A simpler potentiometric method for histamine assessment in blood sera.

Histamine intolerance results from a disequilibrium of accumulated histamine and the capacity for histamine degradation. An impaired histamine degradation based on reduced DAO activity and the resulting histamine excess may cause numerous symptoms mimicking an allergic reaction. For that, the determination of histamine in blood or in food products has great importance to identify risk factors. A new histamine-selective electrode is proposed using cucurbit[6]uril (CB[6]), as ionophore, in the analysis of biological samples. The selection of this smart supramolecular organic framework was based on its apparent stability constant of histamine-CB[6] (log ß) of 4.33. The optimized electrode based on a polymeric membrane (PVC) combines the histamine-selective ionophore with 2-nitrophenyl octyl ether as solvent mediator and potassium tetrakis(4-chlorophenyl)borate as anionic additive. Furthermore, multi-walled carbon nanotubes particles were included in the membrane composition to partly lower the detection limit of the method, while improving stability and lowering the response drift (± 4 mV). The electrodes showed a rapid response (≃ 13 s) in the pH operational range of 2.7-5.4, with a Nernstian slope of 30.9 ± 1.2 mV/dec, a detection limit of (3.00 ± 0.61) × 10-7 mol/L, and a lower limit of the linear range of (3.00 ± 0.00) × 10-7 mol/L. After miniaturization, the electrode was used as a detector in a sequential-injection lab-on-valve flow setup. The optimized flow conditions were achieved for sample injection volumes of 197 µL propelled towards the cell under detection, at a flow rate of 30 µL/s during 100 s, making the analysis of 30 samples per hour possible. The developed system was used to analyze spiked blood serum samples previously cleaned by using solid-phase extraction. The sample pretreatment of the serum samples using Oasis MCX cartridges showed outstanding efficiency for histamine determination. The recovery values for three different levels of histamine concentration (1 × 10-4 mol/L, 1 × 10-5 mol/L, and 1 × 10-6 mol/L) were (97 ± 6)%, (103 ± 1)%, and (118 ± 9)%, respectively, showing that this method was suitable for biological samples.

Potentiometric detection in liquid chromatographic systems: An overview.

Analytical techniques are extensively used in various fields of human activity to define quality and usage safety patterns of goods and consumables. Between those, liquid chromatography is probably the most common, generally combined with optical detectors. Alternatively, electroanalytical techniques provide versatile tools that offer high selectivity and sensitivity in a short time, using simple and low cost instrumentation. Amperometric, coulometric and conductimetric detectors are thus well established in HPLC with commercially available instrumentation. Despite sharing some of the stated features, the use of potentiometric detectors seems however overlooked. Potentiometry with ion-selective electrodes has been highlighted in both batch and flow analysis systems, evidenced by numerous applications performed worldwide. The determination of electrolytes in blood samples, heavy metals in natural water samples and pharmaceutical drugs in bulk drug materials are some of the representative examples. The developments achieved so far in hydrodynamic separation systems proved the great potential of potentiometry to become a competitive detection technique with the many others. Therefore, it is intended to present an overview about potentiometric detection in liquid chromatography with the purpose of enhance its importance for future analytical applications.

Optimizing potentiometric ionophore and electrode design for environmental on-site control of antibiotic drugs: application to sulfamethoxazole.

Potentiometric sensors are typically unable to carry out on-site monitoring of environmental drug contaminants because of their high limits of detection (LODs). Designing a novel ligand material for the target analyte and managing the composition of the internal reference solution have been the strategies employed here to produce for the first time a potentiometric-based direct reading method for an environmental drug contaminant. This concept has been applied to sulfamethoxazole (SMX), one of the many antibiotics used in aquaculture practices that may occur in environmental waters. The novel ligand has been produced by imprinting SMX on the surface of graphitic carbon nanostructures (CN)<500 nm. The imprinted carbon nanostructures (ICN) were dispersed in plasticizer and entrapped in a PVC matrix that included (or not) a small amount of a lipophilic additive. The membrane composition was optimized on solid-contact electrodes, allowing near-Nernstian responses down to 5.2 µg/mL and detecting 1.6 µg/mL. The membranes offered good selectivity against most of the ionic compounds in environmental water. The best membrane cocktail was applied on the smaller end of a 1000 µL micropipette tip made of polypropylene. The tip was then filled with inner reference solution containing SMX and chlorate (as interfering compound). The corresponding concentrations were studied for 1 × 10(-5) to 1 × 10(-10) and 1 × 10(-3) to 1 × 10(-8)mol/L. The best condition allowed the detection of 5.92 ng/L (or 2.3 × 10(-8)mol/L) SMX for a sub-Nernstian slope of -40.3 mV/decade from 5.0 × 10(-8) to 2.4 × 10(-5)mol/L. The described sensors were found promising devices for field applications. The good selectivity of the sensory materials together with a carefully selected composition for the inner reference solution allowed LODs near the nanomolar range. Both solid-contact and "pipette tip"-based sensors were successfully applied to the analysis of aquaculture waters.

Novel LTCC-potentiometric microfluidic device for biparametric analysis of organic compounds carrying plastic antibodies as ionophores: application to sulfamethoxazole and trimethoprim.

Monitoring organic environmental contaminants is of crucial importance to ensure public health. This requires simple, portable and robust devices to carry out on-site analysis. For this purpose, a low-temperature co-fired ceramics (LTCC) microfluidic potentiometric device (LTCC/µPOT) was developed for the first time for an organic compound: sulfamethoxazole (SMX). Sensory materials relied on newly designed plastic antibodies. Sol-gel, self-assembling monolayer and molecular-imprinting techniques were merged for this purpose. Silica beads were amine-modified and linked to SMX via glutaraldehyde modification. Condensation polymerization was conducted around SMX to fill the vacant spaces. SMX was removed after, leaving behind imprinted sites of complementary shape. The obtained particles were used as ionophores in plasticized PVC membranes. The most suitable membrane composition was selected in steady-state assays. Its suitability to flow analysis was verified in flow-injection studies with regular tubular electrodes. The LTCC/µPOT device integrated a bidimensional mixer, an embedded reference electrode based on Ag/AgCl and an Ag-based contact screen-printed under a micromachined cavity of 600 µm depth. The sensing membranes were deposited over this contact and acted as indicating electrodes. Under optimum conditions, the SMX sensor displayed slopes of about -58.7 mV/decade in a range from 12.7 to 250 µg/mL, providing a detection limit of 3.85 µg/mL and a sampling throughput of 36 samples/h with a reagent consumption of 3.3 mL per sample. The system was adjusted later to multiple analyte detection by including a second potentiometric cell on the LTCC/µPOT device. No additional reference electrode was required. This concept was applied to Trimethoprim (TMP), always administered concomitantly with sulphonamide drugs, and tested in fish-farming waters. The biparametric microanalyzer displayed Nernstian behaviour, with average slopes -54.7 (SMX) and +57.8 (TMP) mV/decade. To demonstrate the microanalyzer capabilities for real applications, it was successfully applied to single and simultaneous determination of SMX and TMP in aquaculture waters.

Rapid automated method for on-site determination of sulfadiazine in fish farming: a stainless steel veterinary syringe coated with a selective membrane of PVC serving as a potentiometric detector in a flow-injection-analysis system.

Sulfadiazine is an antibiotic of the sulfonamide group and is used as a veterinary drug in fish farming. Monitoring it in the tanks is fundamental to control the applied doses and avoid environmental dissemination. Pursuing this goal, we included a novel potentiometric design in a flow-injection assembly. The electrode body was a stainless steel needle veterinary syringe of 0.8-mm inner diameter. A selective membrane of PVC acted as a sensory surface. Its composition, the length of the electrode, and other flow variables were optimized. The best performance was obtained for sensors of 1.5-cm length and a membrane composition of 33% PVC, 66% o-nitrophenyloctyl ether, 1% ion exchanger, and a small amount of a cationic additive. It exhibited Nernstian slopes of 61.0 mV decade(-1) down to 1.0 × 10(-5) mol L(-1), with a limit of detection of 3.1 × 10(-6) mol L(-1) in flowing media. All necessary pH/ionic strength adjustments were performed online by merging the sample plug with a buffer carrier of 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid, pH 4.9. The sensor exhibited the advantages of a fast response time (less than 15 s), long operational lifetime (60 days), and good selectivity for chloride, nitrite, acetate, tartrate, citrate, and ascorbate. The flow setup was successfully applied to the analysis of aquaculture waters. The analytical results were validated against those obtained with liquid chromatography-tandem mass spectrometry procedures. The sampling rate was about 84 samples per hour and recoveries ranged from 95.9 to 106.9%.

Sulfadiazine-selective determination in aquaculture environment: selective potentiometric transduction by neutral or charged ionophores.

Solid-contact sensors for the selective screening of sulfadiazine (SDZ) in aquaculture waters are reported. Sensor surfaces were made from PVC membranes doped with tetraphenylporphyrin-manganese(III) chloride, α-cyclodextrin, ß-cyclodextrin, or γ-cyclodextrin ionophores that were dispersed in plasticizer. Some membranes also presented a positive or a negatively charged additive. Phorphyrin-based sensors relied on a charged carrier mechanism. They exhibited a near-Nernstian response with slopes of 52 mV decade(-1) and detection limits of 3.91×10(-5) mol L(-1). The addition of cationic lipophilic compounds to the membrane originated Nernstian behaviours, with slopes ranging 59.7-62.0 mV decade(-1) and wider linear ranges. Cyclodextrin-based sensors acted as neutral carriers. In general, sensors with positively charged additives showed an improved potentiometric performance when compared to those without additive. Some SDZ selective membranes displayed higher slopes and extended linear concentration ranges with an increasing amount of additive (always <100% ionophore). The sensors were independent from the pH of test solutions within 2-7. The sensors displayed fast response, always <15s. In general, a good discriminating ability was found in real sample environment. The sensors were successfully applied to the fast screening of SDZ in real waters samples from aquaculture fish farms. The method offered the advantages of simplicity, accuracy, and automation feasibility. The sensing membrane may contribute to the development of small devices allowing in locus measurements of sulfadiazine or parent-drugs.

Development of a multicommutated flow system with chemiluminometric detection for quantification of gentamicin in pharmaceuticals.

A new flow procedure based on multicommutation with chemiluminometric detection was developed to quantify gentamicin sulphate in pharmaceutical formulations. This approach is based on gentamicin's ability to inhibit the chemiluminometric reaction between luminol and hypochlorite in alkaline medium, causing a decrease in the analytical signal. The inhibition of the analytical signal is proportional to the concentration of gentamicin sulphate, within a linear range of 1 to 4 µg mL(-1) with a coefficient variation <3%. A sample throughput of 55 samples h(-1) was obtained. The developed method is sensitive, simple, with low reagent consumption, reproducible, and inexpensive, and when applied to the analysis of pharmaceutical formulations (eye drops and injections) it gave results with RSD between 1.10 and 4.40%.

Ecotoxicological aspects related to the presence of pharmaceuticals in the aquatic environment.

Pharmaceuticals are biologically active and persistent substances which have been recognized as a continuing threat to environmental stability. Chronic ecotoxicity data as well as information on the current distribution levels in different environmental compartments continue to be sparse and are focused on those therapeutic classes that are more frequently prescribed and consumed. Nevertheless, they indicate the negative impact that these chemical contaminants may have on living organisms, ecosystems and ultimately, public health. This article reviews the different contamination sources as well as fate and both acute and chronic effects on non-target organisms. An extensive review of existing data in the form of tables, encompassing many therapeutic classes is presented.

Cyclodextrin-based potentiometric sensors for midazolam and diazepam.

In this work the implementation of benzodiazepine ion-selective electrodes for pharmaceutical formulations control is described. The solid-contact electrodes for midazolam and diazepam are based on polymeric membranes incorporating respectively beta-cyclodextrin and (2-hydroxiproyl)-gamma-cyclodextrin as ionophores, 2-fluorophenyl 2-nitrophenyl ether as plasticizer and potassium tetrakis (p-chlorophenyl) borate as ionic additive. For conventionally shaped midazolam electrode a slope of 61.9+/-1.3 mVdec(-1), a LLLR of 5.7+/-2.7 x 10(-4)gL(-1) and pH range of 2.6-5.4 was obtained, while the corresponding values for diazepam electrodes were of 67.6+/-3.0 mVdec(-1), 4.9+/-1.5 x 10(-2)gL(-1) and 1.9-2.7 pH units, respectively. Membrane optimization was based on the molar ratio between the ionophore and additive for midazolam and on inclusion cavity of cyclodextrin for diazepam. The miniaturization of the above-described electrodes gave rise to potentiometric detectors for sequential-injection lab-on-valve system with similar characteristics albeit the useful lifetime shortened from 1 year to approximately 15 days under continuous operation. The optimized flow conditions were achieved for sample injection volumes of 20 microL propelled towards the detection cell at the flow rate of 16 microLs(-1) during 80s. Real sample analysis revealed statistical accuracy and between-days precision comparable to the general used chromatographic-based procedure.

Simultaneous determination of potassium and nitrate ions in mouthwashes using sequential injection analysis with potentiometric detection.

Two methods for the determination of potassium nitrate in mouthwashes, used against dentin hypersensitivity, have been simultaneously implemented in an sequence injection analysis (SIA) system. In addition to in-line dilution of the samples, the equipment simultaneously detected potassium and nitrate using two tubular potentiometric detectors, selective to each ion, providing a real-time assessment of the quality of the results. Both determinations were shown to be precise and accurate and the obtained results do not statistically differ from those furnished by applying the AES and HPLC reference methods.

Exploiting sequential injection analysis with lab-on-valve and miniaturized potentiometric detection Epinephrine determination in pharmaceutical products.

Miniaturized potentiometric units were constructed, evaluated and incorporated in a SIA-LOV manifold in order to the control of pharmaceutical analysis. The method validation was done with ephinefrine determinations in commercial pharmaceutical products. The optimization procedures were directed at potential versus epinephrine concentration. This approach was achieved by selecting 60cm of reactor and a flow rate of 11muLs(-1) and injecting 78muL of epinephrine standard solutions in a 1.0x10(-3)molL(-1) IO(4)(-) solution. A linear range was found for epinephrine concentrations between 2.0x10(-4) and 2.5x10(-3)molL(-l) with a slope of 35528mVLmol(-l) and r(2)=0.997. Under these conditions the analytical results for the commercial pharmaceutical formulations of 0.908 and 0.454mgmL(-1), respectively, with a R.S.D. of 0.34 for both, was obtained. Through down scaling periodate-selective electrode it was possible to benefit from the recognized advantages of the lab-on-valve sequential-injection based systems, namely regarding equipment portability, reduced consumption of the sample and the reagents and the reduction of effluent waste. Furthermore, the new periodate electrode configuration is easy to achieve in common laboratories and enables the implementation of low volume detection cell where the electrical noise, that is frequently presented in potentiometric based procedures, is significantly reduced.

Application of sequential injection analysis to pharmaceutical analysis.

Sequential injection analysis is a well established tool for automation of pharmaceutical analysis. A short historical background of this technique is given as well as a brief discussion on the basic principles and potentials. The current applications of SIA in the pharmaceutical analysis are also described and discussed. The manifolds developed offer good analytical characteristics and are suitable for analysis of drug formulations, process analysis, drug-dissolution, drug-release testing and functional assays for screening potential drugs. The results obtained are in good agreement with those furnished by the application of the reference methods presented in the pharmacopoeias.

New PVC nitrate-selective electrode: application to vegetables and mineral waters.

The paper refers the analytical potentialities of the oxa-azamacrocycles as potentiometric ionophores for the construction of electrodes selective to nitrate. Afterward, the membrane selective to nitrate is designed and optimized using a [3.3.3.3]oxazane as an ionophore. The membrane was prepared using dibutylphthalate as a solvent mediator, tetraoctylammonium as a lipophilic membrane additive, and poly(vinyl chloride (PVC) as a polymeric matrix, applied directly onto a conductive graphite/epoxy resin support. The electrodes presented a slope of 60 +/- 0.1 mV log(-1), a low limit of linear response of 4.2 x 10(-6) mol L(-1), a useful lifetime of 1 year, and improved selectivity characteristics when compared with other nitrate electrodes. The good working characteristics of this electrode, constructed without inner-reference solution, made possible its application to the determination of nitrate in different types of vegetables and bottled mineral waters without the use of a conditioning solution. The application of a significant F test proved that the results obtained were similar to those attained by application of the brucine spectrophotometric method adopted as a reference technique. Linear regression analysis also showed good agreement between the results obtained by the proposed method and the reference one.

Amperometric biosensor based on monoamine oxidase (MAO) immobilized in sol-gel film for benzydamine determination in pharmaceuticals.

The development and application of a flow-through amperometric biosensor for benzydamine determination in anti-inflammatory drugs is described. The biosensor was obtained by physical entrapment of monoamine oxidase in a sol-gel film applied on platinum or carbon paste conducting support. The sol-gel membranes were prepared using an optimum concentration of 3-aminopropyltriethoxy silane, 2-(3,4-epoxycyclohexyl)ethyl-trimethoxy silane, double distilled water saturated with polyethylene glycol 6000 and HCl. The developed biosensors were incorporated in a single channel flow injection system to enable the determination of benzydamine in the concentration range of 0.05-2.5 mmol l(-1) (with platinum based electrode) or within 0.1-2.5 mmol l(-1) (carbon paste based electrode). The operational stability of the bioanalytical system developed was about 3 months permitting approximately 4700 substrate measurements. The flow injection system developed enables a sampling rate of 20-25 samples h(-1) and relative S.D. of results less than 4%. The analytical usefulness of the proposed procedure was evaluated through analysis of commercial pharmaceutical products containing benzydamine, available on the Portuguese market. The results obtained did not differ significantly from the values resulting from analysis of the same products by the method described in the BP Pharmacopoeia.