Adsorption Of Cationic Surfactants Research Articles

Magnetic chitosan/calcium alginate double-network hydrogel beads: Preparation, adsorption of anionic and cationic surfactants, and reuse in the removal of methylene blue

Robust and reusable magnetic chitosan/calcium alginate double-network hydrogel beads (CSMAB) with an environmentally benign biocomposite material synthesis approach were used adsorption of surfactant and removal of methylene blue dye sequentially for the first time. Double network hydrogel structure with sodium alginate and chitosan and acidification of the surface with HCl provided the reusability of the beads at the pollutant removal in water. The CSMAB beads were characterized for structural analysis by FESEM, EDX, BET, VSM, and FTIR techniques. They were used for the adsorption of cationic hexadecylpyridinium chloride (HDPCl) and anionic sodium dodecyl sulfate (SDS) surfactants and reused in the removal of cationic methylene blue dye without any pretreatment. The effect of pH, adsorbent dose, and temperature on surfactant removal efficiency was analyzed and pH was found the statistical significance. The adsorption capacity of CSMAB beads with a surface area of 0.65 m2 g−1 was calculated as 1.9 mg g−1 for HDPCl, and 1.2 mg g−1 for SDS, respectively. The SDS and HDPCl adsorption followed the pseudo-second-order kinetic and Freundlich isotherm model. The thermodynamic results showed that the surfactant adsorption process is an exothermic and spontaneous process. SDS-reacted CSMAB beads showed higher efficiency with 61 % in the removal of methylene blue dye.

Adsorption reduction of a gemini surfactant on carbonate rocks using formic acid: Static and dynamic conditions

Surfactant flooding improves oil recovery by lowering the interfacial tension and/or altering the reservoir rock’s wettability. However, surfactant losses caused by adsorption on the surface of the rock weaken the efficiency of this chemical enhanced oil recovery process. This study focuses on reducing the adsorption of a cationic gemini surfactant on carbonate rocks using formic acid. High-performance liquid chromatography integrated with an evaporative light scattering detector was employed to quantify both static and dynamic surfactant adsorptions. The results showed that the surfactant’s adsorption on carbonate rocks was reduced dramatically by adding 1% formic acid to the surfactant solution. Static adsorption was reduced from 2.44, 1.62, and 1.51 mg/g-rock to 0.16, 0.14, and 0.13 mg/g-rock on Guelph dolomite, Guff dolomite, and Indiana limestone, respectively. The dynamic adsorption of the surfactant on Indiana limestone was reduced from 0.269 to 0.041 mg/g-rock. It is believed that the carboxyl group released by the formic acid-rock reaction shields the surfactant from the rock surface resulting in lower adsorption. This is evidenced by the surfactant solution’s pH dropping below the point of zero charge of the rock, causing the repulsion of the cationic surfactant molecules off the surface. This study provides a low-cost option that provides a remarkable reduction in cationic surfactant adsorption on carbonate rocks.

Static adsorption of a novel cationic gemini surfactant: A mineralogical study

Surfactants are deemed as an advantageous chemical in enhanced oil recovery (EOR) because of their potential of lowering the interfacial tension and modifying the wettability. However, the surfactant loss by adsorption on the rock surface is one of the major shortcomings of surfactant-based flooding techniques. The static adsorption of an in-house synthesized cationic gemini surfactant (GS12) is investigated as a function of mineral type, salinity, and concentration. Both clay and non-clay minerals have been examined. Surfactant adsorption was increased continuously by the increase of concentration till 1000 ppm and then an adsorption plateau was observed in all minerals except montmorillonite and kaolinite. It was found that clay minerals may cause more detrimental effects as compared to silicate minerals and carbonate minerals showed the least adsorption. The maximum amount of surfactant adsorbed on the mineral surface was in the order of montmorillonite > kaolinite > illite > K-feldspar > quartz > dolomite > calcite. Lower adsorption of GS12 was detected because of the presence of multivalent ions (Ca2+ and Mg2+). Methylene blue (MB) has been revealed as a novel adsorption inhibitor for cationic GS12 on various minerals. MB adsorbs on the negative binding sites of both clay and non-clay minerals. Therefore, an electrostatic repulsion takes place between the cationic dye (MB) and cationic GS12, leading to the reduction of GS12 adsorption on the mineral surface. Only the addition of 100 ppm of MB in the surfactant solution at the highest concentration (1500 ppm) reduced GS12 adsorption on quartz surface to 0.67 mg/g-rock. This study will help in designing the chemical EOR process using GS12 on carbonate formation containing silica and clay minerals as impurities.

Adsorptive removal of dichlorophenoxyacetic acid (2,4-D) using novel nanoparticles based on cationic surfactant-coated titania nanoparticles.

A novel nanomaterial based on cationic surfactant-coated TiO2 nanoparticle (CCTN) was systematically fabricated in this work. Synthesized titania nanoparticles were thoroughly characterized by XRD, FT-IR, HR-TEM, TEM-EDX, SEM with EDX mapping, BET, and ζ potential measurements. The adsorption of cationic surfactant, cetyltrimethylammonium bromide (CTAB), on TiO2 was studied under various pH and ionic strength conditions. Adsorption of CTAB on TiO2 increased with ionic strength increment in the presence of hemimicelle monolayer structure, indicating that nonelectrostatic and electrostatic forces control CTAB uptake. CTAB adsorption isotherms on TiO2 were according to a two-step model. Potential application in pesticide removal of 2,4-dichorophenoxy acetic acid (2,4-D) using CCTN was also studied. Optimum parameters for 2,4-D treatment through adsorption technique were pH 5, adsorption time of 120min, and CCTN dosage of 10mg·mL-1. Very low 2,4-D removal efficiency using TiO2 without CTAB coating was found to be approximately 28.5% whereas the removal efficiency was up to about 90% by using CCTN under optimum conditions, and the maximum adsorption capacity of 12.79mg·g-1 was found. Adsorption isotherms of 2,4-D on CCTN were more suitable with the Langmuir model than Freundlich. Adsorption mechanisms of 2,4-D on CCTN were mainly governed by Columbic attraction based on isotherms and surface charge changes.

Friction dynamics of human hair treated with water or cationic surfactant aqueous solution

AbstractCationic surfactants are adsorbed on the surface of human hair and exhibit a lubricating effect. Here, we evaluated the friction when the hair treated with water or 1 wt% cationic surfactant (cetyltrimethylammonium bromide) aqueous solution was rubbed by a contact probe equipped in a sinusoidal motion friction evaluation system. Because of the rough structure of the cuticle on the human hair surface, an oscillatory phenomenon with a frequency of 50–70 Hz was observed when untreated hair was rubbed with a contact probe. On the other hand, the oscillatory phenomenon was not observed when the hair contained a large amount of water because stick–slip phenomena were inhibited on the soft, swollen hair surface. Furthermore, the change in kinetic friction coefficient and delay time, which is a normalized value of the time difference between the reaction of the friction force to accelerated motion, from untreated hair, Δμk and Δδ, was almost zero. However, we found a large difference in Δμk and Δδ for the hair treated with cationic surfactant aqueous solution. The treatment with cationic surfactant reduced both friction parameters, Δμk and Δδ, indicating that the treatment induced not only the frictional force but also the profile at the beginning of frictional sliding. The significant lubrication is due to cationic surfactant adsorption on the hair surface. These data imply that the smoothness of hair treated with a cationic surfactant is related to a reduction in friction coefficient and delay time δ.

C.I. Basic Red 46 Removal from Sewage by Carbon and Silica Based Composite: Equilibrium, Kinetic and Electrokinetic Studies.

The worldwide production of colored products and intermediates is increasing year on year. The consequence of this is an increase in the number of liquid effluents containing toxic dyes entering the aquatic environment. Therefore, it is extremely important to dispose of them. One of the techniques for the elimination of environmentally harmful dyes is adsorption. The main purpose of this study was to explore the possibility of using a carbon and silica (C/SiO2)-based composite for the removal of the azo dye C.I. Basic Red 46 (BR46). The adsorption capacity of C/SiO2 was found to be temperature dependent and increased from 41.90 mg/g to 176.10 mg/g with a temperature rise from 293 K to 333 K in accordance with the endothermic process. The Langmuir isotherm model seems to be the better one for the description of experimental data rather than Freundlich or Dubinin–Radushkevich. The free energy (ΔGo) confirmed the spontaneous nature of BR46 adsorption by C/SiO2. Kinetic parameters revealed that BR46 uptake followed the pseudo-second-order equation; however, the external diffusion plays a significant role. Surfactants of cationic, anionic and non-ionic type influenced BR46 retention by C/SiO2. The electrokinetic results (solid surface charge density and zeta potential) indicated that the adsorption of cationic dye and surfactant influences the structure of the electrical double layer formed at the solid–liquid interface.

Adsorption of cationic surfactant as a probe of the montmorillonite surface reactivity in the alginate hydrogel composites.

Adsorption of a cationic surfactant allowed to probe the surface reactivity of montmorillonite encapsulated in a composite of alginate hydrogels (A-MMT). Dodecylbenzyldimethylammonium chloride (BAC-12) was the surfactant used for these studies. BAC-12 is part of the widely used surfactant mixture known as benzalkonium chloride. XRD showed that up to three different types of basal spacing (d 001) were present within the composite indicating that as the concentration of adsorbed BAC-12 increases, populations with different adsorption conformational arrangements are present, even unexpanded clay remains. From the SEM-EDS spectra it is observed that the clay is distributed in the whole composite. In addition, the effect of the presence of cationic and anionic biocides on BAC-12 adsorption was studied. Cationic biocides such as tetradecyllbenzyldimethylammonium chlorides (BAC-14) and paraquat (PQ) show a competitive behavior for the clay adsorption sites at BAC-12 low concentration indicating an electrostatic adsorption mechanism. However, the presence of anionic contaminants such as 2,4-D and metsulfuron methyl do not affect surfactant adsorption. In all scenarios is observed an abrupt increase of BAC-12 adsorbed amount reaching values higher than the clay CEC suggesting strong tail-tail interactions. This occurs at concentrations 10 times lower than the CMC of BAC-12 promoted by clay encapsulation in the composite. In these composites the alginate does not affect the surface reactivity of the clay, but the formation of the hydrogel allows it to be easily extracted from aqueous media which makes it an interesting material with a potential use in water remediation.

Chitosan-Coated Magnetic Calcium Alginate Beads: Adsorption of Anionic and Cationic Surfactants and Reuse in the Removal of Methylene Blue

Chitosan-Coated Magnetic Calcium Alginate Beads: Adsorption of Anionic and Cationic Surfactants and Reuse in the Removal of Methylene Blue

Chitosan-Coated Magnetic Calcium Alginate Beads: Adsorption of Anionic and Cationic Surfactants and Reuse in the Removal of Methylene Blue

Chitosan-Coated Magnetic Calcium Alginate Beads: Adsorption of Anionic and Cationic Surfactants and Reuse in the Removal of Methylene Blue

Twist and Stretch: Assignment and Surface Charge Sensitivity of a Water Combination Band and Its Implications for Vibrational Sum Frequency Spectra Interpretations.

The vibrational spectrum of water at hydrophobic/hydrophilic interfaces is crucial to understanding complex surface chemistry phenomena. Vibrational sum frequency (VSF) spectroscopy is a valuable nonlinear spectroscopic technique for exploring the details of vibrational spectra of molecules at surfaces. However, spectral assignments and analysis of VSF spectra are often more nuanced than in linear spectroscopy. This study is aimed at understanding the source of the broad VSF signal in the oil-water surface water spectrum at energies slightly higher than traditionally examined, beyond the unbound free OH oscillator of surface water molecules. Analyzing isotopic dilutions of the aqueous solvent with VSF spectroscopy, we demonstrate that this signal is due to a combination band of water stretch and libration motions. The spectral characteristics of this band are found to be highly sensitive to the sign and magnitude of the surface charge induced by adsorption of both anionic and cationic surfactants. The results have implications for VSF measurements of the C-H stretching vibrations of various adsorbates when studied with D2O as the aqueous solvent. Because the vibrational signal from the water combination band is dependent on surface charge, it is imperative to include the presence of the combination band when fitting surface spectra.

Rapid and sensitive SERS detection of food contaminants by using nano-Ag aggregates with controllable hydrophobicity

There is an increasing demand for rapid and sensitive detection of hydrophobic contaminants in foods. A rapid and sensitive surface enhanced Raman scattering (SERS) detection method was developed for this purpose, based on the surface modification of nano-Ag aggregates, which had rich hot spots and controllable hydrophobicity. Cationic surfactants with different carbon chain lengths were employed to modify the aggregation of Ag nanoparticles. The adsorption of cationic surfactants on nano-Ag aggregates increased the hydrophobicity of the surface of the nano-Ag aggregates as the SERS substrate. By changing the carbon chain length of the surfactant, the hydrophobicity of the SERS substrate was able to be tuned to match with the hydrophobicity of the contaminants to be detected. Different hydrophobic contaminants such as Auramine O, Sudan I and Sudan III could be quantitatively detected, with a detection limit as low as 6.1 × 10−8, 7.5 × 10−9, 2.1 × 10−9 mol L−1, respectively. Compared with the traditional inorganic salt aggregation method which was unable to meet the requirements of direct quantitative detection in the sample matrices, the developed method was confirmed to have the advantages of low detection limit, good reproducibility (relative standard deviation (RSD) is less 7.6%), short operation time (about 1 min), and no need of any complicate pretreatment for sample preparation.

Dramatic Slowing Down of Oil/Water/Silica Contact Line Dynamics Driven by Cationic Surfactant Adsorption on the Solid.

We report on the contact line dynamics of a triple-phase system silica/oil/water. When oil advances onto silica within a water film squeezed between oil and silica, a rim forms in water and recedes at constant velocity. We evidence a sharp (three orders of magnitude) decrease of the contact line velocity upon the addition of cationic surfactants above a threshold concentration, which is slightly smaller than the critical micellar concentration. We show that, with or without surfactant, and within the range of small capillary numbers investigated, the contact line dynamics can be described by a friction term that does not reduce to pure hydrodynamical effects. In addition, we derive a model that successfully accounts for the selected contact line velocity of the rim. We further demonstrate the strong increase of the friction coefficient with surfactant bulk concentration results from the strongly nonlinear adsorption isotherm of surfactants on silica. From the variations of the friction coefficient and spreading parameter with surface concentration, we suggest a picture in which the part of the adsorbed surfactants that are strongly bound to the silica interface is trapped under the oil droplet and is responsible for the large increase in line friction.

Study of the inhibition effect of a new cationic surfactant on mild steel corrosion in a 1 M HCl solution

6-(2,3-dioxoindolin-1-yl)-N,N,N-trimethylhexan-1-ammonium bromide 3, a cationic surfactant, was synthesized and characterized by different spectroscopic techniques (nuclear magnetic resonance and High-resolution mass spectrometry (1H NMR, 13C NMR, and HRMS)). The effect of the cationic surfactant on the corrosion of mild steel in a 1 M HCl solution at temperatures between 298°K and 328°K has been assessed using the weight loss method and various electrochemical techniques (potentiodynamic polarization and electrochemical impedance spectroscopy (EIS)). The results of this study showed that the synthesized surfactant is an efficient corrosion inhibitor for mild steel in 1 M HCl. The inhibition efficiency reached 92.98% after 6 h of immersion at 298 K using a concentration of 1 mM. Both kinetic and thermodynamic parameters of the corrosion and inhibition process were investigated. As surfactant concentration increases, the corrosion inhibition efficiency (IE%) increases. Besides, it was found that the cationic surfactant adsorption on the surface of the mild steel followed the Langmuir isotherm. Also, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements showed that the inhibitor was considered as a mixed inhibitor with an anodic dominant character.

Adsorption, micellization and antimicrobial activity of formyl-containing cationic surfactant in diluted aqueous solutions

Surfactants based on dynamic covalent bonds have attracted significant interest over the past few decades due to the coexistence of covalent and non-covalent bonds. However, studies on the fundamental properties of their precursors are rare. Herein, we synthesized a series of formyl-containing cationic surfactants (N-alkyl-N,N-dimethyl-N-(2-(4-formyl-phenoxy)ethyl) ammonium bromides) bearing different hydrophobic chains, which can form dynamic imine bonds. The adsorption, micellization and antimicrobial activity were systematically investigated using surface tension, fluorescence, electrical conductivity, and ITC techniques. The results showed that the insertion of the 2-(4-formyl-phenoxy)ethyl group (equivalent to ~7 methylene groups) endows the surfactant with an asymmetrical double-chain structure, enhancing the hydrophobic interaction. As a result, the critical micelle concentration (cmc) and contribution per methylene group to the standard Gibbs free energy of micellization (∆Gmo) were significantly decreased, compared to conventional single surfactant. Upon increasing the hydrophobic chain length, the cmc, the negative logarithm of the surfactant concentration in the bulk phase required to produce a 20 mN·m−1 reduction in the surface tension of the solvent (pC20) and maximum surface excess amount of the adsorbed surfactant (Γmax) all decreased accompanied by an increase in the minimum molecular occupation area (Amin), while the ∆Gmo and standard Gibbs free energy of adsorption (∆Gadso) become more negative and thus more favorable for the formation of micelles and the adsorption film. Moreover, micellization changed from being entropy-driven to enthalpy-driven and is more sensitive toward NaCl than urea. In addition, the current formyl-containing cationic surfactants exhibit excellent antimicrobial activity against both Gram-positive and Gram-negative bacteria and fungi, especially the surfactant with a hydrophobic chain containing ~20 atoms. Such a study will be favorable for the design of new dynamic covalent surfactants and an understanding of the change in their aggregation.

ADSORPTION BEHAVIOUR OF IONIC AND NON-IONIC SURFACTANTS ONTO TALC A NATURALLY HYDROPHOBIC MINERAL-A COMPARATIVE STUDY

In present study, the adsorption behaviour of surfactants which are cationic (hexadecyltrimethylammonium bromide, HTAB), anionic (sodium dodecyl sulphate, SDS) and non-ionic (Triton X-100, TX-100) onto naturally hydrophobic talc were investigated. In this scope, a series of batch adsorption tests at natural pH were performed to determine adsorption isotherms and zeta potential (ZP) measurements of the ionic and non-ionic surfactants onto talc surfaces were measured using electrophoresis technique. To understand the mechanism of the adsorption process, the adsorption of ionic and non-ionic surfactants was studied as a function equilibrium concentration (mol/L). The amount of maximum adsorption of the surfactants onto talc are ordered as in the following: TX-100 (9.0x10-5 mol/m2)>HTAB (8.5x10-5 mol/m2) > SDS (5.32x10-5 mol/m2). Even though both the SDS and talc have negative surface charge, SDS can adsorb onto talc. Moreover, a good correlation was seen between the adsorption isotherms and the zeta potential curves. Considering their adsorption isotherms, the ionic surfactants were showed different adsorption behaviour concerning the non-ionic surfactant molecules. The adsorption isotherms of TX-100 and SDS increase rapidly in a narrow concentration range until the plateau region, while such a sharp increase does not appear for HTAB. The maximum adsorption amount of TX-100 and HTAB is greater than SDS. The results indicate that hydrophobic interaction and hydrogen bonding play a decisive role on the adsorption of non-ionic and anionic surfactants onto talc a naturally hydrophobic mineral, whereas electrostatic interaction becomes more important in the adsorption of cationic surfactant.

Direct Observation of Adsorption Morphologies of Cationic Surfactants at the Gold Metal-Liquid Interface.

Understanding interfacial phenomena is important in processes like corrosion, catalysis, and electrochemical reactions. Specifically, in corrosion inhibition, the assembly of adsorbed surfactants at metal-water interfaces in well-packed, ordered layers is desired. We provide direct evidence of the role of alkyl tails of surfactants in the formation of ordered adsorbed layers at metal-water interfaces. We have employed surface-specific sum frequency generation (SFG) spectroscopy to probe the in situ adsorption and self-assembly of cationic surfactants, alkyldimethylbenzyl ammonium bromides of tail lengths n = 4 (C4) and 12 (C12), without any applied potential or stimulus, at the gold-water interface. Our SFG measurements show that C12 Quat adsorbs as an ordered monolayer, whereas C4 Quat adsorbs in a disordered monolayer. All-atom molecular dynamics (MD) simulations of these surfactants corroborate with SFG results. These findings provide new insights on how hydrophobic interactions between alkyl tails of surfactants affect their self-assembly at metal-water interfaces.

Fly ash based geopolymer for the adsorption of cationic and nonionic surfactants from aqueous solution – A feasibility study

The discharge of wastewaters containing surfactants and other pollutants from industries is contaminating the world’s water resources which needs remediation. This paper describes the adsorption of cationic and nonionic surfactants cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) using fly ash based geoepolymer adsorbent. pH was varied between 2 and 10. Geopolymer could not adsorb CTAB and TX-100 surfactants. This was due to the low hydrophobicity of the geopolymer and the weak nature of forces involved in the adsorption of cationic and nonionic surfactants. The modification of the geopolymer with suitable metals or compounds could potentially enable it to adsorb CTAB and TX-100 surfactants.

Comparison of Same Carbon Chain Length Cationic and Anionic Surfactant Adsorption on Silica

Adsorption of a cationic surfactant dodecyl pyridinium chloride (DPC) on silica was studied to show a comparison with the adsorption of an anionic surfactant sodium dodecyl sulfate (SDS), whose carbon chain length is the same and on the same silica. Results provided a better understanding of the adsorption mechanism of cationic and anionic surfactant on negatively charged silica. The experiment covered different electrolyte concentrations and pH values. Results indicated that at the same pH, the DPC adsorption amounts are higher when the electrolyte concentration is higher; at a higher DPC equilibrium concentration, the adsorption amount difference is larger than that at low DPC equilibrium concentration, and when DPC equilibrium concentration is lower than 0.1 mmol/L, the adsorption amount difference cannot be observed. At charge compensation point (CCP, 0 zeta potential), the negative surface charge of silica was compensated by DP+, a continuous increasing zeta potential indicated a bilayer adsorption of DPC on silica. The adsorption amount increased with increasing pH. The calculated lines by Gu and Zhu model show a two-step property, including a bilayer and hemi-micelle adsorption. DPC adsorbed more strongly on silica than SDS due to the combination of electrostatic and hydrophobic attraction.

Sodium lignosulfonate as sacrificial agent and effectiveness in reducing CTAB cationic adsorption onto kaolinite

Sodium lignosulfonate (SLS) as sacrificial agent (SA) was investigated on the effectiveness in reducing Cetyl Trimethyl Ammonium (CTAB) cationic surfactant adsorption. X-Ray diffractometer (XRD), X-Ray fluorescent (XRF), Scanning electron microscopy (SEM), electron dispersive X-Ray (EDX) and Brunauer-Emmet-Teller (BET) were used to characterize the mineralogy, elemental composition and surface area of kaolinite. Fourier transform infrared-attenuated total reflectance (FTIR-ATR) was used to characterized kaolinite and SLS. The adsorption was done by depletion method using Ultraviolet–visible spectroscopy (UV–Vis). Effectiveness as sacrificial agent in mixture and pre-treatment were studied. The underlying mechanism that responsible for the effectiveness of SA were interpreted and examined. Positive outcome shows that SLS as SA manages to reduce CTAB adsorption. The SLS as SA successfully in reducing CTAB adsorption by using pre-treatment method. Effective underlying mechanism involved is SLS as SA adsorbed readily with the cation bridging assistance from the divalent salt and reversed the surface charge by creating a second layer. As high as 50% CTAB reduction had been seen in the experimental work. This study shows that SLS as SA effectively reducing the CTAB adsorption in pre-treatment.

Multivariate optimization and validation of a new procedure for simultaneous determination of folic acid and folinic acid based on enhancement effect of n-dodecylpyridinium chloride

The present study is a first report about of an electrochemical sensor for simultaneous determination of folic acid (FA) and calcium folinate (CF). Also, the work is a first successful application of n-dodecylpyridinium chloride (DPC) as a modifier in simultaneous measurement of folates. This study is based on the adsorption of cationic surfactants at the surface of a carbon paste electrode (CPE) to improve the electrochemical response of the tow analytes. The enhancement effect of DPC is compared with CTAB by differential pulse voltammetry (DPV) technique and DPC shows the better results as a modifier. Other novelty of the work is application of multivariate optimization for optimization of effective parameters in the voltammetric peak current of the analytes. Under the optimized conditions, a peak separation of CF and FA is higher than 270 mV. CPE in the presence of DPC shows wide linear responses for CF and FA in the concentration ranges of 0.1–100.0 µM and 0.05–10.0 µM with detection limits of 24.0 nM and 7.5 nM (3σ), respectively. CPE in the presence of DPC exhibits good repeatability and stability for the two analytes. At the last, CPE in the presence of DPC was successfully applied to the simultaneous detection of FA and CF in urine real samples.