A multicommuted flow system for fast screening/sequential spectrophotometric determination of dichromate,salicylic acid,hydrogen peroxide and starch in milk samples

In this work a multicommuted flow system for the sequential screening/determination of dichromate, salicylic acid, hydrogen peroxide and starch in milk samples was developed. The concept of multicommutation in flow injection analysis was chosen, resulting in an environmentally friendly system with minimal consumption of reagents and waste generation. The proposed approach is based on a simple binary DETECT or NO-DETECT response, thereby making it possible to determine analytes quickly, with high performance and easy operation. For dichromate determination, the proposed method was based on the reaction between Cr(VI) and 1,5-diphenylcarbazide, enabling a linear working range response, between 1.0 and 10.4 mg L⁻¹, (R = 0.999). In order to determine salicylic acid, the proposed method was based on a complexation reaction of Fe(III) and salicylic acid, with the linear working range response from 103.6 to 414.3 mg L⁻¹ (7.5 × 10⁻⁴–3.0 × 10⁻³ mol L⁻¹) (R = 0.999). The hydrogen peroxide determination was based on the oxidation reaction of hydrogen peroxide with vanadium oxide (V) in an acid environment, with a linear working range of 10.0–200.0 mg L⁻¹ (R = 0.996). Starch determination was based on the complex reaction of starch and triiodide, with a linear working range of 12.5–150.0 mg L⁻¹ (R = 0.999). The mean sampling rate for the four species was 83 determinations per hour. Performance curves were used to verify the quantity of false positives and false negatives. Addition and recovery tests were used for validation of the proposed procedures, resulting in variation between 90.1 and 108.7% for three different samples.     

Method development for the simultaneous determination of methylmercury and inorganic mercury in seafood

This paper reports the method development for the simultaneous determination of methylmercury (MeHg⁺) and inorganic mercury (iHg) species in seafood samples. The study focused on the extraction and quantification of MeHg⁺ (the most toxic species) by liquid chromatography coupled to on-line UV irradiation and cold vapour atomic fluorescence spectroscopy (LC-UV-CV-AFS), using HCl 4 mol L⁻¹ as the extractant agent. Accuracy of the method has been verified by analysing three certified reference materials and different spiked samples. The values found for total Hg and MeHg⁺ for the CRMs did not differ significantly from certified values at a 95% confidence level, and recoveries between 85% and 97% for MeHg⁺, based on spikes, were achieved. The detection limits (LODs) obtained were 0.001 mg Hg kg⁻¹ for total mercury, 0.0003 mg Hg kg⁻¹ for MeHg⁺ and 0.0004 mg Hg kg⁻¹ for iHg. The quantification limits (LOQs) established were 0.003 mg Hg kg⁻¹ for total mercury, 0.0010 mg Hg kg⁻¹ for MeHg⁺ and 0.0012 mg Hg kg⁻¹ for iHg. Precision for each mercury species was established, being ≤ 12% in terms of RSD in all cases.Finally, the developed method was applied to 24 seafood samples from different origins and total mercury contents. The concentrations for Total Hg, MeHg⁺ and iHg ranged from 0.07 to 2.33, 0.003–2.23 and 0.006–0.085 mg Hg kg⁻¹, respectively. The established analytical method allows to obtain results for mercury speciation in less than 1 one hour including both, sample pretreatment and measuring step.     

Saturated aqueous ozone degradation of deoxynivalenol and its application in contaminated grains

Deoxynivalenol (DON) is a secondary metabolite produced by Fusarium graminearum in grains, food and contaminated feed, which can lead to many adverse health effects to humans and livestock. The degradation of DON in different contaminated grains oxidated by saturated aqueous ozone (80 mg L⁻¹) was monitored by ultra-high-performance liquid chromatography, tandem-quadrupole-detection mass spectrometry (UPLC–TQD-MS). Results suggest that ozone has a significant effect on DON reduction in solution. When 80 mg L⁻¹ gaseous ozone was used to treat 10 mg L⁻¹ of DON solution, the degradation rate of DON reached 83% within 7 min, while the respective detoxification rates of contaminated wheat, corn and bran by saturated aqueous ozone (80 mg L⁻¹) were 74.86%, 70.65% and 76.21 in 10 min. Ozone at 80 mg L⁻¹ was applied on various DON solution concentrations at 1 mg L⁻¹, 10 mg L⁻¹ and 20 mg L⁻¹ in ultra-pure water. In this paper, the degradation procedure for DON is calculated and described by a first-order kinetic equation. At lower levels (20 mg L⁻¹) of aqueous ozone, intermediate degradation products were observed by ultra-ne quickly and effectively degrades DON and toxicity in various contaminated grains in a matter of minutes. Therefore, ozonation is projected to be an effective, fast, and safe method for DON degradation.     

Determination of aflatoxin M1 in dairy cattle milk in Khartoum State,Sudan

Aflatoxins are a group of mycotoxins that contaminate various types of food and feedstuff leading to health risk in both humans and animals. Aflatoxin M1 (AfM1), the major metabolite of AfB1, was determined in dairy cattle milk samples of Khartoum State of Sudan using high-performance liquid chromatography (HPLC) with fluorescence detection. A total of 44 bulk dairy cattle milk samples were collected and analyzed. The percentage of AfM1 contamination has been found in 42/44 (95.45%) samples with contamination level ranging between 0.22 and 6.90 μg L⁻¹ and average concentration of 2.07 μg L⁻¹. AfM1 contamination in the samples of dairy cattle milk of Khartoum State of Sudan appears to be prevalent and may pose a public health problem at the moment. Awareness must be conveyed to producers, handlers and specialists.     

A simple analytical method for determining inorganic anions and formate in virgin olive oils by capillary electrophoresis with capacitively coupled contactless conductivity detection

This paper describes a novel and simple method for determining chloride, nitrate, sulfate, fluoride, and formate in virgin olive oil (VOO) by capillary electrophoresis with capacitively coupled contactless conductivity detection. The anions were extracted from VOO by a simple ultrasound-assisted aqueous liquid–liquid extraction procedure. The anions were separated in less than 3 min with good peak resolutions using a background electrolyte composed of 15 mmol L⁻¹ histidine solution at pH 4.0, adjusted with lactic acid, and 0.6 mmol L⁻¹ cetyltrimethylammonium hydroxide as electrosmotic flow (EOF) modifier. Tartrate was used as internal standard (I.S.). The proposed method showed good linearity and had coefficients of determination (R²) ranging from 0.9984 to 0.9999. The limits of quantification (LOQ) were between 0.01 and 0.7 mg kg⁻¹. Recovery tests were used to evaluate the efficiency of the extraction procedure; the recovery percentages ranged from 70.2 to 118%, with a relative standard deviation (RSD) varying from 0.7 to 19.4%. The proposed method was applied to the determination of the anions in five different commercial samples of VOO.     

High performance liquid chromatography method for the determination of patulin and 5-hydroxymethylfurfural in fruit juices marketed in Malaysia

A rapid, simple, improved method for the simultaneous determination of patulin (PAT) and 5-hydroxymethylfurfural (5-HMF) in fruit juices is described. The target compounds were extracted with ethyl acetate using vortex followed by high performance liquid chromatographic separation. PAT and 5-HMF were separated within 4 min using Poroshell C18 column with acetonitrile:water (1:9, v/v) as the mobile phase. Under the optimized conditions, the detection limits of PAT and 5-HMF were 0.25 and 0.46 ng mL⁻¹, respectively while the quantification limits were 0.76 and 1.40 ng mL⁻¹, respectively. The recoveries of PAT and 5-HMF at 50, 750 and 5000 ng g⁻¹ ranged from 92.8 to 108%. The proposed method was applied to fivety-six fruit juices (apple, mango, pineapple, guava, lychee, tamarind, soursop and mixed fruit) and PAT was found in three samples ranging from 13.1–33.7 ug L⁻¹. 5-HMF was found in all the samples ranging from 0.08 to 91.5 mg L⁻¹. Liquid chromatography-tandem mass spectrometry with triple quadrupole analyzer was used to confirm the presence of 5-HMF and PAT in some of the contaminated samples.     

Occurrence of biogenic amines in beers from Chilean market

The presence of tryptamine, phenylethylamine, putrescine, cadaverine, histamine, tyramine, spermidine and spermine was determined for the first time in beers commercialized in Chilean market. Dansylated amines were separated on a Zorbax-XDB C₁₈ column using a binary mobile phase composed of acetonitrile and 20 mmol L⁻¹ ammonium formate, pH 5.5. Chromatographic conditions were optimized using an experimental design, and validation was carried out following ICH recommendations. Calibration data fitted a linear regression model with R² > 0.996. Repeatability (n = 6) and intermediate precision (n = 3) in matrix showed RSD values lower than 5.00% and 5.21%, respectively. Recoveries at three different concentrations ranged from 75.50 to 96.48%. The proposed method was applied to determine the biogenic amines content in 101 beer samples produced by macro- (n = 65) and microbreweries (n = 36) using low (n = 63) and high fermentations (n = 38). Biogenic amines content in beer samples ranged from 0.53 to 85.04 mg L⁻¹, from which beers produced by microbreweries (19.13 ± 16.92 mg L⁻¹) showed a significant higher biogenic amines content (P = 0.0021) than beers produced by macrobreweries (9.65 ± 4.50 mg L⁻¹). Putrescine was the principal biogenic amine found in all kind of beers regardless origin, and the type of fermentation and brewery. Only 2 samples presented relevant levels of histamine and tyramine, but both below the limits reported by the European Food Safety Authority (EFSA). Thus, it can be concluded that beers commercialized in Chile are not a serious toxicological risk (e.g. hypertensive crisis) regarding the type and content of biogenic amines.     

A survey of seasonal variations of aflatoxin M1 in raw milk in Tangshan region of China during 2012–2014

Total 530 samples of raw milk were collected from the dairy farms in the Tangshan region of north China during four seasons each year from 2012 to 2014, and aflatoxin M1 (AFM1) contents were measured using HPLC-MS/MS. The results showed that AFM1 was detected in 280 samples (52.8%) at the range of 10–200 ng L⁻¹, and the mean level of AFM1 was 73.0 ng L⁻¹, which was below the China and US legal limit of 500 ng L⁻¹. The incidences of AFM1 contamination were 27.5% in spring, 39.0% in summer, 71.7% in autumn and 78.9% in winter, respectively. It indicated that seasonal variations should be considered for the AFM1 control particularly during winter season. In comparison with the data from different years, the incidences of AFM1 contamination in raw milk samples were 87.8% with a range of 10.0–160 ng L⁻¹ in 2012, 29.9% with 10.0–190.0 ng L⁻¹ in 2013 and 36.7% with 12.0–111.0 ng L⁻¹ in 2014. Hence, present study exhibits a significant decrease in the incidence of AFM1 contamination in Tangshan region after 2012.     

Scope extension validation of a LC-MS method for the inspection of preservatives in butter

Butters are considered as “natural products” by many consumers, once they are obtained from milkfat without adding of any additive, except sodium chloride, starter cultures and natural dyes. The main goals of this study were to extend the scope of a previously developed method, including a new analyte (benzoic acid) and new matrices (butter and margarine), and thus evaluate the content of preservatives in national and imported butters traded in Brazil. Samples (n = 51) from inspected establishments in Argentina (n = 2), Brazil (n = 40), France (n = 7) and Uruguay (n = 2) were assessed by liquid chromatography-tandem mass spectrometry. Two screening inspection rounds were carried out between November, 2015 and January, 2016. Non-compliance rates were 36.4% in 2015 and 22.2% in 2016 for Brazilian butters. It was shown that preservatives are irregularly added to butters by many factories, contrary to regulation, and without proper declaration on labeling. The limits of quantitation (LOQ) were set to 25.00 mg kg⁻¹ (benzoic acid), 1.25 mg kg⁻¹ (natamycin), 3.13 mg kg⁻¹ (nisin) and 2.50 mg kg⁻¹ (sorbic acid). Except nisin, any of the researched preservatives was detected in a total of 12 samples, in concentrations that ranged from <LOQ–235.67 mg kg⁻¹ (benzoic acid), 8.26–35.60 mg kg⁻¹ (natamycin) and 4.52–1007.17 mg kg⁻¹ (sorbic acid). The method was also checked on margarine samples, revealing concentrations that ranged from 43.72 to 359.17 mg kg⁻¹ (benzoic acid) and from 509.00 to 1102.67 mg kg⁻¹ (sorbic acid), respectively. Our findings demonstrate that there is a need for stricter control in butter processing, with the aim to ensure food safety and to safeguard consumers.     

Natural clay and commercial activated charcoal: Properties and application for the removal of copper from cachaça

The influence of contact time and the amount of adsorbent on the removal of copper from distilled cachaça was evaluated. The adsorption of copper was favored by a 1:50 ratio of mass of adsorbent (g) to volume of sugar cane spirits (mL). An equilibration time of 120 min for clay and 360 min for activated charcoal resulted in the removal of 68.7% and 98.3% of the copper, respectivamente. The isotherms were studied in the range of copper concentrations of 0 to 2000 mg L⁻¹. The amount of copper adsorbed per unit weight of clay was 10.8 mg g⁻¹, and for charcoal, it was 5.9 mg g⁻¹. The isotherm results were tested in the Langmuir and Freundlich models and were found to adapt better to the Freundlich model. The removal of copper by clay and activated charcoal could be explained by a pseudo-second-order kinetic model. Given the organic and inorganic complexity of cachaça, the influence of this process on the flavor of the beverage was also evaluated. To this end, the analyses of aldehydes, higher alcohols, furfural, esters and volatile acidity were performed according to the methods established by the Ministry of Agriculture, Livestock and Supply. The results showed that the samples treated with clay adsorbed 3.6, 8.7, 9.4, 2.2 and 3.9% of the aldehydes, higher alcohols, furfural, esters, and volatile acidity, respectively. For the samples treated with activated charcoal, the results were 6.5, 15.3, 95.31, 2.0 and 34.0% for the aldehydes, higher alcohols, furfural, esters, and volatile acidity, respectively.     

Should chlorate residues be of concern in fresh-cut salads?

Chlorine remains the most popular method used by the fresh produce industry for decontamination. However, the occurrence of disinfection by-products (DBP) derived from chlorine-based disinfectants has been highlighted as a problem. After recent reports, chlorate residues in fresh produce are of concern in Europe. This study evaluated the chlorate accumulation in process wash water and the residues in fresh-cut lettuce when sodium hypochlorite was used as a wash aid. At a commercial processing facility, total chlorine was continually added to achieve a free chlorine level of 1–80 mg L⁻¹ for water disinfection as the organic load measured as chemical oxygen demand (COD) increased over time (1000–1500 mg O₂ L⁻¹). This resulted in chlorate accumulation (19–45 mg L⁻¹) in the process water. When fresh-cut lettuce was washed in that water, chlorate residues were detected in the lettuce and the concentrations increased linearly with the repeated use of the same process water, reaching concentrations of 4.5–5.0 mg kg⁻¹. To understand the chlorate accumulation in the process wash water, several experiments were performed at a pilot plant scale with different levels of COD and free chlorine. There was a significant (p < 0.001) correlation (R = 0.91) between the total added chlorine and the chlorate accumulation in the process water. We demonstrated that the added chlorine needed to maintain a free chlorine level in the process water was the contributing factor to chlorate accumulation. Chlorate residues in the washed fresh-cut lettuce after rinsing for 1 min in tap water and in commercial bags were below the limit of quantification. This study contributes to the knowledge of chlorate accumulation in the process water when sodium hypochlorite was used as a sanitizer.     

Development and validation of a new qualitative ELISA screening for multiresidue detection of sulfonamides in food and feed

An indirect competitive enzyme-linked immunosorbent assay (ELISA) to screen sulfonamide residues in food (muscle, eggs, milk and honey) and feed has been developed and validated according to Commission Decision 2002/657/EC. The immunoreagents were appropriately produced to detect a wide range of sulfonamide antibiotic congeners, obtaining half-maximum inhibition concentration (IC₅₀) values below 10 μg L⁻¹ for 11 sulfonamides widely used in veterinary practices. Taking into account the complexity of involved matrices, specific sample preparation protocols have been optimised combining high method throughput with low detectable concentrations. Accordingly, depending on the congener, the obtained detection capabilities (CCβs) were lower or equal to 20 μg kg⁻¹ (muscle, eggs and milk), 10 μg kg⁻¹ (honey) and 2 mg kg⁻¹ (feed). Finally the developed qualitative test was applied to real samples collected within the official monitoring programmes: results exceeding the established screening cut-off were re-analysed with a suitable confirmatory method. The presence of one or more sulfonamides was found in all the suspect screening samples thus demonstrating that the proposed ELISA can be successfully applied in class-specific detection of sulfonamides in food and feed.     

Donkey's milk safety: POCs and PCBs levels and infant daily intake

In this work 45 donkey milk, 15 forage and 15 feed samples from farms in Sicily, Calabria and Emilia-Romagna were evaluated for the content of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). Analysis was carried out by GC–ECD and GC–MS. The limits of detection (LOD, S/N = 3) were from 0.40 to 1.91 μg L⁻¹ and from 0.16 to 2.11 μg L⁻¹ for the different OCPs and PCBs, respectively. The limits of quantification (LOQ, S/N = 10) were 1.32–6.37 μg L⁻¹ and 0.52–7.53 μg L⁻¹. The results showed few differences among samples of different farms and that contamination is kept at very low and almost always below the maximum residual levels fixed by legislation of 100 ng/g of fat for PCBs, of 0.04 mg/kg for DDTs and 0.006 mg/kg for aldrin with dieldrin (449/1999 and 149/2008). Also in comparison with current values of TDI proposed by European Agencies, the POCs and PCBs daily intakes found in donkey milk were very low for several of samples.     

Analysis of tetracyclines in chicken tissues and dung using LC–MS coupled with ultrasound-assisted enzymatic hydrolysis

The accurate measurement of tetracycline antibiotics (TCs) in complex matrices related to chicken raising is important for food control. It was experimentally demonstrated that conventional acid deproteination methods led to high losses of TCs because TCs were strongly bounded to protein aggregates. To eliminate this effect, an ultrasound-assisted enzymatic hydrolysis method was developed to break the three-dimensional structures of proteins and release the bound TCs. This not only significantly improved the recovery of TCs but also shortened the pretreatment time from 960 to 6 min. By combining this new deproteination method and a solid phase extraction clean-up, a suitable sample preparation was achieved for the analysis of TCs with LC–MS/MS. The established LC–MS/MS analysis of TCs provided good linear ranges in the order of 20–1000 μg L⁻¹ with the limits of detection ranging from 1.05 to 3.50 μg L⁻¹ for the tested TCs. The new method yielded recoveries of TCs in spiked chicken-related samples as high as 89.1%–102.4%, being much higher than those (23.5%–36.2%) obtained using the acid deproteination process. When this method was used to analyze five practical samples of manures, it gave residual concentrations of 0.9–4.2 and 1.3–4.0 mg kg⁻¹ for oxytetracycline and chlortetracycline, respectively.     

Molecularly imprinted polymer for extraction of patulin in apple juice samples

A new molecularly imprinted polymer (MIP) was prepared in a two-step process. First, SiO₂-γ-MPTS was obtained by mixing γ-methacryloxypropyltrimethoxysilane (γ-MPTS) and tetraethoxysilane (TEOS). Second, SiO₂-γ-MPTS was polymerized in the presence of patulin (PAT) as a template, maleic acid (MA) as a functional monomer, ethylene glycol dimethacrylate (EGDMA) as a cross linker, 2,2-azobis- (2- methylpropionitrile) (AIBN) as a precursor and acetonitrile as a porogen solvent. The prepared sorbent was successfully applied to selective solid phase extraction (SPE) of PAT in containing apple juices and the MIP@SPE method was validated. The optimum conditions for PAT extraction using the novel MIP@SPE were: 50 mg mass of adsorbent, sodium bicarbonate with (1%) acetic acid as washing solvent and 5 mL acetonitrile as eluting solvent. The developed MIP@SPE method had high selectivity and good affinity toward PAT and the recoveries of the target analyte were in the range of 82–98% with a precision of 3.03%–3.83% (RSD). In addition, a good linearity (r² > 0.99) within the range 0.1–10 mg L⁻¹ and a low LOD (8.6 μg L⁻¹) and LOQ (28.6 μg L⁻¹) were obtained. The test of reusability showed good results for at least 6 cycles.     

Determination of heavy metals in selected black sea fish species

Heavy metals can be accumulated by marine organisms thought a variety of pathways, including respiration, adsorption and ingestion. The levels of heavy metals are known to increase drastically in marine environment through mainly anthropogenic activities. Fish are good indicators for the long term monitoring of metal accumulation in the marine environment. The aim of this study was to determine the levels of Cd, As, Hg, Pb, Zn and Cu in edible part and gill of seven most consumed Bulgarian fish species collected from north-east coast of Black Sea. These fish species are sprat (Sprattus sprattus sulinus), Mediterranean horse mackerel (Trachurus mediterraneus ponticus), Black sea gobies (Neogobius melanostromus), shad (Alosa pontica), Atlantic bonito (Sarda sarda), bluefish (Pomatomus saltatrix) and grey mullet (Mugil cephalus). The fish samples were collected during 2010. The analytical determination of As, Cd, Pb, Zn and Cu were performed by using flame and graphite furnace atomic absorption spectrometry after microwave digestion procedure. The total mercury determination was determined using a direct mercury analyzer (DMA-80). The metal concentration of analyzed elements was highest in the gill for all fish species. The maximum metal concentration was measured for Cu (1.40 mg kg⁻¹ w.w), Zn (11 mg kg⁻¹ w.w) and Pb (0.08 mg kg⁻¹ w.w) in muscle tissues of shad and sprat. The edible part of horse mackerel has the maximum value for Hg (0.12 mg kg⁻¹ w.w) while Atlantic bonito predominantly accumulates As (1.10 mg kg⁻¹ w.w). The analytical results obtained from this study were compared within acceptable limits for human consumption set by various health institutions.     

Fast screening method for the analysis of trans fatty acids in processed food by CZE-UV with direct detection

In the present work, an alternative method for trans fatty acids (TFA) analysis with direct UV detection using capillary zone electrophoresis (CZE-UV) is proposed. The background electrolyte used consisted of 12.0 mmol L⁻¹ of tetraborate buffer, 12.0 mmol L⁻¹ of Brij 35, 33% methanol and 17% acetonitrile. Trans fatty acids in different samples such as butter toffee, cake mix, stuffed wafers, chocolate and a mix for Brazilian cheese bread were successfully quantified within an analysis time of 13 min, taking into account the statistical approach based on response factor calculation using C19:1 (nonadecaenoic acid) as internal standard. The statistical comparison between CZE-UV and the classical GC method for the analyzed samples did not present significant differences within the 95% confidence interval.     

A survey study on safety and microbial quality of “gluten-free” products made in Italian pasta factories

The rising prevalence of celiac disease leads to an increased demand of “gluten-free” products. A survey study on the gluten content and on the microbiological quality of “gluten-free” flour, and processing flour products, was carried out from 2010 to 2015 in Northern Italy. Overall 12,419 samples were analyzed, and 94.7% contained a gluten concentration less than 5 mg kg⁻¹ (lower limit of detection). Only 0.1% of samples showed a gluten concentration above 80 mg kg⁻¹ (maximum limit of detection). In the remaining 5.2%, the gluten concentration was between 5 and 80 mg kg⁻¹, underlining how a gluten-free diet completely devoid of gluten is unrealistic. The microbiological quality of these products was investigated.Overall, the majority of samples revealed microbial loads of less than 1 l g CFU g⁻¹ (lower limit of detection). High levels of spoilage bacteria were found in egg-containing products. Total mesophilic bacteria were counted in all analyzed food categories with concentrations up to about 6, 8 and 9 l g CFU g⁻¹ in dry pasta, flours and egg products respectively. Listeria monocytogenes was found only in one sample, whereas Salmonella spp. was never found.Buckwheat flour was the most frequently contaminated product by presumptive Bacillus cereus, with a prevalence of 12.5%. Also, a contamination by Coagulase-Positive Staphylococci was found during this investigation, especially in buckwheat dry pasta and flour and in egg dry pasta, with a prevalence of 54.7%.This study aimed to enhance the knowledge about the “gluten-free” products which are still poorly studied, even if their impact on the food market is increasingly considerable.     

The efficacy of grape seed extract,citric acid and lactic acid on the inactivation of Vibrio parahaemolyticus in shucked oysters

The efficacy of grape seed extract (GE), citric acid (CA) or lactic acid (LA) on the inactivation of Vibrio parahaemolyticus in shucked oysters was studied. The minimum inhibitory concentration (MIC) of GE, CA or LA against V. parahaemolyticus in TSB-1% NaCl was also determined. The shucked oysters were artificially inoculated with V. parahaemolyticus, the inoculated shucked oysters (25 g) were then dipped in solution of GE (0.0, 10.0, 20.0, 50.0, 100, 200, 300 and 500 mg mL⁻¹), CA (0.0, 5.0, 10.0, 15.0, 20.0, 50.0, 100, 200 and 300 mg mL⁻¹) or LA (0.0, 1.0, 5.0, 10.0, 15.0, 20.0, 50.0, 100 and 150 mg mL⁻¹) for 10 min. The population of V. parahaemolyticus in shucked oysters was determined. The MICs of GE, CA or LA against V. parahaemolyticus were 10.0, 5.0 or 1.0 mg mL⁻¹, respectively. A 500, 300 or 150 mg mL⁻¹ GE, CA or LA solutions were needed to reduce the population of V. parahaemolyticus to below the detection level (1.0 log g⁻¹) in shucked oysters.     

Interaction study of paraquat and silver electrode using electrochemical impedance spectroscopy: Application in milk and tomato samples

This paper reports on the use of electrochemical impedance spectroscopy (EIS) for analytical determination of paraquat herbicide at a silver electrode. The electrochemical technique was applied to aqueous solution, at pH 7.0, containing different concentrations of paraquat. The impedance measurements were carried out in the frequency range from 100 mHz to 100 KHz at a potential of 0.0 mV versus Ag/AgCl. The Nyquist plots were modeled with a Randle equivalent circuit, by identifying the charge transfer resistance as the relevant concentration dependent parameter. The silver surface adsorbs paraquat and the transfer process is controlled by diffusion. The response of the working electrode was attributed to the electron-exchange mechanism at the electrode–contact interface and the ion exchange at the electrode–solution interface. The proposed methodology offers good repeatability (RSD = 1.03%) with (n = 8) and impedimetric response to paraquat in the range from 1.0 × 10⁻¹⁴ to 8.0 × 10⁻⁴ mol L⁻¹. The detection limit (DL, 3σ) and quantification limit (QL, 10σ) were 7.37 × 10⁻¹⁶ mol L⁻¹ and 24.59 × 10⁻¹⁶ mol L⁻¹ respectively. The method was satisfactorily applied to determine paraquat in milk and tomato samples.