Analytical Letters

Shao, Yuanyuan; Wang, Yongxian; Xuan, Guantao; Gao, Zongmei; Hu, Zhichao; Gao, Chong; Wang, Kaili

doi: 10.1080/00032719.2020.1812622pmid: N/A

Abstract Portable hyperspectral imaging was used for field and indoor spectra acquisition of the strawberries at three ripeness stages: ripe, mid-ripe and unripe. The mean spectra were pre-processed by multiplicative scatter correction (MSC). Principal component analysis (PCA) was employed to generate score scatter plots and visualize score images for differentiating specific grouping of samples. Three methods, including X-loading weight, competitive adaptive reweighted sampling (CARS) and successive projections algorithm (SPA), were applied to extract the effective wavelengths. Two classifiers, partial least squares – discriminant analysis (PLS-DA) and least squares – support vector machine (LS-SVM) were used for ripeness assessment. The results showed that the overall accuracy of all classifiers for field assessment ranged from 91.7% to 96.7%, slightly lower than for indoor assessment. Furthermore, the LS-SVM model combined with effective wavelengths with the CARS method performed better for field assessment of strawberry ripeness, providing an accuracy of 96.7%. It can be concluded that hyperspectral imaging can be used for real-time assessment of strawberry ripeness in the field.

Liu, Qian; Yi, Qin; Yi, Xiang; Van der Bruggen, Bart; Zeng, Lelin

doi: 10.1080/00032719.2020.1813152pmid: N/A

Abstract An extractant forced-circulation three-phase extraction (EC-TPE) device based on extraction-stripping coupling was developed for the preconcentration of Cd2+ in environmental samples. In this three-phase extraction (W1/O↔O/W2) system, Cd2+ in the sample solution (W1) was fully extracted into the stripping phase (W2) by the circular flow of an organic phase (O↔O). The extraction yield (EY) and enrichment factor (EF) reached almost 100% and 100, respectively, under the following operating conditions: 0.1 M HNO3, 2 mL/L di(2-ethylhexyl)phosphoric acid (P204), circulation flow rate of 32 mL/min, circulation time of 45 min and stirring speed of 400 rpm. An extraction yield of more than 98.5% was still achieved after reusing the organic phase eight times. Two theoretical formulas were established for predicting the EY and EF. Thereafter, EC-TPE was applied in the preconcentration of ppb-level Cd2+ for flame atomic absorption spectrophotometer assay with a detection limit of 0.17 μg/L. Addition/recovery tests for Cd2+ were carried out with recoveries exceeding 98%, and three environmental water samples were accurately analyzed. Finally, application of the EC-TPE device was extended to a different extraction system and other metal ions: Zn2+, Cu2+, Ni2+, and Co2+. The EC-TPE device is easily established utilizing common laboratory glassware, and the enrichment operation efficiency can be conveniently improved by using more than one device simultaneously.

Sözüdoğru, Onur; Massara, Theoni Maria; Çalık, Savaş; Yılmaz, Alper Erdem; Bakırdere, Sezgin; Katsou, Evina; Komesli, Okan Tarık

doi: 10.1080/00032719.2020.1815756pmid: N/A

Abstract The effect of applying different hydraulic retention times (HRTs) was investigated for a lab-scale membrane bioreactor (MBR) treating domestic wastewater. The submerged flat-type ultrafiltration MBR was operated under three HRTs (576 min, 462 min, and 372 min) corresponding to three operating periods to investigate its efficiency in removing organic content and nutrients from domestic wastewater. The chemical oxygen demand (COD) decreased from 99 to 96.5% with the HRT decreased from 576 min to 462 min. The bacteria performing nitrification were affected by the HRT change: the ammonium (NH4-N) removal dropped from 98.5% (HRT of 576 min) to 74.2% (HRT of 462 min). With the HRT adjusted to the lowest value of 372 min, the COD and NH4-N removals were 94.4% and 55.8%, respectively. The phosphate (PO4-P) removal was 59.1%, 34.4%, and 28% during periods 1, 2 and 3, respectively. In terms of the COD removal efficiency, the treated effluent met the Turkish limits for discharge to the receiving water during all of the operating periods. The system performance was suitable in terms of NH4-N removal for periods 1 (HRT of 576 min) and 2 (HRT of 462 min). However, applying the operating conditions of period 2 (i.e., maintaining the HRT at 462 min) requires additional post-treatment (e.g., low-cost chemical precipitation) to enhance the PO4-P removal.

Olugbade, Temitope Olumide; Abioye, Taiwo Ebenezer; Farayibi, Peter Kayode; Olaiya, Niyi Gideon; Omiyale, Babatunde Olamide; Ogedengbe, Tunde Isaac

doi: 10.1080/00032719.2020.1815757pmid: N/A

Abstract Steels are majorly used for diverse structural applications; however, they suffer severe degradation in a corrosive environment which necessitates the need for a protective surface coating. In this paper, the electrochemical study of MgZnCa alloy thin film coating on an AISI 304 stainless steel was reported. The study intends to investigate the influence of coating thickness on the electrochemical performance of the ternary MgZnCa alloy thin film. The polarization results indicated that better corrosion resistance is achieved when the MgZnCa coating is applied on the steel substrate, as the corrosion current density of the 4 µm coating (0.28 mA/cm2) is lower than for the uncoated substrate (0.44 mA/cm2). As the MgZnCa coating thickness increases from 4 to 6 µm, a decrease in the corrosion density with a resultant increase in the corrosion potential was observed. The microstructural characterization revealed fewer corrosion attacks for the coated substrates as compared with the uncoated material with the presence of more degradation products. The corrosion resistance of the steel substrate is enhanced by the application of MgZnCa coating and increasing coating thickness is significantly beneficial.

Zhao, Yinghao; Bu, Shengjun; Wang, Chengyu; Ma, Chengyou; Li, Zhongyi; Zhang, Wenhui; Wan, Jiayu

doi: 10.1080/00032719.2020.1817059pmid: N/A

Abstract Here, two types of aptamer (specific to E. coli O157:H7 pathogenic bacteria) Cu3(PO4)2 nanocomposites loaded with Fe3O4 nanoparticles (aptamer@Fe3O4, magnetic separation) and platinum nanoparticles (PtNPs) (aptamer@PtNP) were prepared in house via enzymatic hydrolysis of H2O2 to O2 through a one-step method. In the proposed point-of-care biosensor, these nanocomposites were used as capture and signal probes for the determination of pathogenic E. coli O157:H7 bacteria via hand-held barometers detecting gas pressure signals in a sealed bottle. The pressure signal was linear when the concentration of E. coli O157:H7 was from 103 to 108 CFU/mL. With the easily prepared dual aptamer-Cu3(PO4)2 nanocomposites and the hand-held barometer signal readout, the proposed point-of-care biosensor was shown to be a potential tool for the determination of pathogenic bacteria in underdeveloped areas.

Çalik, Savaş; Sözüdoğru, Onur; Massara, Theoni Maria; Yılmaz, Alper Erdem; Bakırdere, Sezgin; Katsou, Evina; Komesli, Okan Tarık

doi: 10.1080/00032719.2020.1818089pmid: N/A

Abstract The removal of nickel, lead, arsenic, and zinc was investigated by a lab-scale submerged membrane bioreactor (MBR) combined with granular activated carbon (GAC). Membrane fluxes of 16 L m−2 h−1, 20 L m−2 h−1, and 24 L m−2 h−1 with corresponding hydraulic retention times (HRTs) of 12.8 h, 10.4 h, and 9.2 h were applied as variables to examine their influence upon the removal efficiency. Synthetically prepared wastewater was pretreated in the MBR and GAC adsorption was employed as the post-treatment. Under the lowest applied flux value or, equivalently, the highest HRT applied, chemical oxygen demand (COD), ammonium (NH4-N) and phosphate (PO4-P) removals were found to be the highest (96.8%, 98.9% and 46%, respectively) for the MBR effluent. These results may be considered to be the result of alleviated membrane fouling and greater biomass growth. The highest heavy metal removal efficiency after the first treatment stage (i.e. the MBR effluent) was obtained at the lowest flux value of 16 L m−2 h−1. Ni, Pb, Zn, and As removals were measured to be equal to 96.9%, 98.3%, 98% and 8.5%, respectively. More important, the heavy metal concentrations were below the limit of detection after the GAC post-treatment; over 99% removal was achieved for all heavy metals. The adsorption of heavy metal ions onto the GAC may minimize biomass exposure to their toxicity, thereby creating the conditions for further improved MBR-GAC system performance. Coupling MBR technology with GAC adsorption seems a promising option for the effective treatment of wastewater containing heavy metals.

Turan, Nouha Bakaraki; Zaman, Buse Tuğba; Bakırdere, Emine Gülhan; Kartoğlu, Bedrihan; Bakırdere, Sezgin

doi: 10.1080/00032719.2020.1818765pmid: N/A

Abstract A novel preconcentration methodology to enhance the sensitivity of a flame atomic absorption spectrometer for indium determination was investigated in this study. The proposed methodology is based on the application of switchable solvent based liquid-phase microextraction combined with a slotted quartz tube. The isolation of indium was performed using N, N-dimethylbenzylamine as the extraction solvent after complexation with (E)-2,4-dibromo-6-(((3-hydroxyphenyl)imino)methyl)phenol. The detection power was enhanced by approximately 169-fold using the developed method with respect to the conventional flame atomic absorption spectrometry system. The quantification and detection limit values were 28.3 and 8.4 ng mL−1, respectively. The assessment of several interfering ions on the analyte was performed, and spike experiments were used to validate the method’s accuracy. Interferences were observed for a ratio of 1:10 analyte:interferent with a value of 27%. The recovery results obtained using matrix matching strategy indicated the applicability of the developed method for soil matrices.

Lai, Xiaoxia; Zhang, Sizhe; Du, Guorong; Wang, Yuxian; Han, Yang; Ye, Nengsheng; Xiang, Yuhong

doi: 10.1080/00032719.2020.1820022pmid: N/A

Abstract Malathion is a toxic organophosphorus pesticide. When ingested by humans, it affects the nervous system and endangers health. Herein, a new type of aptamer-based sensor was developed for its determination. The results demonstrate that this sensor has high sensitivity and good selectivity and was successfully used for the determination of malathion in apples. The detection mechanism is as follows. The aptamer is adsorbed on the surface of gold nanoparticles (AuNPs) to prevent the aggregation of AuNPs in a high salt solution. After adding malathion, the aptamer specifically binds to malathion and is removed from the surface of the AuNPs. The quantity of aptamer adsorbed on the surface of AuNPs had a negative relationship with the malathion concentration. The unmodified AuNPs aggregated to different degrees in NaCl solution. In the Fehling reaction, various degrees of aggregated AuNPs catalyze the reduction to different size Cu2O and exhibit different resonance scattering intensities. An excellent linear response between the resonance scattering spectra intensity and malathion concentration was obtained. The limit of detection of the developed method was 5.24 ng/L (15.86 pM). The recovery and repeatability for the apple samples were satisfactory.

Moreira, Brayan Machado; Cunha, Jéssica Nogueira da; Paiva, Victor Magno; Honório, Gláucio Gualtieri; Tarley, Ricardo Teixeira; D’Elia, Eliane

doi: 10.1080/00032719.2020.1821040pmid: N/A

Abstract The present work reports the development of a new analytical method for the determination of free glycerol in biodiesel samples using enzymatic-spectrophotometric assay combined with solid phase extraction (SPE) by molecularly imprinted poly(methacrylic acid) (MIP). The spectrophotometric method was performed using a commercial enzyme kit. The enzymatic-spectrophotometric method showed good analytical performance in terms of the linearity (0.998), limit of detection (7.70 × 10−6% w/w), limit of quantification (2.54 × 10−5% w/w), repeatability (0.42% to 7.91%), and recovery (99.4% to 112%). The analyses of several biodiesel samples by SPE and enzymatic-spectrophotometric method provided recovery values between 91.4% and 105%. Therefore, the high selectivity of molecularly imprinted polymer (MIP) was successfully applied to isolate free glycerol from biodiesel samples containing acylglycerols and methyl esters, and thereby allow enzymatic-spectrophometric based quantification. The developed method using SPE with MIP was efficient for the determination of free glycerol in biodiesel and the obtained results are in agreement with gas chromatrography (GC) that was used as a reference protocol.

Simsek, Ilker; Kuzukiran, Ozgur; Yurdakok-Dikmen, Begum; Snoj, Tomaz; Filazi, Ayhan

doi: 10.1080/00032719.2020.1821208pmid: N/A

Abstract Bee products produced in environments with persistent organic pollutants (POPs) may be contaminated by these compounds. Propolis usually consists of beeswax, resins, water, inorganic and phenolic substances, and essential oils. Although there are some studies on the detection of POPs in honey and some bee products, these are quite limited. Because propolis is a botanical-based and highly complex matrix, and thus difficult to analyze, a reliable and selective method based on solid-phase extraction (SPE) combined with gas chromatography-mass spectrometry was developed for the determination of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in the propolis. All analytes were extracted with acetonitrile and centrifuged for 10 min at 4000 rpm and 6 °C in a refrigerated centrifuge. The samples were filtered using a homemade SPE cartridge containing C18, primary-secondary amine, and magnesium sulfate. The residue collected with acetonitrile was subsequently analyzed by gas chromatography – mass spectrometry (GC-MS). The proposed method was validated according to the Eurachem guidelines and applied directly to the collected propolis samples. The results show that the method may be used successfully in residue monitoring laboratories for the determination of OCPs, PCBs and PBDEs in propolis.