Low‐rate dynamic contact angles on poly(methyl methacrylate/ethyl methacrylate, 30/70) and the determination of solid surface tensions

Low‐rate dynamic contact angles of 12 liquids on a poly(methyl methacrylate/ethyl methacrylate, 30/70) P(MMA/EMA, 30/70) copolymer were measured by an automated axisymmetric drop shape analysis‐profile (ADSA‐P). It was found that five liquids yield nonconstant contact angles, and/or dissolve the polymer on contact. From the experimental contact angles of the remaining seven liquids, it is found that the liquid–vapor surface tension times cosine of the contact angle changes smoothly with the liquid–vapor surface tension (i.e., γ_l|Kv cos θ depends only on γ_l|Kv for a given solid surface or solid surface tension). This contact angle pattern is in harmony with those from other methacrylate polymer surfaces previously studied.^45,50 The solid–vapor surface tension calculated from the equation‐of‐state approach for solid–liquid interfacial tensions¹⁴ is found to be 35.1 mJ/m², with a 95% confidence limit of ± 0.3 mJ/m², from the experimental contact angles of the seven liquids. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2039–2051, 1999     

Wettability of biodegradable surfaces

The study of the interfacial characteristics of biodegradable polymers/copolymers is of importance from the point of view of both surface science and pharmaceutical/cosmetic applications. Films formed from biodegradable polymers allow systematic wettability studies on surfaces with a wide range of copolymer (chemical) compositions. The possibility of interchanging these drug carrier polymers, if their wetting characteristics are similar, could be beneficial to diverse applications. Low-rate dynamic contact angles on films (solvent cast on polar substrates, i.e. on silicon wafer) of poly(lactic acid), and its copolymers with poly(glycolic acid), (with four different copolymer ratios of 85/15, 75/25, 65/35 and 50/50) were measured by axisymmetric drop shape analysis-profile (ADSA-P) with four liquids: water, formamide, 2,2′-thiodiethanol and 3-pyridylcarbinol. The solid surface tensions, γ_sv, were calculated from the advancing contact angles, θ_A. The surface topography of the polymer films was investigated by atomic force microscopy (AFM). The surface composition of the polymer layers was analyzed by X-ray photoelectron spectroscopy (XPS). The advancing contact angles were found to be independent of the composition of the copolymers, while the receding angles, θ_R, did decrease with increasing ratio of the polar component [poly(glycolic acid)] in the copolymers. The solid surface tensions calculated from the advancing contact angles of the liquids for all homo- and copolymers were the same within the error limit; the mean value being γ_sv=35.6 ± 0.2 mJ/m². The surface roughness, which was obtained from AFM images, increased with increasing poly(glycolic acid) ratio, without affecting the advancing contact angles. The constancy of γ_sv is attributed to the effect of the surface activity of the nonpolar segments of the polymer chains, which oriented to form the outermost layer of the film. This was confirmed by XPS analysis. Received: 06 November 2000 Accepted: 09 May 2001     

ADSA-TRIS: a new method to study interfacial phenomena at polymer–aqueous solution interfaces

Axisymmetric drop shape analysis-profile (ADSA-P) was combined with total reflectometric interference spectroscopy (TRIS) in one experimental setup to study the interfacial phenomena at solid–liquid and liquid–vapor interfaces caused by adsorption/desorption (dissolution) of surface-active substances. Using sessile liquid droplets on polymer film/chromium-coated glass substrates that were optically matched with an immersion oil to a TRIS reflection prism, the optical thickness (product of physical thickness d and refractive index n) of the polymer film can be estimated by evaluating the wavelength-dependent intensity of reflected light. The sessile droplet is analyzed simultaneously by an ADSA setup arranged in a transverse direction to the path of the white-light beam of TRIS. From this analysis, the solid–vapor interfacial tension γ _lv(t), contact angle θ(t), contact radius r(t), drop volume V(t), and solid–liquid interfacial tension γ _sl(t) can be monitored as a function of time. The new method was applied to study polystyrene and poly(4-hydroxystyrene) surfaces in contact with aqueous buffer solutions and with protein solutions. The time-dependent changes in the optical film thickness caused by the adsorption of human serum albumin (HSA) and lysozyme (LSZ) were accompanied by changes in the solid–liquid interfacial tension. From the detailed study of both parameters, conclusions can be drawn with regard to the adsorption kinetics of the proteins on the hydrophobic polystyrene surfaces and to conformational changes occurring within the adsorbed protein layers. Figure Photo of the ADSA-TRIS setup     

Fast dynamic wetting of polymer surfaces by miscible and immiscible liquids

The initial stages of spontaneous spreading of a solvent drop (toluene) on the surface of a soluble polymer (polystyrene) have been studied with a high-speed camera. For drops of 1–4 μL volume, the increase in contact radius r can be described by a power law r μ t^a r \propto {t^{\alpha }} , with the spreading exponent α = 0.50 and for the first ≈8 ms. Thereafter, the three-phase contact line was pinned leading to a macroscopic static contact angle of Θ₀ = 12–15°. The insoluble liquids ethanol (α = 0.47, Θ₀ = 0) and water (α = 0.35, Θ₀ = 90°) showed a slower spreading. We attribute the fast spreading of toluene to the strong interaction with the polymer, like in reactive wetting. The finite macroscopic contact angle indicates the formation of a ridge by softening of polystyrene due to permeated toluene and the subsequent plastic deformation by the surface tension of the liquid. This interpretation is supported by experiments on polymers grafted from a silicon wafer. Toluene completely wets polymer brush surfaces. Transport of toluene through the vapor phase plays a significant role.     

Determination of accurate surface tensions of maleimide copolymers containing fluorinated side chain from contact angle measurements

Surface energetics of two fluorinated maleimide copolymers containing fluorinated side chain, i.e., poly(ethene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ETMF) and poly(octadecene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ODMF), are studied by contact angle measurements with 10 liquids consisting of fairly bulky molecules. Because of the inertness of octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS) molecules, their contact angles are used to determine the surface tension of the two polymers. It is found that other liquids show specific interactions with the ETMF films, and their contact angles deviate from a smooth curve that represents the surface tension of ETMF, i.e., 11.00 mJ/m². On ODMF surfaces, only OMCTS and DMCPS yield useful contact angles. Other liquids either dissolve the polymer film or show a slip-stick pattern. This finding is discussed in terms of interactions between segments of the polymer chains and the test liquids. OMCTS and DMCPS are suggested as the appropriate probe liquids, meeting specific criteria necessary for the determination of accurate surface tension of fluoropolymers.     

Interpretation of contact angle measurements on two different fluoropolymers for the determination of solid surface tension

Contact angle measurements with a large number of liquids on the semi-fluorinated acryl polymer EGC-1700 films are reported. The surface tension was determined to be gammasv=13.84 mJ/m2 from contact angles of octamethylcyclotetrasiloxane (OMCTS) and decamethylcyclopentasiloxane (DMCPS). Inertness of these two liquids makes them ideal for determination of surface tension of low-energy fluoropolymers. On the other hand, contact angles of many other liquids deviated somewhat from a smooth contact angle pattern that represents the EGC-1700 surface tension. It is argued that noninertness of the molecules of these liquids gives rise to specific interactions with the polymer film, causing the deviations. Furthermore, contact angles of a series of n-alkanes (n-hexane to n-hexadecane) showed systematic deviations from this curve, similar to the trend observed for n-alkanes/Teflon AF 1600 systems studied earlier. Adsorption of vapor of short-chain liquids onto the polymer film caused their contact angles to fall above the gammasv=13.84 mJ/m2 curve, and a parallel alignment of molecules of the long-chain n-alkanes in the vicinity of the solid was the explanation for the deviation of their contact angles below it. It is found that vapor adsorption effect is more significant in the case of Teflon AF 1600, while the alignment of liquid molecules close to the surface is more pronounced for EGC-1700.     

Polyurethane cationomers synthesised with 4,4′-methylenebis(phenyl isocyanate), polyoxyethylene glycol and <Emphasis Type="Italic">N</Emphasis>-methyl diethanolamine

Polyurethane cationomers with increased contents of ions were synthesised in the reaction of 4,4′-methylenebis(phenyl isocyanate) (MDI) with polyoxypropylene glycol (M = 450) and N-methyl diethanolamine (N-MDA). Amine segments were built-in to the urethane–isocyanate prepolymer in the reaction with formic acid and then they were converted to alkyl-ammonium cations. The obtained isocyanate prepolymers were then extended in the aqueous medium with the use of 1,6-hexamethylenediamine. That yielded stable aqueous dispersions, which were applied on the surfaces of test poly(tetrafluoroethylene) samples. After evaporation of water, the dispersions formed thin polymer coatings. ¹H and ¹³C NMR spectral methods were employed to confirm chemical structures of synthesised cationomers and to modify their quantitative composition in relation to that assumed on the basis of the stoichiometry of the reactions, which were conducted on successive stages of the polyaddition process. Furthermore, the GPC method was used to learn the sizes and distributions of mean molecular weights of those cationomers. Based on ¹H NMR spectra, the factor κ was calculated which represented the polarity level of the obtained cationomers. Good correlation was found between that factor and the free surface energy γ _S (increasing in the range 38–42 mJ/m²) as well as its polar and acid-base components, as determined from the van Oss–Good model on the basis of measured wetting angles between the coatings and model liquids with various polarities. The values of κ and γ _S parameters resulted principally from the increasing amounts of cations NH⁺, which were evaluated on the basis of the concentrations of tertiary nitrogen atoms increasing within 1.37–2.66 wt%. Those concentrations and amounts resulted, in turn, from the amounts of amine N-MDA which could be built into cationomers. The effects were discussed of chemical structures and polarity specifications of polyurethane cationomers on the viscosities of produced aqueous dispersions and on the sizes of their colloidal particles, on the values of free surface energy and on its polar and acid-base components, and on the glass transition temperatures T _g2 of the rigid segments as found by the differential scanning calorimetry (DSC) method.     

The surface property and aggregation behavior of a hydrophobically modified cyclodextrin

The surface property of an amphiphilic cyclodextrin 2-O-(hydroxypropyl-N,N-dimethyl-N-dodecylammonio)-β-cyclodextrin (HPDMA-C₁₂-CD) was investigated using oscillating bubble rheometer and electrical conductivity method at different temperatures. The surface tension and dilational viscoelasticity of HPDMA-C₁₂-CD were provided. The results showed that HPDMA-C₁₂-CD could adsorb on the air–water interface, which decreased the surface tension of water efficiently. Critical micelle concentration (cmc) can be clearly defined from the surface tension isotherm. pC₂₀ and π _cmc were derived from the surface tension isotherms as well. The thermodynamic parameters (ΔG   ⁰ _m  , ΔH   ⁰ _m  , −TΔS   ⁰ _m) derived from electrical conductivity indicated that the micellization of HPDMA-C₁₂-CD was entropy-driven at lower temperature, while it was enthalpy-driven at higher temperature. The dilational modulus appeared a maximum value while the phase angle appeared two maxima as a function of HPDMA-C₁₂-CD concentration.     

Silicon-Modified Carbohydrate Surfactants V: The Wetting Behaviour of Low-Molecular-Weight Siloxane,Carbosilane, Silane and Polysilane Precursors on Low-Energy Surfaces

The surface tensions, wetting tensions, contact angles and solid/liquid interfacial tensions of defined siloxanes as well as those of analogous carbosilanes, polysilanes and neopentyl substituted silanes were determined. The wetting experiments were carried out on a glass plate coated with perfluoroalkyl methacrylate (FC 722^®). The siloxanes possess the lowest surface tensions. Due to the presence of oxygen atoms in the siloxane backbone, a donor–acceptor portion (γ^+/−_lv) of the surface tension of about 1–2 mN/m was determined. The solid/liquid interfacial tension also contains a donor–acceptor portion (γ^+/−_sl). Its value is almost identical to that of γ^+/−_lv. The γ^+/−_sl differences between individual molecules of the same surface tension are responsible for contact angle differences of up to 4°. © 1997 John Wiley & Sons, Ltd.     

Dynamic behavior of polymer surface and the time dependence of contact angle

The increased attention has been focused on the re-searches of soft materials proposed by Pierre-Gilles de Gennes, a Nobel Prize Laureate in Physics. A special issue of “Science” on soft surfaces was published in 2002 to review specific surface properti…     

Surface active and aggregation behavior of methylimidazolium-based ionic liquids of type [Cnmim] [X], n?=?4, 6, 8 and [X]?=?Cl?, Br?, and I? in water

The surface active and aggregation behavior of ionic liquids of type [C _n mim][X] (1-alkyl-3-methylimidazolium (mim) halides), where n = 4, 6, 8 and [X] = Cl⁻, Br⁻ and I⁻ was investigated by using three techniques: surface tension, ¹H nuclear magnetic resonance (NMR) spectroscopy, small-angle neutron scattering (SANS). A series of parameters including critical aggregation concentrations (CAC), surface active parameters and thermodynamic parameters of aggregation were calculated. The ¹H NMR chemical shifts and SANS measurements reveal no evidence of aggregates for the short-chain 1-butylmim halides in water and however small oblate ellipsoidal shaped aggregates are formed by ionic liquids with 1-hexyl and 1-octyl chains. Analysis of SANS data analysis at higher concentrations of [C₈mim][Cl] showed that the microstructures consist of cubically packed molecules probably through π–π and hydrogen bond interactions.     

Function and performance of silicone copolymer (VI). Synthesis and novel solution behavior of water-soluble polysiloxanes with different hydrophiles

Silicone surfactants containing different pendant hydrophilic groups such as diethanol tertiary amine (SHE, nonionic), diethanol methyl quaternary amine (cationic) and triethyl quaternary amine (cationic) have been synthesized and characterized by ¹H and ¹³C NMR and gel permeation chromatography. The solution behavior of these novel surfactants has also been investigated by surface tension measurement and a fluorescence method. It has been observed that the surface tension of these surfactants decreases as a function of time at a very low polymer concentration (1 × 10⁻⁴ wt%). At higher concentration (0.1 wt%), the equilibrium surface tensions reached very low values compared to that of typical polymer surfactants, for example, poly(ethylene oxide–propylene oxide) block copolymer (EPE0.8). In addition, the low I ₁/I ₃ values of these silicone surfactants indicate the formation of polymer aggregates in aqueous solution, and an extremely low I ₁/I ₃ value of SHE (1.06) compared to other polymeric surfactants (EPE0.8) and conventional surfactants [poly(ethylene glycol n-nonyl phenyl ethers), cetyltrimethylammonium bromide, and sodium dodecyl sulfate] indicates its stronger hydrophobicity. Received: 15 May 2000 Accepted: 18 October 2000     

Bile salt structural effect on the thermodynamic properties of a catanionic mixed adsorbed monolayer

The interfacial effects of two bile salts (sodium deoxycholate (NaDC) and sodium dehydrocholate (NaDHC)) in a catanionic mixed adsorbed monolayer have been investigated at 25 °C. The surfactant interfacial composition, the interfacial orientation of the molecules and the energy changes are analysed to show a thermodynamic evidence of the hydrophobic BSs effect during its intercalation into interfacial adsorbed didodecyldimethyl ammonium bromide (DDAB) molecules. Both mixed systems (NaDC–DDAB and NaDHC–DDAB) have analogous adsorption efficiencies, which are similar from a pure DDAB monolayer and superior to that obtained for both bile salts molecules. Nevertheless, their adsorption effectiveness is different: NaDC causes an increment of Γ while NaDHC produces the opposite effect. The adsorption efficiency in surface tension reduction is due to the existence of interfacial synergistic interactions (confirmed by the analysis of β ^γ and ΔG _ad ⁰ values). Maximum synergistic interaction is seen for α _BSs = 0.4. The hydrophobic steroid backbone of NaDHC molecule presents a deep interfacial penetration than NaDC. This fact causes a great disturbance of DDAB hydrocarbon tails and conduces to a large separation of molecules (high A _m values) which explains the reduction of adsorption effectiveness (low Γ _m values).     

Preparation of ultramicro-, micro-, and supermicroporous carbon adsorbents by template procedure

The new template procedure for preparing ultramicro-, micro-, and supermicroporous carbon adsorbents is proposed on the basis of the use of two polymers with different thermal stabilities as a template matrix and a carbonizable carbon source. The polymeric template matrix is removed by thermal decomposition in the low-temperature pyrolysis of the polymer mixture, whereas the second polymer component of a mixture is transformed into a carbonizate. The resultant monolithic carbonizate is the polymeric matrix replica and represents a molecular-sieve ultramicroporous carbon adsorbent, which adsorbs water vapor at 293 K and does not adsorb nitrogen vapor at 77 K. The activation of this carbonizate with water vapor leads to a series of micro-and supermicroporous carbon adsorbents with a broad range of the parameters of a pore structure: BET specific surface area S _BET is 610–2130 m²/g, micropore volume W ₀ is 0.20–0.69 cm³/g, micropore half-width x ₀ (slit model) is 0.20–0.70 nm, mesopore specific area S _me is 20–1000 m²/g, and characteristic adsorption energy E ₀ is 15.6–27.4 kJ/mol. Original Russian Text ? O.K. Krasil’nikova, A.M. Voloshchuk, A.E. Evsyukhin, N.Y. Lomovsakaya, 2006, published in Kolloidnyi Zhurnal, 2006, Vol. 68, No. 2, pp. 207–213.     

Development of Passive and Active Barrier Coatings on the Basis of Inorganic–Organic Polymers

Summary. With a new kind of barrier coating material, namely inorganic–organic polymers, it is possible to obtain excellent barrier properties against oxygen, water vapor, and flavor permeation. These hybrid polymers can be synthesized by the sol–gel technique. If extremely low permeation values are needed, the combination of hybrid polymer coatings with thin inorganic oxidic layers (SiO_x, AlO_x) is very effective and leads to permeation values for oxygen and water vapor below 10⁻³ cm³/m² · d · bar or g/m² · d. These passive barrier layers can be further improved by the combination with active oxygen barrier layers which have been developed for the food packaging industry. This approach makes these multilayer laminates promising candidates for special applications in the food packaging industry as well as for sophisticated applications in technical areas: the encapsulation of sensitive organic devices like solar cells, organic light emitting diodes, or polymer electronic systems.     

Synthesis and characterisation of coating polyurethane cationomers containing quaternary ammonium alkyl groups derived from built-in alkyl bromides

Polyurethane cationomers were synthesised in the reaction of 4,4′-methylenebis(phenyl isocyanate) with polyoxypropylene glycol (M = 450) and N-methyl diethanolamine. Amine segments were built-in to the urethane–isocyanate prepolymer in the reaction with 1-bromoalkanes (C₂–C₁₀), and then they were converted to alkyl-ammonium cations. The obtained isocyanate prepolymers were then extended in the aqueous medium. That yielded stable aqueous dispersions which were applied on the surfaces of test poly(tetrafluoroethylene) plates. After evaporation of water, the dispersions formed thin polymer coatings. ¹H and ¹³C NMR spectral methods were employed to confirm chemical structures of synthesised cationomers. Based on ¹H NMR and IR spectra, the factors κ and α₁ or α₁ were calculated, which represented the polarity level of the obtained cationomers. The differential scanning calorimetry method revealed decline of T _g for the hard urethane and urea segments from 60 °C to 46 °C when the number of carbon atoms increased in the alkyl radical attached to the ammonium cation. Changes were discussed in the surface free energy (SFE) and its components, as calculated independently according to the methods suggested by van Oss-Good and by Owens–Wendt, in relation to chemical structures of cationomers. The growing length (from C₂ to C₁₀) of the alkyl radical attached to the N atom in the cationomer chain was found to reduce the value of SFE of the polymer coating from 46 to 28 mJ/m². That is caused by gradual weakening of long-range interactions, within which the highest share is taken by dispersion interactions.     

Miniaturized liquid–liquid extraction coupled with ultra-performance liquid chromatography/tandem mass spectrometry for determination of topramezone in soil,corn, wheat,and water

A rapid and simple miniaturized liquid–liquid extraction method has been developed for the determination of topramezone in soil, corn, wheat, and water samples using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-electrospray ionization (ESI)/MS/MS). The established method for the extraction and purification procedure was based on liquid–liquid partitioning into an aqueous solution at a low pH (pH ≈ 2.5), followed by back-partitioning into water at pH > 9. Two precursor, product ion transitions for topramezone were measured and evaluated to provide the maximum degree of confidence in the results. Under negative ESI conditions, quantitation was achieved by monitoring the fragment at m/z = 334 and the qualitative fragment at m/z = 318, whereas also collecting the corresponding parent ion at m/z = 362. Chromatographic separation was achieved using gradient elution with a mobile phase consisting of methanol and a 0.01% aqueous ammonium hydroxide solution. Recovery studies for soil, corn, wheat, and water were conducted at four different topramezone concentrations (5 or 10, 50, 100, and 1,000 μg kg⁻¹); the overall average recoveries ranged from 79.9% to 98.4% with intra-day relative standard deviations (RSD) of 3.1~8.7% and inter-day RSD of 4.3~7.5%. Quantitative results were determined from calibration curves of topramezone standards containing 1–500 μg L⁻¹ with an R ² ≥ 0.9994. Method sensitivities expressed as limits of quantitation were typically 6, 8, 9, and 1 μg kg⁻¹ in soil, corn, wheat, and water, respectively. The results of the method validation confirmed that this proposed method was convenient and reliable for the determination of topramezone residues in soil, corn, wheat, and water.     

Laser Raman and conductivity studies of plasticized polymer electrolyte P(ECH-EO):propylenecarbonate:<Emphasis Type="Italic">γ</Emphasis>-butyrolactone:LiClO<Subscript>4</Subscript>

The plasticized polymer electrolytes composed of poly(epichlorohydrin-ethyleneoxide) (P(ECH-EO)) as host polymer, lithium perchlorate (LiClO₄) as salt, γ-butyrolactone (γ-BL), and propylene carbonate (PC) as plasticizer have been prepared by simple solution casting technique. The effect of mixture of plasticizers γ-BL and PC on conductivity of the polymer electrolyte P(ECH-EO):LiClO₄ has been studied. The band at 457 cm⁻¹ in the Raman spectra of plasticized polymer electrolyte is attributed to both the ring twisting mode of PC and the perchlorate ν ₂(ClO₄⁻) bending. The maximum conductivity value is observed to be 4.5 × 10⁻⁴ S cm⁻¹ at 303 K for 60P(ECH-EO):15PC:10γ-BL:15LiClO₄ electrolyte system. In the present investigation, an attempt has been made to correlate the Raman and conductivity data.     

Adsorption characteristics and surface free energy of AlPO4-5

The micropores and surface characteristics of aluminophosphate-type zeolite, AlPO₄-5, were analyzed by examining the adsorption behavior of water and other adsorbates. Water adsorption on AlPO₄-5 occurred on both structural defects and nonpolar surfaces. Adsorption on structural defects, accompanied by high heats of adsorption, is attributed to adsorption to surface hydroxyls. Water adsorption increased steeply at a certain relative pressure depending on the adsorption temperature, and this was considered attributable to capillary condensation. The contact angle of water on AlPO₄-5 micropore surfaces can be determined quantitatively by applying the Kelvin equation. The surface free energy of AlPO₄-5 calculated on the basis of the contact angle was revealed to be about 120 mJ/m², in agreement with accepted values of the dispersion component of the surface free energy of metal oxides. Adsorption heat values of adsorbates with different polarities indicate that the AlPO₄-5 surface is essentially nonpolar and interacts only with dispersion interaction. In the case of n-hexane the contact angle was assumed to be zero, showing high affinity with the result of enhanced adsorption due to pore filling. Received: 21 May 1998 Accepted: 28 July 1998     

Quantitative estimation of riluzole in human plasma by LC-ESI-MS/MS and its application to a bioequivalence study

A novel simple, sensitive, selective, and rapid high-performance liquid chromatography coupled with tandem mass spectrometry method was developed and validated for quantification of riluzole in human plasma. The chromatography was performed by using a Zorbax-SB-C18 (4.6 × 75 mm, 3.5 μm) column , isocratic mobile phase 0.1% formic acid/acetonitrile (10:90 v/v), and an isotope-labeled internal standard (IS), [¹³C,¹⁵N₂]riluzole. The extraction of drug and internal standard was performed by liquid–liquid extraction and analyzed by MS in the multiple reaction monitoring (MRM) mode using the respective [M+H]⁺ ions, m/z 235.0/165.9 for riluzole and m/z 238.1/169.0 for the IS. The calibration curve was linear over the concentration range 0.5–500.0 ng/ml for riluzole in human plasma. The limit of quantification (LOQ) was demonstrated at 0.5 ng/ml. The within-batch and between-batch precision were 0.6–2.3% and 1.4–5.7%, and accuracy was 97.1–101.1% and 98.8–101.2% for riluzole respectively. Drug and IS were eluted within 3.0 min. The validated method was successfully applied in a bioequivalence study of riluzole in human plasma.