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PubMed1992

Ektachem slides for direct potentiometric determination of sodium in plasma: effect of natremia, blood pH, and type of electrolyte reference fluid on concordance with flame photometry and other potentiometric methods.

With electrolyte reference fluid (ERF)00, results from Kodak Ektachem slides for the direct potentiometric assay of sodium in plasma were significantly correlated with results from flame photometry, but also appeared to be systematically higher, especially in hypernatremic patients. Indirect potentiometry with the Technicon RA-1000 yielded intermediate values. In 23 hypernatremic patients with greater than or equal to 6 mmol/L difference in sodium between Ektachem ERF00 and flame photometry, a clinical survey disclosed the frequent association of large between-method differences with renal failure, diabetes mellitus, and gastrointestinal disease. However, there was no correlation between differences in sodium on the one hand and anion gaps or (lipo)protein concentrations on the other, nor did in vitro addition studies implicate metabolites that often accumulate in the above-mentioned disorders. Unlike indirect methods, sodium measurements by direct potentiometry on Ektachem and Corning were influenced by in vitro changes of pH between 7.0 and 7.9. However, in a group of patients that included many acidotic individuals, between-method differences in sodium appeared not significantly correlated with in vivo blood pH. Use of the equitransferant ERF04 on Ektachem strongly diminishes the systematic differences with flame photometry, reduces the pH-dependency of the results to that of the direct Corning method, and brings the mean analytical recovery of sodium to below 95% (instead of 115% previously) without affecting the ability of Ektachem slides to avoid spuriously low results in the presence of increased (monoclonal) protein concentrations.

Blood↗
PubMed1988

Reliability of IL Monarch ion-selective electrode module for sodium, potassium, and chloride measurements.

We evaluated the IL Monarch random-access centrifugal analyzer for measurement of Na+, K+, and Cl- by an indirect potentiometric method. For different concentrations of control material, the total precision (CV) ranged between 0.82% and 1.14% for the three electrolytes; linearity was acceptable within a range of 103 to 215 mmol/L for Na+, 1.6-15.25 mmol/L for K+, and 80-173 mmol/L for Cl-. Data correlated well with those by flame photometry for Na+ and K+ and with those by coulometry for Cl-, both for various biological materials--sera, urines, dialysis fluids--and commercial control materials from various producers. Stability of the potentiometric signal was acceptable: daily variations were 0.2 mV for Na+, 0.05 mV for K+, and 0.03 mV for Cl-. Accordingly, we conclude that the system supplies reproducible and accurate results while being easy to use and requiring little maintenance. The use of indirect potentiometry offers results consistent with those obtained with traditional methods, and easily interpretable by clinical staff. However, better information about the actual ion activity in the tested sample for certain pathologies such as hyperlipemia and dysproteinemia could be obtained by methods involving direct potentiometry.

Centrifugation↗
PubMed1983

[Determination of sodium chloride in preserving brines using ion selective electrodes].

The determination of sodium chloride content in salt brines is important for many reasons, including that of influencing the organoleptic properties of final products already prior to production. The method of determination by direct potentiometry is rapid, simple, requires no chemicals and has sufficient accuracy for use in producers' laboratories. The comparison of both methods of sodium chloride determination--direct potentiometry and direct titration without previous adjustment of samples--showed that titration gave higher sodium chloride levels (by 2.5 g per litre, i. e. 2.15%) than did ISE determination. For current laboratory examinations and for sodium chloride determination in meat plants, this difference is almost negligible. However, if sodium chloride is to be determined by the so called conclusive method, the measurement cannot be performed without previous mineralization of samples and without the use of buffer to damp down the effect of interfering ions.

Food Preservatives↗
PubMed1982

Establishing the direct-potentiometric "normal" range for Na/K: residual liquid junction potential and activity coefficient effects.

The observed reference ranges for sodium and potassium as determined by direct potentiometry vary from instrument to instrument, depending on the composition of the calibration standards. To resolve the existing confusion as to which reference intervals are most appropriately considered "normal," we propose a straightforward convention (based on plasma-water concentration units) in which the difference between direct (undiluted sample) and indirect (diluted sample) methodologies is accounted for by the volume displacement effect of proteins, lipids, and other dissolved substances in a typical plasma sample. Thus, the proposed reference intervals for sodium and potassium are approximately 7% greater by direct potentiometry than by procedures involving dilution. Data consistent with this convention can be obtained with a variety of aqueous-based calibrants, provided care is taken to minimize the errors resulting from activity coefficient and liquid junction potential effects. Additional experimental results are presented to show that these effects also account for the apparent suppression of the sodium ion concentration observed in the presence of bicarbonate ion.

Bicarbonates↗
PubMed1981

Determination of sodium with ion-selective electrodes.

The advent of ion-selective electrodes made possible the potentiometry of sodium in serum and plasma. These methods were based on dilution of serum, as done in flame photometry, and the results were identical. Analysis of whole blood precludes dilution and so "direct" potentiometry was developed. Results by this technique are variable but tend to compensate for the spurious hyponatremias found by the "indirect" dilution methods due to displacement of volume by lipids and protein. However, there is no unambiguous theoretical basis on which to choose between the various direct ion-selective-electrode techniques and instruments. As an alternative, I propose use of current indirect methods, with numerical correction for the shift in normal sodium values in the presence of abnormal lipid and (or) protein. A table was constructed for making such corrections.

Blood Proteins↗
PubMed1985

Pseudohyponatremia in acute hyperlipemic pancreatitis. A potential pitfall in therapy.

Six patients had apparent hyponatremia associated with hyperlipidemia and acute pancreatitis. To our knowledge, only one such patient with acute pancreatitis has previously been described, although the association of hyperlipidemia with "pseudohyponatremia" had been well documented. One of the above patients, whose condition was hemodynamically unstable on admission, developed dangerous symptoms of hyperosmolarity and cerebral dysfunction following aggressive resuscitation with hypertonic saline solution. The pseudohyponatremia results from displacement of water in the serum by the lipids, with sodium existing only in the aqueous phase. This volume displacement results in errors of sodium measurement when the latter is determined by flame photometry or indirect potentiometry, but not when determined by ultracentrifugation and direct potentiometry.

Acute Disease↗
PubMed2001

Clavulanate-selective electrodes--application to pharmaceutical formulations.

The construction and assessment of a clavulanate anion-selective electrode and its application to the analysis of pharmaceutical formulations by direct potentiometry are described. The electrode, prepared without inner reference solution, was fabricated by use of a PVC membrane, with bis(triphenyl-phosphoranylidene)ammonium clavulanate as ion-exchanger dissolved in 2-nitrophenyl octyl ether as intermediate solvent and p-t-octylphenol as additive. The response of the electrode was linearly dependent on concentration within the range 2.4 x 10(-3)-1 x 10(-1) mol dm(-3) (ionic strength adjusted to 0.1 mol dm(-3)); the slope of the calibration plot was -59.4+/-0.9 mV decade(-1) and the reproducibility +/-0.6 mV day(-1). The response time was less than 20 s. Relative errors were <3.5% when results from analysis by direct potentiometry were compared with those from the reference method.

Anti-Bacterial Agents↗
PubMed2006

Cyclodextrin/imatinib complexation: binding mode and charge dependent stabilities.

Host-guest interactions in various protonation forms of the anticancer drug imatinib with beta-cyclodextrin (CD) and randomly methylated beta-CD (RAMEB) have been investigated using techniques of proton magnetic resonance spectroscopy ((1)H NMR), phase solubility, pH-potentiometry and electrospray ionization mass spectrometry (ESI-MS). Phase-solubility analysis showed A(L)-type diagram with beta-CD, which suggested the formation of 1:1 inclusion complexes. The 1:1 stoichiometry was confirmed by potentiometry in aqueous solution and by ESI-MS in the gas phase. Charge-specific stability constants of the neutral, mono-, di-, and tricationic forms of imatinib were determined for both the beta-CD and RAMEB. Stability of the beta-CD complexes shows an unexpected minimum at the monoprotonated form, while a stepwise decrease with increasing guest charge was observed for RAMEB. The 1:1 complex stoichiometry and stability constants of selected imatinib protonation species were verified by (1)H NMR titrations. Two-dimensional rotating frame nuclear Overhauser effect spectroscopy (ROESY) experiments were carried out to identify the interacting host-guest moieties. The observed ROESY cross-peaks indicated spatial proximities between several aromatic hydrogens of imatinib and beta-CD protons, revealing that the inclusion occurs by accommodation of the benzamide ring of imatinib.

Antineoplastic Agents↗
PubMed2004

Thermodynamic studies of mixed ionic/nonionic surfactant systems.

Mixtures of alkyltrimethylammonium bromide (CnTAB, n=12, 14, 16, 18) and Triton X-100 were studied at a range of mole fractions of ionic surfactant per nonionic surfactant. For each mixture, the cmc obtained from surface tension measurements differed from that obtained using potentiometry. The behavior of these mixed-surfactant systems showed three different regions with increasing total surfactant concentration. From the surface tension and potentiometry data, we obtained the free monomer concentration of ionic surfactant (mi), the micellar mole fraction of surfactant (xi), and the degree of dissociation (alpha) of ionic surfactant. We also obtained the free monomer concentration of Triton X-100 (m2) using PFG-NMR technique. A new equation was introduced to evaluate the activity coefficient in the micellar phase. The excess free energy (GE) and the synergetic parameters of mixtures were determined at various mole fractions of CnTAB/Triton X-100. Finally, the complexity of the synergism parameters was investigated.

Journal Article↗
PubMed2002

Binding ability of sialic acid towards biological and toxic metal ions. NMR, potentiometric and spectroscopic study.

The binary complexes of 5-amino-3,5-dideoxy-D-glycero-D-galactononulosic acid (NANA), commonly called N-acetyl neuraminic acid, formed with biological metal ions such as Co(II) and Cu(II) and toxic metal ions such as Cd(II) and Pb(II) were investigated in aqueous solution by means of potentiometry, UV and NMR spectroscopy. The corresponding ternary systems with 2,2'-bipyridine were studied in aqueous solution by potentiometry and UV spectroscopy. NANA co-ordinates all metal ions, in both binary and ternary systems through the carboxylic group (protonated or deprotonated according to pH), pyranosidic ring oxygen and glycerol chain alcoholic hydroxy groups. The prevailing species in the pH range 2-7 are of [M(NANA)(2)] type, and their stability constants are greater than those of simple carboxylate complexes. Above pH 7, the species [M(NANA)(2)OH](-) are also formed, but they do not prevent the precipitation of metal hydroxides. This work provides information on the solution state chemistry of NANA in the presence of bivalent metal ions; its great affinity for the toxic metals Cd(II) and Pb(II), near physiological conditions, and the relatively high stability of the complex species found may also account for the mechanism of toxicity.

Binding Sites↗
PubMed2001

Infrared spectra of phthalic acid, the hydrogen phthalate ion, and the phthalate ion in aqueous solution.

The infrared spectra of a series of aqueous solutions containing phthalic acid (1,2-benzenedicarboxylic acid) and varying pH were examined using attenuated total reflection Fourier transform infrared spectroscopy and potentiometry. The basis spectra of phthalic acid, the hydrogen phthalate ion, and the phthalate ion were isolated using a factor analysis in which the absorbance of these species varies with pH and total phthalate concentration according to equilibrium and mass balance relations. Assignments of these basis spectra were made by comparison with spectra calculated ab initio. The conditional formation constants of phthalic acid and the hydrogen phthalate ion were determined at 25.0+/-0.1 degrees C in 0.6 M NaCl ionic media using infrared spectroscopy and in 1.5 M NaCl ionic media using both infrared spectroscopy and potentiometry.

Carboxylic Acids↗
PubMed2005

Ion-selective supported liquid membranes placed under steady-state diffusion control.

Supported liquid membranes are used here to establish steady-state concentration profiles across ion-selective membranes rapidly and reproducibly. This opens up new avenues in the area of nonequilibrium potentiometry, where reproducible accumulation and depletion processes at ion-selective membranes may be used to gain valuable analytical information about the sample. Until today, drifting signals originating from a slowly developing concentration profile across the ion-selective membrane made such approaches impractical in zero current potentiometry. Here, calcium- and silver-selective membranes were placed between two identical aqueous electrolyte solutions, and the open circuit potential was monitored upon changing the composition of one solution. Steady state was reached in approximately 1 min with 25-microm porous polypropylene membranes filled with bis(2-ethylhexyl) sebacate doped with ionophore and lipophilic ion exchanger. Ion transport across the membrane resulted on the basis of nonsymmetric ion-exchange processes at both membrane sides. The steady-state potential was calculated as the sum of the two membrane phase boundary potentials, and good correspondence to experiment was observed. Concentration polarizations in the contacting aqueous phases were confirmed with stirring experiments. It was found that interferences (barium in the case of calcium electrodes and potassium with silver electrodes) induce a larger potential change than expected with the Nicolsky equation because they influence the level of polarization of the primary ion (calcium or silver) that remains potential determining.

Diffusion↗
PubMed1998

Functionalized de novo designed proteins: mechanism of proton coupling to oxidation/reduction in heme protein maquettes.

Proton exchange with aqueous media coupled to heme oxidation/reduction is commonly seen but not understood in natural cytochromes. Our synthetic tetrahelix bundle heme protein maquettes successfully reproduce natural proton coupling to heme oxidation/reduction. Potentiometry reveals major pK shifts from 4.2 to 7.0 and from 9.4 to 10.3 in the maquette-associated acid/base group(s) upon heme reduction. Consequently, a 210 mV decrease in the heme redox potential is observed between the two extremes of pH. Potentiometry with resonance Raman and FTIR spectroscopy performed over a wide pH range strongly implicates glutamate side chains as the source of proton coupling below pH 8.0, whereas lysine side chains are suggested above pH 8.0. Remarkably, the pK values of several glutamates in the maquette are elevated from their solution value (4.4) to values as high as 7.0. It is suggested that these glutamates are recruited into the interior of the bundle as part of a structural rearrangement that occurs upon heme binding. Glutamate to glutamine variants of the prototype protein demonstrate that removal of the glutamate closest to the heme diminishes but does not abolish proton exchange. It is necessary to remove additional glutamates before pH-independent heme oxidation/reduction profiles are achieved. The mechanism of redox-linked proton coupling appears to be rooted in distributed partial charge compensation, the magnitude of which is governed by the dielectric distance between the ferric heme and acid/base side chains. A similar mechanism is likely to exist in native redox proteins which undergo charge change upon cofactor oxidation/reduction.

Amino Acid Sequence↗
PubMed2003

Coordination properties of tris(2-carboxyethyl)phosphine, a newly introduced thiol reductant, and its oxide.

Acid-base properties and metal-binding abilities of tris(2-carboxyethyl)phosphine (TCEP), a newly introduced thiol group protectant, were studied in solution, using potentiometry, (1)H and (31)P NMR, and UV-vis spectroscopy, and also in the solid state by X-ray diffraction. Stability constants of complexes of the P-oxide of TCEP (TCEPO) were established by potentiometry. The list of metal ions studied included Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II). Cu(II) catalyzed oxidation of TCEP to TCEPO. For all other systems ML complexes were found as major species at neutral pH with TCEP and TCEPO. Monoprotonated MHL species were also detected in weakly acidic conditions for all TCEP complexes and for the Pb(II) complex of TCEPO, while hydrolytic MH(-1)L complexes were found for TCEP at the weakly alkaline pH range. The NiL(4) complex was found to form at excess of TCEP. Overall, the complexes were found to be rather weak, with log beta(ML) values around 3-5 for TCEP and 1.5-2.5 for TCEPO. The phosphorus pK(a) value for TCEP, 7.68, suggests that it can be a good buffer for studies at physiological pH.

Journal Article↗
PubMed2004

The ammine, thiosulfato, and mixed ammine/thiosulfato complexes of silver(I) and gold(I).

The M(I)-NH(3), M(I)-S(2)O(3)(2)(-), and M(I)-S(2)O(3)(2)(-)-NH(3) systems (M = Ag, Au) were studied at 25 degrees C and at I = 0.1 M (NaClO(4)) using a variety of analytical techniques. For the Ag(I)-NH(3)-S(2)O(3)(2)(-) system, AgS(2)O(3)NH(3)(-) was detected with formation constant log beta(111) (for the reaction Ag(+) + S(2)O(3)(2)(-) + NH(3) <--> AgS(2)O(3)NH(3)(-)) of 11.2, 10.4, and 10.8 on the basis of silver potentiometry, UV-vis spectrophotometry, and hydrodynamic voltammetry, respectively. Also, the values of log beta(101)(AgNH(3)(+)), log beta(102)(Ag(NH(3))(2)(+)), log beta(110)(AgS(2)O(3)(-)), and log beta(120)(Ag(S(2)O(3))(2)(3)(-)), obtained from silver potentiometry, were 3.59, 7.0, 8.97, 13.1, respectively. In the case of the ammine complexes, the log beta(101)(AgNH(3)(+)) and log beta(102)(Ag(NH(3))(2)(+)) values were found to be 3.5 and 7.1, respectively, from the UV-vis spectrophotometric experiments. The mixed species AuS(2)O(3)NH(3)(-) was detected in UV-vis spectrophotometric, hydrodynamic voltammetric, and potentiometric experiments with the stepwise formation constants (log K(111)) of -4.0, -3.5, -3.8, respectively, for the reaction Au(S(2)O(3))(2)(3)(-) + NH(3) <--> AuS(2)O(3)NH(3)(-) + S(2)O(3)(2)(-). At higher [NH(3)]/[S(2)O(3)(2)(-)] ratios (>10(5)), the formation of Au(NH(3))(2)(+) was also detected in spectrophotometric and potentiometric experiments with stepwise formation constants (log K(102)) of -5.4 and -5.3, respectively, according to the reaction AuS(2)O(3)NH(3)(-) + NH(3) <--> Au(NH(3))(2)(+) + S(2)O(3)(2)(-).

Journal Article↗
PubMed1998

Triethylenetetramine-N,N,N',N",N"',N"'-hexaacetic Acid (TTHA) and TTHA-Bis(butanamide) as Chelating Agents Relevant to Radiopharmaceutical Applications.

The N,N'-bis(butanamide) derivative of TTHA (TTHA = triethylenetetramine-N,N,N',N",N"',N"'-hexaacetic acid), and its Ga(3+) and In(3+) complexes were synthesized and characterized. The crystal X-ray diffraction structure of [Ga(2)(OH)(2)(TTHA)][Na(2)(H(2)O)(6)].2H(2)O was determined. The complex crystallizes in the monoclinic space group P2(1)/n with a = 7.179(2) Å, b = 20.334(3) Å, c = 10.902(5) Å, beta = 101.90(2) degrees, and Z = 2. Each gallium atom is bonded to six donor atoms (N(2)O(4)) in a slightly distorted octahedral geometry. The values of the protonation constants and the protonation sequence were determined by potentiometry and NMR. The stability constants of the Al(3+), Ga(3+), Fe(3+), and In(3+) complexes of TTHA-(BuA)(2) and of the Ga(3+) complex of TTHA were determined by potentiometry. The structures, in solution, of the Al(3+), Ga(3+), and In(3+) complexes of TTHA-(BuA)(2) and TTHA were analyzed by (1)H, (13)C, (27)Al, (71)Ga, and (115)In NMR techniques. Derivatization of two terminal carboxylates by butanamide substituents leads to a significant decrease of the total ligand basicity (5.77 log units) and to a change of the solubility of the resulting complexes. The stability constant of the ML complexes of TTHA-(BuA)(2) with Fe(3+) exhibits the highest value of the series (10(23.92)). The In(3+) complex is more stable than that of Ga(3+) and almost as stable as that of the Fe(3+). However, the decrease in indium and iron complex stability is less drastic going from TTHA to TTHA-(BuA)(2) (about 3 log units) than for Al(3+) or Ga(3+) (about 6 log units). pM values calculated under physiological conditions for DTPA, TTHA, and the bis(butanamide) derivatives have shown that while DTPA remains a ligand of choice to chelate Fe(3+) and In(3+) ions in vivo compared to transferrin as competitor ligand, TTHA, surprisingly, appears to be the best of these four ligands (pM = 22.71) to chelate Ga(3+).

Journal Article↗
PubMed2000

Synthesis of a ligand based upon a new entry into the 3-hydroxy-N-alkyl-2(1H)-pyridinone ring system and thermodynamic evaluation of its gadolinium complex.

The synthesis of a new, more water soluble derivative of TREN-Me-3,2-HOPO (tris[(3-hydroxy-1-methyl-2-oxo-1,2- didehydropyridine-4-carboxamido)ethyl]amine) is presented. The synthesis starts with the condensation reaction of (N-methoxyethylamino)acetonitrile hydrochloride and oxalyl chloride to give 3,5-dichloro-N-(methoxyethyl)-2(1H)-pyrazinone. The 3-position is readily substituted with a benzyloxy group, and the pyrazinone is converted to ethyl 3-(benzyloxy)-N-(methoxyethyl)-2(1H)-pyridinone-4-carboxylate by a Diels-Alder cycloaddition with ethyl propiolate. Basic deprotection of the ester followed by activation, coupling to tren, and acidic deprotection of the benzyl groups gives the ligand TREN-MOE-3,2-HOPO (tris[(3-hydroxy-1-(methoxyethyl)- 2-oxo-1,2-didehydropyridine-4-carboxamido)ethyl]amine). The gadolinium complex of TREN-MOE-3,2-HOPO was prepared by metathesis, starting from gadolinium chloride. The solubility of the new metal complex is significantly enhanced. The four protonation constants (determined by potentiometry) for TREN-MOE-3,2-HOPO (log Ka1 = 8.08, log Ka2 = 6.85, log Ka3 = 5.81, log Ka4 = 4.98) are virtually identical to those reported for the parent ligand. The stability constants for the gadolinium complex of TREN-MOE-3,2-HOPO determined by potentiometry (log beta 110 = 19.69(2), log beta 111 = 22.80(2)) and by spectrophotometry (log beta 110 = 19.80(1), log beta 111 = 22.88(1), log beta 112 = 25.88(1)) differ slightly from those for the parent ligand; this follows from a change in the complexation model in which a new diprotonated species, [Gd(TREN-MOE-3,2-HOPO)(H)2]2+, was included. The presence of this extra species was demonstrated by factor analysis, comparison of spectral data, and nonlinear least-squares refinement. Significant formation of this species is observed between pH 3 and pH 1.5.

Gadolinium↗
PubMed2005

Rigid MIIL2Gd2III (M = Fe, Ru) complexes of a terpyridine-based heteroditopic chelate: a class of candidates for MRI contrast agents.

Rigid chelates of high-molecular weight, [M(tpy-DTTA)2]6- (M = Fe, Ru), are obtained upon self-assembly around one M(II) ion of two terpyridine-based molecules substituted in the 4'-position with the polyaminocarboxylate diethylenetriamine-N,N,N'',N''-tetraacetate, tpy-DTTA4-. The protonation constants of tpy-DTTA4- (log K1 = 8.65(4), log K2 = 7.63(4), log K3 = 5.25(6), log K4 = 3.30(7)) and [Fe(tpy-DTTA)2]6- (log K1 = 8.40(4), log K2 = 7.26(4)) have been determined by potentiometry, 1H NMR and UV-vis titrations. The thermodynamic stability constant log K(GdL) of [Fe(tpy-DTTA)2Gd2(H2O)4] measured at 25 degrees C by potentiometry is 10.87. This relatively low value is due to the direct linkage of the polyaminocarboxylate part to the electron-withdrawing terpyridine. UV-vis absorbance spectra of [M(tpy-DTTA)2Gd2(H2O)4] and 1H NMR spectra of [M(tpy-DTTA)2Eu2(H2O)4] revealed similar solution behavior of the Fe and Ru complexes. An I(d) water-exchange mechanism (DeltaV++ = +6.8 +/- 1 cm3 mol(-1)) with a rate constant of k(ex)298 = (5.1 +/- 0.3) x 10(6) s(-1) has been found for [Fe(tpy-DTTA)2Gd2(H2O)4] by 17O NMR. A slow rotational correlation time (tau(RO) = 410 +/- 10 ps) and the presence of two water molecules (q = 2) in the coordination inner-sphere of each Gd(III) ion have also been determined for this complex. A remarkably high relaxivity has been observed for both [M(tpy-DTTA)2Gd2(H2O)4] complexes (at 20 MHz and 37 degrees C, r(1) = 15.7 mM(-1) s(-1) for the Fe complex, and r(1) = 15.6 mM(-1) s(-1) for the Ru complex).

Journal Article↗