Dioctyl Phenylphosphonate Research Articles

Construction of Dopamine Hydrochloride Liquid Selective Electrodes

Three liquid selective electrodes were synthesized based on particle pair to selective dopamine chloride. The construction electrodes consist of phosphomolybdicacid (dopamine), di-n-butyl phosphate, Di-n-butyl phthalate, and di-octylphenyl phosphonate as plasticizers materials. The construction of preparing probes was examined potentially with successes Nernstain response around 52.50 and 50. 50 mV/decade for electrodes on both DBPH and DOPH were as plasticizers, respectively. The most direct ranges concentrations of dopamine in drug form were found to be around 2.5×10-5-1.0×10-2 for DBPH and 4.30×10-5 -1.0×10-1 M for DOPH. The detection limits were reached to 2.31×10-6 in DBPH and 5. 63×10-6 M in DOPH electrode type. While third electrode relied on di-n-butyl phosphate (DPH), a non-Nernstain equivalent of around 19.10 mV/decade with a range of concentration about 2.2×10-5 -1.0×10-1 with a detection limit equivalent to 6.35×10-6. The pH values in the experimental application were asses to obtain the best determination of dopamine concentration at 10-3M. The optimisation of both electrodes DBPH and DOPH achieved good agreements to lifetime, selectivity, potentiometric techniques and accuracy of measurements. At the same time the standard expansion, various standard expansions and potentiometric titration result in an immediate strategy for the assurance of dopamine in drug form.

Artificial lipid membrane: surface modification and effect in taste sensing

In this work, an artificial lipid membrane was synthesized using tetra-dodecyl ammonium bromide (TDAB) and doped with gold nanoparticles (AuNP). The taste sensor designed using artificial lipid membrane is composed of tetradodecylammonium bromide (TDAB) as a lipid, dioctylphenyl phosphonate (DOPP) as a plasticizer, and polyvinyl chloride (PVC) as a supporting polymer in the ratio of 1:3:2. The lipid/polymer membrane acts as the recognition element which transforms the taste information generated by the chemical substances into an electric potential change. The fundamental taste analytes (like fructose for sweetness, HCl for sourness, NaCl for saltiness, MgCl2 for bitterness and MSG for umami) were used to study the effect of doping on taste sensing at different concentrations (10μM to 10mM). The study was based on the open circuit potential (OCP) change of the membrane with the analytes. The observations implicate that the doping increases the specificity of the artificially synthesized lipid membrane taste sensor for the sweet analytes, particularly for fructose.

Preparation and Application of Tetracycline Hydrochloride Liquid membrane Electrodes.

Two liquid membrane electrodes for (TCH) were prepared by using ion pair which included phosphomolybdic acid (PMA)-(TCH) with plasticizers: Di-n-butyl phthalate(DBPH), and di-octylphenylphosphonate (DOPH). Tetracycline electrodes were gave a Nernstain response equal to 56. 51 and 50. 66 mV/decade for membranes depended on DBPH and DOPH as a plastisizers, respectively. Linear ranges were around 6. 8×10-6- 1. 0×10-1 and 1. 0×10-5-1. 0×10-1 M, respectively. Detection limit were equal to 4. 0×10-6, 5. 0×10-6 M, respectively. PH range were also studied at three different concentration of tetracycline solutions. As well as were studied lifetime, selectivity, potentiometric methods such as direct, standard addition , multiple standard addition and titration methods were applied to determination tetracycline in pharmaceutical preparation

Synthesis New Liquid Selective Electrodes of Ciprofloxacin Hydrochloride for Determination Ciprofloxacin in Pure form and Pharmaceuticals Preparation.

New membrane electrodes for determination of ciprofloxacin hydrochloride were prepared depending on ciprofloxacin hydrochloride - phosphotungstic acid (CFH-PT) as an active material and these electrodes were made with three plasticizers: Di-octylphenylphosphonate(DOPH), Di-butyl phosphate (DBP)Tri-n-butyl phosphate(TBP), in PVC matrix. One of the ciprofloxacin electrodes was gave Nernstian slope equal to 57.21 mV/ decade for DOPH membrane with concentration range from 1.5×10-5 to1.0×10-1 M, and detection limit equal to 1.5×10-6 M .Lifetime was 93 days. Non- Nernstian responses equal to 39.40 and 30.70 mV/ decade for membranes DBP, TBP, respectively. These electrodes were gave concentration range from 1.0× 10-5 to 1.0×10-2 and from 4.0×10-5 to 1.0×10-2 M,respectively. Detection limits were 7.0×10-6, and 1.7×10-6M, respectively. Lifetimes were 5,2 days, respectively. Also selectivity, influence of PH and samples analysis of ciprofloxacin in a pharmaceutical preparations were studied.

Polymeric Membrane Sensors for the Selective Determination of Metoclopramide Hydrochloride and their Applications to Pharmaceutical Analysis

Metoclopramide (MCP) ion selective electrodes based on metoclopramide-phosphotungstic acid (MCP-PT) ion pair complex in PVC matrix membrane were constructed. The plasticizers used were tri-butyl phosphate (TBP), di-octyl phenyl phosphonate (DOPP), di-butyl phthalate (DBPH), di-octyl phthalate (DOP), di-butyl phosphate (DBP), bis 2-ethyl hexyl phosphate (BEHP). The sensors based on TBP, DOPP, DBPH and DOP display a fast, stable and linear response with slopes 59.9, 57.7, 57.4, 55.3 mV/decade respectively at pH ranged 2-6. The linear concentration range between 1.0×10-5 – 1.0×10-2 M with detection limit 3.0×10-6 and 4.0×10-6 M for electrodes using TBP, DOPP and DBPH while electrode using DOP shows a linear concentration range between 3.0×10-5 – 1.0×10-2 M and detection limit 6×10-6 M. The selectivity coefficient values were calculated for MCP with respect to different inorganic cations, sugars and amino acids using the MCP depending on TBP plasticizer which is also used for the determination of MCP in pure solutions and in pharmaceutical preparations by direct, standard addition methods and as an indicator electrode in potentiometric titration with phosphotungstic acid (PT) giving satisfactory results.
 Key words: Metoclopramide-HCl membrane sensors , Metoclopramide determination , pharmaceutical analysis , PVC membrane sensors

Synthesis New Liquid Selective Electrodes of Ciprofloxacin Hydrochloride for Determination Ciprofloxacin in Pure form and Pharmaceuticals Preparation.

New membrane electrodes for determination of ciprofloxacin hydrochloride were prepared depending on ciprofloxacin hydrochloride - phosphotungstic acid (CFH-PT) as an active material and these electrodes were made with three plasticizers: Di-octylphenylphosphonate(DOPH), Di-butyl phosphate (DBP)Tri-n-butyl phosphate(TBP), in PVC matrix. One of the ciprofloxacin electrodes was gave Nernstian slope equal to 57.21 mV/ decade for DOPH membrane with concentration range from 1.5×10-5 to1.0×10-1 M, and detection limit equal to 1.5×10-6 M .Lifetime was 93 days. Non- Nernstian responses equal to 39.40 and 30.70 mV/ decade for membranes DBP, TBP, respectively. These electrodes were gave concentration range from 1.0× 10-5 to 1.0×10-2 and from 4.0×10-5 to 1.0×10-2 M,respectively. Detection limits were 7.0×10-6, and 1.7×10-6M, respectively. Lifetimes were 5,2 days, respectively. Also selectivity, influence of PH and samples analysis of ciprofloxacin in a pharmaceutical preparations were studied.

Highly Sensitive Multi-Channel IDC Sensor Array for Low Concentration Taste Detection.

In this study, we designed and developed an interdigitated capacitor (IDC)-based taste sensor array to detect different taste substances. The designed taste sensing array has four IDC sensing elements. The four IDC taste sensing elements of the array are fabricated by incorporating four different types of lipids into the polymer, dioctyl phenylphosphonate (DOPP) and tetrahydrofuran (THF) to make the respective dielectric materials that are individually placed onto an interdigitated electrode (IDE) via spin coating. When the dielectric material of an IDC sensing element comes into contact with a taste substance, its dielectric properties change with the capacitance of the IDC sensing element; this, in turn, changes the voltage across the IDC, as well as the output voltage of each channel of the system. In order to assess the effectiveness of the sensing system, four taste substances, namely sourness (HCl), saltiness (NaCl), sweetness (glucose) and bitterness (quinine-HCl), were tested. The IDC taste sensor array had rapid response and recovery times of about 12.9 s and 13.39 s, respectively, with highly stable response properties. The response property of the proposed IDC taste sensor array was linear, and its correlation coefficient R2 was about 0.9958 over the dynamic range of the taste sensor array as the taste substance concentration was varied from 1 μM to 1 M. The proposed IDC taste sensor array has several other advantages, such as real-time monitoring capabilities, high sensitivity 45.78 mV/decade, good reproducibility with a standard deviation of about 0.029 and compactness, and the circuitry is based on readily available and inexpensive electronic components. The proposed IDC taste sensor array was compared with the potentiometric taste sensor with respect to sensitivity, dynamic range width, linearity and response time. We found that the proposed IDC sensor array has better performance. Finally, principal component analysis (PCA) was applied to discriminate different types of taste of the mixed taste substances.

PREPARATION AND CHARACTERIZATION ION SELECTIVE ELECTRODE Cd(II) BASED ON CHITOSAN IN PVC MEMBRANE

Preparation of the chitosan membrane of ion-selective electrode for determination of cadmium ion has been conducted. Chitosan is a natural polymer containing nitrogen could coordinate with Cd2+ to increase the membrane conductivity value. Chitosan is a principal material and mixed with polyvinylchloride (PVC) as matrix dissolved previously to solvent tetrahydrofuran (THF) and dioctylphenylphosphonate (DOPP) is added as plasticizer by proportion chitosan:PVC:DOPP (6:3:1). To obtain the dopant optimum concentration, membrane was dipped in Cd2+ for 7 days and its conductivity value was measured using the four-point probe method. From FT-IR spectrum the peaks of amine, acetylamide and hydroxy groups wavelength number was observed to assure that Cd2+ bound to the chitosan. The optimum concentration of Cd2+ dopant was obtained at 1.00 M with conductivity value of 549.45 ohm-1m-1 wich gave a Nernstian factor of 32.03 mV/decade with the detection limit of 2.512 x 10-5 M. The electrodes work in the pH range 3 - 7. The life time of the electrode was 8 weeks. The ions of Ni2+, Fe3+, Pb2+, Cu2+, Zn2+, Cl- and SO42- toward concentration range 10-3 M gave response did not interfere in the determine of Cd2+ ion.

Polyvinyl chloride-based 18-crown-6, dibenzo18-crown-6 and calix-[6]-arene zinc(II)-potentiometric sensors

Polyvinyl chloride (PVC) based membranes of 18-crown-6 (18C6), dibenzo 18-crowen-6 (DB18C6) and calix[6]arene (CAX), as ionophores, with dioctylphenylphosphonate (DOPP), bis(ethylhexyl)sebacate (DOS) dioctyl phthalate (DOP), 2-nitrophenyloctylether (o-NPOE) and didecylphthalate (DDP) as plasticizing solvent mediators are prepared and constructed for the determination of Zn(II). Of the 15 membranes constructed, only the PVC based membranes of DB18C6 and 18C6 ionophores with DOPP, as plasticizer, in the ratio (w/w) PVC:ionophore:DOPP (60:2:120) give the best results in terms of working concentration range (1.0×10−5–1.0×10−1M) with a Nernstian slope of 29.0mV/decade of activity for membrane composed of DOPP+DB18C6(1a) and (1.0×10−5–1.0×10−1M) with a Nernstian slope of 30.0mV/decade of activity for membrane composed of DOPP+18C6(1b). The usable pH range of the sensors is 3.0–8.0, beyond which a drift in potential is observed. The response time of the sensors is ⩽15s with a lifetime of 2months during which they can be used without any measurable divergence. The selectivity coefficient values indicate that the electrode is highly selective for Zn2+ over a number of other cations except Pb2+ and Ag+. The electrodes have successfully been used to determine Zn(II) in real alloys and standard samples with a precision as relative standard deviation (RSD) <2% for each of the cited electrodes. The results obtained by the proposed ISEs are in good agreement with the results obtained by direct flame AAS method.

Ionophore-Based Potentiometric Sensors for the Flow-Injection Determination of Promethazine Hydrochloride in Pharmaceutical Formulations and Human Urine

Plasticised poly(vinyl chloride)-based membranes containing the ionophores (α-, β- and γ-cyclodextrins (CD), dibenzo-18-crown-6 (DB18C6) and dibenzo-30-crown-10 (DB30C10) were evaluated for their potentiometric response towards promethazine (PM) in a flow injection analysis (FIA) set-up. Good responses were obtained when β- and γ-CDs, and DB30C10 were used. The performance characteristics were further improved when tetrakis(4-chlorophenyl) borate (KTPB) was added to the membrane. The sensor based on β-CD, bis(2-ethylhexyl) adipate (BEHA) and KTPB exhibited the best performance among the eighteen sensor compositions that were tested. The response was linear from 1 × 10−5 to 1 × 10−2 M, slope was 61.3 mV decade−1, the pH independent region ranged from 4.5 to 7.0, a limit of detection of 5.3 × 10−6 M was possible and a lifetime of more than a month was observed when used in the FIA system. Other plasticisers such as dioctyl phenylphosphonate and tributyl phosphate do not show significant improvements in the quality of the sensors. The promising sensors were further tested for the effects of foreign ions (Li+, Na+, K+, Mg2+, Ca2+, Co2+, Cu2+, Cr3+, Fe3+, glucose, fructose). FIA conditions (e.g., effects of flow rate, injection volume, pH of the carrier stream) were also studied when the best sensor was used (based on β-CD). The sensor was applied to the determination of PM in four pharmaceutical preparations and human urine that were spiked with different levels of PM. Good agreement between the sensor and the manufacturer’s claimed values (for pharmaceutical preparations) was obtained, while mean recoveries of 98.6% were obtained for spiked urine samples. The molecular recognition features of the sensors as revealed by molecular modelling were rationalised by the nature of the interactions and complexation energies between the host and guest molecules.

The influence of phosphorus containing compounds on steam cracking of n-hexane

In steam cracking of hydrocarbons P-containing compounds are used as additives to control coke formation and/or CO production. However, information concerning the influence of P-containing compounds on the decomposition of hydrocarbons during steam cracking is scarce. In this study, the influence of three P-containing compounds, hexamethyl phosphoric triamide (HMPA), tripiperidinophosphine oxide (TPyPO) and dioctyl phenylphosphonate (DOPP), on the conversion of n-hexane during steam cracking was investigated in a continuous flow micro-reactor with complete mixing. All these compounds accelerate the thermal decomposition of n-hexane. The effect of a P-containing additive on the conversion of n-hexane is quantitatively evaluated using the dimensionless group method proposed by LaMarca et al. [C. LaMarca, C. Libanati, M.T. Klein, Chem. Eng. Sci. 45 (1990) 2059]. To interpret the accelerating effect, the potential elementary radical reactions involved in the steam cracking of these P-containing compounds are proposed. Their rate coefficients are estimated based on thermochemical data. For all of these P-containing compounds the main coupling with n-hexane decomposition occurs through H-abstraction reactions. The accelerated effect can be traced back to the introduction of new initiation steps. The evaluated values are consistent with the experimentally measured values.

Amodiaquine polymeric membrane electrode

The construction and electrochemical response characteristics of two types of poly(vinyl chloride) (PVC) membrane sensors for the determination of amodiaquine hydrochloride (ADQ·2HCl) are described. The sensing membrane comprised an ion-pair formed between the cationic drug and sodium tetraphenyl borate (NaTPB) or potassium tetrakis(4-chlorophenyl) borate (KTCPB) in a plasticized PVC matrix. Eight PVC membrane ion-selective electrodes were fabricated and studied. Several plasticizers were studied namely, dioctyl phthalate (DOP), 2-nitrophenyl octyl ether (NPOE), dioctyl phenylphosphonate (DOPP) and bis(2-ethylhexyl)adipate (EHA). The sensors display a fast, stable and near-Nernstian response over a relative wide ADQ concentration range (3.2 × 10 −6 to 2.0 × 10 −2 M), with slopes comprised between 28.5 and 31.4 mV dec −1 in a pH range comprised between pH 3.7 and 5.5. The assay of amodiaquine hydrochloride in pharmaceutical dosage forms using one of the proposed sensors gave average recoveries of 104.3 and 99.9 with R.S.D. of 0.3 and 0.6% for tablets (Malaritab ®) and a reconstituted powder containing ADQ·2HCl, respectively. The sensor was also used for dissolution profile studies of two drug formulations. The sensor proved to have a good selectivity for ADQ·2HCl over some inorganic and organic compounds, however, berberine chloride interfered significantly. The results were validated by comparison with a spectrophotometric assay according to the USP pharmacopoeia.

Flow-through Chloroquine Sensor and Its Applications in Pharmaceutical Analysis

Poly (vinyl chloride) membrane electrodes that responded selectively towards the antimalarial drug chloroquine are described. The electrodes were based on the use of the lipophilic potassium tetrakis(4-chlorophenyl)borate as ion-exchanger and bis(2-ethylhexyl)adipate (BEHA), or trioctylphosphate (TOP) or dioctylphenylphosphonate (DOPP) as plasticizing solvent mediator. All electrodes produced good quality characteristics such as Nernstian- and rapid responses, and are minimally interfered with by the alkali and alkaline earth metal ions tested. The membranes were next applied to a flow-through device, enabling it to function as flow-injection analysis (FIA) detector. The performance of the sensor after undergoing the FIA optimization was further evaluated for its selectivity characteristics and lifetime. Results for the determination of chloroquine in synthetic samples that contained common tablet excipients such as glucose, starch, and cellulose, and other foreign species such as cations, citric acid or lactic acid were generally satisfactory. The sensor was also successfully used for the determination of the active ingredients in mock tablets, synthetic fluids and biological fluids. The sensor was applied for the determination of active ingredients and the dissolution profile of commercial tablets was also established.

Study of sweet taste evaluation using taste sensor with lipid/polymer membranes

The higher sensitivity for sweeteners can be achieved by newly developed lipid/polymer membranes. The membrane is composed of lipids such as phosphoric acid di- n-hexadecyl ester and tetradodecylammoniumbromid, and a plasticizer, dioctyl phenylphosphonate. As a result of changing electric charge of the membrane surface, the newly developed membrane shows 5–10 times higher sensitivity for sucrose than the conventional ones. We also applied the sensor to other sugars such as sugar alcohol which is used as alternative sweetness or food additives. The experimental results of other sweeteners relatively correspond to human sensory evaluation, though the sensitivity for some sugars need to be improved.

PVC membrane based potentiometric sensors for uranium determination

Two novel uranyl PVC matrix membrane sensors responsive to uranyl ion are described. The first sensor incorporates tris(2-ethylhexyl)phosphate (TEHP) as both electroactive material and plasticizer and sodium tetraphenylborate (NaTPB) as an ion discriminator. The sensor displays a rapid and linear response for UO 2 2+ ions over the concentration range 1×10 −1–2×10 −5 mol l −1 UO 2 2+ with a cationic slope of 25.0±0.2 mV decade −1. The working pH range is 2.8–3.6 and the life span is 4 weeks. The second sensor contains O-(1,2-dihydro-2-oxo-1-pyridyl)- N, N, N′, N′-bis(tetra-methylene)uronium hexafluorophosphate (TPTU) as a sensing material, sodium tetraphenylborate as an ion discriminator and dioctyl phenylphosphonate (DOPP) as a plasticizer. Linear and stable response for 1×10 −1–5×10 −5 mol l −1 UO 2 2+ with near-Nernstian slope of 27.5±0.2 mV decade −1 are obtained. The working pH range is 2.5–3.5 and the life span of the sensor is 6 weeks. Interference from many inorganic cations is negligible for both sensors. However, interference caused by some ions (e.g. Th 4+, Cu 2+, Fe 3+) is eliminated by a prior ion exchange or solvent extraction step. Direct potentiometric determination of as little as 5 μg ml −1 uranium in aqueous solutions shows an average recovery of 97.2±1.3%. Application for the determination of uranium at levels of 0.01–1 wt.% in naturally occurring and certified ores gives results with good correlation with data obtained by X-ray fluorescence.

Calcium-selective electrode based on polyaniline functionalized with bis[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate

A new Ca 2+-selective polyaniline (PANI)-based membrane material suitable for all-solid-state sensor applications is presented. The membrane consists of electrically conducting PANI, bis[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphoric acid (DTMBP-PO 4H), dioctyl phenylphosphonate (DOPP) and cationic (tridodecylmethylammonium chloride, TDMACl) or anionic (potassium tetrakis(4-chlorophenyl)borate, KTpClPB) lipophilic additives. PANI transforms the ionic response to an electronic signal and functions at the same time as the membrane matrix. PANI is made soluble in dichloro methane (DCM) with the Ca 2+-selective DTMBP-PO 4H ligand and membranes can easily be prepared by drop-casting on glassy carbon (GC) substrates. PANI membranes with three different plasticizer ( z) and additive ( s) contents were studied (the molar ratios between the plasticizer or additive and DTMBP-PO 4H are denoted as z and s, respectively). The best electrode performance, considering sensitivity and selectivity, was obtained for PANI membranes prepared with z=0.90 and s=0.10, containing KTpClPB as ionic additive. The Ca 2+-sensitivity of this membrane was 27.8±0.2 mV/ log a Ca 2+ (10 −1 to 10 −4 M CaCl 2, LOD=8×10 −7 M) in 0.1 M NaCl, and the selectivity coefficients ( log K Ca, j pot ) towards j=Na +, K +, Li +, NH 4 + and Mg 2+, determined with the fixed interference method, were −3.9±0.1, −4.0±0.1, −3.5±0.1, −3.5±0.1 and −3.6±0.1, respectively. On the other hand, practically no redox or pH sensitivity was observed when TDMACl was used as the ionic additive. The PANI membranes were characterized with potentiometry, electrochemical impedance spectroscopy (EIS) and UV–VIS.

Transport of Thiourea through an Aliquat 336/Polyvinyl Chloride Membrane

The transport of thiourea in acidic or neutral chloride solutions through a polyvinyl chloride (PVC) membrane containing immobilized Aliquat 336 was studied experimentally. No chemical interaction between thiourea and Aliquat 336 was observed. The acidity constant of thiourea at 1.0 ionic strength was 13.7 and its distribution constant for acidic solutions and neat Aliquat 336 was 4.20. A mathematical model assuming ideal mixing in the solutions on both sides of the membrane and Fickian diffusion in the membrane was developed and used for the determination of the diffusion coefficient of thiourea in membranes with 30, 40, and 50 wt% Aliquat 336 content. The corresponding values are estimated to be 5.5 × 10−13 m2s−1, 1.2×10−12m2s−1 and 3.5 ×10−12m2s−1, respectively. The transport properties of PVC membranes with other plasticizers [bis(1-butylpentyl) adipate, dioctylphenyl phosphonate, and n–decanol] were compared to the Aliquat 336/PVC membrane.

Potentiometric Micro Determination of Some Metal Ions Using Chloranilate PVC Matrix Membrane Electrodes.

ABSTRACT Chloranilate PVC matrix membrane electrodes have been developed. These are based on the use of aliquat-chloranilate ion pair in plasticized PVC matrices. The calibration slope is about 60 mV/decade. The limit of detection is about 10−5 M, the working pH range is 5-10, the electrodes have been used in the determination of lead, mercury, and cadmium ions with chloranilic acid, separately and in binary mixtures. 2-Nitro phenyl octyl ether, 2- nitro phenyl phenyl ether, dioctyl phthalate, dioctylsebacate, dioctyl phenyl phosphonate plasticizers are used; there were no significant differences in the performance characteristics of membranes for the various plasticizers. The life time of the electrodes is greater than one month.

Theory of electric characteristics of the lipid/PVC/DOPP membrane and PVC/DOPP membrane in response to taste stimuli

Electric characteristics of two kinds of membranes in response to NaCl and quinine were theoretically studied; one membrane composed of polyvinyl chloride (PVC) and dioctylphenylphosphonate (DOPP), and the other a lipid/PVC/DOPP membrane containing PVC, DOPP and a negatively charged lipid. We develop a theory by taking into account both the surface electric potential and the diffusion potential within the membrane and succeed in interpreting the observed data. On increasing the NaCl concentration, the lipid/PVC/DOPP membrane changes from weakly charged state to fully charged state by dissociation of H + from the lipids. The hydrophobic interaction between quinine and the PVC/DOPP membrane was strong enough to overcome the electric repulsion.

Carrier mechanism of acidic ionophores in solvent polymeric membrane ion-selective electrodes

The behavior of cation-selective solvent polymeric membrane electrodes based on acidic ionophores is investigated by studying the selectivity coefficients as a function of cationic or anionic additive concentration. This technique allows discrimination between neutral and charged carrier-related mechanisms, resulting in the following findings. Ionophores with a carboxylic acid group act as neutral carriers and sulfonic acid derivatives behave as charged carriers irrespective of the plasticizer used. The Ca 2+ -selective organophosphate ionophore examined (bis-[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate) acts in low dielectric constant plasticizers in a mixed mode where the analyte ion forms two different complexes in the membrane phase-one with the charged form of the carrier and the other with the protonated form (neutral ionophore). From these results it can be seen that when developing novel ion-selective electrodes based on acidic ionophores, both cationic and anionic additives as well as plasticizers of high and low dielectric constant should be tested since completely different selectivity behavior could be obtained due to the charged and neutral forms of the carrier in the organic phase. The addition of potassium tetrakis[3,5-bis(bifluoromethyl)phenyl]borate to the calcium-selective membrane phase based on the organophosphate ligand mentioned above, the plasticizer dioctyl phenylphosphonate, and poly(vinyl chloride) improves the potentiometric properties of the electrodes with respect to membrane resistance and anion interference