Towards a molecular characterization of pharmaceutical excipients: mass spectrometric studies of ethoxylated surfactants

Industry perspective on the use and characterization of polysorbates for biopharmaceutical products Part 1: Survey report on current state and common practices for handling and control of polysorbates

Polysorbates (PS) are widely used as a stabilizer in biopharmaceutical products. Industry practices on various aspects of PS are presented in this part 1 survey report based on a confidential survey and following discussions by 16 globally acting major biotechnology companies. The current practice and use of PS during manufacture across their global manufacturing sites are covered in addition to aspects like current understanding of the (in)stability of PS, the routine QC testing and control of PS, and selected regulatory aspects of PS. The results of the survey and extensive cross-company discussions are put into relation with currently available scientific literature. Part 2 of the survey report (upcoming) will focus on understanding, monitoring, prediction, and mitigation of PS degradation pathways to develop an effective control strategy.

Shape and Structure Formation of Mixed Nonionic-Anionic Surfactant Micelles

Aqueous solutions of a nonionic surfactant (either Tween20 or BrijL23) and an anionic surfactant (sodium dodecyl sulfate, SDS) are investigated, using small-angle neutron scattering (SANS). SANS spectra are analysed by using a core-shell model to describe the form factor of self-assembled surfactant micelles; the intermicellar interactions are modelled by using a hard-sphere Percus–Yevick (HS-PY) or a rescaled mean spherical approximation (RMSA) structure factor. Choosing these specific nonionic surfactants allows for comparison of the effect of branched (Tween20) and linear (BrijL23) surfactant headgroups, both constituted of poly-ethylene oxide (PEO) groups. The nonionic–anionic surfactant mixtures are studied at various concentrations up to highly concentrated samples (ϕ ≲ 0.45) and various mixing ratios, from pure nonionic to pure anionic surfactant solutions. The scattering data reveal the formation of mixed micelles already at concentrations below the critical micelle concentration of SDS. At higher volume fractions, excluded volume effects dominate the intermicellar structuring, even for charged micelles. In consequence, at high volume fractions, the intermicellar structuring is the same for charged and uncharged micelles. At all mixing ratios, almost spherical mixed micelles form. This offers the opportunity to create a system of colloidal particles with a variable surface charge. This excludes only roughly equimolar mixing ratios (X≈ 0.4–0.6) at which the micelles significantly increase in size and ellipticity due to specific sulfate–EO interactions.

Effects of ethylene oxide chain length on crystallization of polysorbate 80 and its related compounds

As a result of the synthesis protocol polyoxyethylene sorbitan monooleate (polysorbate 80, PS80) is a highly complex mixture of compounds. PS80 was therefore separated into its main constituents, e.g. polyoxyethylene isosorbide esters and polyoxyethylene esters, as well as mono- di- and polyesters using preparative high-performance liquid chromatography. In this comprehensive study the individual components and their ethoxylation level were verified by matrix assisted laser desorption/ionization time-of-flight and their thermotropic behavior was analyzed using differential scanning calorimetry and X-ray diffraction. A distinct correlation was found between the average length of the ethylene oxide (EO) chains in the headgroup and the individual compounds' ability to crystallize. Importantly, a critical number of EO units required for crystallization of the headgroup was determined (6 EO units per chain or 24 per molecule). The investigation also revealed that the hydrocarbon tails only crystallize for polyoxyethylene sorbitan esters if saturated. PS80 is synthesized by reacting with approximately 20 mol of EO per mole of sorbitol, however, the number of EO units in the sorbitan ester in commercial PS80 products is higher than the expected 20 (5 EO units per chain). The complex behavior of all tested compounds revealed that if the amount of several of the linear by-products is reduced, the number of EO units in the chains will stay below the critical number and the product will not be able to crystallize by the EO chains.

MSPolyCalc: A web-based App for polymer mass spectrometry data interpretation. The case study of a pharmaceutical excipient

RATIONALE

In contrast to biological polymers, synthetic macromolecules consist of distributions of sizes, chemical compositions, functionalities and eventually architectures. The mass spectrum of a synthetic polymer may exhibit a tremendous number of signals. The availability of suitable IT tools to support interpretation is key.

METHODS

A web-based tool is presented: MSPolyCalc. It offers a set of functionalities, including the calculation of polymer distributions, molecular formulae and a match evaluation for peak assignment based on both mass and spectral accuracy (similarity score). The software was successfully tested with mass spectra exhibiting resolutions ranging from 10,000 to 240,000.

RESULTS

The molecular characterization of a synthetic poly(ethylene glycol)-based excipient was achieved. MSPolyCalc allowed the discrimination of six polymer compositions of variable relative abundance. Secondary ionization adducts with very low intensity consisting of matrix-analyte clusters were also successfully identified.

CONCLUSIONS

MSPolyCalc offers assisted data interpretation to target the needs of polymer chemists. It facilitates structure characterization, ionization adduct identification, and end-group determination together with visual result reporting.

Mass spectrometry in bioresorbable polymer development, degradation and drug-release tracking

A detailed characterization of polymeric matrices and appropriate degradation monitoring techniques are required to sustain the development of new materials as well as to enlarge the applications of the old ones. In fact, polymer analysis is essential for the clarification of the intrinsic relationship between structure and properties that ascertains the industrial applications in diverse fields. In bioresorbable and biodegradable polymers, the role of analytical methods is dual since it is pointed both at the polymeric matrices and at degradation tracking. The structural architectures, the mechanical and morphological properties, and the degradation rate, are of outstanding importance for a specific application. In some cases, the complexity of the polymer structure, the processes of decomposition or the low concentration of the degradation products need the concurrent use of different complementary analytical techniques to give detailed information of the reactions taking place. Several analytical methods are used in bioresorbable polymer development and degradation tracking. Among them, mass spectrometry (MS) plays an essential role and it is used to refine polymer syntheses, for its high sensitivity, to highlight degradation mechanism by detecting compounds present in trace amounts, or to track the degradation product profile and to study drug release. In fact, elucidation of reaction mechanisms and polymer structure, attesting to the purity and detecting defects as well as residual catalysts, in biodegradable and bioresorbable polymers, requires sensitive analytical characterization methods that are essential in providing an assurance of safety, efficacy and quality. This review aims to provide an overview of the MS strategies used to support research and development of resorbable polymers as well as to investigate their degradation mechanisms. It is focused on the most significant studies concerning synthetic bioresorbable matrices (polylactide, polyglycolide and their copolymers, polyhydroxybutyrate, etc.), published in the last ten years.

Screening of Polysorbate-80 Composition by High Resolution Mass Spectrometry with Rapid H/D Exchange

Polysorbate (PS) is a widely used polymeric excipient in biotherapeutic formulations to stabilize and protect protein drugs. Commercial PS is a highly heterogeneous mixture of structurally related components. PS composition can impact the stabilizer performance of PS in formulated protein drugs. Characterization of PS heterogeneity is, however, analytically challenging. In this work, a high-throughput screening protocol is presented for the profiling of the PS-80 polysorbate form using high resolution mass spectrometry (HRMS) coupled with a rapid hydrogen/deuterium (H/D) exchange in deuterated methanol. The protocol takes advantage of accurate mass measurements from HRMS analysis and utilizes H/D exchange-induced mass shifts that are characteristic to structures (particularly the number of terminal hydroxyl groups) of PS molecules to definitively identify species. In particular, mass shifts caused by deuterium uptake were used (1) to confirm molecular identities assigned by accurate mass measurements (which adds an extra level of identification confidence) and (2) to differentiate isomers that have an identical mass (thus, undistinguishable by high mass accuracy), but differ in the number of terminal hydroxyls. These data were input to an automated searching algorithm against a molecular mass database covering over 17000 potential PS-80 molecular species. The identified species were then visualized with Kendrick Mass Defect plots. The analysis protocol identified and profiled over 180 species from PS-80 samples in a high-throughput fashion without requiring chromatographic separation to reduce complexity of mixtures or tandem mass spectrometric analysis to conduct structural elucidation.

Thermogravimetry and Mass Spectrometry of Extractable Organics from Manufactured Nanomaterials for Identification of Potential Coating Components

Manufactured nanomaterials (MNMs) often have a surface-chemical modification in order to tailor their physicochemical properties, including also powder properties and miscibility. Surface-chemical modifications may influence the toxicological properties of the MNM, but the specific chemistry and extent are rarely described in detail in suppliers' technical data sheets. Chemical and quantitative information on any surface-chemical treatment, coating and functionalization are required for chemicals registration in Europe. Currently there is no globally accepted and documented approach to generate such data. Consequently, there is a continued research need to establish a structured approach to identify and quantify surface-chemical modifications. Here we present a tiered approach starting with screening for mass-loss during heating in a furnace or thermogravimetric analysis (TGA) followed by solvent extraction, and analysis by several mass spectrometry (MS) techniques depending on the target analytes. Thermal treatment was assumed to be able to quantify the amount of organic coating and MS was used to identify the extractable organic coatings after pressurized liquid extraction (PLE) using methanol at 200 °C. Volatile organic compounds in extracts were identified with gas chromatography and MS (GC-MS), non-volatile organic compounds with liquid chromatography MS (LC-MS), and polymeric compounds with matrix-assisted laser desorption ionization time-of-flight MS (MALDI-TOF-MS). The approach was demonstrated by analysis of 24 MNM, comprising titanium dioxide, synthetic amorphous silica, graphite, zinc oxide, silver, calcium carbonate, iron oxide, nickel-zinc-iron oxide, and organoclay. In extracts of 14 MNMs a range of organic compounds were identified and the main groups were silanes/siloxanes, fatty acids, fatty acid esters, quaternary ammonium compounds and polymeric compounds. In the remaining 10 MNMs no organic compounds were detected by MS, despite the fact an organic coating was indicated by TGA.

Rapid Analysis of Ingredients in Cream Using Ultrasonic Mist-Direct Analysis in Real-Time Time-of-Flight Mass Spectrometry

A novel method for the simultaneous detection of ingredients in pharmaceutical applications such as creams and lotions was developed. An ultrasonic atomizer has been used to produce a mist containing ingredients. The analyte molecules in the mist can be ionized by using direct analysis in real time (DART) at lower temperature than traditionally used, and we thus solved the problem of normal DART-MS measurement using a high-temperature gas. Thereby, molecular-related ions of heat-unstable components and nonvolatile components became detectable. The deprotonated molecular ion of glycyrrhizic acid (m/z 821), which is unstable at high temperatures, was detected without pyrolysis by ultrasonic mist-DART-MS using unheated helium gas, although it was not detected by normal DART-MS using heated helium gas. The cationized molecular ions of derivatives of polyethylene glycol fatty acid monoesters, which are nonvolatile compounds, were also detected as m/z peaks observed from 800 to 2300. Although the protonated molecular ion of tocopherol acetate was not detected in ionization by ultrasonic mist, it was detected by ultrasonic mist-DART-MS even in the emulsion. It was not necessary to dissolve a sample completely to detect its ions. This method enabled us to obtain the composition of pharmaceutical applications simply and rapidly. Graphical Abstract ᅟ.

Molecular dynamics simulations of structure-property relationships of Tween 80 surfactants in water and at interfaces

We build a united atom model for Tween 80 (polyoxyethylene sorbitan oleates), based on the GROMOS53A6(OXY+D) force field, and apply it to two stereoisomers, three constitutional isomers, and three structures with one, two, and three tails, to represent components in the Tween 80 commercial mixture. In a preassembled micelle containing 60 molecules, the distribution of Tween tail and ethylene oxide head groups is found to be insensitive to stereoisomerization but sensitive to changes in relative lengths of the four polyoxyethylene head groups. At the air-water and oil-water interfaces, the interfacial tension is significantly lower for the constitutional isomer with a shorter W headgroup, which attaches the tail to the sorbitan ring, and for Tween 80 isomers with more than one tail group. The results indicate the possible scope for improvement in the design of polyoxyethylene sorbitan oleates with improved surface tension reduction or better spreading at the oil-water interface. We also report surfactant component distribution profiles within preassembled micelles and at interfaces that can be used for validating coarse-grained surfactant models needed for simulation of self-assembly of Tween 80 surfactant mixtures.

Characterization and stability study of polysorbate 20 in therapeutic monoclonal antibody formulation by multidimensional ultrahigh-performance liquid chromatography-charged aerosol detection-mass spectrometry

Polysorbate 20 is a nonionic surfactant commonly used in the formulation of therapeutic monoclonal antibodies (mAb) to prevent protein denaturation and aggregation. It is critical to understand the molecular heterogeneity and stability of polysorbate 20 in mAb formulations as polysorbate can gradually degrade in aqueous solution over time by multiple pathways losing surfactant functions and leading to protein aggregation. The molecular heterogeneity of polysorbate and the interference from proteins and the excipient in the formulation matrix make it a challenge to study polysorbate in protein formulations. In this work, the characterization and stability study of polysorbate 20 in the presence of mAb formulation sample matrix is first reported using two-dimensional liquid chromatography (2DLC) coupled with charged aerosol detection (CAD) and mass spectrometry (MS) detection. A mixed-mode column that has both anion-exchange and reversed-phase properties was used in the first dimension to separate protein and polysorbate in the formulation sample, while polysorbate 20 esters were trapped online and then analyzed using an reversed-phase ultrahigh-performance liquid chromatography (RP-UHPLC) column in the second dimension to further separate the ester species. The MS served as the third dimension to further resolve as well as to identify the polysorbate ester subspecies. Another 2DLC method using a cation-exchange column in the first dimension and the same RP-UHPLC method in the second dimension was developed to analyze the degradation products of polysorbate 20. Stability samples of a protein drug product were studied using these two 2DLC-CAD-MS methods to separate, identify, and quantify the multiple ester species in polysorbate 20 and also to monitor the change of their corresponding degradants. We found different polysorbate esters degrade at different rates, and importantly, the degradation rates for some esters are different in the protein formulation compared to a placebo that has no protein. The multidimensional UHPLC-CAD-MS approach provides insights into the heterogeneous stability behaviors of polysorbate 20 subspecies in real-time stability samples of a mAb formulation.

Laser desorption/ionization mass spectrometric analysis of folic acid, vancomycin and Triton® X-100 on variously functionalized carbon nanotubes

RATIONALE

Carbon nanotubes (CNTs) have been ascertained to constitute versatile assisting matrices for laser desorption/ionization mass spectrometric analysis of different molecules. The functionalization thereof can lead to obtaining laser desorption/ionization assisting surfaces that would allow the detection of molecules at lower concentration and produce spectra with a better signal-to-noise ratio.

METHODS

Pristine, -OH and -COOH functionalized multi-walled CNTs were obtained from commercial suppliers. Gallic or sinapinic acid was attached covalently to the CNT surfaces by forming an ester bond. Folic acid, vancomycin and Triton(®) X-100 were used as analytes to examine properties of these new assisting surfaces. Mass spectrometry analysis was conducted on a matrix-assisted laser desorption/ionization quadrupole time-of-flight (MALDIQTOF) mass spectrometer.

RESULTS

The functionalization of CNTs was confirmed with Fourier transform infrared (FTIR) spectroscopy. The obtained mass spectra revealed that all the assisting surfaces are capable of transferring energy to the analytes; moreover, the presence of carboxyl groups in the structures of CNTs highly enhances their ionization properties. Nevertheless, the presence of sinapinic acid on CNT surfaces does not increase their properties to absorb pulse laser energy.

CONCLUSIONS

The presented assisting surfaces are effective in LDI mass analysis of folic acid, vancomycin and Triton(®) X-100. The appropriate functionalization of CNTs can lead to the production of assisting surfaces that can become highly effective in the ionization of particular types of analytes.

Laser desorption/ionization mass spectrometric analysis of surfactants on functionalized carbon nanotubes

RATIONALE

Recently, unmodified and carboxylated carbon nanotubes have been used as assisting surfaces laser desorption/ionization (LDI) in mass spectrometry. The functionalization of carbon nanotubes with organic compounds should lead to a gamut of other promising LDI-assisting surfaces.

METHODS

Carboxylated carbon nanotubes were functionalized with sinapinic acid either covalently or by creating an ionic macro-complex. Polyether-based surfactants were used as analytes to examine the properties of these new matrices. Mass spectrometric analysis was conducted on a LDI-quadrupole time-of-flight (QTOF) mass spectrometer. Carbon nanotube surfaces were deposited from suspension using the dried-droplet method.

RESULTS

The functionalization of the carbon nanotubes was confirmed with Fourier transform infrared (FTIR) spectroscopy. The usefulness of each material was examined with two poly(ethylene glycol) hexadecyl ether amphiphiles (Brij® 52 and Brij® 56) and a poly(ethylene glycol) monomethyl ether as analytes. Generally, the mass spectra obtained with carbon nanotubes covalently functionalized with sinapinic acid as a matrix had peaks with higher intensities than those obtained with carbon nanotubes functionalized by ionic macro-complex formation.

CONCLUSIONS

The presented new materials based on functionalized carbon nanotubes are effective in the LDI mass analysis of polyether amphiphiles and poly(ethylene glycol) monomethyl ether. This type of assisting surfaces can be highly modified by appropriate functionalization procedures.

Characterization of complex polysorbate formulations by means of shape-selective mass spectrometry

Complex synthetic formulations based on polysorbates can be challenging to characterize. They may be composed of many similar products including those of the same molecular weight, which cannot be readily separated by separation science approaches. Carbon number variation and ethylene oxide distribution add to the complexity. The properties of these formulations will be dependent on the chemical structure and relative concentration of formulation components. Here we describe the use of two experimental approaches based on mass spectrometry to provide enhanced characterization of these formulations. The first utilizes an atmospheric pressure solids analysis probe to rapidly determine the percentage content of individual esters in a formulation. These are shown to be in good agreement with product specification sheets. In a second approach, mobility separation has been integrated into a MALDI-MS/MS experiment to categorize major, minor, and trace ingredients. Components of identical molecular mass in the polysorbate formulations have been separated by ion mobility and then fragmented for additional characterization. The rapidity and level of structural detail provided by these experiments offers a significant opportunity to develop practical screening methods for complex formulations.

Analysis of polysorbate 80 and its related compounds by RP-HPLC with ELSD and MS detection

The chemical composition of polysorbate 80 strongly influences the physicochemical properties and performance of many products. Consequently, a reliable characterization of polysorbate 80 is crucial for many applications. However, the exact composition of these chemical mixtures cannot be determined by colorimetry, hydrolysis, size-exclusion chromatography, nuclear magnetic resonance or mass spectrometry (MS). Meanwhile, due to the strong retention of higher esters on the reversed-phase (RP) column, the published high-performance liquid chromatography (HPLC) methods suffered from inadequate elution. In the present paper, an HPLC-evaporative light scattering detection (ELSD) and an HPLC-electrospray ionization (ESI)-MS method were developed and validated for the separation and identification of the chemical composition of polysorbate 80. A full separation of the entire composition was achieved in 45 min. In the HPLC-ESI-MS spectra, each class of the compound in polysorbate 80 was directly confirmed and identified by [M + NH(4)](+) and [M + 2NH(4)](2+) ions. The number of polyoxyethylene groups and their distribution within the molecule were determined, in addition to the dehydration and esterification degree of sorbitol. Analysis showed that polysorbate 80 contained different proportions of components (polyoxyethylene sorbitan, polyoxyethylene isosorbide, polyoxyethylene sorbitan monooleate-dioesters-trioleates-tetraoleates and polyoxyethylene isosorbide monoester-dioesters). It was concluded that HPLC-ESI-MS is a useful tool for establishing the compositional profile of polysorbate 80.

Microemulsions as vehicles for topical administration of voriconazole: formulation and in vitro evaluation

This work was undertaken to investigate microemulsion (ME) as a topical delivery system for the poorly water-soluble voriconazole. Different ME components were selected for the preparation of plain ME systems with suitable rheological properties for topical use. Two permeation enhancers were incorporated, namely sodium deoxycholate or oleic acid. Drug-loaded MEs were evaluated for their physical appearance, pH, rheological properties and in vitro permeation studies using guinea pig skin. MEs based on polyoxyethylene(10)oleyl ether (Brij 97) as the surfactant showed pseudoplastic flow with thixotropic behavior and were loaded with voriconazole. Jojoba oil-based MEs successfully prolonged voriconazole release up to 4 h. No significant changes in physical or rheological properties were recorded on storage for 12 months at ambient conditions. The presence of permeation enhancers favored transdermal rather than dermal delivery. Sodium deoxycholate was more effective than oleic acid for enhancing the voriconazole permeation. Voriconazole-loaded MEs, with and without enhancers, showed significantly better antifungal activity against Candida albicans than voriconazole supersaturated solution. In conclusion, the studied ME formulae could be promising vehicles for topical delivery of voriconazole.

Mixed-mode and reversed-phase liquid chromatography-tandem mass spectrometry methodologies to study composition and base hydrolysis of polysorbate 20 and 80

Polysorbate 20 (polyoxyethylenesorbitan monolaurate) and polysorbate 80 (polyoxyethylenesorbitan monooleate) used in protein drug formulations are complex mixtures that have been difficult to characterize. Here, two HPLC methods are used with evaporative light scattering detection (ELSD) and mass spectrometry (MS) to characterize polysorbate from commercial vendors. The first HPLC method used a mixed-mode stationary phase (Waters Oasis MAX, mixed-mode anion exchange and reversed-phase sorbent) with a step gradient to quantify both the total polyoxyethylene sorbitan ester and polyoxyethylene sorbitan (POE sorbitan, a non-surfactant) in polysorbate. The results indicated POE sorbitan was present from 16.0 to 27.6 and 11.1 to 14.5% (w/w) in polysorbate 20 and 80, respectively. The second HPLC method used a reversed-phase stationary phase (Zorbax SB-300 C(8)) with a shallow gradient to separate, identify, and quantify the multiple ester species present in polysorbate. For all lots of polysorbate 20 analyzed, only 18-23% of the material was the expected structure, polyoxyethylenesorbitan monolaurate. Up to 40% and 70% (w/w) di- and triesters were found in polysorbate 20 and polysorbate 80 respectively. Likewise, polyoxyethylenesorbitan monooleate accounted for only 20% of polysorbate 80. A variability of 3-5% was observed for each ester species between multiple lots of polysorbate 20. The reversed-phase method was then used to determine the rate of hydrolysis for each polyoxyethylene sorbitan ester of polysorbate 20 in basic solution at room temperature. Increasing rates of hydrolysis were observed with decreasing aliphatic chain lengths in polysorbate 20.

Quantitative analysis of surfactant deposits on human skin by liquid chromatography/electrospray ionisation tandem mass spectrometry

Surfactants are commonly used as cleansing agents and yet there are concerns that they may also have a role in skin irritation. The lack of suitable methods for the quantitative and qualitative analysis of surfactant deposition on skin has hindered the in-depth investigation of such effects. Here, we report the application of reversed-phase liquid chromatography/electrospray ionisation tandem mass spectrometry (LC/ESI-MS/MS) assays for two surfactants commonly used in consumer products, namely sodium lauryl ether sulfate (SLES) and laurylamidopropyl betaine (LAPB), to a baseline study aiming to assess deposition levels on human skin. The linearity of the assays was established at 3-20 ng, with coefficient of variation below 5%. The detection limits were 100 pg for LAPB and 1 ng for SLES; quantitation limits were 500 pg for LAPB and 2.5 ng for SLES. The baseline study was conducted using a panel of 40 healthy volunteers. Skin extract samples were taken in triplicate from forearms, using ethanol. SLES was detected on most volunteers, with 75% of them having SLES deposits in the range of 100-600 ng/cm(2). LAPB was detected on the skin of all volunteers with 85% of them having deposit levels within the concentration range of 1-100 ng/cm(2). These results demonstrate the extent to which commonly used surfactants remain on the skin during the day. The analytical methods reported here can be applied to the investigation of surfactants in relation to general skin condition and to the development and optimisation of new consumer wash products.

Characterization and quantitative analysis of surfactants in textile wastewater by liquid chromatography/quadrupole-time-of-flight mass spectrometry

A method based on the application of ultra-performance liquid chromatography (UPLC) coupled to hybrid quadrupole-time-of-flight mass spectrometry (QqTOF-MS) with an electrospray (ESI) interface has been developed for the screening and confirmation of several anionic and non-ionic surfactants: linear alkylbenzenesulfonates (LAS), alkylsulfate (AS), alkylethersulfate (AES), dihexyl sulfosuccinate (DHSS), alcohol ethoxylates (AEOs), coconut diethanolamide (CDEA), nonylphenol ethoxylates (NPEOs), and their degradation products (nonylphenol carboxylate (NPEC), octylphenol carboxylate (OPEC), 4-nonylphenol (NP), 4-octylphenol (OP) and NPEO sulfate (NPEO-SO4). The developed methodology permits reliable quantification combined with a high accuracy confirmation based on the accurate mass of the (de)protonated molecules in the TOFMS mode. For further confirmation of the identity of the detected compounds the QqTOF mode was used. Accurate masses of product ions obtained by performing collision-induced dissociation (CID) of the (de)protonated molecules of parent compounds were matched with the ions obtained for a standard solution. The method was applied for the quantitative analysis and high accuracy confirmation of surfactants in complex mixtures in effluents from the textile industry. Positive identification of the target compounds was based on accurate mass measurement of the base peak, at least one product ion and the LC retention time of the analyte compared with that of a standard. The most frequently surfactants found in these textile effluents were NPEO and NPEO-SO4 in concentrations ranging from 0.93 to 5.68 mg/L for NPEO and 0.06 to 4.30 mg/L for NPEO-SO4. AEOs were also identified.

Effect of selected non-ionic surfactants on the flow behavior of aqueous veegum suspensions

The aim of this work was to investigate the influence of some non-ionic surfactants, Tween 80 and Brij 98, on the viscosity and flow behavior of a commercial montmorillonite clay, Veegum Granules. The effect of different concentrations of the surfactants on the shear stress-shear rate rheograms of hydrated concentrated clay suspensions was determined by shear viscometry. The addition of either surfactant increased the plastic viscosity and the yield stress of the suspensions. Furthermore, both surfactants altered the thixotropy of the suspensions to an extent that depended on both the surfactant concentration and the time of equilibration of the surfactant and Veegum. Brij 98 had a greater and more rapid effect. It is proposed that the surfactant polar head-groups anchor at the tetrahedral sheet surface, leaving the alkyl chains extending away from the edges and faces. Consequently, the alkyl chains undergo hydrophobic interactions that facilitate the association between the platelets and increase the physical structure within the suspension. Stereochemical differences between the polar groups may lead to differences in the way the surfactants associate with the tetrahedral sheet and hence their ultimate effect on the rheological behavior. There is a significant interaction between these surfactants and montmorillonite clays, and the rheological changes that occur could have a major impact on any pharmaceutical formulation that uses these ingredients.