Optochemical Sensor for Ammonia Based on a Lipophilized pH Indicator in a Hydrophobic Matrix

Abstract

An optical sensor for the determination of ammonia in water based on ion pairing has been investigated. A pH-sensitive dye is immobilized as an ion pair in a silicone matrix. The colour of the dye changes from yellow to blue depending on the concentration of ammonia in the sample solution. This change is reversible. The concentration of ammonia can be determined by measuring the transmittance at a given wavelength.

All measurements were performed with a dual-beam optical meter. The measurement range was from 5.9 × 10^?7 to 1 × 10^?3 M (0.01 to 17 mg/l) in 0.1 M phosphate buffer of pH 8. The detection limit was 10 μg/l. The response times at a flow rate of 2.5 ml/min were 4 min for t₉₀ and 10 min for t₁₀₀ at a change from 41.9 to 82.5 μM ammonia and 12 min for t₉₀ and 48 min for t₁₀₀ at a change from 160 to 0 μM ammonia. The operational lifetime of the ammonia sensor was limited to a period of a few days only. A continuous decrease in baseline signal and relative signal change was observed over the whole measurement. The storage stability was more than 10 months (dry). With respect to possible application of the ammonia sensor to environmental analysis, the influence of pH, typical interferences, such as amines and various detergents on the sensor response was investigated. No interference due to pH was observed in the range from pH 5 to pH 9. With methyl- and ethylamine the response was not completely reversible. The sensor was affected by cationic detergents, but not by anionic or neutral detergents.     

Preconcentration procedure using cloud point extraction in the presence of electrolyte for cadmium determination by flame atomic absorption spectrometry

This paper describes a micelle-mediated phase separation in the presence of electrolyte as a preconcentration method for cadmium determination by flame atomic absorption spectrometry (FAAS). Cadmium was complexed with ammonium O,O-diethyldithiophosphate (DDTP) in an acidic medium (0.32 mol l^− 1 HCl) using Triton X-114 as surfactant and quantitatively extracted into a small volume (about 20 μl) of the surfactant-rich phase after centrifugation. The chemical variables that affect the cloud point extraction, such as complexing time (0–20 min), Triton X114 concentration (0.043–0.87% w/v) and complexing agent concentration (0.01–0.1 mol l^− 1), were investigated. The cloud point is formed in the presence of NaCl at room temperature (25 °C), and the electrolyte concentration (0.5–5% w/v) was also investigated. Under optimized conditions, only 8 ml of sample was used in the presence of 0.043% w/v Triton X-114 and 1% (w/v) NaCl. This method permitted limits of detection and quantification of 0.9 μg l^− 1 and 2.9 μg l^− 1 Cd, respectively, and a linear calibration range from 3 to 400 μg l^− 1 Cd. The proposed method was applied to Cd determination in physiological solutions (containing 0.9% (w/v) of NaCl), mineral water, lake water and cigarette samples (tobacco).     

An Enzyme Immunoassay for the Determination of Methabenzthiazuron

Abstract

A sensitive enzyme immunoassay is described for the determination of the urea herbicide methabenzthiazuron. The assay is carried out with polyclonal antibodies, which were raised in rabbits by immunization with a methabenzthiazuron-BSA conjugate containing five methabenzthiazuron residues per molecule. The ELISA was optimized on microtiter plates with a peroxidase-methabenzthiazuron tracer. The middle of the test (50% B/B₀) was found at 1.0 μg/l. The lower detection limit of methabenzthiazuron is c. 0.05 μg/l. Samples can be measured up to 10 μg/l methabenzthiazuron (upper detection limit). The assay does not require concentration or clean-up steps for drinking or ground water samples. Validation experiments showed a good accuracy and precision. Work with monoclonal antibodies is in progress.     

Trace Detection of Mercury(II) Using Gold Ultra‐Microelectrode Arrays

The electroanalytical detection of trace mercury(II) at gold ultra‐microelectrode arrays is reported. The arrays consist of 256 gold microelectrodes of 5 μm in diameter in cubic arrangements which are separated from their nearest neighbor by 100 μm. The array was utilized in nitric acid using linear sweep voltammetry where a linear response from mercury additions over the range 10 μg L^?1?200 μg L^?1 (10^?8?10^?6 M) was observed with a sensitivity and detection limit of 0.11 nC/μg L^?1 and 3.2 μg L^?1 (16 nM) respectively from using a deposition time of 30 s at ?0.2 V (vs. SCE). This methodology was explored in 0.1 and 1 M chloride media over the mercury range 10 μg L^?1?200 μg L^?1 (5×10^?8?10^?6 M) where similar sensitivities of 0.087 nC/μg L^?1 and 0.078 nC/μg L^?1 were observed with an identical detection limit. The protocol is demonstrated to be useful for the determination of mercury for analysis of environmental water samples.     

Determination of nanomolar levels of formate in natural waters based on a luminescence enzymatic assay

A light-producing reaction utilizing three enzymes, bacterial luciferase, dehydrogenase and diaphorase, can be used to determine formic acid in natural waters at nanomolar concentrations. The method is rapid and convenient, requiring no preconcentration, desalting or derivatization procedures. Determinations can be done on small sample volumes (25 μl) at room temperature and pH 7. The precision (relative standard deviation for sea water samples containing 1.0 μM formate was 9.0% (n = 15). The reaction is specific for formate with a detection limit of 20 nM (signal-to-noise ratio = 3). Results for applications of the method to sea, estuarine and rain water are given.     

Isomeric Transformation Of 4-Aminobiphenyl by U.V. Radiation and its Influence on the Determination by Flow Injection Analysis with Amperometric and Spectrophotometric Detection.

Abstract

Two flow-injection methods for the determination of 4-aminobiphenyl by amperometry (glassy carbon electrode) and spectrophotometry are proposed. A sample volume of 200 or 400 μl containing an analyte concentration of 0.1–1.0 μg ml^?1 or 0.8–24.0 μg ml^?1 for amperometric or spectrophotometric detection, respectively, is injected into a carrier stream containing 0.04 or 0.02 M Britton-Robinson buffer at pH 10.0 or 8.0, respectively.

The throughput thus achieved is 200 (amperometry) and 240 samples/h (spectrophotometry) and the relative standard deviation less than 2.5% and 4.2% respectively.

Both methods were applied to the determination of 4-aminobiphenyl in commercially available, legally permitted food colouring additive.     

Simultaneous Determination of Nickel and cobalt in Manganese Sulphate Electrolyte by DMGH2-Sensitized Differential Pulse Polarography

Abstract

A method is described for the simultaneous determination of nickel and cobalt in manganese sulphate electrolyte by the dimethylglyoxime (DMGH₂) sensitized differential pulse polarography. The high manganese sulphate background (1.2M) in the concentrated process plant electrolyte interferes only with the nickel determination and precludes its direct determination. A 50% v/v dilution and an excessive amount (2 × 10^?3M) of the chelating agent are required at pH7.7 for the reliable determination of both elements. Under these conditions, the linear concentration ranges are 0-110 μg/1 for nickel and 0-140 μg/1 for cobalt. The minimum detectable amounts above the levels present in the process plant electrolyte are 2 μg/1 and 1 μg/1 for both elements, respectively. The relative standard deviations for all measurements are between 1 and 3%.     

Anodic Stripping Potentiometric Determination of Cu,Pb, Cd and Zn In Natural Waters on a Novel Combined Electrode System

Abstract

A method is described for the reliable determination of copper, lead, cadmium and zinc in natural waters by anodic stripping potentiometry with the use of a novel combined electrode. The method involves two stripping cycles during which copper is initially determined on its own, followed by simultaneous determination of lead, cadmium and zinc after addition of gallium (III) ions. The optimum conditions include 0.01 M HCl as supporting electrolyte, 10 mg/L Hg (II) as chemical oxidant; E_dep(Cu) -700 mV vs Ag/AgCl; E_{dep(Pb,Cd,Zn)} -1200 mV vs Ag/AgCl; t_dep 10s; 150 μg/L Ga (III); sample rotation rate 5 and rest period 30s. Under these conditions, as low as 0.06 μg/L Cu (0.7% RSD); 0.2 μg/L Pb (13% RSD); 0.04 μg/L Cd (7.8% RSD) and 0.06 μg/L Zn (5.5% RSD) can be determined reliably. A linear concentration range of 0–110 μg/L was obtained for the four metals. The successful application of the method to reference fresh water, creek water and tap water is demonstrated.     

Improved Determination of Aluminum in Serum by Electrothermal Atomic Absorption Spectrometry and Zeeman Background Correction

Abstract

A simple but reliable method for the determination of aluminum in serum by flameless atomic absorption spectrometry is described. By use of the Zeeman background correction, the interferences are eliminated. However, considering the numerous possible sources of contamination, extreme precautions are necessary both when taking and storing the serum. The procedures preceding the dosage per se must be minimized. The within-day and clay-to-day precision data (CV %) was 3.28 and 3.82 respectively. The average recovery for aluminum was 97.5 %. We used this method on serum from 30 healthy subjects and from 300 patients on hemodialysis. The mean aluminum concentration for the healthy subjects was 5.35 μg/l (SD ± 0.53) while the values for the hemodialyzed patients ranged from 20 to 220 μg/l.     

High-Performance Liquid Chromatographic Determination of Acetazolamide in Human Plasma

Abstract

A simple, rapid and specific HPLC method has been developed to determine acetazolamide concentrations in human plasma. The assay procedure requires only 250 μl of sample with direct injection of the organic supernatant after protein precipitation with acetonitrile. Chlorothiazide was used as an internal standard. A reversed-phase C₁₈ μBondapak column was employed for the chromatographic separation. The eluent was monitored at 265 nm using a UV variable wavelength detector. The retention times for acetazolamide (ACZ) and chlorothiazide (CTZ) were 6 and 8 min respectively. A linear relationship (r).995) was obtained over the 1-20 μg/ml concentration range. The limit of sensitivity for ACZ was 0.5 μg/ml, with greater than 85% recovery of ACZ and internal standard. The method was applied to human plasma samples obtained after administration of a 250 mg acetazolamide tablet.     

Initial applications of phospholipid-coated mercury electrodes to the determination of polynuclear aromatic hydrocarbons and other organic micropollutants in aqueous systems

Mercury electrodes coated with di-oleoyl lecithin are described for the determination of polynuclear aromatic hydrocarbons (PAHs) and other micropollutants in aqueous solutions. The coated electrodes give a characteristic response in the capacitance/voltage curve to three-, four- and five- ring PAHs. The extent of the negative potential shift in the reversible capacitance peaks (and thus sensitivity) is related to the number of aromatic rings and substituents on the PAH. The capacitance/voltage curves were recorded by phase-sensitive a.c. voltammetry. The response is quantitatively related to the concentration of PAH in solution. Detection limits are about 0.4 μg l^?1 and the reproducibility (RSD) for separate samples is 7%. Intercalibration of the method with fluorescence spectrophotometry of pyrene-spiked sea-water samples, showed recoveries of 80%. The analytical system is useful for sea water and tap water. Bovine serum albumin (1 mg l^?1) enhances the sensitivity to pyrene. The monolayer is sensitive to oil-contaminated waters ( > 40 μg l^?1). The capacitance peaks respond selectively to other groups of compounds and to individual compounds within a group. The monolayer appears highly sensitive to the solution behaviour of PAHs because only soluble unbound PAHs penetrate the monolayer. Humic acid added to the solution decreases the response to PAH presumably by binding a fraction of PAH in the solution.     

Capillary GC Determination of Short-Chain Dicarboxylic Acids in Rain,Fog, and Mist

Abstract

A capillary GC and GC-MS method, employing dibutyl esters is described for determining short-chain dicarboxylic acids in rain, fog and mist samples collected in the Los Angeles area. Approximately twenty dicarboxylic acids (C₂-C₁₀) were identified in the water samples, including cis (maleic) and trans (fumaric) unsaturated, saturated, normal, branched and aromatic. Oxalic acid is the dominant acid, followed by succinic and malonic acids. The total concentrations measured are 2.9–51μM, 64–66 μM and 12 μM for rain, fog and mist samples, respectively. These diacids are probably produced by photooxidation of anthropogenic and possibly biogenic organic compounds in the atmosphere.     

Enzymatic Determination of Ammonia in Lake Water Using a Semi-Automatic Analyser

Abstract

An enzymatic method was developed for the determination of ammonia concentrations in lake water. Lake water samples containing ammonia were mixed with a glutamate dehydrogenase (GIDH), reduced nicotinamide adenine dinucleotide phosphate (NADPH) and 2-oxoglutarate. The decrease in the absorbance intensity caused by the disappearance of NADPH by this reaction was measured at 340 nm. There was a linear relationship (r = 0.9997) between peak height and ammonia concentration over the range 0–29 μM. The detection limit was 0.29 μM for a sample volume of 250 μl. Interference of amino acids and urea at concentrations of 50 mg l^?1 was negligible. Good agreement was found between the enzymatic method and indophenol blue colorimetry.     

A Rapid and Simple High Pressure Liquid Chromatographic Method for Pharmacokinetic Study of Ciprofloxacin in Human Serum

Abstract

A rapid, accurate and sensitive method has been developed for the quantitative determination of ciprofloxacin, a new second-generation quinolone carboxylic acid antimicrobial agent, with high in vitro activity against a wide range of Gram- negative pathogens and Gram-positive cocci.

A Lichrosorb RP-18 250 x 4.0 mm, 5 μm analytical column was used with an eluting system consisting of a mixture of CH₃CN-CH₃OH-Citric acid 0.4 M (1:3:6 v/v). Detection was performed with a variable wavelength UV-visible detector at 275 nm resulting in a limit of detection of 0.2 ng per 20 μl injection. For the quantitative determination theophylline was used as chromatographic internal standard at a concentration of 1.56 ng/μl. A rectilinear relationship was observed up to 20 ng/μl. Analysis time was less than 6 min. The statistical evaluation of the method was examined performing intra-day (n=8) and inter-day calibration (n=8) and was found to be satisfactory with highly accurate and precise results. The method was applied to the direct determination of ciprofloxacin in human blood serum. Sample pretreatment involved only protein precipitation with acetonitrile. Recovery of ciprofloxacin in spiked samples was 98 ± 4% over the range of 0.5–5 mg/μl.     

Preconcentration of submicrogram amounts of nickel by liquid-liquid extraction and micro back-extraction from water for graphite furnace atomic absorption spectrometry

The effective preconcentration of submicrogram amounts of nickel from water is described. Nickel is extracted into xylene as a dithiocarbamate complex and subsequently back-extracted into 100 μl of nitric acid for graphite furnace atomic absorption spectrometry. Conditions for quantitative extraction and back-extraction are described. Data on interferences, precision and detection limits are presented. Sub-μg 1^?1 levels of nickel in water could be determined with concentration factors of 500–1000 by the proposed method. The concentrations of nickel in rain water and surface snow were found to be 0.39 and 0.19 μg 1^?1, respectively. The limit of determination can be lowered by using concentration factors larger than 10⁴, nickel determination at ng 1^?1 levels being feasible.     

Determination of Volatile Halogenated Compounds in Tap and Surface Waters from the Gdańsk District

Abstract

The present method is based on preconcentration of organic contaminants on XAD-4 as sorbent, thermal desorption, mineralization and coulometric argentometric titration for the final determination of halides. The results were calculated as the total parameter VOX (volatile organic halogen) expressed as chlorine. The method has been used for the VOX determination in tap water, Vistula river water and Baltic Sea water. Sampling of the Baltic Sea water has been carried out during the research cruise of the r/v ‘Oceania’. The relatively high anthropogenic pollution of the river Vistula (c _vox = 11–45 μg Cl/cd³), Gulf of Gdańsk (c _vox = 0.6–4.5 μg Cl/dm³) and the Pomerania Bay (c _vox = 2 μg Cl/dm³) has been determined. The VOX concentration in the tap water varied between 13 and 56 μg/dm³; that is, this water is seriously polluted by volatile organic halogen compounds.     

The impact of nitrogen fertilizers on degradation and leaching of chlorotoluron in soil

Abstract

This study presents the developed and applied methods for the determination of carbendazim in environmental samples originating from several field studies.

For water samples sample pretreatment consisted of a solid phase extraction (SPE) on cartridges packed with 200 mg SDB-1. In case of solid samples the performance of microwave assisted solvent extraction (MASE) and classical ultrasonic extraction with acetone-ethyl acetate were studied. The latter technique was selected because of the reduced time of manual operations. Instrumental analysis of extracts of water samples was performed on-line with coupled column reversed phase liquid chromatography (LC/LC) and UV detection (280 nm) allowing to assay carbendazim to a level of at least 0.1 μg/l. Improved column life time was obtained by performing the favorable LC separation of carbendazim at high pH on newly developed 5 μm Extend-pH bidentate C18 material.

The combination of a short column packed with 5 μm Inertsil ODS-5 and a mobile phase at low pH material was most adequate as the regards the robust and fast processing of extracts of solid samples and allowed in most cases the screening of carbendazim in soils and sediments to a level of 10μg/kg.

The developed procedures yield overall recoveries for carbendazim of 101, 80 and 71 % in water (levels, 0.1—1.2 μg/l: n=12), soil (levels, 10 and 100 μg/kg; n=22) and sediments (levels, 10 and 100 μg/kg; n=11), respectively, with a repeatability and reproducibility below 7 % for all method/matrix combinations. Soil samples with aged residues (level, 100 μg/kg; n=10) provided an overall recovery of 71% and no significant decrease of carbendazim was observed during nine weeks of storage in the refrigerator.     

Determination of Barium in Bottled Drinking Water by Graphite Furnace Atomic Absorption Spectrometry

Abstract

In relation to the wide environmental spread of barium and to its cardiovascular effects, barium levels were determined by graphite furnace atomic absorption spectrometry in 60 different brands of bottled water marketed in Italy.

Matrix interferences were investigated in order to evaluate the use of an analytical calibration function rather than the much more time consuming addition technique.

The barium content ranged from limit of detection C_L (7.0 μg/l) up to 660 μg/l, the median value being 80 μg/l, while the recovery tests varied between 90 and 110 % and the precision of the method (s_yx) was 2.5 %.     

The cloud point extraction of copper(II) with monocarboxylic acids into non-ionic surfactant phase

The possibility to use monocarboxylic acids and their mixtures with amines for copper concentrating by the way of micellar extraction at cloud point temperature, and later atomic absorption spectrometry (AAS) determination was investigated. Under the optimum conditions, preconcentration of 100 ml of water sample in the presence of 1% non-ionic surfactant OP-10, 0.005 M capric acid and 0.01 M octylamine permitted the detection of 0.01 μg ml⁻¹ copper. The proposed method has been applied to the AAS determination of copper in water samples after cloud point extraction.     

BHC Residues in Milk: A Gas Chromatographic Investigation

Abstract

BHC residues were determined in milk samples of cows and buffaloes (Indore, M.P., India), α-, β- and γ-BHC were identified in samples from four different localities using gas chromatography. All samples were contaminated with BHC, with the toxic gamma isomer appearing in the largest concentration. Buffalo milk was more contaminated than cow milk, with maximum values of 17 and 12 μg/l, respectively.