Concentration Of Surface-active Substances Research Articles

INFLUENCE OF SURFACTANT CONCENTRATION ON CHANGES IN THE PLANE OF POLARIZATION OF LIGHT WHEN PASSING THROUGH THE LCD MEDIUM

The effect of surfactants in the form of cetyltrimethyl ammonium bromide (CTAB) in nematic liquid crystal cells of type 5CB have been studied by the polarization-optical method. The relationship between the concentrations of the introduced surfactant and the angle of rotation of the polarization plane is established. The clear boundaries of the linear and elliptical polarization of the light transmitted through the cell are indicated, depending on the concentration of surface-active substances (surfactants). Possible applications of such materials in semiconductor and solid-state laser technology and display technologies are proposed.

The possible role of the surface active substances (SAS) in the airborne transmission of SARS-CoV-2

Surface active substances (SAS) have the potential to form films at different interfaces, consequently influencing the interfacial properties of atmospheric particulate matter (PM). They can be derived from both human activities and natural processes and can be found in an indoor and outdoor environment. This paper's fundamental question is the possible role of the SAS in stabilizing respiratory aerosols in the closed space. In that context, we discuss results of preliminary measurements of the SAS and dissolved organic carbon (DOC) concentrations in the water-soluble fractions of PM2.5 and PM10 that were sampled simultaneously in primary school inside and outside of the building. The concentrations of SAS were determined using highly sensitive electrochemical measurements. It was observed that SAS and DOC concentrations have been enhanced indoor in both PM fractions. Consistent with these results, a discussion arises on the possibility that SAS could play a crucial role in respiratory droplet dispersion as stabilizers, especially in a closed space. At the same time, we assume that they could prolong the lifetime of respiratory aerosols and as well viability of some (possible SARS-CoV-2) virus inside of the droplets.

Effect of Ship-Induced Langmuir-Type Circulations on Distribution of Surface-Active Substances and Damping of Short Wind Waves

It has recently been shown that the interaction of ship-generated nonuniform currents with ambient surface waves can lead to the generation of Langmuir-type circulations (LTCs) (Basovich 2011) and a persistent wake (Somero et al. 2018). Based on this work, it is shown here that the LTC and surface currents of the persistent wake are responsible for the redistribution of surface-active substances (SAS) and a corresponding change in the damping of short surface waves. The persistent wake is a region of the ship wake, where initial ship-generated perturbations have mostly decayed. The LTCs are similar in nature to Langmuir circulations which arise as a result of instability of wind-driven current. LTCs produce a secondary flow with velocity transverse to the direction of the ship, and width significantly larger than the ship beam. Because LTCs are generated in large scale, they persist for a long time after the passage of the ship. Transverse surface currents produced by LTCs in the ship wake redistribute the SAS films at the sea surface. These currents create strong convergence and divergence zones which in turn produce streaks with different concentrations of SAS. The change in concentration of SAS affects the film pressure and the damping effect of SAS on the short surface waves. This effect is represented by a damping factor and is a crucial parameter in determination of the spectral density of short wind waves. Therefore, the damping effect of the film, as represented by the damping factor, is responsible for sea surface roughness modification and is important for prediction of synthetic-aperture RADAR (SAR) imagery of ship wakes on the ocean surface. In this article, we present the mathematical and computational methods, along with simulation results for a naval surface combatant operating in calm, head, and following seas. The simulation results clearly show that the convergence and divergence zones strongly influence the relative SAS concentration and the spatial distribution of the damping factor, the latter of which defines the structure of SAR images of the persistent wake. Comparisons of the magnitude of the damping factor with available SAR data are shown to be in good agreement.

Study of the influence of concentration of surface-active substances on trifuzol release from veterinary intrauterine suppositories

The main direction in increasing meat and milk production for the coming years is the intensification of all livestock industries. Disease animals with lesions of the genitals are fairly common, causing considerable economic damage due to loss of productivity of animals and even infertility. At the present time the search continues for veterinary medicines, which would ensure the effectiveness of treatment of diseases of the sexual sphere, in particular, cattle, and the extension of the range of veterinary medicines and their dosage forms. So, the goal is to improve the existing veterinary intrauterine suppositories by the use of more effective active substances and foaming agent in its composition that improves the efficiency of the funds and consequently the effectiveness of treatment of inflammatory diseases of the reproductive organs in cattle.
 Use piperidine 2-(5-(2-furyl)-4-phenyl-1,2,4-triazole-3-ylthio)acetate (trifuzol) as active substances in veterinary intrauterine suppository provides increased therapeutic effectiveness in the treatment, particularly of catarrhal endometritis in cows compared with the known means. Its use allows to improve the course of the pathological process.
 Introduction sodium lauryl sulfate in the composition of the suppository can improve the clinical effect of the proposed use of the funds due to the fact that the melting means it begins to foam, grow in volume and take in this view of the entire uterine cavity of the animal and thus distribute the active substance evenly over the entire inner surface of the uterus as a result of biopharmaceutical research determined that the optimal release trifuzol of intrauterine suppositories is provided by a combination of auxiliary substances – the fundamentals-media (a mixture of polyethylene oxides with a molecular weight of 1 500 and 400 in the ratio 9:1) and surfactant (sodium lauryl sulfate).
 The aim of this study was scientific substantiation of surfactant concentration (sodium lauryl sulfate) in-utero drug trifuzol in the form of suppositories.
 Suppositories were prepared by the method of pouring with the use of forms from semi-automatic Franco-Crespi. The concentration of the surfactant (sodium lauryl sulfate) were 0,5%, 1%, 2%, 3% and 5% by weight of the drug, the content trifuzol – 0.1 g each suppositories.
 Research on the scientific basis of the concentration of surfactant in the suppository was carried out according to plan one-way with repeated observations.
 It is proved that the concentration of the surfactant (sodium lauryl sulfate) significantly affects its release from the dosage form. Found that 0.5% concentration of sodium lauryl sulfate for optimal release trifuzol of veterinary intrauterine suppositories.

Automation of determining the contact angle of washing liquids wetting

The physicochemical activity of the washing environment is related to the value of the contact wetting angle of the solution and the body being washed and changes rather quickly. In this study a technique and software tool were developed for the rapid determination of the dependence of the contact wetting angle on the concentration of surface-active substances (surfactants) and the selection of optimal values. The technique was based on pixel-by-pixel processing of photographs of cleaning solutions droplets on various types of the studied surfaces with using color contrasting. The data were processed by statistical methods which allow determining the value of the derivative of the surface equation and finding the contact wetting angle. The dependence of the wetting angle on the surfactant concentration was studied using multiplicative power functions. The results showed a decreasing return value of the contact wetting angle from increasing surfactant concentration. It was defined that the influence of potassium monoborate (PMB) together with MS-8 is the most effective. The obtained results allow calculating and optimizing surfactants percentage defining the quality and performance of the washing process at the design stage of the technological process for various options for the combined use of surfactants.

Simple, insensitive to environmental matrix interferences method of trace cadmium determination in natural water samples

A simple, fast, and inexpensive anodic stripping voltammetric procedure for trace determination of cadmium in natural water samples containing high concentrations of surface-active substances was described. It was proved that interferences from the organic matrix such as surface-active substances could be removed by the addition of Amberlite XAD-7 resin to the analyzed sample prior to the voltammetric measurement. A renewable mercury film silver-based electrode (Hg(Ag)FE) was used as the working electrode. The following optimum conditions were found: 0.1 mol L−1 acetic acid, accumulation potential of − 0.8 V, and accumulation time of 30 s. The linear range of Cd(II) was observed over the concentration range from 5 × 10−8 mol L−1 to 6 × 10−5 mol L−1, with a correlation coefficient equal to 0.997. The detection limit of Cd(II) for preconcentration time of 30 s was 1.3 × 10−8 mol L−1. The proposed procedure was successfully tested for the detection of cadmium in different non-pretreated and non-deaerated real water samples.

Reconsideration of seawater surfactant activity analysis based on an inter-laboratory comparison study

Surfactants, or surface-active substances (SAS), are amphipathic organic substances that adsorb on aquatic phase boundaries, including the air-sea interface that covers ~70% of Earth's surface. SAS thus mediate all mass transfer across the air-sea interface and are central to planetary scale biogeochemical processes. SAS are routinely quantified in seawater and freshwater in terms of total surfactant activity (SA), using alternating current (AC) out-of-phase voltammetry with a hanging mercury drop electrode (HMDE). Although this technique is well established, method modifications have been implemented and differing calibration procedures adopted in individual research laboratories. Increasing interest in the environmental roles of SAS prompts a timely inter-comparison of these varying analytical approaches. Using sea-surface microlayer (SML: uppermost 80 μm layer sampled) and sub-surface (SSW: 1 m depth sampled) seawater from Jade Bay (south-eastern North Sea), we carried out the first inter-laboratory comparison for SA, using methods and calibration protocols previously established in three participating laboratories. The internal calibration protocol follows direct calibrations of individual samples against the model surfactant Triton-X-100 during analysis, whereas external calibration produces independent Triton-X-100 calibration curves; both protocols express SAS concentrations in Triton-X-100 equivalents (T-X-100 eq.). There was no significant difference between SA derived via internal or external calibration protocols, or by using different analytical instruments (range in Kruskall-Wallis and Dunn-Bonferroni post-hoc test p-values: 0.062–1.000), except where freeze/thaw degradation was suspected to have occurred during transit (p < .001). We recommend using discrete calibration standards during external calibration. Irrespective of any differences in SA determined by the three laboratories, the SA enrichment factor (EF: =SASML/SASSW) was not affected for any sample; the root mean square error (±one standard deviation) between all laboratories was 0.156 ± 0. 226 (n = 45). We present and discuss recommendations for a standard analytical protocol to ensure the inter-laboratory compatibility of SAS measurements into the future.

Study of influence of the surface-active substances concentration on releasing of praziquantel from the rectal suppository

Acne dermatosis (rosacea, perioral dermatitis, seborrheic dermatitis etc.) are one of the most actual problem in dermatology. Praziquantel is an antiparasitic medication effective towards trematodes, cestodes. Investigations developed by domestic scientists revealed antidemodicosis activity of praziquantel. Use of semisolid dosage forms for rectal administration will allow to increase its efficacy and minimize the risks of adverse reactions.&#x0D; On the department of technology of medications Zaporizhzhia State Medical University research of development of praziquantel rectal dosage form for therapy of acne dermatosis, complicated with demodicosis, and its technology is carried out. As a result of biopharmaceutical investigations it was determined that combination of excipients – the base (confectionary fat 60%, 10% paraffin, 30% cocoa butter) and surfactant (distilled monoglycerides) provides with the optimal praziquantel releasing.&#x0D; The aim of this work is study of excipient using in manufacturing of suppository (bases and surfactants) influence on the biopharmaceutical characteristics of praziquantel rectal dosage form.&#x0D; Investigation was carried out by the one-factors dispersive analysis with repeated observations By way of a parameter of optimization praziquantel releasing was chosen as the first step of bioavailability investigation. Praziquantel releasing from suppository was studied by the equilibrium dialysis by Kruvchinsky’s method at temperature 37 ± 0,5 °С through a cellophane semipermeable membrane «Kuprofan» film using Franz diffusion cell apparatus. Ethyl alcohol was chosen as a dialysis medium considering the solubility of praziquantel. Concentration of released praziquantel after 30 minutes of the dialysis was determined by spectrophotometric analysis.&#x0D; As a result of biopharmaceutical investigation of praziquantel suppositories it was determined that surface-active substances (distilled monoglycerides) concentration has a statistically significant influence on its releasing from rectal dosage form. It was ascertained that 0,5% concentration of distilled monoglycerides provides with the optimal releasing of praziquantel from rectal suppositories.

Size-Resolved Surface-Active Substances of Atmospheric Aerosol: Reconsideration of the Impact on Cloud Droplet Formation.

Our current understanding of the importance of surface-active substances (SAS) on atmospheric aerosol cloud-forming efficiency is limited, as explicit data on the content of size-resolved ambient aerosol SAS, which are responsible for lowering the surface tension (σ) of activating droplets, are not available. We report on the first data comprising seasonal variability of size-segregated SAS concentrations in ambient aerosol particulate matter (PM). To assess the impact of SAS distribution within PM on cloud droplet activation and growth, a concept of surfactant activity was adopted and a parametrization developed; i.e., surfactant activity factor (SAF) was defined, which allowed translation of experimental data for use in cloud parcel modeling. The results show that SAS-induced σ depression during cloud activation may affect droplet number ( Nd) as much as a 2-fold increase in particle number, whereas by considering also the size distribution of particulate SAS, Nd may increase for another 10%. This study underscores the importance of size-resolved SAS perspective on cloud activation, as data typically obtained from aqueous extracts of PM2.5 and PM10 may result in misleading conclusions about droplet growth due to large mass fractions of supermicron particles with SAS deficit and little or no influence on CCN and Nd.

Study of influence of surface-active substances concentration on clopidogrel releasing from the rectal suppository

During the last years clopidogrel which together with strong polyvalent antiaggregatory action on platelets decreases the level of triglycerides and optimizes other indexes of lipidogramm has ranked the leading place from the medications with antiplatelet mechanism. In the Ukrainian pharmaceutical market clopidogrel is presented in form of domestic and imported film-coated tablets. Alternative to oral administration of clopidogrel is rectal route which thanks to increasing of medical substance bioavailability allows to decrease the active ingredient dose and minimize the risks of unwanted side effects in the organism. At the Medicinal Preparations Technology Department of Zaporozhye State Medical University the research of composition development and technology of clopidogrel rectal dosage form for prevention of atherothromboses for the patients with myocardial infarction, acute coronary syndrome, ischemic stroke, occlusive arterial disease. As a result of biopharmaceutical investigations it was established that combination of excipients – the base (mixture of polyethyleoxydes with molecular weight 1500 and 400 in ratio 9:1) and surface-active substance (twin-80) provides optimal releasing of clopidogrel from the rectal suppository. The aim of this work is scientific substantiation of surface-active substance (twin-80) concentration in rectal dosage form with clopidogrel. Materials and methods . Suppositories were made by the fusiom method using the forms from the Franco-Krespy semi-automatic device. Concentration of surfactant (twin-80) was 0,5%, 1%, 2%, 3% and 5% of drug mass, clopidogrel content was 0,075 g in each suppository. As a parameter of optimization a clopidogrel releasing from suppository compositions was chosen as a first stage of bioavailability study. Clopidogrel releasing from the suppository was studied using the equilibrium dialysis method by Kruvchinsky at 37±0,5 0 С temperature throuth the semipermeable membrane – cellophane film «Kuprofan» in a station with Franz diffusion cells (producer is «Permegear, Inc»., USA). As a dialysis medium taking into account clopidogrel solubility methyl alcohol was chosen. Concentration of clopidogrel released after 30 min was determined by the spectrophotometric method using the spectrofotometer UV – 2600 (producer is«Shimadzu Corp»., Japan). Results . Analysis of variance showed significant influence of surfactant (twin-80) concentration on the clopidogrel releasing from the suppository compositions. Verification of average results of clopidogrel releasing by the Dunkan’s multiple rank test showed that increasing of twin-80 concentration in rectal suppository with clopidogrel more than 2% doesn’t lead to increasing of its releasing from the dosage form. Conclusions . As a result of carried out biopharmaceutical study of clopidogrel suppository it was determined that surfactant (twin-80) concentration has a statistically significant influence on its releasing from the dosage form. It was found out that 2% concentration of twin-80 provides with the optimal level of clopidogrel releasing from the rectal suppository.

INFLUENCE OF EMULATOR'S NATURE ON DISPERSION AND STABILITY OF ARTIFICIAL LATEX

In this paper, we consider methods for producing artificial latexes based on butadiene-styrene thermoplastic elastomer in the presence of cationic surfactants, as well as their mixtures with nonionic and silicone surfactants. The obtained results are compared for the particle size distribution, and conclusions are drawn about the stability of the polymer suspension. The size of particles of polymer suspensions was determined by the method of photon correlation spectroscopy (dynamic light scattering) using a laser particle analyzer. This method allows us to consider the properties of the resulting polymer suspensions and directly draw conclusions about the effect of nature and the concentration of surface active substances on the stability of the resulting latexes. It can be assumed that in this case, structural- mechanical and electrostatic barriers form in the surface layers of the particles. The combined action of these barriers has made it possible to obtain stable polymer emulsions. Thus, it can be concluded that the used surfactant mixtures make it possible to increase the stability of artificial latexes in the stages of emulsification and distillation.

OPTIMIZATION OF MODIFYING MATERIAL DISTRIBUTION DURING LASER PROCESSING OF THE METAL SURFACE

The improvement of operational properties of metal parts during the laser surface treatment can be obtained by modifying the melt with the prepared nano-sized particles of refractory compounds (carbides, nitrides, and others.). It allowsthe number of crystallization centersto be increased, the structure to be grinded and the uniformity of the solidified metal to be raised. It is known that thermocapillary convection promotes the homogeneous distribution of materials penetrating into the molten metal. It is also known that the presence of surface-active substances in the melt influences the character of convection. There is evidence that the structure of flow in the melt depends on the amount of surface-active substances in the metal. Therefore, the studies were conducted to obtain data on the relationship of characteristics of metal processing by laser and the uniformity degree of modifying additives distribution. Using the numerical modeling the effects of characteristics of pulsing laser action on allocation of modifying particles are estimated at the presence of surface-active substance in metal. With the help of mathematical proposed model the following non-stationary processes are considered: heating and melting of the metal, heat transfer in the melt, fluid motion, nucleation and growth of the solid phase after termination of the pulse. During the numerical realization of the model the heat conduction equation was firstly solved. Upon appearance of molten metal the boundary of the liquid phase was determined. Further the coupled equations of convective heat transfer and motion of an incompressible fluid were solved. After the laser pulse termination, the calculations are continued until the complete solidification of the substrate material is achieved. It was supposed that modifying nano-sized particles under the influence of convective flows penetrate into depth of a melt from its surface. The movement and distribution of particles in a fluid was modeled using markers. The movement of the markers was determined by the local velocity of the melt. According to the results of numerical experiments, the effect of the parameters of pulsed laser action on the nature of the flow and distribution of the particles in the melt were determined. Optimum parametersfor the melting of the metalsubstrate by a laser pulse are proposed for various surface-active substances concentrations.

Influence of surface active substances on the intensification of extraction when changing hydrodynamic indices of the technology of organopreparations

An influence of surface-active substances (SAS) on the change of physical characteristics of extractants of the group of organic preparations (chonsorid, heparin, and ronidase) was studied. Authors established rational concentrations of SAS in extractants, at which the minimum of coefficient of surface tension and the decrease in coefficient of dynamic viscosity are reached. For the solution of extractant of chonsurid – SAS butanol in the concentration of 0,05–0,06 % by weight, of heparin – butanol in the concentration of 0,5–0,6 % by weight, of ronidase – butanol in the concentration of 0,45–0,6 % by weight. Mean values of a near–surface laminar layer were established with the help of theoretical calculations, namely: for heparin – 1 mm, for chonsurid – 3 mm, for ronidase – 1 mm. Kinetics of extracting demonstrated an increase in the amount of the mass of extract when using extractants with SAS: for chonsurid – by 1,4 times, for heparin – by 1,7 times, for ronidase – by 1,9 times. Mathematical calculations proved a change in the similarity numbers under the influence of the surfactants, the Archimedean, Euler and Reynolds numbers were calculated and their values were compared. The Archimedean number changes its value for the extractants of chonsurid from 1028 to 10028, for those of heparin – from 3463 to 5910, for those of ronidase – from 990 to 6236. The value of the Reynolds number changes with the use of industrial extractants and the proposed extractants with the addition of SAS for chonsurid – from 18,6 to 91,6, for heparin – from 34,8 to 265, for ronidase – from 17,5 to 65,1. The Euler number with the use of industrial extractants for chonsurid is 170, for heparin – 92,2, for ronidase – 69,9, and when using the proposed extractants with the addition of SAS, it is: 37,5; 11,3; 12, respectively. Authors assessed hydrodynamic situation on the border of the contact “solid body – liquid” using the ratio of forces of surface tension to inertial forces on the basis of dimensionless set – surface number. Surface number changes its value when using industrial extractants and the proposed extractants with the addition of SAS for chonsurid from 2295 to 2164, for heparin from 530 to 346, for ronidase from 4641 to 197. The expediency of applying surface number was proved.

Inčukalna sērskābā gudrona dīķu piesārņotā pazemes ūdens kustības datormodelēšana

At the Incukalns district, two abandoned gravel pits from 1955 to 1970 were used as dump sites for storing liquid sulphuric goudron (mixture of sulphuric acid and oil products). The dump sites were named the Northern and Southern pools. The Northern pool was filled with sand. Presently, the Southern pool contains goudron in the state of liquid, paste and stone. During sixty years, the pools are polluting groundwater that moves towards the Gauja river. Excavation of the goudron body of the Southern pool continues. The contaminated sand of the Northern pool will be taken away. In order to optimize the ongoing process of environmental recovery of the place, the researchers of Riga Technical University carried out computer based modelling of mass transport of contaminants (especially surface active substances (SAS)) by the groundwater flow. The research was done to the request from the company INTERGEO. It was found out that the SAS plumes of the Northern and Southern pools will reach the river, after 25 and 80 years (from 2015), accordingly. The SAS mass of the plumes was evaluated, respectively, 8000kg and 30000kg, for the Northern and Southern pool in 2015. The rate of the SAS inflow from the Northern pool plume into the Gauja river was estimated for 2039–2099 if no SAS destruction takes place: 660 kg – in 2039–2054; 2800 kg – in 2059-2079; 4000 kg – in 2079–2099. After 2119, the mass of zone SAS plume will be 540 kg. The unevenness of the SAS inflow rate is due to the smaller SAS concentration for the exterior part of the plume than for its central part. This fact was also confirmed by the hydrographs for the SAS concentration of the virtual monitoring wells. It was found that the SAS inflow into the Gauja river will have no real influence (even without SAS destruction) on the quality of river water, because its flow is much more stronger than that of the contaminated groundwater flow from the Northern pool.

Electrochemical Evaluation of the Organic Matter Content of Edible Sea and Rock Salts Retailed in the Greek Market.

The release of copper-complexing ligands in 14 sea and 10 rock edible salts retailed in the Greek market has been examined. The concentration of ligands (LT) and the copper-binding strength (logKapp) of salt solutions were determined with Differential Pulse Anodic Stripping Voltammetry (DPASV). The tested salt samples were found to have Cu complexing ligands, at concentrations ranging from &lt;0.1 to 61.2 nmol g-1. In none of the salt samples examined (except a single one) were LTvalues exceeded by the corresponding total copper concentrations, indicating that Cu is fully complexed. Aiming to partially characterize the physico-chemical properties of the organic material contained in salts, the surface active substances (SAS) and catalytically active compounds (CAC) were measured, for the first time, in salt solutions by sensitive electrochemical techniques. Higher concentrations of organic carbon and SAS were determined in sea samples compared to rock salts.

Control of Kinetic Parameters and Rate-Determining Step Nature of Hydrogen Evolution Reaction on Iron

Influence of nature and concentration (1-10 mM) of surface-active substances (SAS) phenylbiguanidine and m-nitrophenylbiguanidine on hydrogen evolution reaction (HER) kinetics on iron has been studied in acidic chloride solutions with constant ionic strength equal to 1. The rate-determining stage of HER changes dependending on SAS nature and concentration according to the consequence: discharge → chemical recombination → surface diffusion → discharge. With some SAS concentrations, two consecutive stages proceed at commensurable rates. The possibility of discharge or chemical recombination stage proceeding on ad-atoms or adsorbate molecules forming the first monolayer is considered.

Influence of non-ionic and ionic surfactants on kinetics of the bubble attachment to hydrophilic and hydrophobic solids

Abstract The paper is devoted to kinetics and mechanism of the three-phase contact (TPC) formation by the colliding bubble at model hydrophobic (polytetrafluoroethylene – Teflon) and hydrophilic (muscovite mica) solid surfaces. To determine influence of type of the surfactant polar group the experiments were carried out in solutions of non-ionic (n-hexanol and n-octanol), cationic (n-octyl-(OTABr), n-dodecyl-(DDTABr) and n-hexadecyl-trimethylammonium (CTABr) bromides, and anionic (sodium hexadecyl sulfate (SHS)) surface active substances (SAS). The time of the TPC formation (tTPC) and timescale of rupture of the thin liquid film separating the colliding bubble and a solid surface was determined using high-speed video registrations. The tTPC was defined as the time span from the moment of the bubble first collision up to the liquid film rupture and formation of the TPC (dewetted) hole. It was shown that the influence of SAS on the kinetics of the TPC formation could be completely different depending on the hydrophilic/hydrophobic properties of the solid surface. At the Teflon surface the TPC was formed always, both in distilled water and in SAS solutions of various composition and concentration. Moreover, the tTPC was significantly prolonged at higher SAS concentrations, independently on the SAS type (ionic, non-ionic). At the mica surface the wetting film was stable and the TPC was never registered in distilled water as well as in solutions of non-ionic and anionic surfactants. However, the TPC was formed at the mica surface in solutions of cationic surfactants, but the tTPC values were decreasing with increasing cationic surfactants concentration. Mechanism of the TPC formation is presented and reasons of the completely different influence of SAS on kinetics of the TPC formation at the hydrophilic and hydrophobic solid surfaces are explained.

Simple and fast voltammetric procedure of U(VI) determination in the presence of high concentrations of surface active substances

In this work, a simple and fast procedure for elimination of interfering surface active substances and for U(VI) adsorptive stripping voltammetric determination was developed. The adsorption in the form of U(VI)-cupferron complexes was performed, because as it was proved before, U(VI) forms with cupferron stable complexes, which were employed in voltammetric procedures. The procedure is based on two steps: the first is an adsorption of surface active substances onto an Amberlite XAD-16 or XAD-7 resin and the second is a voltammetric determination of U(VI) with a pulsed potential of accumulation alternate –0.65–0.3 V with the frequency of 0.5 Hz and then the differential pulse voltammogram was recorded, whereas the potential was scanned from –0.65 to –1.2 V. The detection limit estimated from three times the standard deviation for a low U(VI) concentrations was equal to 1.7 × 10−10 mol L−1 (7.2 × 10−8 g L−1). The linear range of U(VI) was observed over the concentration range from 5.0 × 10−10 mol L−1 (2.1 × 10−7 g L−1) to 2.0 × 10−8 mol L−1 (8.5 × 10−6 g L−1) for an accumulation time of 60 s. The influence of different kinds of surfactants, such as non-ionic, cationic and anionic on the uranium voltammetric signal was studied. The results confirm the possibility of U(VI) determination in water samples containing high concentrations of surface active substances even up to 50 mg L−1.

Constant current chronopotentiometric stripping characterisation of organic matter in seawater from the northern Adriatic, Croatia

Environmental context We determined seasonal changes in the organic matter content of the northern Adriatic with newly applied electrochemical techniques able to measure catalytically active organics. The inflow of the Po River and its nutrient load are responsible for the observed changes in the type and concentrations of organic matter in the area. Abstract Catalytically active polysaccharides (Cat PSs) and nitrogen-containing polymeric organic material (N-POM) were determined in seawater from the northern Adriatic station ST101. Catalytically active organics were measured by applying electrochemical methods of adsorptive transfer chronopotentiometric stripping with medium exchange and chronopotentiometric stripping in unmodified seawater. Their concentrations were expressed in milligrams per cubic decimetre–3--&gt; of equivalents of the model calibrating substances, polysaccharide xanthan and protein human serum albumin. The optimal electroanalytical conditions for determination of Cat PSs in seawater were evaluated and defined. Seasonal changes of Cat PSs and N-POM were observed during the period 2011–2013. The highest values were determined in the spring–summer period and the lowest in winter. Cat PSs and N-POM were present in both the dissolved and particulate organic carbon fractions. Cat PSs and N-POM showed a statistically significant positive correlation with the concentrations of surface-active substances. A weak but statistically significant correlation was found between Cat PSs and dissolved organic carbon concentrations. Copper complexing capacities in the period 2011–2013 were in the range of 41–130nmoldm–3.

Characterization of adsorbed microlayer thickness on an oceanic glass plate sampler

The thickness of solution layers adsorbed onto rotating glass plates designed for use on an oceanic glass plate sampler was investigated in laboratory experiments using optical techniques. Using the Beer‐Lambert Law, light attenuation measurements were used to calculate the thickness of adsorbed solution layers on a rotating glass disk with and without salt and surfactants. The observations have shown that the adsorbed film thickness can vary between 80 and 40 µm for glass rotation speeds between 4 and 16 cm s−1, depending on salinity and surfactant concentrations. For example, the thickness of a film of water with 40 ppt of salt and 5 cm s−1 rotation speed was in the range of 80 µm. The adsorbed layer thickness increases with increasing salt concentration and with increasing concentrations of surface active substances. These results are comparable to results obtained by vertically dipping a glass plate and determining film thickness from the collected volume of water. Because the glass disk rotational speed significantly influences the thickness of the adsorbed solution layer, it is important that the speed is maintained at a value for which the adsorbed thickness has been calibrated. At typical oceanic salinities, the dependence of the adsorbed film thickness on rotation speed was limited. However, even small changes in surface active substances resulted in significant thickness changes.