Calcium selective test strip for water and milk

We have developed a selective and reversible test strip based on an ion-exchange mechanism to determine calcium. The optical test strip contains a polymeric film of plasticised PVC that contains all of the reagents necessary to produce a response to calcium, among them the new ionophore, 4,13-bis[(N-adamantylcarbamoyl)propionyl]-1,7,10,16-tetraoxa-4,13-diazacyclooctadecane. The measurement of the absorbance at 655 nm in a standard photometer makes it possible to determine calcium activities. The composition of the membrane and reaction conditions have been adjusted to obtain adequate selectivity. The test strip responded linearly to calcium between 0.050 and 135 mM in activities. The reproducibility intermembrane at a medium level of the range was 6.2%, as RSD, of log a(Mg(2+)), and 3.4% as RSD intramembrane. The procedure was applied to the determination of calcium ion in different types of waters (tap, well, spring and mineral) and milks (whole, skimmed, skimmed with calcium added, special types) validating the results against a reference procedure.     

A test strip for diamines in tuna.

This study describes the production of a solid-phase assay (test strip/dipstick test) for putrescine and cadaverine in tuna based on the coupling of an amine oxidase to a peroxidase/dye system. The assay was linear to 75 microM in phosphate buffer, and the minimum detectable concentration was 0.5 microM (< 0.1 ppm), corresponding to 0.01 mg% in spiked extracts. Intra- and interassay precisions were < 20%. Test strips were stable at 4 degrees C for at least 12 months. Lysine, ornithine, and histidine did not react with the assay, and histamine reacted only minimally. Sixteen fish samples were tested by test strip and the standard AOAC protocol, and results were in good agreement.     

Determination of hypochlorite in water using a chemiluminescent test strip

We have developed a selective and reusable chemiluminescent test strip to determine hypochlorite. The hypochlorite-sensitive test strip contains a 10 mm × 9 mm piece of anionic cellulose paper in fluoresceinate cycle, glued to a 10 mm × 4 cm × 0.5 mm polyester strip. The measurement of the chemiluminescence in a luminometer when 1 ml of sample is injected into a conventional cell containing the strip makes it possible to determine hypochlorite. The composition of the membrane and reaction conditions have been adjusted to obtain adequate sensitivity and selectivity. The test strip responded linearly to hypochlorite over two linear ranges, the first 2.0-10.3 mg L⁻¹ and the second 10.3-51.4 mg L⁻¹, with a detection limit of 0.4 mg L⁻¹. The reproducibility using the same disposable test strip at a medium level of the range was 6.6%, as relative standard deviation (R.S.D.), and 12.3% using different test strips. The procedure was applied to the determination of hypochlorite in different types of waters.     

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.     

Magnesium-selective test strip

A selective test strip based on an ion-exchange mechanism to determine magnesium is described. This optical and reversible test strip, made on a transparent polyester sheet, has a circular polymeric film of plasticised PVC that contains all of the reagents necessary to produce a response to magnesium, namely, a cation-selective neutral ionophore, 2-amino-N,N′-diheptyl-N,N′-dimethyl-butanediamide, a chromoionophore, N,N-diethyl-5-(octadecanoylimino)-5H-benzo[a]phenoxazine-9-amine, and potassium tetrakis (4-chlorophenyl)borate (TCPB) as a lipophilic salt, which is evaluated by absorbance measurement at 655 nm in a standard photometer. The experimental variables that influence test strip response, especially in terms of selectivity and response time, have been studied. The test strip responded linearly to magnesium between 0.009 and 160 mM in activities. The reproducibility intermembrane at a medium level of the range was 8.0%, as R.S.D., of log aMg2+, and 5.9% as R.S.D. intramembrane. The procedure was applied to the determination of magnesium in different types of waters (tap, well and mineral) validating the results against a reference procedure. This proposed method is quick, inexpensive, selective and sensitive and uses only conventional instrumentation.     

Test strip for determination of nitrite in water

A disposable test strip is proposed for the determination of nitrite in waters. The strip is an inert rectangular strip of polyester with a 6 mm o.d. circular, transparent and colorless film attached to its surface. This film contains the chemicals required for reaction and fixation of the dye formed, sulfanilamide, N-(1-naphthyl)ethylenediamine on Nafion. When the test strip is placed in an acidified (pH 2.0) sample solution containing nitrite a red-violet color develops; the absorbance of this is measured at 536 nm. The linear range of the method depends on the time of equilibration of the test strip with the sample solution. When the equilibration time was 45 min, the linear range was 8.9-500 microg L(-1) whereas for an equilibration time of 60 min it was 4.7-200 microg L(-1). The detection limit was 1.4 microg L(-1) for an equilibration time of 60 min. The precision of the method, expressed as RSD, was 8.8 % at 100.0 microg L(-1). The method was applied, and validated chemometrically, for the determination of nitrite in different types of water (spring, mineral, tap, well, and sea).     

Multiplexed paper test strip for quantitative bacterial detection

Rapid, sensitive, on-site detection of bacteria without a need for sophisticated equipment or skilled personnel is extremely important in clinical settings and rapid response scenarios, as well as in resource-limited settings. Here, we report a novel approach for selective and ultra-sensitive multiplexed detection of Escherichia coli (non-pathogenic or pathogenic) using a lab-on-paper test strip (bioactive paper) based on intracellular enzyme (β-galactosidase (B-GAL) or β-glucuronidase (GUS)) activity. The test strip is composed of a paper support (0.5 × 8 cm), onto which either 5-bromo-4-chloro-3-indolyl-β-D: -glucuronide sodium salt (XG), chlorophenol red β-galactopyranoside (CPRG) or both and FeCl(3) were entrapped using sol-gel-derived silica inks in different zones via an ink-jet printing technique. The sample was lysed and assayed via lateral flow through the FeCl(3) zone to the substrate area to initiate rapid enzyme hydrolysis of the substrate, causing a change from colorless-to-blue (XG hydrolyzed by GUS, indication of nonpathogenic E. coli) and/or yellow to red-magenta (CPRG hydrolyzed by B-GAL, indication of total coliforms). Using immunomagnetic nanoparticles for selective preconcentration, the limit of detection was ~5 colony-forming units (cfu) per milliliter for E. coli O157:H7 and ~20 cfu/mL for E. coli BL21, within 30 min without cell culturing. Thus, these paper test strips could be suitable for detection of viable total coliforms and pathogens in bathing water samples. Moreover, inclusion of a culturing step allows detection of less than 1 cfu in 100 mL within 8 h, making the paper tests strips relevant for detection of multiple pathogens and total coliform bacteria in beverage and food samples.     

Mass-spectrometry of frozen matrix-assisted water in environmental analysis

Summary CO₂ laser evaporation/KrF-laser ionization combined with reflectron time-of-flight mass-spectrometry have been used for the analysis of drinking water polluted with phenol. A minimum phenol concentration level of 10^–8% was detected. Considerable temperature reduction (up to 50 K) due to laser evaporated molecules from the frozen water surface has been observed.     

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.     

A novel approach for the determination of detection limits for metal analysis of environmental water samples

Despite the widespread use of the USEPA method (U.S. Environmental Protection Agency, 40 CFR 136 Appendix B) for the determination of method detection limit (MDL), criticisms have been raised that the method does not account for measurement bias and outliers that subsequently lead to a common misunderstanding of the requirement for the determination of MDL. This paper demonstrates that it is difficult to follow the USEPA method for verifying the MDL for analysis involving multiple metals and proposes a precision and bias criterion for determining the MDL. A multiple-point fitted profile, based on the correlation between relative standard deviation (RSD) and concentration, is used to derive a robust MDL value. Representative examples of As, Ca, Cr, and Cu are used to illustrate this procedure. A procedure for identifying outliers is also discussed.     

A test method for determining water in organic solvents

A test procedure is developed for determining water in acetone, dioxane, isobutanol, ethanol, petroleum ether, and ethyl acetate in the ranges 0.5–12; 0.5–10; 0.5–8; 0.5–6, and 0.5–4 vol %, respectively. Determination is based on the measurement of the acidity of a solution obtained upon adding citric acid or sodium hydrogen sulfate to organic solvents using an indicator test strip containing Congo red. The relative standard deviation of the results of analysis is 0.05–0.1; the duration of analysis is about 30 min.     

Capillary electrophoresis in the analysis of pharmaceuticals in environmental water: A critical review

Determination of residual pharmaceutical compounds in environmental water is gaining increasing interests. The task represents a substantial challenge to analysts because analytes present in quite complicated matrices and at very low concentrations. Despite the inherent low sensitivity associated with capillary electrophoresis (CE), it has been used successfully to determine different types of pharmaceutical compounds at very low levels that rival those reported by more commonly used methods for that purpose such as high performance liquid chromatography-mass spectrometry (HPLC-MS). Attempts to use CE for the determination of drugs in environmental water samples started nearly in the late 1990s; since then, different modes of CE including capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography together with different detection techniques (UV, fluorescence, MS) have been investigated and shown to be of adequate performance. A key to the success of CE for such low-level determination was the sample concentration steps that have been used including solid-phase extraction and more advanced approaches such as in-line sample concentration, large volume sample stacking, and others. The different reports that have been reported for this application in particular have been reviewed since late 1990s with emphasis on the attained limits of detections and sample treatment. The particularities of the separation conditions in each case have been discussed with some elaboration.     

New block-grafted anion exchanger for environmental water analysis by ion chromatography

The IonPac AS14A is a recently developed stationary phase that was produced using a new block-grafting technique, which enables the preparation of high-water-content anion exchangers with excellent peak shape and good chromatographic efficiency. The performance of this column for the analysis of inorganic anions was compared to that obtained using an IonPac AS4A column, which is specified in US Environmental Protection Agency Method 300.0, in addition to another commonly used alternative; the AS14 column. The AS14A column is available in two different formats; 250×4 mm I.D. (7.0 μm diameter particle) and 150×3 mm I.D. (5.5 μm diameter particle). The IonPac AS14A (in 4 mm I.D. format) was found to provide similar performance to the AS14 column with increased peak efficiency and better pH stability and is a suitable alternative for the analysis of anions in moderate- to high-ionic-strength samples. The IonPac AS14A (in 3 mm I.D. format) provides comparable run times to the AS4A column with better overall peak selectivity and improved fluoride resolution, hence this column would be a suitable column to substitute in place of either the AS4A or AS14 columns for the analysis of inorganic anions in low- to moderate-ionic-strength environmental waters. The AS14A column used with an Atlas electrolytic suppressor provides equivalent method detection limits to those obtained when using a micromembrane suppressor but with the operational convenience of a self-regenerating suppressor.     

流动注射双安培法测定环境水样中苯酚

基于苯酚在铂电极上的氧化和不可逆电对的双安培检测原理,建立了流动注射双安培测定环境水样中苯酚的新方法。通过偶合苯酚在一支铂电极上的氧化和KMnO4在另一支铂电极上的还原这两个不可逆电对,构建双安培检测体系,在外加电位差为0V时,苯酚的氧化电流与其浓度在1.0×10-6～1.0×10-4mol/L范围内呈线性关系,检出限为5.0×10-7mol/L,连续30次测定2.0×10-5mol/L苯酚,电流值RSD为1.4%。用本方法分别对几种含酚废水样品中苯酚含量进行测量,并与4 氨基安替比啉比色法进行了对照。     

A new spot test for aromatic hydrazides using 2,3,5-triphenyl tetrazolium chloride

Summary A spot test using 2,3,5-triphenyl tetrazolium chloride for the detection of benzoic acid hydrazide, and itsm- andp-nitro derivatives, isonicotinic acid hydrazide, salicylic acid hydrazide and phenylacetic acid hydrazide is described. The method consists of treating 0.1 to 0.2 ml of 0.001 % hydrazide (for benzoic acid hydrazide a 0.0001 %) solution with 0.2 to 0.4 ml of 0.02M sodium hydroxide, 0.2 ml of 1% 2,3,5-triphenyl tetrazolium chloride and 0.2 ml of nitrobenzene oriso-butyl methyl ketone in a micro test tube. A reddish-brown colour in the organic phase confirms the presence of an aromatic hydrazide. The identification limits for benzoic acid hydrazide, itsm- andp-nitro derivatives, isonicotinic acid hydrazide, salicylic acid hydrazide, phenylacetic acid hydrazide respectively are: 0.2, 1.0, 1.0, 3.5, 3.0, 2.0g in 1 ml in nitrobenzene and 0.2, 0.2, 0.1, 3.0, 0.2, 1.5g in 1 ml iniso- butyl methyl ketone. The interference of various substances and anions has been studied.

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Zusammenfassung Eine Tüpfelreaktion mit 2,3,5-Triphenyltetrazoliumchlorid zum Nachweis von Benzoesäurehydrazid und dessenm- undp-Nitroderivaten, von Isonikotinsäurehydrazid, Salicylsäurehydrazid und Phenylessigsäurehydrazid wurde angegeben. 0,1 bis 0,2 ml einer 0,001% igen (bei Benzoesäurehydrazid einer 0,0001% igen) Lösung werden mit 0,2 bis 0,4 ml 0,02-m Natronlauge, 0,2 ml 1%iger Triphenyltetrazoliumchloridlösung und 0,2 ml Nitrobenzol oderi-Butylmethylketon in einem Mikroreagensglas behandelt. Rotbraune Färbung der organischen Phase zeigt die Anwesenheit eines aromatischen Hydrazids an. Die Nachweisgrenzen der angeführten Säurehydrazide in 1 ml Nitrobenzol betragen 0,2, 1,0, 1,0, 3,5, 3,0 bzw 2,0g, in 1 mli-Butylmethylketon 0,2, 0,2, 0,1, 3,0, 0,2 bzw. 1,5g Die störende Wirkung verschiedener Substanzen und Anionen wurde geprüft.