A new tool for direct non-invasive evaluation of chlorophyll a content from diffuse reflectance measurements.

Chlorophyll is a key biochemical component that is responsible for photosynthesis and is an indicator of plant health. The effect of stressors can be determined by measuring the amount of chlorophyll a, which is the most abundant chlorophyll, in vegetation in general. Nowadays, invasive methods and vegetation indices are used for establishing chlorophyll amount or an approximation to this value, respectively. This paper demonstrates that H-point curve isolation method (HPCIM) is useful for isolating the signal of chlorophyll a from non-invasive diffuse reflectance measurements of leaves. Spinach plants have been chosen as an example. For applying the HPCIM only the registers of both, a standard and the sample are needed. The results obtained by HPCIM and the invasive method were statistically similar for spinach leaves: 144±6mg/m2 (n=5) and 155±40mg/m2 (n=5), respectively. However, more precise values were achieved with the HPCIM, which also involved minimal experimental effort. The HPCIM method was applied to spinach plants stressed by the action of several pesticides and water scarcity, showing a decrease of chlorophyll a content with time, which is related with a loss of health. The results obtained were compared with those achieved by two different reflectance vegetation indices (Macc01 and NDVI). Although NDVI and HPCIM gave similar footprints for the plants tested, vegetation indices fail in the estimation of real content of the chlorophyll a. The HPCIM could contribute to improve the knowledge of the chlorophyll a content of vegetation like health indicator, by applying it to a much employed non-invasive technique such as diffuse reflectance, which can be used in place or in remote sensing mode.

A solid device based on doped hybrid composites for controlling the dosage of the biocide N-(3-aminopropyl)-N-dodecyl-1,3-propanediamine in industrial formulations.

A colorimetric composite device is proposed to determine the widely used biocide N-(3-aminopropyl)-N-dodecyl-1,3-propanediamine (ADP).This sensing device is based on a film of 1,2-Naphthoquinone-4-sulfonate (NQS) embedded into polydimethylsiloxane-tetraethylortosilicate-SiO2 nanoparticles composite (PDMS-TEOS-SiO2NPs). Semiquantitative analysis can be performed by visual inspection. Digitalized image or diffuse reflectance (DR) measurements can be carried out for quantitative analysis. Satisfactory detection limit (0.018%, w/v) and relative standard deviations <12% were achieved. The proposed device has been applied for the determination of ADP in detergent industrial formulations with recovery values between 80% and 112%. The method has been successfully validated, showing its high potential to control and monitor this compound because the device is easy to prepare and use, robust, portable, stable over time and cost effective. This device allows a green, simple and rapid approach for the analysis of samples without pretreatment and does not require highly trained personnel. These advantages give the proposed kit good prospects for implementation in several industries.

Polydimethylsiloxane composites containing 1,2-naphtoquinone 4-sulphonate as unique dispositive for estimation of casein in effluents from dairy industries.

A unique dispositive to determine casein which is the most abundant protein in dairy sewages has been proposed. In this sensing technology, the derivatization reagent 1,2-naphtoquininone 4-sulphonate (NQS) is embedded into a polydimethylsiloxane-tetraethylortosilicate-SiO2 nanoparticles composite (PDMS-TEOS-SiO2NPs). When the composite is immersed into the samples, casein is extracted from the solution and derivatized inside the PDMS matrix after 10 min at 100°C. The sensing support changes its color from yellow to orange depending on the casein concentration. Quantitative analysis can be carried out by measuring the absorbance with a reflection probe or by image-processing tool (GIMP). This sensor provides good sensitivity and precision (RSD% <12%). The method validation has been done by applying the biocinchoninic acid method (BCA). Moreover, semiquatitative analysis of casein can be performed by visual observation. Taking into account the advantages of small size, rapidity, simplicity, good stability and high compatibility in aqueous solution, this sensor is expected to have potential practical applications for in-situ determination of casein. Finally the method has been applied to analyze effluents from dairy industries.

On-line in-tube solid phase microextraction-capillary liquid chromatography method for monitoring degradation products of di-(2-ethylhexyl) phthalate in waters.

The main di-(2-ethylhexyl) phthalate (DEHP) degradation products, (2-ethylhexyl) phthalate (MEHP), diethyl phthalate (DEP) and dibutyl phthalate (DBP), have been tested. The proposed cost-effective method combines on-line, in-tube solid-phase micro extraction (IT-SPME) in in-valve configuration and capillary liquid chromatography with UV diode array detection (Cap-LC-DAD). Acidification of the samples at pH 3 improved markedly the estimation of MEHP. Aliquots of 4mL of acidified water samples were directly processed. After sample loading, the analytes were desorbed with the mobile-phase and transferred to the monolithic capillary column. Satisfactory linearity and precision, absence of matrix effect and suitable limits of detection (LODs): 0.005, 0.1, 0.1 and 1.5µg/L for MEHP, DEP, DEHP and DBP, respectively have been achieved. The main advantages are speed and the reduction of background signal by minimizing sample preparation. Real water samples have been analyzed.

Rapid analysis of effluents generated by the dairy industry for fat determination by preconcentration in nylon membranes and attenuated total reflectance infrared spectroscopy measurement.

This paper describes a new approach for the determination of fat in the effluents generated by the dairy industry which is based on the retention of fat in nylon membranes and measurement of the absorbances on the membrane surface by ATR-IR spectroscopy. Different options have been evaluated for retaining fat in the membranes using milk samples of different origin and fat content. Based on the results obtained, a method is proposed for the determination of fat in effluents which involves the filtration of 1 mL of the samples through 0.45 µm nylon membranes of 13 mm diameter. The fat content is then determined by measuring the absorbance of band at 1745 cm(-1). The proposed method can be used for the direct estimation of fat at concentrations in the 2-12 mg/L interval with adequate reproducibility. The intraday precision, expressed as coefficients of variation CVs, were ≤ 11%, whereas the interday CVs were ≤ 20%. The method shows a good tolerance towards conditions typically found in the effluents generated by the dairy industry. The most relevant features of the proposed method are simplicity and speed as the samples can be characterized in a few minutes. Sample preparation does not involve either additional instrumentation (such as pumps or vacuum equipment) or organic solvents or other chemicals. Therefore, the proposed method can be considered a rapid, simple and cost-effective alternative to gravimetric methods for controlling fat content in these effluents during production or cleaning processes.

A cost-effective method for estimating di(2-ethylhexyl)phthalate in coastal sediments.

This study describes the development of a new method for the analysis of di(2-ethylhexyl)phthalate (DEHP) using 0.1-0.3 g of sediment sample, based on matrix solid phase dispersion (MSPD) using C18 as dispersant phase (0.4 g) and acetonitrile-water as eluting solvent (3.4 mL 1:3.25, v/v). No evaporation step is required. 3 mL of extracts were processed on-line by in-tube solid phase microextraction (IT-SPME) coupled to capillary liquid chromatography (CapLC) and diode array detector (DAD). A short analytical column Zorbax SB C18 (35×0.5 mm, 5 µm) provided suitable results. FTIR-ATR was employed for characterizing sediment samples and MSPD procedure. The total analysis time was less than 20 min (MSPD takes about 10 min). The utility of the described approach has been tested by analyzing several real samples. No matrix effect was found. Achieved precision was less than 10% for DEHP estimation. Detection limits in samples were 270 and 90 µg/kg for 0.1 and 0.3 g of taken sediment, respectively.

Multiresidue analysis of organic pollutants by in-tube solid phase microextraction coupled to ultra-high performance liquid chromatography-electrospray-tandem mass spectrometry.

In this work, in-tube solid phase microextraction (IT-SPME) coupling with ultra-high-pressure liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) multiresidue analytical method has been proposed for the first time for on-line enrichment of 9 analytes included in Water Frame Directive 2000/60/EC (WFD). The device was equipped with a GC TRB-5 capillary column, used as pre-concentration loop, and two conventional six-port injection valves. Water sample and desorption solvent volumes were tested. The optimum conditions were 4mL of processed sample followed by elution with 40µL of methanol. The analytes were detected with a mass spectrometer after being ionized positively using an electrospray ionization (ESI) source. The method presents good linearity over the range assayed, 0.025-2.5µg/L for chlorpyriphos and 0.25-25µg/L for the other tested compounds and LODs between 0.025µg/L and 2.5µg/L. Enrichment factors ranged from 2.5 to 10. Intra and inter-day variation coefficients were <26 and 31.6% respectively. Once validated, the method was applied to several water samples from different sources demonstrating that it achieves the on-line enrichment of the analytes with the advantage of minimum sample manipulation, and the identification and quantification of some organic pollutants in water samples in the range of low parts-per-billion. The method provided similar analytical characteristics as those obtained in the established couple IT-SPME-Capillary Liquid Chromatography (CapLC).

A miniaturized method for estimating di(2-ethylhexyl) phthalate in bivalves as bioindicators.

This work has developed a miniaturized method based on matrix solid phase dispersion (MSPD), using C18 as dispersant and acetonitrile-water as eluting solvent, for the analysis of di(2-ethylhexyl) phthalate (DEHP) in biota samples by capillary liquid chromatography coupled to in-tube solid phase microextraction and diode array detection. Recovery studies showed that the combination of C18-Florisil® was optimal using low amount of samples (0.1 g) and with low volumes of acetonitrile-water (2.6 mL 1:3.25, v/v). The sample is processed in less than 30 min, no evaporation step is required. The proposed method was applied to the analysis of DEHP in mussels and of the coastal waters in which they live. The average value of recoveries obtained, with ten spikes realized before MSPD treatment and after, was 91±15%. The detection limit achieved in mussels was 170 µg/kg. Bioconcentration factor values (BCFs) have been discussed, because DEHP can be bioconcentrated in aquatic organisms.