Development of a rapid procedure for the measurement of uranium in drinking water by PERALS® spectrometry

A new method has been developed for the measurement of U in water samples by selective and quantitative extraction from DTPA solution into an extractive scintillator containing HDEHP and alpha-counting by PERALS^® spectrometry. Because this method offers several advantages over the current EPA and ASTM standard test methods for U in drinking water, including speed, simplicity and isotopic information, it has been proposed as a new ASTM standard test method. Sample preparation requires from 1–4 h. Less than 0.5% of Am, Pu, Po, Ra and Th were found to extract under the prescribed conditions. Typical backgrounds are ≤0.01 cpm. A comparison of this method with EPA standard method 908.0 and the results of two interlaboratory tests of this method are reported.     

Paper test strip for silver ions detection in drinking water samples based on combined fluorometric and colorimetric methods

In this study, a portable silver ion (Ag⁺) sensor was fabricated based on a dual signal output system using black phosphorus quantum dots (BPQDs) as probes. It is the first work for Ag⁺ detection using paper test strip based on BPQDs. The color change of BPQDs paper sensor for the determination of Ag⁺ was easily identified by naked eye. BPQDs were synthesized from bulk black phosphorus (BP) by mechanical exfoliation combined with a solvothermal method. BPQDs exhibited blue fluorescence with a quantum yield of 8.82 %. The fluorescence of BPQDs can be quenched by Ag⁺, and the absorbance of BPQDs is increased with increasing Ag⁺ concentration. The mechanism of the interaction between BPQDs and Ag⁺ involving fluorescence quenching and bonding was investigated by experimental and computational methods. The detection limit of Ag⁺ was 1.56 μg/mL and 0.19 μg/mL using fluorometry and colorimetry methods, respectively. A portable visual sensor based on paper test strip was constructed for Ag⁺ detection using the colorimetric approach. The strategy was employed to determine Ag⁺ successfully in drinking water samples. Therefore, the proposed portable Ag⁺ sensor can be potentially utilized for the lab-free analysis of drinking water and even dietary samples.     

Development of a drinking water regulation for perchlorate in California

Perchlorate is an environmental contaminant often associated with military installations and rocket propellant manufacture and testing facilities across the U.S. Highly water soluble, perchlorate has been found by federal and state agencies at almost 400 sites within the U.S. in groundwater, surface water, soil or public drinking water. There is no federal drinking water standard for perchlorate, but it is on the drinking water Contaminant Candidate List, and falls under the Unregulated Contaminant Monitoring Rule (UCMR) for which monitoring is required. The recent National Academy of Science (NAS) report on the potential health effects of perchlorate recommended a perchlorate reference dose of 0.0007 mg/kg of body weight which would be equivalent to a drinking water concentration of 24.5 μg/L.In California, approximately 395 wells in 96 water systems have been shown to contain perchlorate, and about 90% of these are located in Southern California. Water taken from the Colorado River, a major surface water supply to Southern California, has had reported detections of perchlorate ranging from non-detect to 9 μg/L. California has established a Public Health Goal (PHG) of 6 μg/L for perchlorate, and a proposed drinking water regulation is imminent. This review details the regulatory process involved with particular attention given to the occurrence of perchlorate in California drinking water sources and analytical methodology utilized.     

Characterisation of a transparent optical test strip for quantification of water hardness

An optical and reversible test strip that uses an ion-exchange mechanism which responds equally to calcium and magnesium and makes it possible to determine water hardness is described. The transparent test strip, made of a polyester sheet, has a circular polymeric film of plasticised poly(vinyl chloride) (PVC) that contains all of the reagents necessary to produce an equal response to calcium and magnesium, namely, a cation-selective neutral ionophore, such as 4,13-[bis(N-adamantylcarbamoyl)acetyl]-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane, a chromoionophore, such as lipophilised Nile Blue, and potassium tetrakis (4-chlorophenyl)borate as a lipophilic salt, which it is evaluated by absorbance measurement at 655 nm in a standard photometer.All experimental variables that influence test strip response, especially in terms of selectivity and response time, have been studied. The sensor responded linearly to hardness up to 14,800 mg l⁻¹, in activities, expressed as CaCO₃. The detection limit is 1.9 mg l⁻¹ as CaCO_3, the reproducibility intermembrane at a medium level of the range was 7.0%, as R.S.D., of and 2.6% as intramembrane. The procedure was applied to the determination of hardness in different types of waters (tap, well, mineral and spring) validating results against a reference procedure. This proposed method is quick, inexpensive, selective and sensitive and uses only conventional instrumentation.     

Development of an efficient protein phosphatase-based colorimetric test for okadaic acid detection

Okadaic acid (OA), responsible for gastrointestinal problems, inhibits protein phosphatase 2A (PP2A). Therefore, the inhibition exerted by the toxin on PP2A could be used to detect the presence of OA in aqueous solution and in shellfish sample.In this work, two commercial PP2As (from ZEU Immunotec and Millipore) and one produced by molecular engineering (from GTP Technology) were tested. Enzymes were used in solution and also immobilized within a polymeric gel. In solution, best performances were obtained using PP2A purchased from ZEU Immunotec (Spain). OA was detected in aqueous solution in concentration as low as 0.0124 μg L⁻¹ using the enzyme from ZEU Immunotec whereas the detection limits were 0.47 μg L⁻¹ and 0.123 μg L⁻¹ with PP2As from Millipore and GTP Technology, respectively. Considering that the immobilization step contributes to stabilize the PP2A activity, enzymes were entrapped within a photopolymer and an agarose gel. These different polymeric matrices were optimized, tested and compared. Agarose gel seems to be a good alternative to the photopolymer largely used in our group. For instance, the IC₅₀ value obtained with the test based on PP2A from ZEU Immunotec immobilized within an agarose gel was 1.98 μg L⁻¹. This value was 1.8-fold lower than those obtained with the photopolymer test using the same enzyme. The proposed test is sensitive, fast and does not require expensive equipment. To evaluate the efficiency of the assay, PP inhibition tests based on PP2A from ZEU Immunotec in solution or immobilized within a gel were used for OA detection in contaminated shellfish.     

Development of a solid surface fluorescence-based sensing system for aluminium monitoring in drinking water

A novel, single and robust solid surface fluorescence-based sensing device assembled in a continuous flow system has been developed for the determination of trace amounts of aluminium in water samples. The proposed method is based on the transient immobilization of the target species on an appropriate active solid sensing zone (C₁₈ silica gel). The target species was the fluorogenic chelate, formed as a result of the on-line complexation of Al(III) with chromotropic acid (CA) at pH 4.1. The fluorescence of the complex is continuously monitored at an emission wavelength of 390 nm upon excitation at 361 nm. The instrumental, chemical and flow-injection variables affecting the fluorescence signal were carefully investigated and optimized. After selecting the most suitable conditions, the sensing system was calibrated in the range 10–500 μg l⁻¹, obtaining a detection limit of 2.6 μg l⁻¹, and a R.S.D. of 2.2%, with a sampling frequency of 24 h⁻¹. In addition, the selectivity of the proposed methodology was evaluated by performing interference studies with different cations and anions which could affect the analytical response. Finally, the proposed method, which meets the EU regulations regarding the aluminium content in drinking waters, was satisfactorily applied to different water samples, with recoveries between 97 and 105%. The simplicity, low cost and easy operation are the main advantages of the present procedure.     

Neutron activation analysis of uranium in human bone,drinking water and daily diet

Uranium in human bone, drinking water and daily diet has been determined by neutron activation analysis using the²³⁸U(n, γ)²³⁹U reaction. An improved scheme for the separation of the²³⁹U is proposed; with this scheme, after neutron irradiation in a 100 kW TRIGA reactor, a uranium content as low as 5·10⁻¹¹ g can be determined reliably, rapidly and easily. A wide range of uranium concentrations, from about 0.1 ppb up to about 10 ppb has been found in the bones of normal Japanese. Water from several Japanese city water services, and the daily diet taken in two Japanese cities, have been found to contain an average 9·10⁻⁹ g/l and 1.5 μg per person-day uranium, respectively.     

Detection and quantification of PAH in drinking water by front-face fluorimetry on a solid sorbent and PLS analysis

The direct determination in drinking water of perylene, chrysene, pyrene, benzo[a]pyrene, and benzo[k]fluoranthene, by front-face synchronous fluorimetry on a commercial SPE disk, has been evaluated. Sorbent treatment, influence of humic substances, and pH effect are discussed. In pure water the detection limits were estimated to be in the range 0.03–0.01 g L^–1. A working pH in the range 10–11 was found to minimize the fluorescence quenching effect of humic substances. The proposed method combined with a partial-least-square (PLS) treatment was tested for quantitative analysis of mixtures of four PAH in a spiked drinking water.     

A colorimetric sensor array for organics in water

Molecular recognition of organic compounds in aqueous solutions is inherently challenging due to the potential interference from the very high concentration of water. Here we present a simple colorimetric sensor array that probes a wide range of chemical properties. By printing hydrophobic dyes on a hydrophobic membrane, sensor arrays are easily prepared that provide substantial chemical selectivity for the identification and quantification of various organics (both single compounds and complex mixtures) dissolved in water. It is possible to differentiate easily even among closely related organic compounds. Upon immersion in aqueous solutions, digital imaging of the dye array before and after exposure to an analyte provide a color change profile that is a fingerprint for the organic components of the solution. Facile identification of a wide variety of aqueous organic solutions is possible over a concentration range of 0.1 M to 1 muM. Complex mixtures present no inherent difficulty; for example, a series of commercial soft drinks were easily distinguished using the colorimetric sensor array approach.     

Development of a quantitative high-performance thin-layer chromatographic method for sucralose in sewage effluent, surface water, and drinking water

Sucralose, a persistent chlorinated substance used as sweetener, can already be found in waste water, and various countries focused on the release of sucralose into the aquatic environment. A quantitative high-performance thin-layer chromatography (HPTLC) method, which is orthogonal to existing methods, was developed to analyze sucralose in water. After sample preparation, separation of up to 17 samples was performed in parallel on a HPTLC plate silica gel 60 F(254) with a mixture of isopropyl acetate, methanol and water (15:3:1, v/v/v) within 15 min. Due to the weak native UV absorption of sucralose (≤200 nm), various post-chromatographic derivatization reactions were compared to selectively detect sucralose in effluent and surface water matrices. Thereby p-aminobenzoic acid reagent was discovered as a new derivatization reagent for sucralose. Compared to the latter and to β-naphthol, derivatization with aniline diphenylamine o-phosphoric acid reagent was slightly preferred and densitometry was performed by absorbance measurement at 400 nm. The limit of quantification (LOQ) of sucralose in drinking and surface water was calculated to be 100 ng/L for a given recovery rate of 80% and the extraction of a 0.5 L water sample. The sucralose content determined in four water samples obtained during an interlaboratory trial in 2008 was in good agreement to the mean laboratory values of that trial. According to the t-test, which compares the results with the target value, the means obtained by HPTLC were not significantly different from the respective means of six laboratories, analyzed by HPLC-MS/MS or HPLC-TOF-MS with the use of mostly isotopically labeled standards. The good accuracy and high sample throughput capacity proved HPTLC as a well suited method regarding quantification of sucralose in various aqueous matrices.     

An improved colorimetric method for chlorine dioxide and chlorite ion in drinking water using lissamine green B and horseradish peroxidase

Lissamine Green B (LGB) was carefully selected as a potential candidate for the development of a new U.S. Environmental Protection Agency (EPA) method that is intended for use at water utilities to determine chlorine dioxide (ClO₂) in drinking water. Chlorine dioxide reacts with LGB in aqueous solution to decrease the absorbance of LGB in direct proportion to the ClO₂ concentration. LGB was confirmed to have adequate sensitivity, and to suffer less interference than other dyes reported in the literature. The stoichiometry for the reaction between LGB and ClO₂ was found not to be 1:1 and is dependent on the LGB concentration. This required calibration of each LGB stock solution and prompted the investigation of alternate means of calibration, which utilized a horseradish peroxidase (HRP)-catalyzed conversion of chlorite ion (ClO₂⁻) to ClO₂. This approach allowed the simultaneous determination of ClO₂⁻ concentration, which is also required each day at water plants that use ClO₂. Studies were conducted to characterize and carefully optimize the HRP-conversion of ClO₂⁻ to ClO₂ in order to yield reaction conditions that could be accomplished in less than 30 min at modest cost, yet meet EPA's sensitivity and robustness requirements for routine monitoring. An assessment of method detection limit, linearity and slope (or sensitivity), precision, and accuracy in finished drinking water matrices indicated that this approach was suitable for publication as EPA Method 327.0.     

Development of a novel colorimetric indicator pad for detecting aldehydes

A colorimetric indicator was developed and a colorimetric indicator pad was fabricated for the rapid detection of aldehydes. The detection pad has two sides: an observation side on top and a barrier on the bottom. The top side contains a reagent which reacts directly with aldehydes to produce a color change, while the bottom side is coated with a double-sided plastic tape barrier to prevent the escape of chemicals. Sensitivity of the indicator pads was determined using the vapor sensitive ASTM F739 technique with the presence of the indicator. A significant indicator color change (yellow to red) occurred about 5 min before the infrared analyzer response of the ASTM method. The chemical principle and reaction characterization of the test are described. The stability and potential interferences of the indicator pad were also examined by directly spiking aldehydes and compounds with other functional groups, respectively, onto the indicator pads. The newly developed aldehyde indicator pad should find utility in detecting aldehydes in both liquid and vapor phases and in collecting aldehyde permeation through PPE for further study.     

A colorimetric and ratiometric fluorescent probe for quantification of bovine serum albumin

A 4-aminonaphthalimide-based ratiometric fluorescent probe 1 employing the internal charge transfer (ICT) mechanism was designed and synthesized to detect bovine serum albumin (BSA). The interaction of 1 and BSA was investigated by fluorescence and UV-vis absorption spectroscopy. Upon treatment with BSA, the probe successfully exhibited a ratiometric fluorescent response at 540 nm and 480 nm. The fluorescent intensity ratio at 540 nm and 480 nm (F(540)/F(480)) increases linearly with BSA concentration in the range of 0-75.0 μg mL(-1) and the detection limit was about 2.4 ng mL(-1). Our strategy is expected to provide a methodology to quantify BSA either by a normal or by a ratiometric and colorimetric way with high sensitivity.     

Nuclear analytical techniques for quantification of uranium for its recovery from seawater

Nuclear analytical techniques namely fission track technique using solid state nuclear track detector (SSNTD) and instrumental neutron activation analysis (INAA) have been standardized and applied for quantification of low uranium concentrations in liquid samples such as feed, elute and brine and solid sorbent samples respectively. The quantification of uranium is required for its recovery study from seawater, which is one of the potential sources of uranium. The uranium concentration of a liquid sample obtained by SSNTD method was compared with the other well established conventional techniques like ICP-MS, ICP-AES, adsorptive stripping voltametry and alpha spectrometry. INAA was applied for uranium concentration determination in the radiation grafted polyamidoxime sorbent samples.     

DDTC-Na-based colorimetric chemosensor for the sensing of cyanide in water

Sodium diethyldithiocarbamate (DDTC-Na) was demonstrated to be a new colorimetric cyanide chemosensor by utilizing an indirect trick. First, some copper ions were added to the colorless aqueous solution of DDTC-Na. Then, the resultant brown solution was studied upon the addition of different anions, including Cl⁻, I⁻, IO₃⁻, SO₄²⁻, NO₂⁻, Br⁻, H₂PO₄⁻, F⁻, SCN⁻, HSO₄⁻, ClO₄⁻ and CN⁻. It was observed by naked eyes that the brown solution changed to colorless immediately after the addition of the trace cyanide, but there were no changes towards other anions, making DDTC-Na a good selective cyanide chemosensor in pure water. Supported by the National Natural Science Foundation of China (Grant Nos. 20674059 & 20402011)     

Strategy for pesticide control in ground water and drinking water

Summary The analysis of pesticides is quite difficult and expensive. It is shown in this paper which analytical methods and systems have to be used for pesticide-monitoring in ground water and drinking water. Clear identification, control of positive results, quantitative determination, accuracy and precision are very important points for pesticide analysis.     

A new device for in-line colorimetric quantification of polypropylene degradation under multiple extrusions

An in-line colorimeter that is able to quantify color changes in real time during extrusion was developed and validated. It is composed of LEDs emitting at three different wavelengths and a photocell that measures the intensity of the light transmitted through the polymer melt flow. The colorimeter was validated at the bench by employing colored aqueous solutions and in-line during the extrusion of a colored polypropylene. Furthermore, it was used to in-line quantify the color changes in a polypropylene as generated over multiple extrusions due to thermo-mechanical degradation. The technique was proved to be fast and suitable to measure color changes in real time during extrusion.