Atmospheric pressure ionization mass spectrometry techniques for the analysis of alkyl ethoxysulfate mixtures.

This paper compares two liquid introduction atmospheric pressure ionization techniques for the analysis of alkyl ethoxysulfate (AES) anionic surfactant mixtures by mass spectrometry, i. e., electrospray ionization (ESI) in both positive and negative ion modes and atmospheric pressure chemical ionization (APCI) in positive ion mode, using a triple quadrupole mass spectrometer. Two ions are observed in ESI(+) for each individual AES component, [M + Na](+) and a "desulfated" ion [M - SO3 + H](+), whereas only one ion, [M - Na](-) is observed for each AES component in ESI(-). APCI(+) produces a protonated, "desulfated" ion of the form [M - NaSO3 + 2H](+) for each AES species in the mixture under low cone voltage (10 V) conditions. The mass spectral ion intensities of the individual AES components in either the series from ESI(+) or APCI(+) can be used to obtain an estimate of their relative concentrations in the mixture and of the average ethoxylate (EO) number of the sample. The precursor ions produced by either ESI(+) or ESI(-), when subjected to low-energy (50 eV) collision-induced dissociation, do not fragment to give ions that provide much structural information. The protonated, desulfated ions produced by APCI(+) form fragment ions which reveal structural information about the precursor ions, including alkyl chain length and EO number, under similar conditions. APCI(+) is less susceptible to matrix effects for quantitative work than ESI(+). Thus APCI(+) provides an additional tool for the analysis of anionic surfactants such as AES, especially in complex mixtures where tandem mass spectrometry is required for the identification of the individual components.

Quantitative similarity of zinc and calcium binding to heparin in excess salt solution.

Zn2+ binding to the anticoagulant heparin was examined using a dye spectrophotometric method, with added NaCl concentrations of 0.005, 0.0075, 0.01, 0.02 and 0.04 mol/l. The results are shown as Scatchard plots and demonstrate the entropy-driven anticooperativity of Zn2+ binding to heparin. From these Scatchard plots, intrinsic binding constants are determined and are compared to our earlier data for Mg2+ and Ca2+ binding to heparin at similar ionic strengths (J. Mattai and J.C.T. Kwak, Biochim. Biophys. Acta 677 (1981) 303), and to Manning's two-variable theory (G.S. Manning, Q. Rev. Biophys. 2 (1978) 179) for a generalized system of polyelectrolyte + divalent cations + univalent cations. While Mg2+ binding to heparin is purely electrostatic (delocalized or territorial), Zn2+ and Ca2+ binding is much stronger and more specific. Binding constants for these two cations are identical, suggesting similar mechanisms for Zn2+ and Ca2+ binding to heparin.

The binding of cationic surfactants by DNA.

Isotherms for the binding of dodecyltrimethylammonium (DTA+) and tetradecyltrimethylammonium (TTA+) ions by DNA in aqueous solution at 30 degrees C are reported. The binding isotherms were determined using a potentiometric technique with cationic surfactant-selective electrodes. The DNA concentrations used are 5 X 10(-4) and 10(-3) equiv./kg, surfactant concentrations varying from 3 X 10(-6) M to the critical micelle concentration. The influence of added NaCl (0.01 M) on the binding process is studied. The binding process is shown to be highly cooperative. Applying the binding theory of Schwarz and of Satake and Yang, binding constants and cooperativity parameters can be calculated. The binding constant K is found to be 1.2kT larger for TTA+ than for DTA+ in salt-free solution, and 1.4kT larger for TTA+ than for DTA+ in 0.01 M NaCl. The cooperativity parameter mu is about 1.1kT larger for TTA+ in salt-free solution, and 1.2kT larger in 0.01 M NaCl. It is concluded that the hydrophobic part of the bound surfactant is not completely immersed in the hydrophobic DNA core, but also interacts with other surfactant molecules. This situation is compared to the case of micelle formation.

A dye spectrophotometric method for binding studies of Zn2+ and Mn2+ by biopolyelectrolytes.

A dual-wavelength dye spectrophotometric method is reported for measuring zinc and manganese activities using the dyes tetramethylmurexide (TMMX) and murexide (MX) respectively. The method is applied to the measurement of the activities of these metal ions in solutions of the polyelectrolyte dextransulfate with added sodium chloride. Polyion concentrations, Cp (expressed as moles sulfate ion litre ) of 0.001 and 0.002 are studied at total ionic strengths 0.005, 0.0075, 0.01, 0.02 and 0.03 mole/1. Divalent metal ion concentrations are varied between 0 and 1.0 Cp. The results for the metal ion activities are expressed in the form of binding isotherms, theta2 versus C2/Cp (theta2 = C2b/Cp; C2b = bound divalent metal ion concentration) and Scatchard plots, K2 versus theta2/(C2-C2b), at different ionic strengths. The experimental data are correlated with the "two-variable theory" eveloped for these mixed counterion systems by Manning. This comparison shows that the observed decrease in theta2 and K2 with ionic strength at fixed C2 and Cp is generally well predicted by the two-variable theory. Both Zn and Mn bind to the same extent to dextransulfate. This observation, and the reasonable agreement of the data with the "two-variable theory" may be interpreted as indicating a delocalized form of binding of these metal ions to the polymer.

The binding of divalent metal ions to polyelectrolytes in mixed counterion systems. I. The dye spectrophotometric method.

The dye spectrophotometric method for the measurement of the activity of divalent metal ions in polyelectrolyte solutions containing added electrolytes is discussed. The method is applied to mixtures containing the dextransulfate polyanion, NaCl, and MgCl2 or Ca2. A two wavelength ratio method as applied to polyelectrolyte solutions is compared to the standard method which makes use of the previous determination of the dye-metal ion formation constant. The ratio method is found to be a convenient and reliable method which is not influenced by decomposition of the dye or by statistical errors in the extrapolation procedure. The activity coefficients as determined by the two wavelength dye spectrophotometric method are compared to results of Donnan exclusion measurements, and of EMF measurements using a calcium ion selective electrode. The results of the spectrophotometric method are equal to those of the two other methods within the limits of error in the latter. The spectrophotometric measurements can extend to much lower ion activaties than the other two methods, and can be done in the presence of a large excess of added electrolyte, yielding results of considerably improved precision when compared to Donnan and EMF methods.

The binding of divalent metal ions to polyelectrolytes in mixed counterion systems. II. Dextransulfate-Mg2+ and dextransulfate-Ca2+ in solutions containing added NaCl or KCl.

Measurements of magnesium and calcium ion activities in solutions of the polyelectrolyte dextransulfate, with added sodium chloride or potassium chloride are presented. A two wavelength dye spectrophotometric method is used. Dextransulfate concentrations Cp (expressed as moles sulfate ion/litre) vary between 0.001 and 0.007, total ionic strengths between 0.005 and 0.08 mole/XXX. Divalent metal ion concentrations are varied between 0 and 1.2 Cp. The results for the metal ion activities are expressed in the form of parameters theta2 = C2/Cp (C(2bp) = bound divalent metal ion concentration) and K2 = theta2/(C2-C2b). For each divalent/univalent counterion pair the values obtained for theta2 and K2 as a function of C2,Cp, and ionic strength are compared to predictions of the "two variable theory" developed for these mixed counterion systems by Manning. This comparison shows that the observed decrease in theta2 with increasing ionic strength at fixed C2 and Cp is generally well predicted by the two variable theory. The extent of divalent ion binding at a given C2, Cp, and ionic strength is largest for the Ca/Na counterion combination, and lowest for the Mg/K combination.

Mean activity coefficients for the simple electrolyte in aqueous mixtures of polyelectrolyte and simple electrolyte. V. Common counterion mixtures of alkali-metal dextransulfates with alkali metal chlorides.

Mean molal activity coefficients of simple electrolyte in aqueous solutions of Li, Na, K or Cs salts of dextransulfate (DS) with added LiCl, NaCl, KCl or CsCl are reported. The measurements were carried out by means of an electrochemical cell method using a cation exchange membrane as cation selective electrode and Ag/AgCl electrodes. For LiDS-LiCl, NaDS-NaCl and CsDS-CsCl systems the polymer concentration, mp, was varied from 0.0088 to 0.113 m and at a given mp the ratio X of the polymer to salt concentration was varied from 0.5 to 16. Due to the insolubility of KDS in high concentration of KCl, the measurements on KDS-KCl system were performed in the mp range of 0.0088--0.089 m and some of the smaller X values were omitted. The activity coefficient results are compared to Manning's limiting laws, the additivity rule, and to new limiting laws. The additivity rule can give an excellent representation of the data for all mp values when gammap is used as an adjustable parameter.

The equivalent conductivity of aqueous solutions of alkali metal salts of a number of ionic polysaccharides.

Measurements of the equivalent conductivity of aqueous solutions of alkalimetal salts of a number of ionic polysaccharides at 25 degrees C are reported. The polysaccharides studied are: (1) three carboxymethylcelluloses of various degrees of substitution (Li+, Na+, Cs+ salts) in the concentration range 4 X 10(-4) - 6 X 10(-2) equivalents alkali ion per liter, (2) Polypectate (Li+, Na+, K+, Cs+ salts) in the range 1.5 X 10(-4) - 2 X 10(-2) equivalent alkali ion per liter, and (3) Dextransulfate (Li+, Na+, K+ salts) in the range 3 X 10(-4) - 10(-1) equivalent alkali ion per liter. The results are compared to some earlier data and to a limiting law for conductance of rod-like polyions derived by Manning. It is concluded that although qualitative agreement is obtained between observed data and the limiting law when various polyions of different charge densities are compared at a given concentration, the concentration dependence predicted by the limiting law is in agreement with the observed curves only for polyions of a relatively low charge density. At higher charge densities appreciable deviations occur, and dextransulfate which does not have the rod-like polyion structure required by theory does not conform to the predicted concentration dependence at all.