method. As the method is accurate, reliable, quick and simple it could be useful for clinical and toxicological practice.     

A long pathlength spectrophotometric pCO(2) sensor using a gas-permeable liquid-core waveguide

The first long pathlength fiber optic-based sensor system to measure pCO(2) in natural waters and the atmosphere is described. The sensor is based on a liquid-core (an indicator-HCO(3)(-)/CO(3)(2-) buffer solution) waveguide made of a low refractive index amorphous fluoropolymer tubing, the wall of which serves as a gas-permeable membrane to sense pCO(2) changes. The system detects the indicator absorbance changes when the liquid-core reaches CO(2) equilibrium with the surrounding sample. Theoretical calculations demonstrate that due to indicator buffer effects, increasing the optical pathlength is a more efficient way to obtain higher sensitivity than increasing the indicator concentration. Using an 18-cm cell with low indicator concentrations (10 muM), this system achieves a precision and an accuracy of +/-2-3 muatm in the pCO(2) range of 200-500 muatm. The sensor also features a response time (99%) of only 2 min for low-level (<1000 muatm) pCO(2) measurements as a result of high CO(2) permeability of the amorphous fluoropolymer membrane. Field tests indicate that this new sensor is capable of handling both atmospheric and aquatic pCO(2) monitoring.     

Rapid method for the preparation of a robust optical pH sensor

A simple and rapid method for the preparation of a fluorescence-based optical pH sensor is described. The sensor is based on excitation ratiometric detection of a methacryloyl-modified analog of the well-known fluorescent pH indicator dye, 8-hydroxy-1,3,6-pyrene trisulfonic acid (HPTS). The modified dye, 6-methacryloyl-8-hydroxy-1,3-pyrene disulfonic acid (MA-HPDS), is similar in structure and function to HPTS. However, unlike HPTS, the presence of the methacrylate moiety allows MA-HPDS to participate as a comonomer in a free radical polymerization reaction. Covalent immobilization by this method is simple, as the preparation of the modified dye is accomplished in a single reaction step and its subsequent reaction with a comonomer results in simultaneous immobilization and purification. Sensors were prepared by copolymerization of the MA-HPDS with poly(ethylene glycol) diacrylate. Minimal leaching of the immobilized dye was observed from the HPDS-PEG matrix. The copolymer of HPDS and PEG-DA is fully autoclavable. The sensor is useful over the pH range of 6-9, with excellent reproducibility. Ionic strength effects on the apparent pKa of the immobilized dye are small and predictable.     

A rapid spectrophotometric method for the determination of transparent exopolymer particles (TEP) in freshwater

A simple and rapid spectrophotometric method is proposed for the determination of transparent exopolymer particles (TEP) in freshwater samples. In this method, TEP reacts with excess of alcian blue solution yielding a low solubility dye-TEP complex. After centrifugation, the concentration of the remaining dye in the supernatant was determined at 602 nm and its concentration was related to the concentration of TEP in freshwater. The effect of alcian blue concentration from 1.5×10⁻³ to 9.0×10⁻³% (m/v), solution pH from 2.5 to 6.9 and stirring time from 20 to 120 s on the analytical curve was investigated. Under the optimum conditions established, such as alcian blue concentration of 3.0×10⁻³% (m/v); pH of 4.0 (0.2 mol l⁻¹ acetate buffer solution) and stirring time of 1 min, the analytical curve was linear from 0.50 to 10 μg ml⁻¹ (A=0.34−0.037[GX]; r²=0.9999; where A is the absorbance and [GX] the gum xanthan concentration in μg ml⁻¹) with a detection limit of 0.10 μg ml⁻¹. The recovery of TEP (as gum xanthan) for two samples ranged from 95.3 to 108 and the relative standard deviations (R.S.D.s) were lower than 0.8% for gum xanthan solutions at concentrations of 1.0 and 1.5 μg ml⁻¹ (n=8). The results obtained for TEP in freshwater samples using the proposed spectrophotometric method and those obtained using a literature method are in agreement at the 95% confidence level and within an acceptable range of error.     

Single crystal HPGe (80%) versus BGO shielded CLOVER detector for high precision decay rate measurements: a comparative study

In this study, various detector configurations have been investigated in order to explore the optimal condition for decay rate measurements of radioactive samples using gamma spectroscopy technique. A limitation of detecting low energy gamma rays from decaying radioactive nuclei, is the Compton background which can be significantly reduced by rejecting Compton scattered events through active Bismuth germanate (BGO) shielding. On the other hand, for a CLOVER detector without BGO shielding, one can place the radioactive samples very close to the detector for enhancing geometrical efficiency. A single crystal High Purity Germanium (HPGe) detector can also be used for decay rate measurements. In order to measure the decay rate of nuclei decaying via gamma emission with reasonable intensity, optimal close geometry options have been investigated for various HPGe detector configurations.

     

A fully automated on-line preconcentration and liquid chromatography-tandem mass spectrometry method for the analysis of anti-infectives in wastewaters

We developed and validated a novel on-line preconcentration liquid chromatography-tandem mass spectrometry method for the determination of anti-infectives in wastewaters. The presented method preconcentrates 1 mL of sample in a load column using a switching-valve technique. The method was optimized with respect to sample load flow rate, volume of the load column wash and organic solvent content of the load column wash. The sample is cleaned using a 30% organic solvent washing step and then gradually eluted to an analytical column for separation. To compensate for matrix effects, quantitation was performed using standard additions. Confirmation of the presence of the detected compounds was done using a second selective reaction monitoring transition. Method intra-day precision was less than 9% and inter-day precision %R.S.D. varied between 2.5 and 23%. Limits of detection for the selected anti-infective compounds ranged from 13 to 61 ng L⁻¹. All the target anti-infectives were found in the city of Montréal WWTP effluent in concentrations ranging from 71 to 289 ng L⁻¹. This automated method eases the rapid quantitation of those trace contaminants using small sample volumes.     

A spectrophotometric method for the determination of nickel

A photometric method for the determination of nickel using versene is described. Up to 20 mg of nickel can be determined with a maximum deviation of ± 0.10 mg. The effect of interfering elements, concentrations, accuracy and limitations of the method are discussed.     

A spectrophotometric method for the determination of nitrite

Nitrite reacts with dichromate quantitatively under suitable conditions of temperature and acid concentration. A linear relationship was found to exist between nitrite concentration and the absorbance at 580 nm of the chromium (III) species produced. This was used to determine the nitrite. The influence of a number of ions on the determination of nitrite was investigated; up to 100-fold excess nitrate has no influence on the determination of nitrite.     

A new method for the spectrophotometric determination of pertechnetate with tris(1,10-phenanthroline)iron(II) ion

A new spectrophotometric determination of technetium has been developed by means of the solvent extraction of tris(1,10-phenanthroline)iron(II) ([Fe(phen)₃ ²⁺]) with pertechnetate into nitrobenzene. The concentration of technetium can be determined by measuring the characteristic absorbance at 516 nm (=11,700M^–1·cm^–1) in the organic phase. An important feature of the proposed method is that the concentration of pertechnetate can be determined without complicated processes such as the reduction of pertechnetate and the subsequent formation of a colored chelate.     

Simple solid-phase spectrophotometric method for free iron(III) determination

A simple and rapid solid-phase spectrophotometric procedure to determine free Fe(III) in environmental and biological samples is proposed. In particular, a deferoxamine (DFO) self assembled monolayer on mesoporous silica (DFO SAMMS) is developed and here applied as a sensor for iron(III). The solid product became brownish when put in contact with iron(III) solutions; so an immediate application as colorimetric sensor is considered. In order to optimize the DFO SAMMS synthesis and to obtain the best product for iron(III) sensing, a factorial experimental design is performed selecting the maximum absorption at 425 nm as response. The robustness of the spectrophotometric method is also proved.     

Kinetic spectrophotometric method for o-phenylenediamine in the presence of gold(III)

From the color developing reactions of o-phenylenediamine oxidizing agent and gold(III), the kinetic reactions between both of them in aquaeous solutions were studied using spectrophotometric and differential method. Light absorbances in the visible spectral range are measured as a function of mole fractions of phenylenediamine at a fixed gold(III) concentration and as a function of mole fraction of gold(III) at a fixed o-phenylenediamine concentration at periodic time internal. In the differential method, which was suggested by van't Hoff, one deals with the actual rates of reactions as determined by measuring the slopes of absorbance-time curves. Optimum condition of the reaction were established as pH 6 at lambda=466 nm and room temperature. When the oxidation of o-phenylenediamine by gold(III) was investigated, it was observed that the following rate formula and rate constant were found: v=k[Au+3]1/2[o-phenylenediamine]1/2, k=2.33x10(-2) s-1.     

自动调节光谱响应的高精度多组分分析研究: 人工神经网络分光光度法

本文论证了人工神经网络(ANN)对多组分光度分析的应用。探讨了人工神经网络算法及其影响因素。用此法做五组分体系(维生素B1, B2, B6, C和菸酰胺)紫外光度分析, 并与CPA方法作比较。该方法的特点在于可由调节不同光谱范围的线性及非线性响应的计算过程来自动校正。研究结果证实了该方法的优越性。