改进镉柱分光光度法测定奶制品中硝酸盐及亚硝酸盐

目的：建立镉柱还原分光光度法测定奶制品中硝酸盐和亚硝酸盐的方法。方法：采用进口镉粒,用耐酸碱的活塞旋钮滴定管替代镉柱玻璃管,对国家标准方法镉柱法进行改进后,测定奶制品中硝酸盐和亚硝酸盐,结果：测定结果与国标测定方法一致。结论：经改进后的镉柱法测定奶制品中硝酸盐及亚硝酸盐,制备镉柱简单,再生镉粒冲洗简便,还原效率高,方法简单,省时省力,准确快速。     

牛乳与乳粉中亚硝酸盐和硝酸盐的固相萃取离子色谱测定法

目的建立离子色谱同时测定牛乳与乳粉中亚硝酸盐和硝酸盐含量的方法。方法采用甲醇-乙腈对样品进行萃取并离心,上清液经C18小柱净化后,利用IonPac AS 11—HC柱分离和电导检测器测定,外标法定量。结果亚硝酸盐:线性范围0.02～0.20 mg/L,相关系数0.999 5,样品加标回收率90.0%～104.8%,RSD 3.5%,检出限为牛乳0.002 mg/kg,乳粉0.006 mg/kg;硝酸盐:线性范围0.20～2.0 mg/L,相关系数0.999 4,样品加标回收率90.0～105.8%,RSD 2.3%,检出限为牛乳0.006 mg/kg,乳粉0.03 mg/kg。结论该方法简便,快速,适合牛乳与乳粉中亚硝酸盐和硝酸盐含量的测定。     

Assessment of nitrate,nitrite and chloride in selected cured meat products and their exposure to school children in Brunei Darussalam

The readily available, good taste and easy to prepare cured meat products have become a prominent feature in children’s diet, leading to possible overconsumption of certain food additives. In this study, amount of nitrite, nitrate and salt, with mean values of 12.8 mg/kg, 20.2 mg/kg and 0.94 g/100 g, respectively and their intake from consumption of cured meat products (sausages, salamis, meatloaves and meatballs), were estimated for 2339 school children. The estimated salt intake for overall children was 0.53–1.01 g/day, where none of the children’s salt intake exceeded their age group’s Tolerable Upper Intake level. While the average estimated intake of nitrate and nitrite were at 0.08 mg/kg b.w/day and 0.05 mg/kg b.w/day, respectively. Based on the above estimation, ∼20% of the total children exceeded the Acceptable Daily Intake (ADI) of nitrite of 0.07 mg/kg b.w/day while none of the children exceeded the ADI of nitrate of 3.7 mg/kg b.w/day.     

Capillary isotachophoresis as rapid method for determination of orthophosphates, pyrophosphates, tripolyphosphates and nitrites in food samples

Environmentally friendly, simple and sensitive isotachophoretic method to identify and quantify orthophosphates, pyrophosphates, tripolyphosphates, nitrites and nitrates in various food products was developed. Two electrolyte systems (A) and (B) were tested and applied for determination of the above ions in meat (different canned products, smoked, cooked and long-matured pork ham, headcheese) and seafood (raw and cocktail prawns, squids and different mixes of seafood) products. For nitrogen compounds, both systems fulfilled the criteria for separation, precision and recovery. The better separation of pyrophosphates (pyroP) and tripolyphosphates (tripolyP) was obtained from system (B) with the following electrolytes: leading – 10 mM hydrochloric acid + 0.02% hydroxyethylcellulose and glycine to pH = 3.0 and terminating – 10 mM phosphoric acid. This system was characterised by linearity (R² = 0.999 for all ions), accuracy (recoveries ranged from 97 to 98% for pyroP and 95 to 97% for tripolyP), detection: 0.64 (pyroP) and 0.27 mgP L⁻¹ (tripolyP) and quantification: 2.12 (pyroP) and 0.91 mgP L⁻¹ (tripolyP) limits and intra-assay of relative step height RSH (1.27–10.73%) and inter-assay of RSH (3.95–11.17%). Additionally, the obtained results of phosphate additives determination were compared at the level of added phosphorus calculating as the difference between the total phosphorus and protein bound phosphate.     

Simultaneous enrichment/determination of six sulfonamides in animal husbandry products and environmental waters by pressure-assisted electrokinetic injection coupled with capillary zone electrophoresis

Pressure-assisted electrokinetic injection (PAEKI) as the online method was developed for the simultaneous enrichment of six sulfonamides (SAs), including sulfamethazine (SMZ), sulfamerazine (SMR), sulfamonomethoxine (SMM), sulfadizine (SDZ), sulfamethoxazole (SMX) and sulfacetamide (SFA) in different animal husbandry products and environmental waters samples, followed by capillary zone electrophoresis (CZE) determination. Various parameters affecting the separation performance of CZE and the enrichment efficiency of PAEKI were optimized in detail. Under optimal conditions, the six SAs were completely separated within 8.5 min, and the enrichment factors for SMZ, SMR, SMM, SDZ, SMX and SFA were 39, 47, 53, 50, 54 and 62 folds, respectively, compared with the direct CZE. The limits of detection (LOD) ranged from 0.0018–0.0163 μg/mL, 0.0083–0.0638 μg/mL and 0.0052–0.0478 μg/mL in milk, pork and egg samples, respectively, as well as limits of quantification (LOQ) within 0.0061–0.0503 μg/mL, 0.0253–0.1826 μg/mL and 0.0164–0.1475 μg/mL, respectively. Tap water, lake water and seawater were also examined for investigation of applicability of the proposed method. Satisfactory recoveries in the range of 89–113 % were obtained with the three spiked food samples, and the relative standard deviations were from 1.6 to 7.3%. Simple and effective online enrichment method provides a promising perspective for CZE measurements of SAs in complex matrices with high accuracy, sensitivity and rapidity.     

Ultrasensitive determination of melamine in milk products and biological fluids by luminol-hydrogen peroxide chemiluminescence

An ultrasensitive chemiluminescence (CL) method for determination of melamine at picogram level was reported in a flow system. It was found that melamine can accelerate the electrons transferring rate of excited 3-aminophthalate with notable enhanced CL intensity of luminol-hydrogen peroxide reaction. The increased CL intensity was proportional to the concentration of melamine in the range from 2.5 to 250 pg mL⁻¹ (R² = 0.9953), with a detection limit of 0.9 pg mL⁻¹ (3σ) and the relative standard deviations lower than 5.0%. The proposed method was successfully applied to determine the melamine in liquid milk, yogurt, human urine and serum samples with the recovery of 98–105%, 93–105%, 98–105%, 97–109%, respectively.     

Fluorometric method based on molecular recognition solid-phase extraction for determination of riboflavin in milk and infant formula

Riboflavin (vitamin B₂) is involved in several biological processes, particularly in energy production, and it is acquired from food ingestion, principally from supplemented food during the first years of life. Therefore, a simple, fast and cost-effective high-throughput method for determination of riboflavin in milk and infant formula is proposed, based on selective extraction using commercially available molecularly imprinted polymers targeted to riboflavin, followed by direct fluorometric determination. Several aspects were studied, namely microplate assay conditions, the composition of eluting solution and the stability of riboflavin in the eluate. Hence, elution using 1% (v/v) acetic acid in methanol or in acetonitrile is recommended, followed by immediate analysis or solvent evaporation, with reconstitution and analysis within 24 h. The proposed method provided a LOD of 0.03 mg L⁻¹, with working range for undiluted samples between 0.125 and 2 mg L⁻¹, and sample throughput of 24 h⁻¹. It was successfully applied to certified reference material NIST-1846 and also to commercial milk and infant formula samples.     

A rapid and sensitive method for the determination of dibutyl phthalate in wine by flow-injection chemiluminescence analysis

A sensitive method for the determination of picogram level dibutyl phthalate (DBP) in wine by flow-injection chemiluminescence (FI–CL) analysis is presented for the first time, which was based on the quenching effect of DBP on the luminol–myoglobin (Mb) CL system. The decrement of CL intensity was linearly proportional to the logarithm of DBP concentration in the range of 0.1–100 pg mL⁻¹ with the detection limit of 0.03 pg mL⁻¹ (3σ). At a flow rate of 2.0 mL min⁻¹, a complete determination of DBP including sampling and washing could be accomplished in 0.5 min, giving the maximum sample throughput of 120 h⁻¹. The proposed method was successfully applied to the determination of DBP in wine, human serum and urine samples with the relative standard deviations (RSDs) of less than 3.0% (n = 5). The molecule docking results showed that DBP interacted with the amino acid residues near the heme moiety of Mb. The possible CL mechanism of luminol–Mb–DBP reaction should be that the binding of Mb with DBP forming a 1:1 complex (binding constant K = 1.55 × 10⁴ L mol⁻¹) led to the conformational change of Mb and resulted in the quenching of CL intensity.     

A method for the simultaneous extraction and quantitation of lipophilic antioxidants in Triticum sp. by HPLC-DAD/FLD-MSn

A method for the simultaneous determination of carotenoids, tocopherols, tocotrienols, alk(en)ylresorcinols, and steryl ferulates from whole grain wheat flour was developed and validated using HPLC-DAD/FLD-MSⁿ. After comparing various solvents and extraction techniques, samples were extracted with acetone without previous saponification. Extraction recoveries ranged from 93.2 to 101.6% for carotenoids, tocopherols, and steryl ferulates, while 83.4–99.4% were determined for alkylresorcinols. The inter-day CV for all analytes was below 5%. HPLC separation was compared on porous particle C₁₈- and C₃₀- as well as a core–shell particle C₁₈-column, achieving optimum separation on the latter within 40 min after gradient optimization. The limit of detection (LOD) ranged from 0.03 to 20.41 ng on column for lutein and tricosylresorcinol, respectively. Further validation parameters are reported in detail. HPLC–MSⁿ supported the identification of minor compounds, when standards were unavailable. This method is proved to be suitable for high-throughput screening of a large number of lipophilic compounds in wheat.     

Synthesis and characterization of functionalized silica with 3,6-ditia-1,8-octanediol for the preconcentration and determination of lead in milk employing multicommuted flow system coupled to FAAS

Novel functionalized silica, containing 3,6-dithia-1,8-octanediol (Si-DIO), was synthesized and characterized by infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) of ¹³C and ²⁹Si. The Si-DIO was used to pre-concentrate and determine the amount of Pb(II) in milk samples employing a multicommuted flow system coupled to flame atomic absorption spectrometry (FAAS). For the adsorption process, a pre-concentration minicolumn with 100 mg of Si-DIO, a solution of 0.005 mg L⁻¹ Pb(II) at pH 9.0 and HNO₃ as the eluent was used, obtaining an enrichment factor of 28 times with retention efficiency higher than 99%. The Pb(II) ion, using the multicommuted flow system coupled to FAAS, showed a linear response between 0.005 and 20.0 mg L⁻¹; a linear coefficient where r = 0.9939 and n = 7; a detection limit estimated at 0.001 mg L⁻¹ and a relative standard deviation of 3.8% (n = 50). Fifty pre-concentrations runs were tested in the minicolumn without significant variation in the analytical signal. The proposal system showed analytical applicability to determine Pb(II) ion in milk samples, presenting recovery of 90.7–102.5%.     

Fast and accurate alternative UV-chemometric method for the determination of chlorophyll A and B in broccoli (Brassica oleracea Italica) and cabbage (Brassica oleracea Sabauda) plants

The aim of this work was to establish a multivariate method for the rapid quantification of chlorophyll A and B in broccoli and cabbage plants using photometric signals. A partial least squares (PLS) model was optimized using the UV spectra of a set of calibration samples. Limit of detection (0.174 and 0.304 μg mL^?1 for chlorophyll A and B respectively), selectivity (0.946 and 0.942 respectively) and sensitivity (0.0324 and 0.0183 absorbance mL μg^?1 respectively) were calculated in order to establish the robustness of the proposed methodology. After method validation, the PLS model was applied to determine the concentration of both pigments in different broccoli and cabbage plants. The concentrations of these pigments, calculated by the optimized chemometric method, were compared with those obtained by a chromatographic and photometric method based on the absorbance of sample at two different wavelengths. The accuracy of our results was comparable with that of results obtained by a chromatographic method improving significantly the accuracy compared with that of previously reported photometric approaches.     

UNE-EN ISO/IEC 17025:2005 accredited method for the determination of 121 pesticide residues in fruits and vegetables by gas chromatography–tandem mass spectrometry

A rapid, sensitive, accurate and reliable multiresidue method for quantification and confirmation of 121 common agricultural pesticides in fruits and vegetables by gas chromatography in tandem with mass spectrometry was developed, validated and applied to 1463 vegetable and fruit samples collected over one year from extensive greenhouse cultures in Almería (Spain). Prior to instrumental analysis an extraction procedure, based on a sample extraction of multi-class analytes according to QuEChERS method (quick, easy, cheap, effective, rugged and safe) with some modifications was used. Mass spectrometric conditions were individually optimized for each analyte to achieve maximum sensitivity in the Selected Reaction Monitoring (SRM) mode. The scan times for each segment were between 0.8 and 1.0 s, with a maximum of 35 transitions per segment. Use of two reactions for each pesticide allowed simultaneous quantification and identification in one run. The pesticides were separated in less than 30 min. Recovery and precision were evaluated in nine representative matrices (tomato, pepper, lettuce, cucumber, eggplant, zucchini, melon, watermelon and apple). The mean recoveries ranged from 80% for thiometon to 116% for heptenophos, with relative standard deviations lower than 20% for all components. Only three pepper samples, one of tomato and one of cucumber had residues above the maximum allowable residue (0.01 mg kg⁻¹) according to European Union directives. The method was accredited according to UNE-EN ISO/IEC 17025:2005 international standard.     

Ion-pair dispersive liquid–liquid microextraction solidification of floating organic droplets method for the rapid and sensitive detection of phenolic acids in wine samples using liquid chromatography combined with a core–shell particle column

This study describes a novel sample preparation method for extraction of phenolic acids from wine using ion pair dispersive liquid–liquid microextraction based on the solidification of a floating organic droplet (IP-DLLME-SFO). The ion-pairing technique combined with DLLME-SFO dramatically enhanced the extraction efficiency for very polar phenolic acids, such as gallic acid and protocatechuic acid, which could not be extracted by DLLME-SFO in the absence of an ion-pairing reagent. The effects of the parameters that can affect the extraction efficiency were systematically investigated, including the type and concentration of ion-pairing reagent, type and volume of extraction and dispersive solvents, extraction time, sample pH, and ion strength. The method linearity was constructed in the range of 0.01–15 μg/mL, and the sensitivity expressed as limit of detection was as low as 10 ng/mL. The method that we developed was applied for the analysis of commercial wine samples, revealing different levels of phenolic acids among these products.