Determination of the percentage of milk (cow's, ewe's and goat's) in cheeses with different ripening times using near infrared spectroscopy technology and a remote reflectance fibre-optic probe

In the present work we studied the use of near infrared spectroscopy (NIRS) technology employing a remote reflectance fibre-optic probe (with a 5 cm × 5 cm quartz window) for the analysis of the percentage of milk (cow's, ewe's and goat's) used in the elaboration of cheeses with different ripening times. To do so, cheeses with known and varying percentages of cow's, ewe's and goat's milk were elaborated (112 samples with milk collected in winter and 112 samples with milk collected in summer) and used as reference material, and ripening controls were performed over 6 months. The method allows immediate control of the cheese without prior sample treatment or destruction by direct application of the fibre-optic probe to the sample. The regression method employed was modified partial least squares (MPLS). Of all the samples (224), 200 formed to so-called calibration set and the other 24 were used for external validation. The calibration results obtained using 200 samples of cheese allowed the percentage of cow's, ewe's and goat's milk to be measured. The multiple correlation coefficients (RSQ) and prediction corrected standard errors (SEP(C)) obtained were respectively, 0.834 and 11.6% for cow's milk; 0.871 and 9.8% for goat's milk; 0.880 and 10.6% for ewe's milk. The ratio performance deviation (RPD) values obtained indicate that the NIRS equations can be applied to unknown samples.     

Near-infrared spectroscopy (NIRS) reflectance technology for the determination of tocopherols in alfalfa

The vitamin E (α- and (β+γ)-tocopherol) contents present in alfalfa (fresh or dehydrated) were analysed using near-infrared spectroscopy (NIRS) technology together with a remote reflectance fibre-optic probe. The range of vitamin E was 0.55–5.16 mg/100 g for α-tocopherol and 0.07–0.48 for (β+γ)-tocopherol. The regression method employed was modified partial least squares (MPLS). The equations developed using the fibre-optic probe for 69 samples of alfalfa (dehydrated and fresh) to determine the content of vitamin E in feeds had multiple correlation coefficients (RSQs) and prediction corrected standard errors (SEP (C)) of 0.946 and 0.321 mg/100 g for α-tocopherol and 0.956 and 0.022 mg/100 g for (β+γ)-tocopherol. The predicted values of vitamin E in feeds using NIRS technology applying the fibre-optic probe directly on the sample with neither previous treatment nor manipulation are comparable to those obtained using the chemical method, which included alkaline hydrolysis and hexane extraction of the vitamin from the unsaponifiable fraction before chromatographic determination.     

Use of NIRS technology with a remote reflectance fibre-optic probe for predicting mineral composition (Ca,K, P,Fe, Mn,Na, Zn), protein and moisture in alfalfa

In the present work we study the use of near-infrared spectroscopy (NIRS) technology together with a remote reflectance fibre-optic probe for the analysis of major (Ca, K, P) and minor (Fe, Mn, Na, Zn) elements, protein and moisture in alfalfa. The method allows immediate analysis of the alfalfa without prior sample treatment or destruction through direct application of the fibre-optic probe on ground samples in the case of the mineral composition and on-ground and compacted (baled) samples in the case of protein and humidity. The regression method employed was modified partial least-squares (MPLS). The calibration results obtained using samples of alfalfa allowed the determination of Ca, K, P, Fe, Mn, Na and Zn, with a standard error of prediction (SEP(C)) and a correlation coefficient (RSQ) expressed in mg/kg of alfalfa of 1.37 × 10³ and 0.878 for Ca, 1.10 × 10³ and 0.899 for K, 227 and 0.909 for P, 103 and 0.948 for Fe, 5.1 and 0.843 for Mn, 86.2 and 0.979 for Na, and of 1.9 and 0.853 for Zn, respectively. The SEP(C) and RSQ values (in %) for protein and moisture in ground samples were 0.548 and 0.871 and 0.150 and 0.981, respectively; while in the compacted samples they were 0.564 and 0.826 and 0.262 and 0.935, respectively. The prediction capacity of the model and the robustness of the method were checked in the external validation in alfalfa samples of unknown composition, and the results confirmed the suitability of the method.     

Use of NIRS technology with a remote reflectance fibre-optic probe for predicting major components in bee pollen

In the present work, we study the use of near infra-red spectroscopy (NIRS) technology together with a remote reflectance fibre-optic probe for determination of the major components in bee pollen. The method allows immediate control of the bee pollen without prior sample treatment or destruction through direct application of the fibre-optic probe to the sample.The regression method employed was modified partial least squares (MPLS). The calibration results obtained using 45 samples of bee pollen allowed the measurement of protein, moisture, ash, reducing sugars, and pH with multiple correlation coefficients (RSQ) and prediction corrected standard errors (SEPC) of 0.91, 0.56% for protein, of 0.78 and 0.49% for moisture; 0.92 and 0.049% for ash; 0.81 and 1.32 g of glucose/100 g of bee pollen; 0.84 and 0.15 for pH, respectively.The prediction capacity of the pattern was checked by applying it to samples of unknown pollen in external validation.     

Dynamic ultrasound-assisted leaching of essential macro and micronutrient metal elements from animal feeds prior to flame atomic absorption spectrometry

A method for routine analysis of essential metal elements in animal feeds using a dynamic and automated ultrasound-assisted extractor is proposed here. Owing to the different concentration of the essential metal elements in the samples, two macronutrients—namely, Ca and Mg—and three micronutrients or trace elements—namely, Fe, Cu and Zn—were selected as models for the optimisation and characterisation of the proposed method by using experimental design methodology. Moreover, the extraction kinetics and influence of the particle size on the extraction efficiency were studied. The detection and quantification limits ranged between 2.9 and 40 g kg^–1 and between 7.9 and 95.5 g kg^–1, respectively. The precision, expressed as repeatability relative standard deviation (RSD) and as within-laboratory RSD, ranged between 1.86 and 5.66% and between 5.06 and 6.15%, respectively. The proposed approach allows the extraction of these metal elements from animal feeds with extraction efficiencies similar to those provided by the AOAC Official Method 968.08, but with a drastic reduction in both the extraction time (18 min versus 4.5 h) and sample handling, and using smaller volumes of extractant (an acid aqueous solution).     

Analysis of fluoroquinolones in animal feeds by liquid chromatography with fluorescence detection

An analytical method for the analysis of six fluoroquinolones (FQs) in animal feeds was developed. The sample treatment consists of a simple and rapid extraction of the analytes by manual shaking with an acetonitrile-water mixture containing hydrochloric acid without further sample cleanup. Matrix effects were minimized by diluting the extract with water. Determination was carried out by liquid chromatography using fluorimetric detection. The method was validated in-house in four different feed matrices (poultry, cow, pig, and lamb feed). Mean recoveries ranging from 80 to 105%, with relative standard deviations below 12%, were achieved from spiked animal feed samples on the 0.2-2.0 μg/g level. No relevant differences were observed between the studied feeds, this ensuring that the method was reliable for a wide variety of feed matrices. Decision limit and detection capability values are below 0.08 and 0.13 mg/kg, respectively, for most FQs. The results obtained demonstrate the feasibility of the analytical method developed for a routine use to control the illegal use of these substances in feeding stuffs.     

Use of NIRS technology with a remote reflectance fibre-optic probe for predicting major components in cheese

In the present work the potential of near infra-red spectroscopy technology (NIRS) together with the use of a remote reflectance fibre-optic probe for the analysis of fat, moisture, protein and chlorides contents of commercial cheeses elaborated with mixtures of cow's, ewe's and goat's milk and with different curing times was examined. The probe was applied directly, with no previous sample treatment. The regression method employed was modified partial least squares (MPLS). The equations developed for the cheese samples afforded fat, moisture, protein, and chloride contents in the range 13-52%, 10-62%, 20-30%, and 0.7-2.9%, respectively. The multiple correlation coefficients (RSQ) and prediction corrected standard errors (SEP (C)) obtained were respectively 0.97 and 0.995% for fat; 0.96% and 1.640% for moisture; 0.78% and 0.760% for protein, and 0.89% and 0.112% for chlorides.     

近红外光谱法测定ABS树脂中氮含量

根据58个丙烯腈-丁二烯-苯乙烯(ABS)树脂样品的近红外漫反射光谱数据结合偏最小二乘法(PLS)建立了ABS树脂中氮含量定量分析的校正模型。结果表明;在近红外光谱区(7501.8～5449.9cm~(-1))内,主因子数为9时,定量模型的准确度最好。通过对模型进行t-检验,在显著性水平为0.05的条件下,其测定结果与标准方法的测定结果对比,两者无显著性差异。预测相关系数(r)和相对标准偏差(RSD)分别为0.9924和3.3%。     

The natural abundance of C with different agricultural management by NIRS with fibre optic probe technology

In the present study the natural abundance of ¹³C is quantified in agricultural soils in Mexico which have been submitted to different agronomic practices, zero and conventional tillage, retention of crop residues (with and without) and rotation of crops (wheat and maize) for 17 years, which have influenced the physical, chemical and biological characteristics of the soil. The natural abundance of C13 is quantified by near infrared spectra (NIRS) with a remote reflectance fibre optic probe, applying the probe directly to the soil samples.Discriminate partial least squares analysis of the near infrared spectra allowed to classify soils with and without residues, regardless of the type of tillage or rotation systems used with a prediction rate of 90% in the internal validation and 94% in the external validation. The NIRS calibration model using a modified partial least squares regression allowed to determine the δ¹³C in soils with or without residues, with multiple correlation coefficients 0.81 and standard error prediction 0.5‰ in soils with residues and 0.92 and 0.2‰ in soils without residues. The ratio performance deviation for the quantification of δ¹³C in soil was 2.5 in soil with residues and 3.8 without residues. This indicated that the model was adequate to determine the δ¹³C of unknown soils in the −16.2‰ to −20.4‰ range. The development of the NIR calibration permits analytic determinations of the values of δ¹³C in unknown agricultural soils in less time, employing a non-destructive method, by the application of the fibre optic probe of remote reflectance to the soil sample.     

近红外光谱法测定卷烟纸中钙和镁

应用傅里叶变换近红外(FT-NIR)光谱分析技术结合偏最小二乘法(PLS),建立了卷烟纸中钙和镁含量的数学预测模型。结果表明:钙和镁模型的相关系数分别为0.9870和0.9851,内部交叉验证均方差为0.462和0.0082,近红外光谱法预测值与原子吸收光谱法测定值的平均相对偏差各为3.1%和7.4%。该方法简便、快速、不破坏样品,可用于大批量卷烟纸样品中钙和镁的快速测定。     

气相色谱-质谱法确证分析饲料中6种利尿剂的研究

研究建立了气相色谱.质谱确证分析配合饲料中依他尼酸、氢氟噻嗪、氯噻嗪、呋噻米、氯噻酮和氢氯噻嗪等6种利尿剂的方法.本研究用磷酸盐缓冲液和甲醇混合提取液提取饲料中6种利尿剂,通过液液提取净化,在碳酸钾催化下用碘甲烷衍生,气相色谱-质谱定性和定量分析.确定了磷酸盐缓冲液和甲醇的提取体系,优化了6种利尿剂的色谱分离条件和质谱检测条件.在优化条件下,6种利尿剂线性范围为0.05～1.0μg/mL,线性相关系数高于0.99,方法的定量限为0.5μg/g.在饲料样品中,不同添加浓度水平回收率高于57.6%,相对标准偏差低于12%.该方法适用于饲料样品中6种利尿剂的定性和定量分析.     

A liquid chromatography method using a monolithic column for the determination of corticoids in animal feed and animal feeding water

An HPLC-DAD method for determining corticoids in calf feed and in animal feeding water samples using a monolithic column has been developed and validated. The method optimization included the study of binary mobile phases of water and acetonitrile. The optimum separation was achieved at 40 °C, with acetonitrile:H₂O 29:71 v/v used as mobile phase and a 3 ml/min flow-rate, which resulted in their separation in about 5 min. Two reported sample procedures were applied to feed and for animal feeding water samples prior to HPLC. Method validation was carried out according to the EU criteria established for quantitative screening methods. The results indicate that this method is highly specific, reproducible and accurate. The proposed method was found to be robust and unaffected by small variations in the extraction procedure and in HPLC conditions. The developed method for the determination of corticoids in feed and water samples was also found to be suitable for different kinds of feeds and waters.     

高效液相色谱法测定动物组织中四环素类抗生素残留量的研究

建立了动物组织中四环素、金霉素、土霉素、强力霉素、去甲基金霉素、甲烯土霉素和二甲胺四环素等7种四环素类抗生素残留量的液相色谱同时测定方法。方法采用Inertsil C8-3(5μm,250 mm×4.0 mm i.d)反相色谱柱,以pH 4.0的EDTA-Mcllvaine缓冲溶液为提取溶液,以HLB固相萃取柱为净化柱,流动相为甲醇+乙腈+0.01mol/L三氟乙酸(梯度洗脱),流速1.5 mL/min,检测波长350 nm,进样量100μL。方法的检出限为1.5~5.0μg/kg,测定低限为50μg/kg,线性范围为50~1200μg/kg,加标回收率为73.8%~103%,相对标准偏差为0.5%~8.5%。方法适用于动物肌肉、肝脏和肾脏组织中7种四环素类抗生素残留量的同时检测。     

毛细管电泳定量检测环境水样中无机阴离子

详细讨论了胶束浓度、间接吸收背景物质的浓度及有机添加剂组成等对部分卤素及其含氧酸根的毛细管电泳分离影响;在优化的条件下,3.5min内高效、快速地完成了Cl-、Br-、ClO3-、BrO3-四种无机阴离子的分离分析,分离的理论塔板数在1.6×106～2.8×105/m之间,检出限在11.2～23.3mg/L之间,迁移时间的相对标准偏差小于1%,峰面积的相对标准偏差在5.2%～2.2%之间;并将方法用于环境水样的分析。     

Simultaneous separation of inorganic anions and cations by capillary zone electrophoresis

A new capillary electrophoretic approach for simultaneous separation of fast anions and cations is demonstrated. Indirect UV detection at 214 nm in conjunction with electromigration sampling from both ends of the capillary was developed. Two electrolyte systems based on imidazole-nitrate and copper(II)-ethylenediamine-nitrate were investigated for the simultaneous separation of chloride, sulphate, hydrocarbonate, potassium, ammonium, calcium, sodium and magnesium ions. Experimental parameters that were evaluated included a nature of UV chromophore, pH of electrolyte, a nature of complexing agent. The method permits the excellent separation of three anions and five cations in only 4 min using electrolyte system containing 2.5 mmol l⁻¹ Cu(NO₃)₂, 5 mmol l⁻¹ ethylenediamine and 1 mmol l⁻¹ fumaric acid at pH 8.5 adjusted with tetraethylammonium hydroxide.     

Determination of decoquinate in animal feeds by liquid chromatography: collaborative study

The performance characteristics of a liquid chromatographic (LC) method for the analysis of decoquinate (DEC) in supplements, premixes, and complete animal feeds at medicating and trace levels were collaboratively studied. DEC is extracted from ground feed samples with 1% calcium chloride-methanol solution using mechanical agitation for 90 min. After centrifugation for 5 min and dilution (if necessary), an aliquot of the extract is diluted with water. The diluted extracts are filtered and analyzed by reversed-phase LC with fluorescence detection. Suspect positive trace-level samples are confirmed by using an alternate excitation wavelength. Fourteen test samples of medicated feeds, supplement, and medicated premix, along with 8 test samples for trace-level analysis, were sent to 13 collaborators (one in Canada, 4 in Europe, and 8 in the United States). Test samples were analyzed as blind duplicates. Acceptable results were received from 12 laboratories for the medicated test samples and from 13 laboratories for the trace-level samples. Repeatability relative standard deviation estimates ranged from 1.3 to 5.6%. Reproducibility relative standard deviations estimates ranged from 2.8 to 6.1%, and HorRat values ranged from 0.22 to 0.74.     

Determination of non-protein cysteine in human serum by a designed BODIPY-based fluorescent probe

A novel fluorescent probe is designed and synthesized for the determination of cysteine in biological samples by incorporating 2,4-dinitrobenzenesulfonyl (DBS) group as a quencher into the BODIPY skeleton. The BODIPY-based probe itself shows weak fluorescence due to the strong intramolecular charge transfer process. Upon reaction with cysteine, however, the probe produces a rapid and large fluorescence enhancement through the removal of the DBS unit by nucleophilic aromatic substitution. This valuable property leads to the development of a new and simple method for cysteine assay. Under the optimized conditions, the fluorescence enhancement value is directly proportional to the concentration of cysteine in the range 2-12 μM, with a detection limit of 30 nM (S/N = 3). The applicability of the developed method has been successfully demonstrated on the determination of non-protein cysteine in human serum. Compared to most of the existing fluorescent probes proposed for cysteine, the BODIPY-based one exhibits an excellent overall performance in terms of selectivity, sensitivity and simplicity.     

Analysis of zearalenone and α-zearalenol in animal feed using high-performance liquid chromatography

Different extraction and clean-up techniques used before HPLC analysis were compared in order to obtain a reliable method for the quantitative determination of zearalenone (ZEA) and α-zearalenol (α-ZOL) in animal feed. Immunoaffinity clean-up was compared to C₁₈ and Florisil column clean-up. Extracted samples were analysed by reversed-phase HPLC with fluorescence detection (λ_ex=274 nm, λ_em=440 nm). A mobile phase of acetonitrile:water (50:50 (v/v)) and a flow-rate of 1.0 ml min⁻¹ resulted in a good separation between ZEA and α-ZOL. Using immunoaffinity clean-up the linear range was between 25 and 600 μg kg⁻¹ for ZEA and α-ZOL in maize. Intra-laboratory coefficients of variation (CV) (under repeatability conditions) were 9.16% for ZEA and 2.18% for α-ZOL. Recoveries for spiked ZEA and α-ZOL samples ranged from 89 to 110% with CVs between 5.2 and 11.2% (under within-laboratory reproducibility conditions). Using C₁₈ and Florisil solid-phase clean-up, matrix interference was too high. Therefore, naturally contaminated animal feed samples were analysed using the developed HPLC method coupled to the immunoaffinity clean-up.     

Determination of oxytetracycline, tetracycline and chloramphenicol antibiotics in animal feeds using subcritical water extraction and high performance liquid chromatography

A rapid analytical method for the determination of oxytetracycline (OTC), tetracycline (TC) and chloramphenicol (CAP) antibiotics in animal feeds has been developed based on subcritical water extraction (SWE) without further sample clean-up followed by high performance liquid chromatography (HPLC) with ultraviolet (UV) detection. On extracting target antibiotics from spiked samples, the efficiency of the water extraction device was evaluated in terms of pH and volume of the extractant, temperature and time of the static extraction. The best extraction conditions were obtained by using 5.5 mL of water adjusted to pH 2 with hydrochloric acid as the extractant at 100 °C with 5-min static extraction. After filtration, 20 μL of the aqueous extract was directly injected into the HPLC column. Recoveries between 82.1% and 90.0% with relative standard deviations ranging between 1.6% and 4.8% were achieved from spiked animal feed samples by using this method. Compared with the traditional ultrasonic extraction, this procedure was remarkably more efficient in extracting OTC, TC and CAP, simpler to perform, and there was no use of toxic organic solvents.