SWCNT-modified carbon paste electrode as an electrochemical sensor for histamine determination in alcoholic beverages

In this work, a simple and rapid electrochemical method is presented for the voltammetric determination of histamine based on carbon paste electrodes bulk-modified with single-walled carbon nanotubes. As monitored in cyclic voltammetry histamine undergoes an irreversible electrochemical oxidation with a peak potential of ca. +1.25 V (vs. Ag/AgCl, 3 mol L-1 KCl) in phosphate buffer solution (PBS, 0.1 mol L-1, pH 6.0). At optimized differential pulse voltammetric parameters, the current response of histamine was linearly proportional to its concentration in the range from 4.5 to 720 mu mol L-1. A low limit of detection of 1.26 mu mol L-1 and a limit of quantification of 3.78 mu mol L-1 of histamine, as well as good reproducibility (RSD = 0.48-3.40 %) were obtained using the carbon paste electrode modified with single-walled carbon nanotubes. The proposed sensor was successfully applied to the determination of histamine in commercial beer and wine samples

Primena tečne hromatografije sa DAD detektorom za određivanje ostataka acetamiprida i 6-hlornikotinske kiseline u uzorcima trešanja

A rapid and simple method for simultaneous determination of acetamiprid and its metabolite 6-chloronicotinic acid in sweet cherry samples has been developed. This residue analysis method is based on the reversed phase separation on C18 column with gradient elution. Analytes’ determination and quantification were performed by high performance liquid chromatography (HPLC) with diode-array detector and chromatograms were extracted at 230 nm. Extraction efficiency experiments demonstrated the ability of this method to extract neonicotinoids from sweet cherry samples. These insecticides were extracted with a mixture of acetonitril/0.1N ammonium-chloride (8/2, v/v). The average recoveries of acetamiprid and 6-chlornicotinic acid from sweet cherry samples were in the range of 95-101% and 73-83%, respectively, with the associated relative standard deviations (RSDs) <5%. Expanded measurement uncertainties for the analyzed compounds were 2.7 and 3.01%. The limit of quantification (LOQ) was 10 μg/kg and 30 μg/kg for acetamiprid and 6-chloronicotinic acid, respectively. Thus, the developed HPLC/DAD method can be considered a useful tool for sensitive and rapid determination of acetamiprid and 6-chloronicotinic acid. Hence, the method may find further application in the analysis of real sweet cherry samples contaminated with these insecticides at a ppb level.U radu je predstavljena jednostavna metoda za određivanje acetamiprida i njegovog metabolita, 6-hlornikotinske kiseline, u uzorcima trešanja. Metoda je bazirana na primeni reverzno- faznog razdvajanja na C18 koloni primenom gradijentnog eluiranja. Određivanje i kvantifikacija analita je vršena tečnom hromatografijom (HPLC) sa DAD detektorom, pri čemu je korišćena talasna dužina od 230 nm. Tačnost metode je ocenjena procenom merne nesigurnosti. Ekstrakcija acetamiprida i 6-hlornikotinske kiseline iz uzoraka trešanja je vršena smešom acetonitril/amonijum-hlorid (0,1N) u odnosu 80:20 (v/v). Sva merenja su vršena u tri ponavljanja, pri čemu su dobijeni prinosi određivanja acetamiprida i 6-hlornikotinske kiseline u rasponima 95-101% i 73-83%, respektivno. Relativne standardne devijacije (RSD) merenja su u svim slučajevima bile ispod 5%. Limiti kvantifikacije za acetamiprid i 6-HNK iznosili su 10 i 30 μg/kg, respektivno. Kombinovana merna nesigurnost rezultata analize acetamiprida i njegovog metabolita procenjena je na 1,35, odnosno 1,50%, a proširena na 2,7 i 3,01%, upotrebom faktora pokrivanja (k=2) koji odgovara nivou poverenja od 95%, za normalnu raspodelu. Nakon validacije i procene merne neizvesnosti dobijeni rezultati pokazuju da se razvijena HPLC/DAD metoda može primeniti za određivanje sadržaja acetamiprida i 6-hlornikotinske kiseline u uzorcima trešanja i relevantnim matriksima kontaminiranim ovim jedinjenjima

Razgradnja acetamiprida u plodovima trešanja

Degradation of acetamiprid in sweet cherry samples was evaluated at several intervals from the product application until the end of the pre-harvest interval. An orchard of sweet cherries located at Stepanovićevo village near Novi Sad was used in this study. Acetamiprid was applied according to the manufacturer’s recommendation for protecting sweet cherries from their most important pests. Sweet cherry fruit samples were collected at eight intervals: immediately after acetamiprid application and 2, 4, 6, 8, 10, 12 and 14 days after application. The extraction of acetamiprid from sweet cherry samples was performed using a QuEChERS-based method. Determination was carried out using an HPLC-UV diode array detection system (Agilent 1100, United States) with an Agilent Zorbax Eclipse C18 column (50 mm × 4.6 mm internal diameter, 1.8 μm particle size). The method was subjected to a thorough validation procedure. The recovery data were obtained by spiking blank sweet cherry samples at three concentration levels (0.1-0.3 mg/ kg), yielding 85.4% average recovery. Precision values expressed as relative standard deviation (RSD) were below 1.61% for the intraday precision. Acetamiprid showed linear calibrations from 0.05 to 2.5 μg/ml with correlation coefficient (R2) of 0.995%. The limit of detection and limit of quantification were found to be 5 μg/kg and 14 μg/kg, respectively. The validated method was applied in the analysis of acetamiprid in sweet cherry samples. During the study period, the concentration of acetamiprid decreased from 0.529 mg/kg to 0.111 mg/kg. The content of acetamiprid in sweet cherry samples at the end of the pre-harvest interval was below the maximum permissible level specified by the Serbian and EU MRLs.U cilju praćenja razgradnje acetamiprida u plodovima trešanja u periodu od primene preparata do isteka karence, izvršen je tretman preparatom na bazi ove aktivne materije u preporučenoj dozi. Ogled je postavljen u zasadu srednje kasne sorte trešnje na lokalitetu Stepanovićevo u okolini Novog Sada. Plodovi su uzorkovani osam puta – odmah nakon primene preparata, 2, 4, 6, 8, 10, 12 i 14 dana. Ekstrakcija acetamiprida iz trešanja izvedena je QuEChERS metodom. Za određivanje acetamiprida korišćena je tečna hromatografija sa DAD detektorom (Agilent 1100, United States) i Agilent Zorbax Eclipse C18 kolonom (unutrašnji prečnik 50 mm x 4.6 mm, veličina čestica 1.8 μm). Kao mobilna faza upotrebljeni su acetonitril i 1.5% rastvor CH3COOH (30/70), sa protokom 1 ml/min, temperaturom kolone 25 oC i injektovanom zapreminom 2,5 μl, dok je kao odgovarajuća talasna dužina usvojena vrednost od 254 nm. Validacija metode je u potpunosti sprovedena u skladu sa zahtevima standarda SANCO/12495/2011 (EU Commission Health and Consumer Protection Directorate- General, 2011). Prosečna vrednost prinosa ekstrakcije acetamiprida iz trešanja proverena na tri nivoa obogaćenja (0.1-0.3 mg/kg) iznosila je 85.4%. Preciznost merenja razmotrena proverom ponovljivosti određivanja acetamiprida izražena je relativnom standardnom devijacijom (RSD) sa vrednošću manjom od 1.61%. U opsegu masenih koncentracija acetamiprida od 0,05 do 2,5 μg/ml postignuta je dobra linearnost odziva detektora sa koeficijentom varijacije od 0,995%. Limit detekcije i kvantifikacije za određivanje acetamiprida u trešnjama prikazanom metodom iznose 5 μg/kg i 14 μg/kg. Tokom ispitivanog perioda koncentracija acetamiprida u trešnjama se smanjivala od 0,592 mg/kg neposredno nakon primene insekticida do 0,111 mg/kg po isteku karence od 14 dana. Analizom je utvrđeno da je sadržaj acetamiprida u uzorcima plodova trešnje nakon isteka perioda karence ispod maksimalno dozvoljene količine za ovu aktivnu materiju propisane Pravilnikom Republike Srbije (0,2 mg/kg) i Evropske Unije (1,5 mg/kg)

Trace Determination of Carbendazim Fungicide Using Adsorptive Stripping Voltammetry with a Carbon Paste Electrode Containing Tricresyl Phosphate

In this study, a carbon paste electrode based on tricresyl phosphate (TCP-CPE) as a binder has been applied to the voltammetric characterization and determination of Carbendazim fungicide (methyl-1H-benzimidazol-2-yl-carbamate, MBC). The pH effect (in Britton-Robinson buffers, pH 2.0-8.0), as well as the presence of 2-hydroxypropyl-beta-cyclodextrin (HPCD) on the electrochemical behavior of MBC were investigated. In the potential range of interest, the oxidation signal was observed with the overall shape strongly dependent upon pH and exhibiting the most favorable signal-to-noise ratio in mild acidic solutions (pH 4.0). This has indicated that also protons are involved in the electrode transformation of MBC. Furthermore, it was confirmed that addition of 3.6.10(-5) mol L-1 HPCD significantly enhanced the sensitivity towards the target analyte. The experimental conditions optimised for the determination of MBC in the differential pulse adsorptive stripping voltammetric mode (DPAdSV) were as follows: initial potential, -0.10 V vs. Ag/AgCl; final potential, +1.30 V; accumulation potential, -0.35 V; accumulation time, 120 s, and the scan rate, 100 mV s(-1). The method developed offers linearity in the concentration range of 5.0 .10(-7) - 1.0.10(-5) mol L-1 MBC, with r = 0.995 and the limit of detection of about 3.0.10(-7) mol L-1. In a model sample of spiked river water, the recovery rate achieved was 101.9 % (at the concentrations from 1.0.10(-6) to 3.0.10(-6) mol L-1 MBC), suggesting one that the procedure can be applied in analysis of real samples

Trace Determination of Carbendazim Fungicide Using Adsorptive Stripping Voltammetry with a Carbon Paste Electrode Containing Tricresyl Phosphate

In this study, a carbon paste electrode based on tricresyl phosphate (TCP-CPE) as a binder has been applied to the voltammetric characterization and determination of Carbendazim fungicide (methyl-1H-benzimidazol-2-yl-carbamate, MBC). The pH effect (in Britton-Robinson buffers, pH 2.0-8.0), as well as the presence of 2-hydroxypropyl-beta-cyclodextrin (HPCD) on the electrochemical behavior of MBC were investigated. In the potential range of interest, the oxidation signal was observed with the overall shape strongly dependent upon pH and exhibiting the most favorable signal-to-noise ratio in mild acidic solutions (pH 4.0). This has indicated that also protons are involved in the electrode transformation of MBC. Furthermore, it was confirmed that addition of 3.6.10(-5) mol L-1 HPCD significantly enhanced the sensitivity towards the target analyte. The experimental conditions optimised for the determination of MBC in the differential pulse adsorptive stripping voltammetric mode (DPAdSV) were as follows: initial potential, -0.10 V vs. Ag/AgCl; final potential, +1.30 V; accumulation potential, -0.35 V; accumulation time, 120 s, and the scan rate, 100 mV s(-1). The method developed offers linearity in the concentration range of 5.0 .10(-7) - 1.0.10(-5) mol L-1 MBC, with r = 0.995 and the limit of detection of about 3.0.10(-7) mol L-1. In a model sample of spiked river water, the recovery rate achieved was 101.9 % (at the concentrations from 1.0.10(-6) to 3.0.10(-6) mol L-1 MBC), suggesting one that the procedure can be applied in analysis of real samples

Voltametrické stanovení Zn(II) na stopové úrovni ve zvolených vzorcích doplňků stravy pomocí uhlíkové kompozitní elektrody na bázi uhlíkových nanotrubic a chloridu bismuthylu

Bismuth-oxychloride-multiwalled carbon nanotube composite material was applied as surface modifier of glassy carbon electrode (BiOCl-MWCNT/GCE) for rapid and reliable trace level determination of Zn(II) in selected foodstuffs. The method development encompasses the optimization of electrode preparation including the transmission electron microscopic study of the modifier suspension, selection of the supporting electrolyte pH, the adjustment of the operation parameters of the SW-ASV measurements and the investigation of matrix effects. By the BiOCl-MWCNT/GCE recorded calibration curve showed an excellent linearity towards Zn reoxidation peak intensity in the concentration range from 2.50 to 80.0 mu g L-1 with the calculated LOD of 0.75 mu g L-1 which was associated with 120 s accumulation time and accumulation potential -1.40 V vs SCE in acetate buffer pH 4.5. A satisfactory repeatability expressed as relative standard deviation of 4.8% was obtained in the case of 10.0 mu g L-1 Zn(II) in model solution. The Zn(II) reoxidation signal from BiOCl-MWCNT/GCE received by the optimized SW-ASV method was compared with those recorded with bare, classical bismuth-film, multiwalled carbon nanotubes and by in situ made advanced bismuth-film-MWCNTs working electrodes. The applicability of the proposed BiOCl-MWCNT/GCE based method was corroborated via measuring the target analyte in two nutrition related real samples: in a dietary supplement and in a brewer&apos;s yeast sample. Comparative flame atomic absorption spectrometric measurements verified the obtained results in the case of yeast sample.Jako povrchový modifikátor elektrody ze skelného uhlíku (BiOCl-MWCNT / GCE) byl použit kompozitní materiál na bázi uhlíkových nanotrubic a oxidu bimuthylu pro rychlé a spolehlivé stanovení úrovně obsahu Zn (II) ve vybraných potravinových doplňcích. Vývoj metody zahrnuje optimalizaci přípravy elektrod včetně elektronové mikroskopické studie suspenze modifikátoru, výběr pH nosného elektrolytu, nastavení přístrojových parametrů u měření SW-ASV a zkoumání vlivu. Na BiOCl-MWCNT / GCE zaznamenaná kalibrační křivka vykazovala vynikající linearitu vůči obsahu Zn v koncentračním rozmezí od 2,50 do 80,0 μg L-1 s LOD 0,75 μg L-1 (akumulace: 120 s, akumulační potenciál: -1,40 V vs. SCE v acetátovém pufru, pH 4,5). Uspokojivá opakovatelnost vyjádřená jako relativní směrodatná odchylka 4,8% byla získána pro 10,0 ug L-1 Zn (II) v modelovém roztoku. Reoxidační signál Zn (II) na BiOCl-MWCNT / GCE získaný optimalizovanou metodou SW-ASV byl porovnán s odezvami, zaznamenanými u nemodifikované GCE a elektrod s tradičními bismutovými filmy, uhlíkových nanotrubic a pokročilými pracovními elektrodami bismutového filmu-MWCNT vyrobenými in-situ . Použitelnost navrhované metody založené na BiOCl-MWCNT / GCE byla potvrzena měřením cílového analytu ve dvou skutečných vzorcích souvisejících s výživou: v doplňcích výživy a ve vzorku pivovarských kvasinek. Referenční měření pomocí plamenové atomové absorpční spektrometrie potvrdily získané výsledky v případě vzorku kvasinek