Optimal conditions for determination of bacitracin, bacitracin zinc and bacitracin methylene disalicylate in animal feed by ultra-performance liquid tandem mass spectrometry.

An integrated method combining solid-phase extraction (SPE) with ultra-performance liquid tandem mass spectrometry (UPLC-MS/MS) has been established for quantifying bacitracin (BTC), bacitracin zinc (BZ), and bacitracin methylene disalicylate (BMD) in animal feed. A pretreatment procedure that can effectively, quickly, and simultaneously extract and purify BTC, BZ, or BMD in feed was developed for the first time through the optimization of extraction and SPE conditions. After extraction with acetonitrile + methanol + 15 % ammonia solution (1:1:1, v:v:v) and dilution with EDTA solution (1.5 mmol/L, pH 7.0), a SPE procedure was carried out with C18 cartridge. Following LC-MS/MS analysis utilized a Waters Peptide BEH C18 column with a gradient elution of 0.1 % formic acid in water/acetonitrile with. This method demonstrated a strong linear correlation (R2 > 0.9980) across a 0.01-1.0 mg/L concentration span, based on a matrix-matched standard curve. Satisfactory recoveries of BTC (bacitracin A, B1, B2, and B3), BZ, and BMD in different feeds were obtained from 80.7 % to 108.4 %, with relative standard deviations below 15.7 %. Low limits of quantification ranging within 7.2-20 µg/kg were achieved for bacitracin A, B1, B2, and B3. This method provided an effective and reliable detection method to prevent the addition of BTC and different BTC formulations in feeds.

Simple and rapid determination of triclabendazole and its metabolites in bovine and goat muscle tissue.

Triclabendazole (TCB) is widely used for prevention and treatment of parasitic infections in animals. Improper use can result in drug residues in animal tissues and cause health problems to humans through consumption. A simple and reliable analytical method for the determination of TCB and its metabolites in bovine and goat muscle using liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed and validated. Analytes were extracted using acetonitrile and purified using enhanced matrix removal cartridge. Chromatographic separation was carried out on a BEH Shield RP18 column. The analytes were detected in positive-mode electrospray ionization mass spectrometry using multiple reaction monitoring. Average recoveries of 96.1%-105.6% with coefficients of variation of 1.9%-8.4% were obtained at fortification levels of 0.5, 2.5, 25, and 50 µg/kg for TCB and 5.0, 25, 250, and 500 µg/kg for its metabolites (triclabendazole sulfoxide, triclabendazole sulfone, and keto-TCB). A good linear regression was obtained with the mixed standard solutions in the range of 0.05-20 µg/L for TCB and 0.5-200 µg/L for its metabolites. The limit of quantification and limit of detection ranged from 0.05 to 0.75 µg/kg and from 0.1 to 1.5 µg/kg, respectively. Moreover, this method was successfully applied to 33 real samples.

Preoperative albumin-to-globulin ratio and prognostic nutritional index predict the prognosis of colorectal cancer: a retrospective study.

The immunonutritional status has important effects on outcomes for cancer patients. Albumin-to-globulin ratio (AGR) and the prognostic nutrition index (PNI) are often used to assess the immunonutritional status of cancer patients. However, the clinical significance of these factors in colorectal cancer (CRC) remains unclear. We aimed to evaluate the clinical significance of the AGR and PNI in CRC. We reviewed the clinical data of 511 patients with CRC in two hospitals. Data from one institution was used as the training cohort. The optimal cutoff values for AGR and PNI in the training cohort were 1.4 and 48.65, respectively. Patients in both the low AGR and low PNI groups had poor overall survival (OS) and progression-free survival (PFS), while those in the low AGR-low PNI group had the lowest OS and PFS. Multivariate analysis revealed that preoperative AGR, preoperative PNI, gross type, and TNM stage were independent prognostic factors influencing OS in patients with CRC. Preoperative AGR, preoperative PNI, and TNM stage were independently associated with PFS in patients with CRC. According to the results of multivariate analysis in the training cohort, we developed the nomograms for OS and PFS and performed internal and external validation, which showed good prediction ability of the nomograms. In conclusion, preoperative AGR and PNI can be used as effective indicators to predict survival for patients with CRC. AGR and PNI may help develop effective adjuvant-therapy schedules.

Precise detection of water surface through the analysis of a single green waveform from bathymetry LiDAR.

Determination of the correct water surface height (WSH) from green laser (532 nm) echoes alone in bathymetry LiDAR is challenging, as the green laser return near the water surface involves both specular reflection from the air-water interface and backscattered return from the water volume. In this paper, a low-complexity method based on linear approximation of the leading edge (LLE) is proposed. The results of this LLE method were compared with those of three common algorithms of peak detection, half peak power, and surface-volume-bottom implemented on airborne datasets with various surface roughness conditions. In addition, the method was evaluated in waters with a wide range of optical properties through a controllable tank experiment. The uncertainties in the WSHs of all algorithms were greater when the water volume backscattering dominated the surface return; they were sensitive to variations in the optical properties of water, and increased exponentially with decreasing LiDAR attenuation coefficient (KLiDAR). Comparatively, the LLE algorithm had the fastest computational speed and demonstrated the best performance in situations where specular reflection or volume backscatter return was dominant, with average and maximum errors of less than 0.06 and 0.13 m, respectively.

Pan-immune-inflammation value is associated with the clinical stage of colorectal cancer.

Objective: We investigated the clinical significance of preoperative pan-immune-inflammation value (PIV) in patients with colorectal cancer (CRC). Methods: In this retrospective study, 366 cases who underwent surgery for CRC were enrolled. Their clinical data were collected. PIV was calculated with the formula PIV = [neutrophil count (109/L)× platelet count (109/L) × monocyte count (109/L) /lymphocyte count (109/L). Patients were divided into high PIV (> median PIV) and low PIV (< median PIV) groups. The relationship between PIV and clinicopathological features of CRC was investigated. Receiver operating characteristic (ROC) curve was plotted to indicate the value of immune-inflammatory biomarkers (IIBs) in predicting the TNM stage of CRC, and the area under the curve (AUC) was calculated to evaluate the actual clinical value of IIBs. AUC > 0.5 and closer to 1 indicated the better predictive efficacy. The influencing factors of PIV in CRC were analyzed. Results: We found that PIV was positively correlated with tumor size (r = 0.300, p < 0.05), carcinoembryonic antigen (CEA) (r = 0.214, p < 0.05) and carbohydrate antigen 125 (CA-125) (r = 0.249, p < 0.05), but negatively correlated with albumin (Alb) (r = -0.242, p < 0.05). PIV was significantly different in patients with different tumor locations (left or right), surgical methods (laparotomy versus laparoscopic surgery) (p < 0.05), and patients with different pathological T stages, N-stage and TNM stages (p < 0.05). ROC curve analysis of IIBs showed the AUC of PIV was greater than other markers when combined with CEA or carbohydrate antigen 19-9 (CA19-9). Multivariate regression analysis identified T stage, CEA, Alb, and tumor size as the independent influential factors of PIV in CRC. Conclusion: PIV is associated with the tumor stage in patients with CRC, which may be useful in preoperative assessment of CRC.

A green and rapid analytical method for determination of kitasamycin in animal feedstuffs by ultra-high performance liquid chromatography tandem mass spectrometry.

A rapid, simple, highly efficiency analytical method for detecting kitasamycin A1, A4, A5, and A13 in different feedstuffs was successfully developed by combining enhanced matrix removal (EMR) lipid cartridge and ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS). After extraction with acetonitrile, the sample supernatants were directly passed through the EMR lipid cartridge. Then, the cartridge was rinsed and eluted with acetonitrile and methanol, respectively, followed by UHPLC-MS/MS analysis with positive mode using multiple reaction monitoring. Optimized pretreatment procedure without solvent conversion, multiple nitrogen drying steps and activated cartridge before loading, and no significant interference were found during the analysis of different types of animal feedstuffs. Excellent sensitivity (Limit of quantification, LOQ) of kitasamycin A1, A4, A5, and A13 was 1.1-2.0 µg/kg. Satisfactory recoveries of kitasamycin A1, A4, A5, and A13 in different feedstuffs were from 74.0% to 98.8%, with the relative standard deviations (RSDs) below 10.4%, and good linear correlation coefficient (r)>0.9990 in the matrix matched standard curve range of 0.02-50.0 µg/L. Results demonstrated that the developed method exhibited excellent linearity, accuracy, precision, sensitivity, and the feasibility of using this method in kitasamycin determination of animal feedstuffs. The method was evaluated using the greenness analysis method through Eco-Scale assessment tool.

Simulation and Design of Circular Scanning Airborne Geiger Mode Lidar for High-Resolution Topographic Mapping.

Over the last two decades, Geiger-mode lidar (GML) systems have been developing rapidly in defense and commercial applications, demonstrating high point density and great collection efficiency. We presented a circular scanning GML system simulation model for performance prediction and developed a GML system for civilian mapping. The lidar system used an eye-safe fiber laser at 1545 nm coupled with a 64 × 64 pixels photon-counting detector array. A real-time data compression algorithm was implanted to reduce half of the data transmission rate and storage space compared to the uncompressing situation. The GML system can operate at aircraft above-ground levels (AGLs) between 0.35 km and 3 km, and at speeds in excess of 220 km/h. The initial flight tests indicate that the GML system can operate day and night with an area coverage of 366 km2/h. The standard deviations of the relative altimetric accuracy and the relative planimetric accuracy are 0.131 m and 0.152 m, respectively. The findings presented in this article guide the implementation of designing an airborne GML system and the data compression method.

Evaluation of a New Lightweight UAV-Borne Topo-Bathymetric LiDAR for Shallow Water Bathymetry and Object Detection.

Airborne LiDAR bathymetry (ALB) has proven to be an effective technology for shallow water mapping. To collect data with a high point density, a lightweight dual-wavelength LiDAR system mounted on unmanned aerial vehicles (UAVs) was developed. This study presents and evaluates the system using the field data acquired from a flight test in Dazhou Island, China. In the precision and accuracy assessment, the local fitted planes extracted from the water surface points and the multibeam echosounder data are used as a reference for water surface and bottom measurements, respectively. For the bathymetric performance comparison, the study area is also measured with an ALB system installed on the manned aerial platform. The object detection capability of the system is examined with placed small cubes. Results show that the fitting precision of the water surface is 0.1227 m, and the absolute accuracy of the water bottom is 0.1268 m, both of which reach a decimeter level. Compared to the manned ALB system, the UAV-borne system provides higher resolution data with an average point density of 42 points/m2 and maximum detectable depth of 1.7-1.9 Secchi depths. In the point cloud of the water bottom, the existence of a 1-m target cube and the rough shape of a 2-m target cube are clearly observed at a depth of 12 m. The system shows great potential for flexible shallow water mapping and underwater object detection with promising results.

Subpixel sampling moiré method for in-plane displacement measurement considering the symmetric errors induced by interpolation.

Sampling moiré method (SMM) is a highly accurate vision-based deformation measurement method, whose measurement error is minimized when an integer that is closest to the grating pitch is selected as the sampling pitch. We propose a subpixel SMM by applying subpixel interpolation operation before the downsampling in traditional SMM; the sampling pitch was selected as a noninteger nearest to the grating pitch in the subpixel resolution image. Meanwhile, the average filter method was used to eliminate the symmetric error cause by interpolation. As a result, the period of moiré fringe was enlarged greatly, and the measurement accuracy was also increased. To investigate the efficiency of the subpixel SMM, a computer simulation was applied to analyze the accuracy of the subpixel SMM. Then a simple tensile experiment was conducted to validate the efficiency of this method, and the result of the subpixel SMM accorded well with the fiber Bragg grating. In summary, the proposed novel subpixel SMM is capable of being used for high accuracy in-plane deformation measuring.

Simultaneous determination of 25 pesticides in Zizania latifolia by dispersive solid-phase extraction and liquid chromatography-tandem mass spectrometry.

An improved quick, easy, cheap, effective, rugged, and safe (QuEChERS) method combined with ultrapressure liquid chromatography tandem mass spectrometric method (UPLC-MS/MS) was developed to simultaneously determine 25 pesticides in Zizania latifolia. The samples were extracted with methanol(MeOH) and 0.1% formic acid (80:20, v/v) and cleaned with C18 absorbent and primary-secondary amine (PSA). LC separation was performed on a BEH C18 UPLC column under the condition of gradient elution with the mobile phase consisted of 0.5% formic acid (10 mM ammonium acetate)/MeOH. External standard calibration method with matrix-matched was used for quantification, and good linearity was obtained over a concentration range of 0.5-100 µg/l, with correlation coefficients greater than 0.9901. The limit of detection (LOD) and the limit of quantitation (LOQ) of the 25 pesticides were in the range of 0.2-1.0 µg/kg and 0.5-3.3 µg/kg, respectively. The recoveries ranged from 72% to 118%, and the relative standard deviations (RSDs) were less than 20%. Thus, the proposed method is suitable for the simultaneous determination of 25 pesticides in Z. latifolia.

Wettability of a quartz surface in the presence of four cationic surfactants.

Advancing contact angle (θ) measurements were carried out for aqueous solutions of four cationic surfactants, hexadecanol glycidyl ether ammonium chloride (C(16)PC), guerbet alcohol hexadecyl glycidyl ether ammonium chloride (C(16)GPC), hexadecanol polyoxyethylene(3) glycidyl ether ammonium chloride (C(16)(EO)(3)PC), and guerbet alcohol hexadecyl polyoxyethylene(3) glycidyl ether ammonium chloride (C(16)G(EO)(3)PC), on the quartz surface using the sessile drop analysis. The influences of surfactant type and bulk concentration on contact angle were expounded, and the changes in adhesional tension and adhesion work were discussed. The contact angle increases up to a maximum with the increasing concentration for all cationic surfactants. Surfactants with branched chain have more hydrophobic group density on the quartz surface, which results in higher values of maxima in contact angle curves. When ethylene oxide groups CH(2)CH(2)O were incorporated in the hydrophobic group, the decrease in contact angle maximum was observed for C(16)(EO)(3)PC and C(16)G(EO)(3)PC. Moreover, an increase in quartz-water interfacial free energy (γ(SL)) has been observed due to the adsorption of four cationic surfactants. The four cationic surfactants can form a monolayer with alignment structure on the quartz surface through electrostatic interaction and then form the bilayer with increasing bulk concentration. In contrast with literature, the maximal contact angles may not necessarily correspond to the beginning of the formation of bilayer for cationic surfactants at the quartz-water interface. Moreover, the concentrations corresponding to maximal contact angles for C(16)PC and C(16)(EO)(3)PC were much lower than their CMC. The contact angle passes through a maximum at a concentration obviously higher than CMC for C(16)G(EO)(3)PC.

Dilational properties of anionic gemini surfactants with polyoxyethylene spacers at water-air and water-decane interfaces.

The dilational properties of anionic gemini surfactants (oligooxa)-alpha,omega-bis(m-octylbenzene sulfonate) (C(8)E(x)C(8)) with polyoxyethylene spacers at the water-air and water-decane interfaces were investigated via the oscillating barriers method. The influences of oscillating frequency and bulk concentration on dilational properties were explored. The interfacial tension relaxation method was employed to obtain dilational parameters in a reasonably broad frequency range. The experimental results show that the number of ethylene oxide groups is one of the principal factors to control the nature of the interfacial film. With an increase of ethylene oxide groups, the dilational modulus of C(8)E(8)C(8) shows two maxima with the increasing concentration. Furthermore, the dilational moduli at the water-decane interface are remarkably lower than those at the water-air interface for C(8)E(1)C(8) and C(8)E(4)C(8), while the dilational modulus at the water-decane interface is close to that at the water-air interface for C(8)E(8)C(8), which indicates that the structure of the adsorption sublayer plays a more important role. Possible schematic diagrams of adsorbed molecules with different polyoxyethylene spacers at the water-air and water-decane interfaces are proposed. The results of relaxation experiments and Cole-Cole plots can support our provided mechanism strongly.

Interfacial dilational properties of tri-substituted alkyl benzene sulfonates at air/water and decane/water interfaces.

The dilational rheological properties of absorbed film of three pairs of structural isomers, tri-substituted alkyl benzene sulfonates, at the air-water and decane-water interfaces have been investigated by drop shape analysis method. The influences of bulk concentration on dilational elasticity and viscosity were expounded. Interfacial tension relaxation method was employed to obtain dilational parameters in a reasonably broad frequency range. The experimental results showed that the meta-alkyl to sulfonate group plays a crucial role in the interfacial dilational properties: the longer meta-alkyl will lead to higher dilational parameters for air-water interface and lower ones for decane-water interface when the total alkyl carbon numbers are equal. For alkyl benzene sulfonates with shorter meta-alkyl, the surface dilational properties are similar to interfacial dilational properties, whereas the surface dilational parameters are obviously higher than the interfacial dilational parameters for alkyl benzene sulfonates with longer meta-alkyl in general. The possible mechanism has been proposed and ensured by Cole-Cole plots.

Dynamic interfacial dilational properties of hydroxy-substituted alkyl benzenesulfonates.

Synthesis, characterization, and interfacial properties of hydroxy-substituted alkyl benzenesulfonates, sodium 2-hydroxy-3-decyl-5-octylbenzenesulfonate (C10C8OHphSO3Na) and 2-hydroxy-3-octyl-5-decylbenzenesulfonate (C8C10OHphSO3Na), are reported. The dynamic dilational properties of the surfactants are expounded by means of oscillating the bubble/drop method at both water-air and water-decane interfaces. The distinct maxima appear in dilational modulus vs time curves in some cases, which is believed to be attributed to the change of surfactant conformation and the arrangement of surface layer. Our results show that the measurement of dynamic interfacial dilational properties is a powerful tool to probe the structure of the surfactant adsorption film.

The interfacial dilational properties of hydrophobically modified associating polyacrylamide studied by the interfacial tension relaxation method at an oil-water interface.

The interfacial dilational viscoelastic properties of hydrophobically associating block copolymer composed of acrylamide (AM) and a low amount of 2-phenoxylethyl acrylate (POEA) (<1.0 mol%) at the octane-water interfaces were studied by means of the interfacial tension relaxation method. The dependencies of interfacial dilational elasticity and viscous component on the dilational frequency were investigated. The interaction of hydrophobically associating block copolymer [P(AM/POEA)] with sodium dodecyl sulfate (SDS) has been explored. The results show that at lower frequency, the dilational elasticity for different concentration copolymer is close to zero; at higher frequency, the dilational elasticity shows no change with increased frequency; At moderate frequency (10(-3)-1 Hz), the dilational elasticity decreased with a decrease in the dilational frequency. The results show that the hydrophobic groups of [P(AM/POEA)] chains can be associated by inter- or intrachain liaisons in water solution. The dilational viscous component for P(AM/POEA) comes forth a different maximum value at different frequencies when the polymer concentration is different. It is generally believed that the dilational viscous component reflects the summation of the various microscopic relaxation processes at and near the interface and different relaxation processes have different characteristic frequencies. The spectrum of dilational viscous component may appear more than once maximum values at different frequencies. The influence of SDS on the limiting dilational elasticity and viscous component for polymer solution was elucidated. For 5000 ppm polymer solution, the limiting dilational elasticity decreased with an increase in SDS concentration. The dilational viscous component passed through a maximum value with a rise in the dilational frequency, which appeared at different frequency when SDS concentration is different; and the higher is the concentration, the lower is the dilational frequency. It can be explained that macromolecules may be substituted by SDS molecules in the interface and the interaction of molecules decrease, which makes the limiting dilational elasticity decrease. For 200 ppm polymer solution, the limiting dilational elasticity increased firstly and then decreased with SDS concentration increasing. This may be explained that the interfacial polymer concentration is so low that SDS molecules absorbed in the interface dominate dilational properties of the interfacial film even at very low SDS concentration. However, SDS molecules can gradually substitute the polymer molecules in the interface with a rise in SDS concentration, which results in the decrease in the limiting dilational elasticity.

Aggregation of sodium 1-(n-alkyl)naphthalene-4-sulfonates in aqueous solution: micellization and microenvironment characteristics.

In aqueous solution, the micellization and microenvironment characteristics of the micelle assemblies of three anionic surfactants, sodium 1-(n-alkyl)naphthalene-4-sulfonates (SANS), have been investigated by steady-state fluorescence and time-resolved fluorescence decay techniques using pyrene, Ru(bpy)3(2+), and 1,6-diphenyl-1,3,5-hexatriene as fluorescence probes. The critical micelle concentrations (cmc's), effective carbon atom numbers (neff's), hydrophilic-lipophilic balances (HLBs), mean micelle aggregation numbers, micropolarities, and microviscosities of these surfactant micelles have been determined. The logarithmic cmc of the alkylnaphthalene sulfonates decreases linearly with an increase in the neff. The logarithmic aggregation number of the alkylnaphthalene sulfonates increases linearly with an increase in the neff. However, in contrast to the alkylsufonates and the alkylbenzene sulfonates, the aggregation for these alkylnaphthalene sulfonate molecules is less sensitive to the increase in the neff. The micropolarity of these alkylnaphthalene sulfonate micelles is less sensitive to the increase in the alkyl chain length and is lower than that of sodium dodecyl sulfate (SDS). The microviscosity of these alkylnaphthalene sulfonate micelles increases with an increase in the alkyl chain length and is lower than those of nonionic surfactants and zwitterionic surfactants. These results suggest that naphthyl rings have a notable effect on the micellization of SANS.

Studies of synergism for lowering dynamic interfacial tension in sodium alpha-(n-alkyl) naphthalene sulfonate/alkali/acidic oil systems.

Alkylnaphthalene sulfonates with high purity were selected as model components to research synergism for lowering interfacial tension (IFT) in surfactant/alkali/acidic oil systems. The dynamic IFTs between alkylnaphthalene sulfonates with different alkyl chain length and n-decane, oleic acid model oil, or Shengli crude oil were measured. The results showed that the alkylnaphthalene sulfonates with different alkyl chain lengths had different synergism with different acidic components and their ionized acids under the same conditions. The synergism for lowering dynamic IFT in alkylnaphthalene sulfonate/alkali/acidic oil systems was controlled by alkylnaphthalene sulfonate concentration, alkyl chain length, alkali concentration, alkali type, and oleic acid concentration: optimal physicochemical conditions were necessary to the best synergism. This indicates that the synergism among added surfactant acidic components in crude oil and their ionized acids is controlled by the ratio of their interfacial concentrations.

Properties of polyethylene glycol (23) lauryl ether with cetyltrimethylammonium bromide in mixed aqueous solutions studied by self-diffusion coefficient NMR.

NMR self-diffusion coefficient measurements have been used to study the properties of polyethylene glycol (23) lauryl ether (Brij-35) with cetyltrimethylammonium bromide (CTAB) in the mixed aqueous solutions with different mole fractions of CTAB. By fitting the self-diffusion coefficients to the two-state exchange model, the critical micelle concentrations of the two solutes in the mixed solutions (cmc*1 and cmc*2) were obtained. The critical mixed micelle concentrations (cmc*) were then evaluated by the sum of cmc*1 and cmc*2, which are in good agreement with the results measured by the surface tension method. The cmc* values are lower than those of the ideal case of mixing, which indicates that the behavior of the CTAB/Brij-35 system is nonideal. Moderate interactions between CTAB and Brij-35 in their mixtures can be deduced from the interaction parameters (betaM) based on the cmc* obtained by the NMR self-diffusion method. The compositions (x1) of the mixed micelles at different total surfactant concentrations were also evaluated. By using these results, a possible mechanism of mixed micellar formation and a picture of the formation of nonsimultaneous CTAB/Brij-35 binary mixed micelle were proposed. In contrast to the case of CTAB/TX-100 system, Brij-35 molecules have a tendency to form micelles first at any mole fraction of CTAB. The mixed micellar self-diffusion coefficients (Dm) increase slightly at lower CTAB molar ratios, and then speed up with increasing CTAB mole fraction.

A study of interfacial dilational properties of two different structure demulsifiers at oil-water interfaces.

The interfacial dilational viscoelastic properties of two demulsifiers with straight chain (SP-169) and branched chain (AE-121) at the oil-water interfaces were investigated by means of the longitudinal waves method and the interfacial tension relaxation method, respectively. The results obtained by the longitudinal waves method showed that the dilational viscous component for AE-121 and SP-169 also passed through a maximum value with increasing concentration. It was found that the maximum value appeared at different demulsifier concentrations during our experiment frequency; and the higher is the dilational frequency, the lower is the concentration. The influences of AE-121 and SP-169 on the dilational viscoelastic properties of the oil-water interface containing surface-active fraction from Iranian crude oil have been measured. The results clearly stated that both demulsifiers could obviously decrease the dilational elasticity of oil-water interface containing surface-active fraction. At low concentration, because of stronger adsorption ability, SP-169 has stronger ability to decreasing the dilational modulus than AE-121. We also found that the dilational modulus of the interface contained surface-active fraction passed through a minimum value with increasing demulsifier concentration for both demulsifiers. This result indicated the dosage of demulsifier had an optimum value. The results obtained by means of interfacial tension relaxation method showed that the slow relaxation processes involve mainly rearrangement in the conformation of the molecules appeared with increasing demulsifier concentration.

Studies of synergism/antagonism for lowering dynamic interfacial tension in surfactant/alkali/acidic oil systems. 3. Synergism/antagonism in surfactant/alkali/acidic model oil systems.

Experimental studies have been conducted to elucidate the mechanisms responsible for synergism/antagonism for lowering dynamic interfacial tension (IFT) in surfactant/alkali/hydrocarbon and surfactant/alkali/acidic model oil systems. Dynamic IFTs between hydrocarbon/acidic model oil and alkali/surfactant solutions were measured. We learned from our experimental results that alkali has the function of decreasing n(min) values of surfactant solutions. The synergism/antagonism for lowering the stable values of dynamic IFTs in surfactant/alkali/hydrocarbon and surfactant/alkali/acidic model oil systems depends on factors that can change the EACN/n(min) value, such as the oleic acid in the oil phase and the n(min) values of surfactant and alkali. A new explanation with respect to EACN/n(min) values is provided.