rss_2.0Chemistry FeedSciendo RSS Feed for Chemistry Feed and pharmacological evaluation of some benzylidene-4-nitroanilines<abstract> <title style='display:none'>Abstract</title> <p>A number of nine benzylidene-4-nitroanilines were synthesized by condensation method. The formation of the substituted (<italic>E</italic>)-N-benzylidene-4-nitrobenzenamines has been confirmed from their physical and Ultra-Violet, Infra-Red, NMR spectral data. The evaluation of antimicrobial screening of substituted (<italic>E</italic>)-N-benzylidene-4-nitrobenzenamines was conducted by using standard Bauer-Kirby method. Three gram-positive microbes namely <italic>Bacillus subtilis</italic>, <italic>Micrococcus luteus</italic> and <italic>Staphylococcus aureus</italic>, and two gram-negative microbes, <italic>Escherichia coli</italic> and <italic>Pseudomonas aeruginosa</italic>, were used for the antibacterial evaluation. The antifungal activities against <italic>Aspergillus niger</italic> and <italic>Penicilium scup</italic> fungal species were also performed. A good antibacterial effect has been possessed by some of the substituted (<italic>E</italic>)-N-benzylidene-4-nitrobenzenamines on the microorganisms utilized in the present study</p> </abstract>ARTICLE2020-09-18T00:00:00.000+00:00Enhancement of tartaric acid modified washing solutions for lead decontamination of tropical soils<abstract> <title style='display:none'>Abstract</title> <p>Tartaric acid is generally not an effective soil washing solution, hence this study focuses on enhancing its usage for soil-Pb decontamination. Three tropical soil types (sandy, clay and loamy) with different lead concentrations were subjected to single batch washing using 0.01, 0.1, 0.5 and 1 M tartaric acid with 5% and 10% KCl modification at 3% soil-pulp-density for 2, 6, 12 and 24 h washing time. The optimum washing conditions were 1 M tartaric acid at 24 h washing time, with Pb removal efficiency: sandy- 94.3%, clay-67.6% and loamy-36.8%. Modification of tartaric acid with 5% and 10% KCl brought about some degree of enhancement of Pb removal efficiency especially for clay and loamy soils. Removal efficiency for 5% KCl modification were: sandy-97.9%, clay-96.2% with 1 M tartaric acid at 24 h washing time, loamy-76.7% for 0.5 M tartaric acid. Similarly, 10% KCl modification were: sandy-96.7%, clay-97.2% for 1 M tartaric acid at 24 h, loamy-82.1% for 0.5 M tartaric acid. Removal efficiency was soil concentration dependent. Generally, removal efficiency increased with increasing tartaric acid concentrations and washing time. Tartaric acid washing is promising and recommended in events of moderate contamination and 10% KCl modification in event of high level contamination. Further study is needed on enhancing very low concentrations of tartaric acid for large scale applications.</p> </abstract>ARTICLE2020-05-04T00:00:00.000+00:00The influence of extraction method on the composition and analgesic activity of phenolic extracts<abstract> <title style='display:none'>Abstract</title> <p>The aim of this study was to evaluate the analgesic activity and the effect of extraction methods (ultra-sound: UM and maceration: MM) and solvents (ethanol: EtOH and methanol: MeOH) on the composition of phenolic extracts from <italic>Calligonum comosum</italic>. The results obtained by HPLC analysis demonstrated that the ethanol extracts have shown the highest content of total phenolic and flavonoid compounds. Also, the presence of most known phenolic compounds has been identified in all extracts, especially in the MeOH UM extract. The HPLC analysis showed the presence of ascorbic acid in methanol extracts and caffeic acid in ethanol extracts, and the maceration method shows a high concentration of phenolic compounds, the vanillin was detected in MeOH UM and the appearance of chlorogenic acid in UM extracts, finally the emergence of gallic acid, quercetin and rutin in some extracts. According to the results of the analgesic power, the methanolic extract of the maceration method induces a significant decrease in abdominal cramps compared to the control group and the values obtained are very close from those obtained with the standard anti-inflammatory drug (indomethacin). This result confirmed the beneficial effect of this Saharan plant.</p> </abstract>ARTICLE2020-06-08T00:00:00.000+00:00Isolation of an isoflavonoid and a terpenoid from the heartwood of Lodd. (camwood)<abstract> <title style='display:none'>Abstract</title> <p>Chromatographic separation of methanolic extract of <italic>Baphia nitida</italic> heartwood gave two crystalline solids characterized as 3,9-dimethoxy-6aR,11aR-dihydro-6H-benzofuro(3,2-C)[1]benzopyran (also known as homopterocarpin) with molecular formula C<sub>17</sub>H<sub>16</sub>O<sub>4</sub> (1.57% yield) and 2,4-dimethoxybenzaldehyde C<sub>9</sub>H<sub>10</sub>O<sub>3</sub> (2.27% yield). Each of the isolated compounds showed a single spot on developed thin layer chromatographic plate under ultra-violet light (254 nm) and spray reagent (10% sulfuric acid in methanol solution). Structural elucidation was achieved using Fourier transform infrared (FT-IR) spectroscopy, one and two-dimension nuclear magnetic resonance (NMR) techniques. Distortionless enhancement by polarization transfer-edited-heteronuclear single quantum coherence (DEPT-ed-HSQC) was also a useful tool that aided the characterization of the two secondary metabolites isolated from <italic>Baphia nitida</italic> heartwood.</p> </abstract>ARTICLE2020-03-03T00:00:00.000+00:00Consideration of phthalates distribution in underground water in some selected regions in Delta State, Southern Nigeria<abstract> <title style='display:none'>Abstract</title> <p>The choice of phthalates as plasticizers have been on the increase especially in household products. They are ubiquitous environmental pollutants due to their physical attribute. This study was carried out to determine the occurrence and level of phthalates in the groundwater in some regions of Delta State. Groundwater samples were collected from fourteen sampling points and analyzed using standard procedures. The obtained results showed that the concentration (µg/l) of six phthalate ester compounds present in the water samples was of the order: &lt; 0.05 - 0.05 BBP, &lt; 0.05 - 3.71 BEHP, &lt; 0.05 - 0.54 DBP, &lt; 0.05 - 0.55 DEP, &lt; 0.05 - 0.13 DMP, and &lt; 0.05 - 0.48 DnOP. BEHP was observed to be the major compound of the phthalate acid esters present in most sampling stations, whilst others, especially BBP, were found to be in low concentration and does not pose any immediate threat to human health. The presence of BEHP in most samples from different locations suggests an inflow of the phthalate to underground water, hence it becomes imperative for continuous monitoring and a call to various governments and environmental regulatory agencies to establish standards for phthalate esters in order to monitor its presence in the environment.</p> </abstract>ARTICLE2020-09-18T00:00:00.000+00:00Optimization of process factors using the Taguchi method of DOE towards the hydrodeoxygenation of acetic acid<abstract> <title style='display:none'>Abstract</title> <p>This paper reports the optimization of process factors using the Taguchi method towards the conversion of acetic acid and ethanol yield during the hydrogenation of acetic acid over 4% Pt/TiO<sub>2</sub>. The acidity of 4% Pt/TiO<sub>2</sub> was characterized using NH<sub>3</sub>-Temperature Programmed Desorption analysis (NH<sub>3</sub>-TPD). Afterwards, the effect of temperature on the hydrogenation of acetic acid as an individual feed was investigated. The reaction space explored in the following ranges: temperature 80-200 °C, pressure 10-40 bar, time 1-4 h, catalyst 0.1-0.4 g and stirring speed 400-1000 min<sup>−1</sup> using 4% Pt/TiO<sub>2</sub>, was investigated for the optimization study, while the effect of temperature was studied in a temperature range of 145 to 200 °C. NH<sub>3</sub>-TPD analysis reveals that moderate acidity was suitable for the hydrogenation of acetic acid to ethanol. It was also found that 200 °C, 40 bar, 4 h, 0.4 g and 1000 min<sup>−1</sup> for acetic acid conversion, and 160 °C, 40 bar, 4 h, 0.4 g and 1000 min<sup>−1</sup> were the optimum conditions for ethanol production. In addition, the selectivity of ethanol was favored at lower temperatures which decreases with increasing temperature.</p> </abstract>ARTICLE2020-09-18T00:00:00.000+00:00Effect of acryloylation on superabsorbency of starch copolymers<abstract> <title style='display:none'>Abstract</title> <p>Starch is acryloylated and copolymerised without incorporating any vinyl monomer such as acrylic acid or acrylonitrile monomers to produce a superabsorbent copolymer. Fenton’s initiation system was used to produce polyacryloylated starch ester with varying degree of substitution. The copolymer from starch ester exhibited improved solubility, and an impressive water, saline, and solvents uptake. The superabsorbency of the samples is affected by the number of acryloyl groups on starch backbone. The starch ester with degree of substitution 0.8 had the highest water absorbency (102 g/g) in this experiment. Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and thermogravimetric (TGA) analyses were used to characterize the products.</p> </abstract>ARTICLE2020-03-13T00:00:00.000+00:00Spectral investigations of some piperidin-4-one molecular addition compounds<abstract> <title style='display:none'>Abstract</title> <p>In the present study, some 2- and 3-substituted piperidin-4-ones (<bold>A<sub>1</sub>-A<sub>3</sub></bold>) were chosen as proton acceptor and maleic anhydride was chosen as proton donor. Piperidin-4-ones (<bold>A<sub>1</sub>, A<sub>2</sub> ---amp--- A<sub>3</sub></bold>) were mixed with maleic anhydride in ether medium and the corresponding molecular adduct products (<bold>B<sub>1</sub>, B<sub>2</sub> ---amp--- B<sub>3</sub></bold>) thus obtained were collected and purified. The <sup>1</sup>H and <sup>13</sup>C NMR spectra were recorded for piperidine-4-one and their addition compounds. The <sup>1</sup>H and <sup>13</sup>C NMR chemical shifts of products (<bold>B<sub>1</sub>, B<sub>2</sub> ---amp--- B<sub>3</sub></bold>) are analyzed and compared with those of the corresponding piperidine-4-ones (<bold>A<sub>1</sub>, A<sub>2</sub> ---amp--- A<sub>3</sub></bold>). In order to confirm the formation of molecular addition compounds the GC-Mass spectrum was recorded for all adducts B1-B3 and the fragmentations patterns were analyzed.</p> </abstract>ARTICLE2020-05-04T00:00:00.000+00:00Texture and rheological evaluation of aerated confectionery<abstract> <title style='display:none'>Abstract</title> <p>Confectionery industry represents a field that uses a large number of ingredients and techniques to develop unique sweet products. To produce aerated confectionery samples two different procedures were used to incorporate the ingredients in the beating vegetable or dairy cream. The objective of this research was to determine the texture parameters and the viscoelastic properties of aerated confections using compression stress-relaxation test and applying a modified Maxwell model. The highest fat content was presented by dairy cream aerated samples (20.04-20.25%), while the samples based on vegetable cream displayed a lower fat content. By applying the modified Maxwell mechanical model to the relaxation curves the equilibrium stress, σ<sub>e</sub>, relaxation time, λ<sub>rel</sub>, viscosity, η, and modulus of elasticity, G<sub>0</sub>, were determined. The aerated samples’ viscosity was greater than 137.96 kPa·s and less than 451.793 kPa·s; furthermore, Pearson correlation showed that density influences positively this rheological parameter (<italic>r</italic> = 0.955*). Fixing air into the product structure causes a decrease in density (0.388-0.788 g/cm<sup>3</sup>), leading to a lower equilibrium stress, a lower elasticity modulus and also a decrease of viscosity and relaxation time.</p> </abstract>ARTICLE2020-09-18T00:00:00.000+00:00The influence of extraction method on antioxidant potential of flowers and bracts<abstract> <title style='display:none'>Abstract</title> <p>The objective of this work was to compare the extraction of phenolic compounds from <italic>Tilia argentea</italic> flowers and bracts by using conventional (solvent extraction) and novel (ultrasound assisted) extraction methods. Ethanol (70 %) extracts were analyzed for their antioxidant activities. Total phenolic content was determined using Folin-Ciocalteu method and the antioxidant potential was determined by DPPH radical scavenging and Ferric Reducing Antioxidant Power (FRAP) assays. To determine the effect of ultrasound treatment on the extraction, same extraction parameters were applied in both methods. The results showed that extracts obtained by ultrasound assisted extraction have higher total phenolic content and antioxidant activity.</p> </abstract>ARTICLE2020-04-27T00:00:00.000+00:00Life cycle assessment of fermented milk: yogurt production<abstract> <title style='display:none'>Abstract</title> <p>Yogurt is a fermented milk product, resulted through milk acidification by lactic acid bacteria, highly appreciated worldwide. In this study, life cycle assessment (LCA) methodology was applied for modelling of environmental impacts associated with yogurt production. The system boundaries include the following activities: milk processing, transport, solid waste and wastewater treatments. Functional unit set for this study is 1 kg of produced yogurt. The input and output data were collected from various sources like reports, databases, legislation. All these data were used further in the impact assessment stage performed with GaBi software which includes LCA methods like CML2001 - Jan. 2016, ReCiPe 1.08, UBP 2013, EDIP 2003 and others. Results showed that the global warming potential (GWP) determined for yogurt was 2.92 kg CO<sub>2</sub> eq. per kg of yogurt, while acidification potential (AP) was approximately 0.014 kg SO<sub>2</sub> eq. per kg of yogurt. It was observed that the main contributor to all impact categories is consumption of electricity during the yogurt production, mainly in the pasteurization, evaporation and cooling stages. 61.4% of the emissions resulted from transportation of raw materials contributes to GWP, while 38.3% to photochemical ozone creation potential (POCP). Emissions from wastewater treatment are contributing especially to the eutrophication potential (EP), while emission from solid waste landfilling are contributing mainly to POCP.</p> </abstract>ARTICLE2020-09-18T00:00:00.000+00:00Activity and stability of urease enzyme immobilized on Amberlite resin<abstract> <title style='display:none'>Abstract</title> <p>Immobilization of enzymes is a good field of study to extend the life of enzyme and reduce the cost of the chemical processes, such as separation processes. Urease is an important enzyme with medical and industrial applications. The aim of the present study is to prepare an immobilized urease on a strong cation exchange resin (Amberlite IR120 Na) and study its activity and stability. We monitored the release of Na ions in the collected fractions and searching for enzyme in the fractions as indicators of immobilization by ion exchange phenomenon. Sodium is determined by using atomic absorption spectroscopy technique, while the enzyme concentration was tested by Bradford’s method. Immobilized urease activity was evaluated by salicylate-hypochlorite method. The results indicated a complete immobilization of urease enzyme on the resin surface with reserving 92% of the activity of free enzyme. The immobilized urease enzyme on resin showed good stability and it has a 62% of its activity after 154 days of storage at room temperature. It is concluded that a new immobilized urease enzyme system is prepared with good enzyme activity and stability.</p> </abstract>ARTICLE2020-02-04T00:00:00.000+00:00Quantitative and qualitative basement of microbial presence during phytoremediation of heavy metal polluted soil using<abstract> <title style='display:none'>Abstract</title> <p>The presence and impact of bulk and rhizosphere microorganisms in contaminated soils can be huge, given that they have the ability to increase plants tolerance against abiotic stress, and also enhance plant growth, while supporting hastened remediation of disturbed soils. The present study quantitatively and qualitatively assessed presence of cultural fungi and bacteria during phytoremediation of heavy metal polluted soils using <italic>Chromolaena odorata</italic>. Stem cuttings of <italic>C. odorata</italic> were planted in soils polluted with Pb, Mn, Zn, Cd, and Cu at once (1ESC), thrice (3ESC) and five (5ESC) times their respective ecological screening concentrations (ESC). ESC of Pb, Mn and Zn is 50 mg/kg, Cd is 4 mg/kg, and Cu is 100 mg/kg. After 6 months, results showed that more than 10 species of bacteria and fungi were identified in the study, with <italic>P. aeruginosa</italic> and <italic>Bacillus subtilis</italic> being the most occurring bacteria while, <italic>Penicillium</italic> sp. and <italic>Aspergillus niger</italic> the most occurring fungi in both bulk and rhizospheric soils. The presence of known plant growth promoting rhizobacteria in plants rhizosphere including <italic>Azotobacter</italic> sp., <italic>Bacillus subtilis</italic>, <italic>B. pumilus, Clostridium</italic> sp., <italic>P. aeruginosa</italic>, and <italic>Klebsiella</italic> sp. was also reported.</p> </abstract>ARTICLE2020-12-21T00:00:00.000+00:00Chemical speciation and mobility of heavy metals in soils of refuse dumpsites in some urban towns in the Niger Delta of Nigeria<abstract> <title style='display:none'>Abstract</title> <p>Refuse dumpsites often contain materials which are capable of polluting surrounding soils especially if the dumpsites are not adequately shielded from the surrounding area. This study examined chemical speciation and mobility of heavy metals in three urban towns in the Niger Delta. Soil samples were collected from three dumpsites in each of the three selected urban towns at 0-15 cm, 15-30 cm and 30-45 cm depths. The chemical speciation of the heavy metals in the soils was determined using the Tessier’s sequential extraction procedure. The results showed that on the average, the residual fraction was the predominant fraction of all the metals except Pb which was dominant in the organic fraction. The mobility factor followed the order Zn &gt; Fe &gt; Pb &gt; Cr &gt; Ni &gt; Cd &gt; Cu. The study indicates that the metals studied do not pose environmental risk considering their relatively low concentrations and the chemical forms they are associated with. It is however recommended that the sites be continuously monitored because of the deleterious health effects of exposure to heavy metal pollution in the events of reclaim.</p> </abstract>ARTICLE2020-09-18T00:00:00.000+00:00Occurrence and sources of aliphatic hydrocarbons in anthropogenic impacted soils from petroleum tank-farms in the Niger Delta, Nigeria<abstract> <title style='display:none'>Abstract</title> <p>The occurrence and compositional pattern of priority pollutants are vital in understanding the anthropogenic contributions, origin, and risks of these pollutants to the surrounding environment. Thus, the focus of this study was to determine the concentrations, compositional profiles, and sources of aliphatic hydrocarbons (AHCs) in anthropogenic impacted soils from petroleum tank-farms environment in the Niger Delta, Nigeria. Forty-five soil samples were collected from the vicinity of petroleum tank-farms at the top (0-15 cm), sub (15-30 cm), and bottom (30-45 cm) soil depths. The concentration of AHCs was determined using gas chromatography-mass spectrometer (GC-MS) after extraction by ultrasonication with hexane/dichloromethane and clean-up in silica gel/alumina packed column. The mean concentrations of AHCs in the samples ranged from 0.52 ± 0.90 to 35.26 ± 35.69 mg/kg. The AHCs results show that the equivalent carbon number index (ECn-) ECn-13-35 had the highest concentration when compared to ECn-8-12 and ECn-36-40. The linear regression and ANOVA indicate that there is no significant positive correlation between TOC and the total concentration of AHCs in the soil profiles, and a significant variation in AHCs levels between soil profiles respectively. Results also showed that soils from the tank-farms are moderately contaminated with AHCs when compared to the UNEP recommended limit. However, when compared to other regulatory thresholds, the observed concentrations of AHCs, human and environmental health risks are likely. Source apportionments depict that the principal sources of AHCs were petrogenic and plant diagenesis. Appropriate clean-up and mitigation measures and further study to determine the occurrence, composition, and exposure risks of other priority pollutants in water and sediment samples from the surrounding creeks should be determined.</p> </abstract>ARTICLE2020-11-06T00:00:00.000+00:00Ultrasound assisted synthesis and pharmacological evaluation of some ()-1,2,3-triphenylprop-2-en-1-ones<abstract> <title style='display:none'>Abstract</title> <p>More than 85% yield of (<italic>E</italic>)-1,2,3-triphenylprop-2-en-1-ones were synthesized using disodium hydrogen phosphate (Na<sub>2</sub>HPO<sub>4</sub>) catalyzed ultrasound assisted aldol condensation of 1,2-diphenylethanone and various substituted benzaldehydes. Synthesized (<italic>E</italic>)-1,2,3-triphenylprop-2-en-1-ones were examined by their spectroscopic data, yield, micro analysis and physical constants. The effect of solvent on the yield was investigated. The pharmacological effects such as antibacterial and antifungal activities of synthesized enones were evaluated with Bauer-Kirby disc diffusion method.</p> </abstract>ARTICLE2020-12-21T00:00:00.000+00:00Cellulose fibers extraction from from the Black Sea<abstract> <title style='display:none'>Abstract</title> <p>Cellulose fibres are known for their good mechanical properties, therefore they are used as fillers in structural composite materials, including as nanofibrils in nanomaterials. Also, they are biocompatible, non-toxic and biodegradable, reason for their use in the food industry as packaging materials or in obtaining medical materials. One source of cheap, easy- to- extract cellulose is the algal mass of <italic>Ulva lactuca</italic>, one of the most frequent species found in the Black Sea. In this study, cellulose extraction from <italic>Ulva lactuca</italic> was achieved by a simple low cost physical-chemical treatment. Freshly harvested seaweed was dried at 45 °C for 48 hours, transformed into a fine powder in order to increase the contact surface between the solvents and the alga. Extraction of lipids and chlorophyll took place in Soxhlet apparatus with ethanol. Successive steps of chemical treatment, having in view removal of hydrosoluble ulvans, pigments and hemicellulose lead to a yield of 15.36% in dry matter (DM) of cellulose-rich insoluble fraction proving that <italic>Ulva Lactuca</italic> species is a viable alternative resource in cellulose production.</p> </abstract>ARTICLE2020-12-21T00:00:00.000+00:00Phenolic profile and antioxidant activity of bee pollen extracts from different regions of Algeria<abstract> <title style='display:none'>Abstract</title> <p>Due to its complex biochemical properties, the bee pollen is considered one of the functional foods. Bee pollen collected from pollen grains from different botanical sources offers almost a full diet such as carbohydrates, proteins, amino acids, vitamins, minerals. In this study, methanol extracts of 13 honeybee pollen samples were evaluated for flavonoids, phenolic compounds, and antioxidant capacity. Caffeic acid, chlorogenic acid, vanillic acid, <italic>p-</italic>coumaric acid, gallic acid, quercetin, rutin, vanillin, and naringin were identified as main phenolic compounds in pollen extracts by High-Performance Liquid Chromatography (HPLC) analysis. The obtained results are: total phenolic content - 379.8 to 915.6 mg GAE/100 g, total flavonoid content - 207.1 to 550 mg QE/100 g, and antioxidant activity - 808.2 to 3311 mg GAE/100 g in bee pollen extracts.</p> </abstract>ARTICLE2020-09-18T00:00:00.000+00:00Spectrophotometric indicators of the stability of anthocyanin-containing extracts depending on the color of plant materials<abstract> <title style='display:none'>Abstract</title> <p>This paper aims at spectrophotometric determination of changes in stability of extractable anthocyanins during drying of plant materials depending on their color. Raw and dried colored parts of 50 plant species from 25 families were used for the study. The extracts were prepared over 95% ethanol acidified with hydrochloric acid (pH ~ 1). The absorption spectra were registered within the range of 210 to 680 nm. The extinction variability factor, coefficient of intensity absorption relative and generalized stability factor were used to determine the anthocyanin degradation. The highest values of the stability factor were obtained for the extracts from fruit shells of burgundy or violet color within the range of 0.934±0.024 to 0.973±0.024, while the extracts from flower petals of the same care featured the stability factor that was 1.19 to 1.44 times less. The values of the stability factor of the extracts from black, red and blue materials are 1.15 to 1.19 times, 1.74 to 2.48 times and 4.65 to 4.84 times less respectively than those of the extracts from violet-burgundy materials. It is appropriate to apply the spectrophotometric factors of anthocyanins stability used in this study to selection of promising plants for industrial cultivation as material of anthocyanin-containing herbal preparations. The most stable anthocyanins are those of burgundy-purple and black fruits.</p> </abstract>ARTICLE2020-09-18T00:00:00.000+00:00Optimization of SPE method for the extraction of 12 neurotransmitters from sheep brain<abstract> <title style='display:none'>Abstract</title> <p>The present paper presents our attempts concerning the development of an extraction method for catecholamines. In order to achieve the extraction of all the selected solutes using a single SPE cartridge, several types of support were tested, among them: cation exchange supports, hydrophilic-lipophilic supports, C18 supports and PGC supports. As unfortunately none of the supports tested offered us the possibility of carrying out the extraction of 12 catecholamines from our standard mixture, we chose to use a coupling of two different cartridges: Oasis HLB and PGC which together ensure the extraction of all the compounds of the mixture with good extraction yields and with simple protocols. The selected cartridges were successfully tested for the extraction of a sample spiked from sheep brain with the 12 catecholamines in our mixture. The SPE method that we have developed allows the purification of the samples (a significant part of the components of the matrix is eliminated during this step) and also a preconcentration of the samples.</p> </abstract>ARTICLE2020-11-06T00:00:00.000+00:00en-us-1