Rectilinear Relationship Research Articles

PH-controlled charge transfer sensitive 2-aminobenzimidazole modified poly(styrene-co-maleic anhydride) copolymer for selective extraction, pre-concentration and determination of trace Hg2+ and CH3Hg+ in vinegar by combination of ultrasound assisted-cloud point extraction with UV–VIS spectrophotometry

In this study, a separation/pre-concentration procedure, ultrasound assisted-cloud point extraction with modified 2-aminobenzimidazole (2-ABzI), was developed for the extraction of trace Hg2+ and CH3Hg+ and from vinegar samples- modified copolymer coupled with Hg-binding chelator, 2-ABzI. The imidic copolymer was characterized, and used for detection of the enriched Hg species by spectrophotometer at 332 nm. The method is based on their pH-induced charge transfer sensitive complexation with copolymer matrix via 2-AmBzI moiety at pH 6.0 and 4.5, and their extraction into the mixed micellar phase of the mixed non-ionic/ionic surfactants as extractant/sensitivity enhancer. The variables influencing the extraction efficiency were optimized. From pre-concentration of 25-mL sample, with a changing calibration sensitivity and pre-concentration factor of 62.5, a good rectilinear relationship between absorbance and concentrations of Hg species in ranges of 1–15, 15–150 µg L−1 was obtained. The detection limits are 0.30 and 0.31 µg L−1, respectively. Its precision/accuracy were in range of 3.1–7.6 % and 90.5–96 % after spiking (n: 5, for measurements of 5, 25 and 100 µg L−1 in same day and three consecutive days). The matrix effect was also studied (n: 3, 100 µg L−1). The method is simple, cost-effective, fast, accurate, safe, highly stable and selective, which has successfully been applied to the speciation of mercury in vinegar.

Bioactive compounds in blackberry fruits under the conditions of Central Russia

Background. Blackberry is becoming increasingly popular in Russia for its rapid early-fruiting, high self-fertility and late flowering, contributing to longer consumption of fresh berries, a source of antioxidant compounds. There is a need to study the biochemical composition of blackberries.Materials and methods. Fruits of 25 blackberry cultivars and hybrid seedlings from the Institute of Fruit Crop Breeding (VNIISPK) were analyzed for the contents of catechins, leucoanthocyanins, anthocyanins, and total phenolic compounds using the photometric method, and the content of ascorbic acid using the titrimetric method. Statistical data processing was carried out using the methods of variation and correlation analyses.Results. Bioactive compounds (BAC) accumulating in blackberry fruits were studied: ascorbic acid, catechins, leukoanthocyanins, anthocyanins, and total phenolics, with medium and significant variability of the studied indicators (V > 10%). Among the genotypes, 73% accumulated more than 20.0 mg/100 g of ascorbic acid in fruits. All genotypes were identified as sources of anthocyanins. About 50% of the accessions accumulated catechins in fruits above the average level. Leucoanthocyanins were stored in blackberry fruits in slightly larger amounts than catechins. In 10 accessions the level of phenolics was higher than 1000.0 mg/100 g.Conclusion. Genotypes with high BAC content were identified. Correlation coefficients were obtained: they indicate the presence of an medium degree of rectilinear relationship between the content of ascorbic acid and anthocyanin compounds, ascorbic acid and total phenolics. Cvs. ‘Black Satin’, ‘Cacanska Bestrna’, ‘Chester’, ‘Natchez’ and ‘Triple Crown’, plus hybrid seedlings LN-14, LN-1 and LN-7, were identified according to a set of indicators (ascorbic acid and phenolics) and recommended for breeding to improve the quality of blackberry fruits.

Eco-friendly HPTLC method for simultaneous analysis of sofosbuvir and ledipasvir in biological and pharmaceutical samples: Stability indicating study

Recently, many single-pill combinations are used as a promising choice in hepatitis C treatment. However, this trend made a serious challenge to drug analysts due to difficulty of analysis of two or more drugs simultaneously. In this study, sofosbuvir (SF) and ledipasvir (LD) were simultaneously analyzed by developing a simple, inexpensive, rapid and eco-friendly high-performance thin layer chromatographic (HPTLC) method with densitometric detection. Separation was carried out using aluminum HPTLC plates silica gel 60 F254 as the stationary phase developed using the mobile phase ethyl acetate: methanol: water: glacial acetic acid (30: 1.5: 1: 0.2% v/v). Development was done in a twin-trough chamber followed by densitometric detection of SF and LD at 260 and 320 nm, respectively. The calibration curves for standard solutions showed a rectilinear relationship for SF and LD in the range of 2 –12 and 0.45–6.0 μg band−1, respectively with correlation coefficients > 0.9995 and limits of detection of 0.6 and 0.1 μg band−1 for SF and LD, respectively. While, calibration curves for biological samples showed linear relationships for SF and LD in the range of 1.0–20 and 0.2–6.0 μg mL−1, respectively with correlation coefficients > 0.99 and limits of detection of 0.21 and 0.27 μg mL−1 for SF in plasma and urine samples, respectively and 0.05 and 0.03 μg mL−1 for LD in plasma and urine samples, respectively. Also, it was effectively used in the analysis of the investigated drugs within their pharmaceutical form and biological fluids without any matrix interference with high precision (% RSD < 2%) and good accuracy with% Er value < 2%. Moreover, SF and LD were analyzed along with their degradation products after performing forced degradation studies.

Versatile Sensor Modified with Gold Nanoparticles Carbon Paste Electrode for Anodic Stripping Determination of Brexpiprazole: A Voltammetric Study

A variety of voltammetric methods have been carried out for determination of brexpiprazole (BRX) using cyclic voltammetry (CV) and two different type anodic stripping methods; differential pulse (AS-DP) and square wave (AS-SWV) at modified carbon paste electrode with gold nanoparticles (AuNPs-CPEs). Additionally, electrochemical impedance spectroscopy (EIS) technique has been utilized for characterization of the different electrodes. Electrochemical oxidation behavior of BRX shows an irreversible anodic peak at 0.88 V versus Ag/AgCl, in Britton–Robinson buffer (BR) at pH 4.0, 50s preconcentration time and −0.5 deposition potential. Rectilinear relationship between the peak current versus concentration was obtained over the ranges of 1.32 × 10−6–6.45 × 10−6 and 1.32 × 10−7– 6.45 × 10−7 mol L−1 for AS-DP and AS-SWV respectively. The lowest concentration that can be detected for both for AS-DP and AS-SWV was 3.99 × 10−7 and 3.32 × 10−8 mol L−1 respectively; the utilized methods have been devoted adequately for the estimation of BRX in its pure and dosage form.

Community‐level natural selection modes: A quadratic framework to link multiple functional traits with competitive ability

AbstractResearch linking functional traits to competitive ability of coexisting species has largely relied on rectilinear correlations, yielding inconsistent results. Based on concepts borrowed from natural selection theory, we propose that trait–competition relationships can generally correspond to three univariate selection modes: directional (a rectilinear relationship), stabilising (an n‐shaped relationship), and disruptive (a u‐shaped relationship). Moreover, correlational selection occurs when two traits interact in determining competitive ability and lead to an optimum trait combination (i.e., a bivariate nonlinear selection mode).We tested our ideas using two independent datasets, each one characterising a group of species according to (a) their competitive effect on a target species in a pot experiment and (b) species‐level values of well‐known functional traits extracted from existing databases. The first dataset comprised 10 annual plant species frequent in a summer‐rainfall desert in Argentina, while the second consisted of 37 herbaceous species from cool temperate vegetation types in Canada. Both experiments had a replacement design where the identity of neighbours was manipulated holding total plant density in pots constant. We modelled the competitive ability of neighbours (i.e., the log inverse of target plant biomass) as a function of traits using normal multiple regression.Leaf dry matter content (LDMC) was consistently subjected to negative directional selection in both experiments as well as to stabilising selection among temperate species. Leaf size was subjected to stabilising selection among desert species while among temperate species, leaf size underwent correlational selection in combination with specific leaf area (SLA): selection onSLAwas negative directional for large‐leaved species, while it was slightly positive for small‐leaved species.Synthesis. Multiple quadratic regression adds functional flexibility to trait‐based community ecology while providing a standardised basis for comparison among traits and environments. Our analyses of two datasets from contrasting environmental conditions indicate (a) that leaf dry matter content can capture an important component of plant competitive ability not accounted for by widely used competitive traits, such as specific leaf area, leaf size, and plant height and (b) that optimum relationships (either univariate or bivariate) between competitive ability and plant traits may be more common than previously realised.

The analysis of force and surface electromyogram of agonist and antagonist during isometric elbow flexion at different joint angles

Kinematic and electrophysiological performance can effectively elaborate the characteristic of muscle contraction which can provide beneficial proof of rehabilitation program to treat motor dysfunction. In this study, we aimed to analyze the difference and regularity of force and surface electromyogram (sEMG) of agonist and antagonist during isometric elbow flexion at different joint angles. Twenty-one young volunteers were recruited and then performed maximum voluntary isometric contraction (MVIC) of elbow flexion continuously until exhaustion at four different elbow flexion angles (i.e., 30°, 60°, 90° and 120°). Isokinetic dynamometer was used to assess the torque during MVIC and synchronous sEMG signal recorded from biceps brachii (BB) and triceps brachii (TB). The corresponding experimental results showed that PT at elbow flexion 60° was the highest among four angles. BB-RMS and BB-AEMG at flexion 30° and 60° were both significantly higher than those at flexion 90° and120°, while no difference was found in TB-RMS among different angles. The MF and MPF of BB and TB increased with increasing in elbow flexion angle. It was found that both PT and Av-T correlated positively with BB-RMS and BB-AEMG and there is stronger correlation with smaller elbow flexion angle. Extensive analysis displayed that the torque under 0∼70% MVIC at four elbow flexion angles had a good linear relationship with corresponding rectified EMG-amplitude but not rectilinear relationship. It can be concluded that the joint angle can affect the force and sEMG signal and elbow flexion around 60° may produce the maximum force. Joint angle should be introduced to interpret the muscle force with the EMG-amplitude. Furthermore, an important conclusion is made in this study that muscle strength under 0∼70% MVIC may be interpreted accurately by sEMG.

Extraction, Preconcentration, and Quantification of Low Levels of Free Formaldehyde from Some Beverage Matrices by Combination of Ultrasound-Assisted-Cloud Point Extraction with Spectrophotometry

In the present study, due to use of formaldehyde (FA) as a food additive as well as its endogenous and natural occurrence in aquatic products, a new preconcentration method for the quantification of free formaldehyde (FA) in beverages was developed before analysis by spectrophotometry at 538 nm. The method is based on spontaneously Cannizzaro disproportionation of FA with Variamine blue (VBH2) in the presence of ionic surfactant, sodium dodecylsulfate (SDS) as both sensitivity enhancer and counter ion at pH 7.0, and then extraction of the formed ion-pairing complex into the nonionic surfactant, polyethylene glycol tert-octylphenyl ether (Triton X-114). The effect of analytical variables was evaluated in detail, and the optimal working conditions were established. There was a rectilinear relationship in the range of 2–400 μg L−1 with changing sensitivity. The limits of detection and quantification of the method with a sensitivity enhancement of 65 after preconcentration were 0.53 and 1.76 μg L−1, respectively. The accuracy was validated by using two spiked quality control samples in linear working range and by comparing the results obtained from the samples with those of independent method, which is known as a slight modified acetylacetone method. It has been observed that the results obtained by both methods are statistically compatible with a t value ranging from 0.09 to 0.65 (t critical 2.31). The intra-day and inter-day precisions as a result of stabilization of mixed micellar system were lower than 4.9% (as RSD%, n 5), and the recoveries were quantitatively higher than 95% for the two quality control samples spiked with 10, 25, and 50 μg L−1 with satisfactory results. The method was successfully applied to the quantification of low levels of free FA in selected beverage matrices.

NEED FOR PROFESSIONALISM AND QUALITY SERVICE OF THE TOURIST GUIDES IN OMAN

PURPOSEThe objectives of the study are to investigate the factors impeding the professionalism of the tourist guides in Oman and to analyze the service quality improvement of the tourist guides.DESIGN/METHODOLOGY/APPROACH56 samples were collected from the tourist guides in Oman working in public and private sector, and the samples were selected on a random sampling basis. Using a well-defined questionnaire data was collected, analyzed and interpreted to derive the conclusion.FINDINGSThe empirical results reveal that there is a rectilinear relationship between the Finance, Societal factors and the Success of Tourist Guide profession. But it is observed that from the negative coefficients that the finance and societal factors make a negative impact on the tourist guide job.PRACTICAL IMPLICATIONSIt is suggested that specialized courses should be offered by the Government to tourist guides to improve their performances and, financial and moral support should also be provided by the Government to take up Tourist guide profession. The tourist guides prefer the Government should support tourist guides to participate in global events of tourism. Social ImplicationsIt is found that the tourist guides profession is considered neither as a decent job nor as a prestigious job by the society and the media only can correct the view of the society.ORIGINALITY/VALUENo study has investigated the professionalism and quality of service of the tourist guides in Oman, and this study will help the planners and the Government to boost tourism.

Ultra-trace detection of methimazole by surface-enhanced Raman spectroscopy using gold substrate

Gold nanoparticles (AuNPs) were set up by a reduction technique and fabricated as SERS substrates for methimazole detection, which is of therapeutic significance. The morphology of the nanoparticles were characeterized utilizing Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), UV–vis spectroscopy, Scanning Electron Microscopy (SEM) and Raman spectroscopy. The regular size of the AuNPs was around 10nm. The maximum absorbance for the UV–vis spectrum appeared at 524nm. Density Functional Theory (DFT) computations and surface Enhanced Raman Spectroscopy (SERS) were used to study to the adsorption behavior of methimazole on the AuNPs substrates. SERS experiment and DFT calculations suggested the possibility of molecular interactions between the AuNPs and methimazole. SERS experiment showed an improvement in the bands which was used to obtain a rectilinear relationship between the concentration of methimazole and the intensity of the SERS signal. AuNPs showed a good coefficient of correlation and improved limit of detection.

Directional, stabilizing, and disruptive trait selection as alternative mechanisms for plant community assembly.

How plant functional traits (e.g., seed mass) drive species abundance within communities remains an unsolved question. Borrowing concepts from natural selection theory, we propose that trait-abundance relationships can generally correspond to one of three modes of trait selection: directional (a rectilinear relationship, where species at one end of a trait axis are most abundant), stabilizing (an n-shaped relationship), and disruptive (a u-shaped relationship). Stabilizing selection (i.e., the functional convergence of abundant species) would result from positive density-dependent interactions (e.g., facilitation) or due to generalized trade-offs in resource acquisition/use, while disruptive selection (i.e., the divergence of abundant species) would result from negative density-dependent interactions (e.g., competition) or due to environmental heterogeneity. These selection modes can be interpreted as proxies for community-level trait-fitness functions, which establish the degree to which traits are truly "functional". We searched for selection modes in a desert annual-plant community in Argentina (which was divided into winter and summer guilds) to test the hypothesis that the relative importance of disruptive mechanisms (competition, disturbances) decreases with the increase of abiotic stress, a stabilizing agent. Average density was analyzed as a function of eight traits generally linked to resource acquisition and competitive ability (maximum plant height, leaf size, specific leaf area, specific root length), resource retention and stress tolerance (leaf dissection, leaf dry matter content, specific root volume), and regeneration (seed mass) using multiple quadratic-regression models. Trait selection was stabilizing and/or directional when the environment was harshest (winter) and disruptive and/or directional when conditions were milder (summer). Selection patterns differed between guilds for two important traits: plant height and seed mass. These results suggest that abiotic stress may drive within-community functional convergence independently of the trait considered, opposing the view that some traits may be inherently convergent while others divergent. Our quadratic model-based approach provides standardized metrics of both linear and nonlinear selection that may allow simple comparisons among communities subjected to contrasting environmental conditions. These concepts, rooted in natural selection theory, may clarify the functional link between traits and species abundance, and thus help untangle the contributions of deterministic and stochastic processes on community assembly.

Quantification of Aceclofenac and Pregabalin in Pharmaceutical Formulations using Nucleophilic Aromatic Substitution Reactions

Aceclofenac and Pregabalin in combination have significant reduction in pain as compared to individual drug in chronic low back pain. Literature reveals that all the reported spectrophotometric methods are either need tedious extraction procedures do not offer high sensitivity, uses non specific reagent and/or recommend the measurement of absorbance in the near UV region where interference most probably occurs that do not offer suitable linearity range. A novel, accurate, precise and extraction free UV spectrophotometric method has been developed for simultaneous estimation of Aceclofenac and Pregabalin in combined dosage form. The method employed was Dual wavelength method. The method is based on the reaction of Pregabalin with 1,2-naphthaquinone-4-sulphonate sodium, yielding an orange colored product. The different experimental parameters affecting the development and stability of the reaction product were carefully studied and optimized. Method involves measurement of Aceclofenac at 268.5 and 280.0 nm and measurement of Pregabalin at 324.0 and 339.5 nm. Rectilinear relationship with good regression coefficient 0.999 and 0.999 were found over the concentration ranges of 5-25 μg/ml and 3.75-18.75 μg/ml for Aceclofenac and Pregabalin, respectively with detection limit 0.62 and 0.50 μg/ml and Quantitation limit 1.87 and 1.52 μg/ml. The mean percentage recoveries were ranged 99.60 – 99.83 and 98.85 – 100.05 for Aceclofenac and Pregabalin, respectively. The developed methods were successfully applied to the analysis of the drug in its commercial tablet.

Practical Implication of Chromatographic Method for Estimation of Aceclofenac and Pregabalin in Bulk and Pharmaceutical Dosage Forms

Background. Aceclofenac and Pregabalin in combination significantly reduce pain as compared to individual drug in chronic low back pain. Literature reveals that all the reported spectrophotometric methods either need tedious extraction procedures, do not offer high sensitivity, use nonspecific reagent, or recommend the measurement of absorbance in the near UV region where interference most probably occurs that does not offer suitable linearity range. Result. A selective, sensitive, accurate, and precise, high performance liquid chromatographic method with UV detector analysis of Aceclofenac and Pregabalin was investigated. Good chromatographic separation was achieved using an ODS-BP hypersil C18 column (250 mm × 4.6 mm, i.d., 5 μm) and a mobile phase consisting of 0.05 M phosphate buffer (KH2PO4) (pH 6.0) : methanol (60 : 40, v/v) at a flow rate 1 mL/min. The ultraviolet detector was set at wavelength 218 nm. Retention time for Aceclofenac and Pregabalin was found to be 3.220 and 5.910 min, respectively. Rectilinear relationship with good regression coefficients 0.999 and 0.999 was found over the concentration ranges of 5–25 μg/mL and 3.75–18.75 μg/mL for ACF and PGB, respectively, with detection limits 0.64 and 0.35 μg/mL and quantitation limits 1.95 and 1.06 μg/mL. Conclusion. The mean percentage recoveries were in the range of 98.45–100.08 and 99.69–100.48 for ACF and PGB, respectively. The developed method was successfully applied to the analysis of the drugs in their commercial tablets.

Determination of dimethylsulfide and dimethylselenide in human urine by portable gas chromatography–photoionization detection with headspace sampling

A simple and sensitive method for the determination of dimethylsulfide (DMS) and dimethylselenide (DMSe) employing a gas chromatograph–photoionization detector with headspace sampling (HS-GC-PID) was developed. Parameters affecting the HS-GC-PID sensitivity including matrix effect, heating temperature, extraction time and carrier gas flow-rate were optimized. The matrix effect was required for standard addition calibration method for quantification purposes. The method has been validated when rectilinear relationship was between the concentrations of analytes and peak area in the range of 0.2–50ngmL−1 for DMSe and 0.5–100ngmL−1 for DMS, the correlation coefficients were from 0.995–0.998, and the limits of detection for DMS and DMSe were 25pgmL−1 and 48pgmL−1, respectively. The proposed method was further applied to quantification of DMS and DMSe in urine samples.

Accelerated crystal growth of sulphathiazole by temperature cycling

AbstractA novel method is suggested for accelerating the physical changes in suspensions. The suspension is stirred in a jacketed vessel and is alternately heated and cooled. Results indicate a rectilinear relationship between the median particle size of sulphathiazole in suspension and the number of temperature cycles. Crystal growth is measured by the Coulter counter and growth rates are compared arithmetically to indicate which additives (surface-active agents) may be used to inhibit crystal growth.

Solid-phase extraction combined with headspace single-drop microextraction of chlorophenols as their methyl ethers and analysis by high-performance liquid chromatography-diode array detection

Solid-phase extraction (SPE) of phenol and chlorophenols, their derivatization to methyl ethers, headspace single-drop microextraction (HS-SDME) of methyl ethers using 1-butanol as extraction solvent, and direct transfer of the drop into the injector for high performance liquid chromatography with diode array detection (HPLC-DAD) have been reported. A flanged-end polytetrafluoroethylene sleeve, 3 mm × 0.5 mm, placed at the tip of the syringe needle, allowed the use of 10 μL solvent drop for extraction. The procedure has been optimized for variables involved in SPE and HS-SDME. A rectilinear relationship was obtained between the amount of chlorophenols and peak area ratio of their methyl ethers/internal standard (4-methoxyacetophenone) in the range 0.01–10 mg L −1, correlation coefficient in the range 0.9956–0.9996, and limit of detection in the range 1.5–3.9 μg L −1 when HS-SDME alone was used for sample preparation. When using coupled SPE and HS-SDME, the linear range obtained was 0.1–500 μg L −1, correlation coefficient in the range 0.9974–0.9998, and the limit of detection in the range 0.04–0.08 μg L −1. Spiked real samples have been analyzed with adequate accuracy, and application of the method has been demonstrated for the analysis of chlorophenols formed upon bamboo pulp bleaching.

Ionic liquid for single‐drop microextraction followed by high‐performance liquid chromatography‐ultraviolet detection to determine carbonyl compounds in environmental waters

A sensitive method based on ionic liquid for single-drop liquid microextraction coupled with HPLC-UV was developed for the determination of carbonyl compounds in environmental waters using 1-octyl-3-methylimidazolium hexafluorophosphate [C(8)min][PF(6)] as extraction solvent and 2,4-dinitrophenylhydrazine as derivatizing agent. The extraction parameters affecting the enrichment factors such as solvent volume, pH, extraction time and salt concentration were investigated. A homemade funnel form polytetrafluoroethylene sleeve was fixed at the tip of the syringe needle and this allowed the use of 10 microL drop of ionic liquid for direct immersion extraction. Under the optimal conditions, the remarkable enrichment factors up to 150-fold were obtained depending on the target analytes. The method has been validated when rectilinear relationship was obtained between the concentrations of analytes and peak area in the range of 5-100 ng/mL, the correlation coefficients were from 0.995 to 0.998, and the limit of detection was in the range of 0.04-2.03 ng/mL. The method was applied to monitor the concentration of carbonyl compounds in environmental waters with spiked recovery in the range of 84.2-106.9%.

Energy Expenditure During an Ultraendurance Alpine Climbing Race

Accurate reports of energy expenditure (EE) during prolonged mountaineering activity are sparse. The purpose of this study was to estimate EE during a winter ultraendurance climbing race and individual mountaineering activities in Mont Blanc, France. Seven days before the race, resting metabolic rate (RMR) and maximal oxygen consumption (Vo2(max)) were measured in 10 experienced male climbers (30.0 +/- 0.9 years). Three days before (reference period) and during the race, heart rate (HR) was recorded for estimation of total daily EE (TDEE), and the type and duration of all activities were collected through questionnaires. Total DEE was calculated by adding DEE during sleep (DEE sleep), sedentary (DEE sedentary), and during exercise (DEE exercise). Daily energy expenditure during exercise was determined through assumption of the rectilinear relationship between heart rate (HR) and Vo2. Anthropometric measurements were performed 7 days before, just before, and immediately after the race. Total time of the race averaged approximately 29 hours and 29 minutes, including 11 hours and 24 minutes in the hut, plus 18 hours and 5 minutes dedicated to climbing. During the race, TDEE was 43.6 +/- 1.2 MJ x d(-1). Energy expenditures for cross-country skiing and alpine climbing were similar (57.3 +/- 2.1 kJ x min(-1) and 54.0 +/- 2.9 kJ x min(-1), respectively). An energy deficit of 33.5 +/- 2.3 MJ resulted after the race, with a mean weight loss of 1.52 +/- 0.31 kg (P < .001). Experienced climbers expended a high level of energy during a winter ultraendurance alpine climbing race at moderate altitude under high degrees of difficulty and risk exposure. These results provide comparative data on the energy cost of the main mountaineering activities during a race: cross-country skiing and alpine climbing.

Headspace in-drop derivatization of carbonyl compounds for their analysis by high-performance liquid chromatography-diode array detection

A simple and rapid method has been reported for the determination of carbonyl compounds involving sample preparation by headspace single drop microextraction using 1-butanol as extraction solvent containing 2,4-dinitrophenylhydrazine for hydrazone formation, and direct transfer of the drop into the injector for high-performance liquid chromatography with diode array detection. An angle-cut polytetrafluoroethylene sleeve, 3 mm × 0.5 mm, was fixed at the tip of the syringe needle and this allowed the use of 7 μL drop of solvent drop for extraction and derivatization. The procedure has been optimized with respect to suitable solvent for headspace drop formation, drop volume, concentration of reagent, sample temperature, reaction time, and headspace-to-sample volume ratio. The method has been validated when rectilinear relationship was obtained between the amount of analyte and peak area ratio of hydrazones in the range 0.01–15 mg L −1, the correlation coefficient over 0.996–0.999, and the limit of detection in the range 1.7–24.1 μg L −1. Spiked real samples have been analyzed with adequate accuracy, and application has been demonstrated of the method for analysis of carbonyl compounds formed as oxidation products.

Gross growth efficiency as a function of food intake level in the “Pulpito” Octopus tehuelchus: A multimodel inference application

Multimodel inference theory was used to investigate the relationship between gross growth efficiency (GGE) and food intake level (FI) in Octopus tehuelchus for immature octopus kept at 10 °C and 15 °C. Multimodel inference was carried out using the model averaging methodology over the entire set of candidate models. The main results indicated that in O. tehuelchus GGE is an increasing and asymptotic function of FI showing a maximum approaching the partial growth efficiency (PGE). The model-averaged estimates of PGE and maintenance level (MaL) did not differ from those estimated using the rectilinear relationship between growth and FI in previous work. For FI higher than MaL, both GGE and PGE were higher in immature octopus at 10 °C than octopus at 15 °C. It is noteworthy that as FI increases to a satiability state, the difference between GGE at 10 °C and 15 °C decreases as a potential function of FI. These results would indicate that O. tehuelchus maximizes the energy used in growth by keeping a constant MaL for any value of FI. Multimodel inference theory proved to be an efficient tool to build averaged functions taking each candidate model into account. On the other hand, the present work presents a method to understand the intensity feeding needed to reach an optimum growth efficiency, avoiding wasting of food, work energy and investment for octopus rearing or culture activities.

A Bioreactor for Growth of Sulfate-Reducing Bacteria: Online Estimation of Specific Growth Rate and Biomass for the Deep-Sea Hydrothermal Vent Thermophile Thermodesulfatator indicus

essential requirement during growth experiments. With balanced exponential growth there is a rectilinear rela tionship between biomass concentration and the rate of change of substrate and product concentrations in the culture medium, which allows for indirect growth mea surements. The uptake of substrates and formation of products are often associated with changes in the proton concentration in the culture medium, and the rate of acid or base titrant addition to maintain constant pH is a measure of the rate of biomass formation. Recording ti trant addition therefore provides a simple method for measuring specific growth rates, changes in biomass con centration, and other aspects of energetics and metabolic function [8]. Titrant addition has been used for many years [9], to assess the growth parameters of a variety of different microorganisms [7, 8, 17, 18, 21]. For example, titrant addition has been used to estimate biomass concentra