Measurement of condensed tannins and dry matter in red grape homogenates using near infrared spectroscopy and partial least squares

Samples (n = 620) of homogenized red grape berries were analyzed using a visible and near-infrared (NIR) spectrophotometer (400-2500 nm) in reflectance. The spectra and the analytical data were used to develop partial least-squares calibrations to predict dry matter (DM) content and condensed tannins (CT) concentrations. The coefficient of determination in cross-validation and the standard error of cross-validation were 0.92 and 0.83% w/w for DM and 0.86 and 0.46 mg/g epicatechin equivalents for CT, respectively. The standard error in prediction was 1.34% w/w for DM and 0.89 mg/g epicatechin equivalents for CT, respectively. By implementing a NIR spectroscopy method to measure DM and CT in red grape homogenates, we have developed an approach that is suited to large-scale compositional analysis in commercial wine production facilities, as it enables the analysis of large numbers of samples needed to stream batches of fruit. From an economical point of view, the calibration models could be achieved with relatively small data sets. Thus, NIR offers a suitable and efficient tool for the simultaneous measurement of DM and CT in addition to other important parameters in red grape homogenates such as total anthocyanins, total soluble solids, and pH, with minimal sample preparation and low cost.     

Radical-scavenging activities of citrus essential oils and their components: detection using 1,1-diphenyl-2-picrylhydrazyl

Thirty-four kinds of citrus essential oils and their components were investigated for radical-scavenging activities by the HPLC method using 1,1-diphenyl-2-picrylhydrazyl (DPPH). To examine the oils' relative radical-scavenging activities compared with that of a standard antioxidant, Trolox was employed. All of the essential oils were found to have scavenging effects on DPPH in the range of 17. 7-64.0%. The radical-scavenging activities of 31 kinds of citrus essential oils were comparable with or stronger than that of Trolox (p < 0.05). The oils of Ichang lemon (64.0%, 172.2 mg of Trolox equiv/mL), Tahiti lime (63.2%, 170.2 mg of Trolox equiv/mL), and Eureka lemon (61.8%, 166.2 mg of Trolox equiv/mL) were stronger radical scavengers than other citrus oils. Citrus volatile components such as geraniol (87.7%, 235.9 mg of Trolox equiv/mL), terpinolene (87.4%, 235.2 mg of Trolox equiv/mL), and gamma-terpinene (84.7%, 227.9 mg of Trolox equiv/mL) showed marked scavenging activities on DPPH (p < 0.05).     

Influence of Soil Particle Size on the Measurement of Sodium by Near-Infrared Reflectance Spectroscopy

This study evaluates the effect of soil particle size (SPS) on the measurement of exchangeable sodium (Na) (EXC-Na) by near-infrared reflectance (NIR) spectroscopy. Three hundred thirty-two (n = 332) top soil samples (0–10 cm) were taken from different locations across Uruguay, analyzed by EXC-Na using emission spectrometry, and scanned in reflectance using a NIR spectrophotometer (1100–2500 nm). Partial least squares (PLS) and principal component regression (PCR) models between reference chemical data and NIR data were developed using cross validation (leaving one out). The coefficient of determination in calibration (R²) and the root mean square of the standard error of cross validation (RMSECV) for EXC-Na concentration were 0.44 (RMSECV: 0.12 mg kg^–1) for soil with small particle size (SPS-0.053) and 0.77 (RMSECV: 0.09 mg kg^–1) for soils with particle sizes greater than 0.212 mm (SPS-0.212), using the NIR region after second derivative as mathematical transformation. The R² and RMSECV for EXC-Na concentration using PCR were 0.54 (RMSECV: 0.07 mg kg^–1) and 0.80 (RMSECV: 0.03 mg kg^–1) for SPS-0.053 and SPS-0.212 samples, respectively.     

Estimating hydrogen cyanide in forage sorghum ( Sorghum bicolor ) by near-infrared spectroscopy

Hydrogen cyanide (HCN) is a toxic chemical that can potentially cause mild to severe reactions in animals when grazing forage sorghum. Developing technologies to monitor the level of HCN in the growing crop would benefit graziers, so that they can move cattle into paddocks with acceptable levels of HCN. In this study, we developed near-infrared spectroscopy (NIRS) calibrations to estimate HCN in forage sorghum and hay. The full spectral NIRS range (400-2498 nm) was used as well as specific spectral ranges within the full spectral range, i.e., visible (400-750 nm), shortwave (800-1100 nm) and near-infrared (NIR) (1100-2498 nm). Using the full spectrum approach and partial least-squares (PLS), the calibration produced a coefficient of determination (R(2)) = 0.838 and standard error of cross-validation (SECV) = 0.040%, while the validation set had a R(2) = 0.824 with a low standard error of prediction (SEP = 0.047%). When using a multiple linear regression (MLR) approach, the best model (NIR spectra) produced a R(2) = 0.847 and standard error of calibration (SEC) = 0.050% and a R(2) = 0.829 and SEP = 0.057% for the validation set. The MLR models built from these spectral regions all used nine wavelengths. Two specific wavelengths 2034 and 2458 nm were of interest, with the former associated with C═O carbonyl stretch and the latter associated with C-N-C stretching. The most accurate PLS and MLR models produced a ratio of standard error of prediction to standard deviation of 3.4 and 3.0, respectively, suggesting that the calibrations could be used for screening breeding material. The results indicated that it should be feasible to develop calibrations using PLS or MLR models for a number of users, including breeding programs to screen for genotypes with low HCN, as well as graziers to monitor crop status to help with grazing efficiency.     

A simple high-performance liquid chromatography method for the determination of throat-burning oleocanthal with probated antiinflammatory activity in extra virgin olive oils

A high-performance liquid chromatography (HPLC) method was developed to quantitatively analyze oleocanthal in extra virgin olive oils. Oleocanthal, a deacetoxy ligstroside aglycone, is known to be responsible for the back of the throat irritation of olive oils and to have probated antiinflamatory activity. Oleocanthal was isolated from small amounts of olive oil sample (1 g) by liquid-liquid extraction. Hexane-acetonitrile was found to be the best solvent system to extract oleocanthal from the oil matrix. The solvent extract was analyzed by reversed-phase HPLC with UV detection at 278 nm. Chromatogaphic separation of oleocanthal from other extracted compounds and of the two geometric isomers of oleocanthal was achieved by an elution gradient with acetonitrile and water. Both the external standard calibration curve and the internal standard calibration curve were established, and quantitation using both calibration curves gave essentially the same result. The reproducibility (RSD = 4.7%), recovery (> 95%), and limit of quantitation (< 1 microg/g) were also determined. Concentrations of oleacanthal in 10 selected throat-burning extra virgin olive oils were determined using the method (ranged from 22 to 190 microg/g) with external standard calibration.     

A Comparative Study of Fourier Transform Raman and NIR Spectroscopic Methods for Assessment of Protein and Apparent Amylose in Rice

Fourier‐transform Raman (FT‐Raman) spectroscopy and near‐infrared (NIR) reflectance spectroscopy were used to compare calibration models for determining rice cooking quality parameters such as apparent amylose and protein. Samples from two seasons were used in each calibration set. The laboratory values ranged from 4.89 to 12.48% for protein and from 0.2 to 25.7% for amylose. The data for both FT‐Raman and NIR were preprocessed with orthogonal signal correction (OSC) for standardization. For both spectroscopic methods, five models were optimized by partial least squares regression (PLSR) and by Martens' uncertainty regression (MUR), including no processing, smoothing, normalization, first derivative (D1), and second derivative (D2). Based solely on standard error of cross‐validation (SECV), the FT‐Raman method was superior to the NIR method for protein. For amylose, the FT‐Raman and NIR methods resulted in similar calibration statistics with a high precision, with the FT‐Raman requiring fewer factors. The best FT‐Raman models were generated from OSC preprocessing with MUR for protein (SECV 0.15%, five factors) and from OSC without MUR for amylose (SECV 0.70%, seven factors). The best NIR models were obtained with D2 transform of OSC spectra for protein (SECV 0.22%, four factors) and with OSC spectra for amylose (SECV 0.57%, 11 factors).     

Fast kinetic determination of 1-naphthylacetic acid in commercial formulations, soils, and fruit samples using stopped-flow phosphorimetry

A kinetic method has been developed for the determination of 1-naphthylacetic acid by means of micellar-stabilized room temperature phosphorescence (MSRTP) using the stopped-flow mixing technique. The main feature of this system is that it diminishes the time required for the deoxygenation of the micellar medium and for the phosphorescence development. Phosphorescence enhancers such thallium(I) nitrate, sodium dodecyl sulfate (SDS), and sodium sulfite were optimized to obtain maximum sensitivity. The pH was also optimized as it strongly affects the luminescent properties of 1-naphthylacetic acid. A pH of 6.6 was selected as adequate for the phosphorescence development. The kinetic curve of 1-naphthylacetic acid phosphorescence was scanned at lambda(ex) = 278 nm and lambda(em) = 490 nm, and the maximum rate of phosphorescence was taken as the analytical signal. This was obtained by calculating the maximum slope of the curve in an interval of 3.6 s as it provided a good noise-to-signal ratio. This method permitted the determination of 1-naphthylacetic acid throughout a concentration range of 100-1800 ng mL(-1) with high precision (relative standard error = 0.91% and relative standard deviation = 2.30%; 1-naphthylacetic acid concentration = 800 ng mL(-1)). According to the Clayton criterion, the detection limit was 45 ng mL(-1). The same limit resulted in 39.3 ng mL(-1) when the error propagation theory was applied. The applicability of the method was successfully demonstrated by determining 1-naphthylacetic acid in different kind of samples, such as phytosanitary products, soils, pears, and apples. Recovery values not significantly different from the nominal content or the spiked amount were found for these determinations.     

Simultaneous quantitation of 2-acetyl-4-tetrahydroxybutylimidazole, 2- and 4-methylimidazoles, and 5-hydroxymethylfurfural in beverages by ultrahigh-performance liquid chromatography-tandem mass spectrometry

An ultrahigh-performance liquid chromatography (UHPLC) tandem mass spectrometric (MS/MS) method was developed for the simultaneous quantification of 2-acetyl-4-tetrahydroxybutylimidazole (THI), 2- and 4-methylimidazoles (2-MI and 4-MI), and 5-hydroxymethylfurfural (HMF) in beverage samples. A C30 reversed-phase column was used in this method, providing sufficient retention and total resolution for all targeted analytes, with an MS/MS instrument operated in selected reaction monitoring (SRM) mode for sensitive and selective detection using isotope-labeled 4-methyl-d(3)-imidazole (4-MI-d(3)) as the internal standard (IS). This method demonstrates lower limit of quantification (LLOQ) at 1 ng/mL and coefficient of determination (r(2)) >0.999 for each analyte with a calibration range established from 1 to 500 ng/mL. This method also demonstrates excellent quantification accuracy (84.6-105% at 5 ng/mL, n = 7), precision (RSD < 7% at 5 ng/mL, n = 7), and recovery (88.8-99.5% at 10, 100, and 200 ng/mL, n = 3). Seventeen carbonated beverage samples were tested (n = 2) in this study including 13 dark-colored beverage samples with different flavors and varieties and 4 light-colored beverage samples. Three target analytes were quantified in these samples with concentrations in the range from 284 to 644 ng/mL for 4-MI and from 706 to 4940 ng/mL for HMF. THI was detected in only one sample at 6.35 ng/mL.     

Analysis of nitrogen fractions in silage by near-infrared spectroscopy

Total nitrogen, soluble nitrogen (SN), nonprotein nitrogen (NPN), and acid-detergent insoluble nitrogen (ADIN) were analyzed in grass silage by near-infrared (NIR) spectroscopy. A set of 144 samples was used to calibrate the instrument by modified partial least-squares regression, and the following statistical results were achieved: standard error of calibration (SEC) = 0.449 and square correlation coefficient (R (2)) = 0.98 for total nitrogen x 6.25, SEC = 0.425 and R (2) = 0.95 for SN x 6.25, SEC = 0.414 and R (2) = 0.94 for NPN x 6.25, and SEC = 0.139 and R (2) = 0.84 for ADIN x 6.25. To validate the calibration performed, a set of 48 silage samples was used. Standard errors of prediction were 0.76, 0.64, 0.63, and 0.25 for total nitrogen, SN, NPN, and ADIN (all of them multiplied by 6.25), respectively, and R (2) for the regression of measurements by reference method versus NIR analysis were 0.94, 0.92, 0.90, and 0.48 for total nitrogen, SN, NPN, and ADIN, respectively. To compare the results obtained by NIR spectroscopy with those obtained by the reference methods for total nitrogen, SN, and NPN of the validation set, linear regression and paired t tests were applied, and the results were not significantly different (p = 0.05). When mean square prediction error analysis was applied, it could be concluded that for total nitrogen, SN, and NPN, a robust calibration model was obtained and that the main error was unexplained error. Statistical data for ADIN were worse than those of the other parameters; as a result NIR spectroscopy is not an effective method for quantitative analyses of ADIN in silage; nevertheless, it may be an acceptable method for semiquantitative evaluation.     

Determination of the pesticide napropamide in soil, pepper, and tomato by micelle-stabilized room-temperature phosphorescence

A selective and sensitive method for determining napropamide by room-temperature phosphorescence in SDS micelles is proposed and applied to the determination of this substance in a technical formulation and in spiked soil, pepper, and tomato samples. The use of phosphorescence enhancers such as sodium dodecyl sulfate (micellar agent), thallium (I) nitrate (external heavy atom), and sodium sulfite (deoxygenation agent) was studied and optimized to obtain maximum sensitivity. The determination was performed in 66 mM SDS, 30 mM thallium (I) nitrate, and 8 mM sodium sulfite. Taking into account both maximum phosphorescence intensity and the time required to reach that, a pH value of 7.2 was selected. After the samples were left standing at room temperature for 10 min, the phosphorescence was totally developed. The intensity was then measured at lambda(ex) = 282 nm and lambda(em) = 528 nm. The calibration graph was linear for 50-600 ng mL(-1) napropamide. The detection limit, according to the error propagation theory, was 16 ng mL(-1). The method has been demonstrated for the analysis of soils, peppers, and tomatoes, but, because of matrix interference, the method of standard additions was applied to determine napropamide in the vegetable samples. Recoveries from all these matrixes of added napropamide were near 100%.     

可见/近红外光谱技术无损检测果实坚实度的研究

该研究的目的是建立可见/近红外光谱与梨果实坚实度之间的数学模型,评价可见/近红外光谱技术无损测量梨果实坚实度的应用价值.在可见/近红外光谱区域(350～1800nm),试验对比分析了不同测量部位、不同光谱预处理方法和不同校正建模算法的梨果实坚实度校正模型.结果表明:赤道部位吸光度一阶微分光谱的偏最小二乘回归所建梨果实坚实度校正模型的预测性能较优,其校正和预测相关系数分别为0.8779和0.8087,校正和预测均方误差分别为1.0804N和1.4455N.研究表明:可见/近红外光谱技术无损检测梨果实坚实度是可行的.     

Rapid determination of the main organic acid composition of raw Japanese apricot fruit juices using near-infrared spectroscopy

The potential of near-infrared (NIR) spectroscopy to rapidly determine citric and malic acid contents of raw Japanese apricot (Japanese "ume", also known as the Japanese plum) fruit juice was investigated. In total, 314 raw juice samples with different organic acid compositions were collected over a long growth period, and spectra (1100-1850 nm) of these samples were acquired using an NIR spectrophotometer with a 1-mm path length. Calibrations were performed using a partial least-squares regression method based on a calibration sample set (211 samples), while validations were performed based on a validation sample set (103 samples). The results revealed good agreement between NIR spectroscopy and capillary electrophoresis, including the correlation coefficient (r2), standard error of prediction (SEP), and bias; no statistically (p = 0.05) significant differences were found for these parameters. Moreover, standard deviation ratios of reference data in the validation sample set to the SEP were higher than 3, indicating that NIR spectroscopy may represent an acceptable method for quantitative evaluation of citric and malic acids in raw Japanese apricot fruit juice.     

Glucosinolates and fatty acid, sterol, and tocopherol composition of seed oils from Capparis spinosa Var. spinosa and Capparis ovata Desf. Var. canescens (Coss.) Heywood

Seed oils of 11 samples of Capparis ovata and Capparis spinosa from different locations in Turkey were characterized with regard to the composition of fatty acids, tocopherols, and sterols as well as the content of glucosinolates. The oil content of the seeds ranged from 27.3 to 37.6 g/100 g (C. spinosa) and from 14.6 to 38.0 g/100 g (C. ovata). The dominating fatty acid of both species was linoleic acid, which accounted for 26.9-55.3% in C. ovata seed oils and for 24.6-50.5% in C. spinosa seed oils. Oleic acid and its isomer, vaccenic acid, were both found in the seed oils in concentrations between 10 and 30%, respectively. The seed oils of both species were rich in tocopherols with the following composition: gamma-tocopherol, 124.3-1944.9 mg/100 g; delta-tocopherol, 2.7-269.5 mg/100 g; and alpha-tocopherol, 0.6-13.8 mg/100 g. The concentration of total sterols ranged from 4875.5 to 12189.1 mg/kg (C. ovata) and from 4961.8 to 10009.1 mg/kg (C. spinosa), respectively. In addition to sitosterol, which amounted to approximately 60% of the total amount of sterols, campesterol and stigmasterol accounted for 16 and 10% of the total sterols, respectively. The seed oils showed remarkably high contents of Delta5-avenasterol (between 138.8 and 599.4 mg/kg). The total content of glucosinolates of C. ovata and C. spinosa samples was determined as 34.5-84.6 micromol/g for C. ovata and 42.6-88.9 micromol/g for C. spinosa, respectively, on a dry weight basis, with >95% as glucocapperin.     

Improved high-performance liquid chromatography (HPLC) method for qualitative and quantitative analysis of allantoin in Zea mays

A high-performance liquid chromatography (HPLC) method for the qualitative and quantitative analysis of allantoin in silk and seed of Zea mays has been developed. Allantoin separation in crude extract was achieved using a C 18 column and phosphate buffer solution (pH 3.0) as a mobile phase at ambient temperature at a flow rate of 1.0 mL/min and detected at 210 nm. The results showed that the amount of allantoin in samples was between 14 and 271 mg/100 g of dry plant material. A comprehensive validation of the method including sensitivity, linearity, repeatability, and recovery was conducted. The calibration curve was linear over the range of 0.2-200 microg/mL with a correlation coefficient of r2>0.999. Limit of detection (LOD, S/N=3) and limit of quantification (LOQ) values of the allantoin were 0.05 and 0.2 microg/mL (1.0 and 4.0 ng) respectively. The relative standard deviation (RSD) value of the repeatability was reported within 1.2%. The average recovery of allantoin added to samples was 100.6% with RSD of 1.5%.     

基于小波变换的番茄总糖近红外无损检测

分别采用小波消噪、常数偏移消除等11种光谱预处理方法,对番茄总糖含量（质量分数）的近红外光谱进行预处理,通过偏最小二乘法定量校正模型预测值比较得出,小波消噪是适合番茄近红外光谱的最佳预处理方法,小波消噪的总糖质量分数近红外光谱优选区域为11 998.9～6 097.8 cm-1和4 601.3～4 246.5 cm-1,在此光谱区内建立的番茄总糖质量分数偏最小二乘法模型预测值与实测值的相关系数为0.930,内部交叉验证均方差为0.466%,校正标准差为0.469%,预测标准差为0.260%。试验结果表明：小波消噪后建立的近红外光谱模型能准确地对番茄总糖含量进行快速无损检测。     

Rapid classification of basil chemotypes by various vibrational spectroscopy methods

The potential of vibrational spectroscopy methods (attenuated total reflectance/Fourier-transform-infrared (ATR/FT-IR), FT-Raman and near infrared (NIR) spectroscopy) for the identification and quantification of valuable as well as carcinogenic substances in different basil chemotypes is described. It is shown that all main volatile components occurring in different basil accessions can be reliably determined in the isolated essential oils or solvent extracts but also in the air-dried herbs. While NIR data can be interpreted only by chemometric methods, IR and Raman spectra present characteristic key bands of the individual volatiles; therefore, in the latter case, a discrimination of basil chemotypes is frequently possible without applying chemometric algorithms. NIR calibrations are successfully established for various terpenoids and phenylpropanoids; on the basis of these data, the content of the two carcinogenic compounds methyleugenol (range: 2-235 microg/100 g) and estragole (range: 34-138 microg/100 g) can be reliably predicted in air-dried basil leaves (R (2) (coefficient of determination) = 0.951; SECV (standard error of cross validation) = 19.1 microg/100 g and R (2) = 0.890; SECV = 12.8 microg/100 g, respectively). The described methods were found to be very useful tools for the efficient selection of special basil single plants, adapted to the new demands set by the legislator and the consumer. Furthermore, they can be applied in industry to very easily control the purifying, blending, and redistilling processes of basil oil.     

Near-infrared spectroscopy for measurement of total dietary fiber in homogenized meals

Near-infrared (NIR) reflectance spectroscopy was investigated as a method for prediction of total dietary fiber (TDF) in mixed meals. Meals were prepared for spectral analysis by homogenization only (HO), homogenization and drying (HD), and homogenization, drying, and defatting (HDF). The NIR spectra (400-2498 nm) were obtained with a dispersive NIR spectrometer. Total dietary fiber was determined in HDF samples by an enzymatic-gravimetric assay (AOAC 991.43), and values were calculated for HD and HO samples. Using multivariate analysis software and optimum processing, partial least squares models (n = 114) were developed to relate NIR spectra to the corresponding TDF values. The HO, HD, and HDF models predicted TDF in independent validation samples (n = 37) with a standard error of performance of 0.93% (range 0.7-8.4%), 1.90% (range 2.2-18.9%), and 1.45% (range 2.8-23.3%) and r(2) values of 0.89, 0.92, and 0.97, respectively. Compared with traditional analysis of TDF in mixed meals, which takes 4 days, NIR spectroscopy provides a faster method for screening samples for TDF. The accuracy of prediction was greatest for the HDF model followed by the HD model.     

Antioxidant capacity and cytotoxicity of essential oil and methanol extract of Aniba canelilla (H.B.K.) Mez

The leaves and fine stems, bark, and trunk wood oils of Aniba canelilla showed yields ranging from 0.2 to 1.3%. The main volatile constituent identified in the oils was 1-nitro -2-phenylethane (70.2-92.1%), as expected. The mean of DPPH radical scavenging activity (EC 50) of the oils (198.17 +/- 1.95 microg mL(-1)) was low in comparison with that of wood methanol extracts (4.41 +/- 0.12 microg mL(-1)), the value of which was equivalent to that of Trolox (4.67 +/- 0.35 microg mL(-1)), used as antioxidant standard. The mean amount of total phenolics (TP) (710.53 +/- 23.16 mg of GAE/g) and this value calculated as Trolox equivalent antioxidant capacity (TEAC) (899.50 +/- 6.50 mg of TE/g) of the wood methanol extracts confirmed the high antioxidant activity of the species. On the other hand, in the brine shrimp bioassay the values of lethal concentration (LC50) for the oils (21.61 +/- 1.21 microg mL(-1)) and 1-nitro-2-phenylethane (20.37 +/- 0.99 microg mL(-1)) were lower than that of the wood methanol extracts (91.38 +/- 7.20 microg mL(-1)), showing significant biological activities.     

Feasible application of a portable NIR-AOTF tool for on-field prediction of phenolic compounds during the ripening of olives for oil production

Olive fruits of three different cultivars (Moraiolo, Dolce di Andria, and Nocellara Etnea) were monitored during ripening up to harvest, and specific and total phenols were measured by HPLC (High Pressure Liquid Chromatography). On the same olive samples (n = 450), spectral detections were performed using a portable NIR (Near Infrared)-AOTF (Acousto Optically Tunable Filter) device in diffuse reflectance mode (1100-2300 nm). Prediction models were developed for the main phenolic compounds (e.g., oleuropein, verbascoside, and 3,4-DHPEA-EDA) and total phenols using Partial Least Squares (PLS). Internal cross-validation (leave-one-out method) was applied for calibration and prediction models developed on the data sets relative to each single cultivar. Validation of the models obtained as the sum of the three sample sets (total phenols, n = 162; verbascoside, n = 162; oleuropein, n = 148; 3,4-DHPEA-EDA, n = 162) were performed by external sets of data. Obtained results in term of R(2) (in calibration, prediction and cross-validation) ranged between 0.930 and 0.998, 0.874-0.942, and 0.837-0.992, respectively. Standard errors in calibration (RMSEC), cross-validation (RMSECV), and prediction (RMSEP) were calculated obtaining minimum error in prediction of 0.68 and maximum of 6.33 mg/g. RPD ratios (SD/SECV) were also calculated as references of the model effectiveness. This work shows how NIR-AOTF can be considered a feasible tool for the on-field and nondestructive measurement of specific and total phenols in olives for oil production.     

Development of an immunoassay (ELISA) for the quantification of thiram in lettuce

Two competitive immunoassays, a laboratory assay based on microwell plates and a field test based on the use of polystyrene tubes, have been developed for the quantification of thiram in lettuces. Concerning the laboratory assay, the calibration curve for thiram had a linear range of 11 to 90 ng/mL and a detection limit of 5 ng/mL. Precision of the assay presented coefficient of variation values <9% and the recovery of thiram from lettuce averaged 89% across the range of the immunoassay method using 30 min extraction with water/acetone (50:50, v/v). The tube-based method was developed in order that an extract of lettuce, containing thiram at the MRL (8 ppm), would be found on the linear part of the standard curve. The calibration curve for thiram has a linear range of 100 to 800 ng/mL (1.39 to 11.1 ppm in lettuce) and a detection limit of 40 ng/mL.