Aerosol-Phase Extraction Method for Determination of Ca, K, Mg, and Na in Biodiesel through Inductively Coupled Plasma Optical Emission Spectrometry.

A novel extraction method was developed, optimized, and validated for the elemental analysis of organic samples. The method, called aerosol-phase extraction (APE), is based on nebulization of the extracting aqueous solution (0.1 mol·L-1 nitric acid) on the sample. Extraction was performed at the interface of generated extractant droplets as they entered into contact with the samples. Afterward, the phases were allowed to separate and Ca, K, Na, and Mg were determined in aqueous phase by means of inductively coupled plasma optical emission spectroscopy (ICP-OES). Measurement of aerosol characteristics demonstrated that a water-in-oil emulsion was generated. Therefore, once the aqueous solution was dispersed into the sample, the phases spontaneously separated. Furthermore, the interfacial specific surface area exhibited values on the order of 1 m2·mL-1, hence enhancing the extraction kinetics over conventional extraction methods. Key variables affecting the extraction yield were the nebulization gas flow rate, liquid flow rate, extraction time, acid concentration, nebulizer tip to sample surface gap, and morg/maq ratio. Once the optimal conditions were selected, the method was applied and validated for the determination of Ca, K, Na, and Mg by ICP-OES in 0.5 mL biodiesel samples with an expanded uncertainty lower than 2%. With the APE method, the extraction time was around 1 min, whereas conventional methods employed to perform this kind of extraction required from 4 to 50 min. Additionally, the APE involved preconcentration of analytes, thus lowering the limit of detection (LOD) to the nanograms per milliliter level (i.e., LODs based on the 3sb criterion were 32, 20, 19, and 24 ng·mL-1 for Ca, K, Na, and Mg, respectively). Furthermore, accuracy of quantification of Ca, K, Na, and Mg concentration by APE was not significantly different as compared to that afforded by conventional liquid-liquid extraction. Finally, Ca, K, Na, and Mg contents were determined in four real samples in the 0.5-13 mg·kg-1 range. The obtained results were not statistically different from those encountered with a microwave-based digestion method.

Determination of fat-soluble vitamins in vegetable oils through microwave-assisted high-performance liquid chromatography.

In this manuscript, a study of the effect of microwave radiation on the high-performance liquid chromatography separation of tocopherols and vitamin K1 was conducted. The novelty of the application was the use of a relatively low polarity mobile phase in which the dielectric heating effect was minimized to evaluate the nonthermal effect of the microwave radiation over the separation process. Results obtained show that microwave-assisted high-performance liquid chromatography had a shorter analysis time from 31.5 to 13.3 min when the lowest microwave power was used. Moreover, narrower peaks were obtained; hence the separation was more efficient maintaining or even increasing the resolution between the peaks. This result confirms that the increase in mobile phase temperature is not the only variable for improving the separation process but also other nonthermal processes must intervene. Fluorescence detection demonstrated better signal-to-noise compared to photodiode arrayed detection mainly due to the independent effect of microwave pulses on the baseline noise, but photodiode array detection was finally chosen as it allowed a simultaneous detection of nonfluorescent compounds. Finally, a determination of the content of the vitamin E homologs was carried out in different vegetable oils. Results were coherent with those found in the literature.

Microwave high performance liquid chromatography with UV-visible detection. Application to vitamins determination.

The present work describes the first attempt to use microwave reversed phase high performance liquid chromatography (MW-HPLC) to carry out the separation of organic compounds. Biotin and riboflavin were selected for the characterization of the new separation technique. Additional vitamins (nicotinamide, pyridoxine and thiamine) were used as reference compounds. In order to perform the separation, a chromatographic column was placed inside a domestic microwave oven in a hanging position. The column particular location was an extremely critical point, since it precluded the actual power absorbed by the sample. In order to avoid magnetron damage, a heat well (i.e., water vessels) was used. Vitamins were detected using a UV-VIS detector. Results obtained showed that the application of microwave radiation, even at low power levels, gave rise to a significant modification in the characteristics of the chromatograms. It was found that retention times for biotin and riboflavin shortened as the power increased. Furthermore, the peak shape also changed, with the modification being more significant for the former vitamin than for the latter one. Furthermore, sensitivity also increased as the column was exposed to the action of microwave. Comparatively speaking, MW-HPLC was more efficient in terms of compound separation than when performed at room temperature or thermostatted at 45 °C HPLC. This was likely due to the combined action of a moderate and quick heating of the mobile phase with an increase in the analytes diffusivity caused by the radiation.

Rapid and sensitive determination of carbohydrates in foods using high temperature liquid chromatography with evaporative light scattering detection.

In the present work, an evaporative light scattering detector was used as a high-temperature liquid chromatography detector for the determination of carbohydrates. The compounds studied were glucose, fructose, galactose, sucrose, maltose, and lactose. The effect of column temperature on the retention times and detectability of these compounds was investigated. Column heating temperatures ranged from 25 to 175°C. The optimum temperature in terms of peak resolution and detectability with pure water as mobile phase and a liquid flow rate of 1 mL/min was 150°C as it allowed the separation of glucose and the three disaccharides here considered in less than 3 min. These conditions were employed for lactose determination in milk samples. Limits of quantification were between 2 and 4.7 mg/L. On the other hand, a temperature gradient was developed for the simultaneous determination of glucose, fructose, and sucrose in orange juices, due to coelution of monosaccharides at temperatures higher than 70°C, being limits of quantifications between 8.5 and 12 mg/L. The proposed hyphenation was successfully applied to different types of milk and different varieties of oranges and mandarins. Recoveries for spiked samples were close to 100% for all the studied analytes.

Total polyphenol content and metals determination in Spanish virgin olive oils by means of a dispersive liquid-liquid aerosol phase extraction method and ICP-MS.

This report presents a study on the determination of total polyphenols together with metals in several samples of olive oil produced in Spain. The results provided by applying a conventional extraction method were compared against those encountered by means of the so-called Dispersive Liquid-Liquid Aerosol Phase Extraction method. The novel method is based on the dispersion of the extracting solution in the sample. To accomplish this, an aerosol is pneumatically generated and directed against the surface of the oil sample. The aerosol was generated in order to increase as much as possible the surface area of the interface between the two involved non-miscible phases. As a result, the partition equilibrium was quickly achieved. The critical variables dictating the characteristics of the obtained aerosols as well as those influencing the partition equilibrium state were studied. With the aerosol phase extraction method, the values corresponding to the total polyphenols and metals in real samples were not statistically different as compared to those obtained by the conventional liquid - liquid extraction method. The new method provided shorter extraction times and lower mass of consumed reagents than the conventional one, thus giving rise to a more environmentally friendly method. For polyphenols, calculated limits of detection and quantification were 0.48 and 1.5 mg of gallic acid kg-1, respectively. The absorbance linearity, in turn, was kept from 0 to 50 mg kg-1 (R2 = 0.998). In the case of metal and metalloid quantification, the limits of detection found with a sample digestion method ranged from 1.3 (Cu) to 291 (Na) ng mL-1. Meanwhile, because of the lower dilution factor, this parameter was one order of magnitude lower when these elements were extracted according to the new method. The new extraction method was applied to the analysis of 42 extra virgin olive oils both bottled and directly collected from the oil press, containing single cultivars or blends and produced from different areas. Fresh oils were analyzed and a preliminary study on the oil thermal degradation was also done. Dispersing the extracting solution as an aerosol into the sample can be considered a versatile method able to provide extensive oil chemical information in a rapid way what is especially important in the case of polyphenols.

Tools Used to Measure the Physical State of Women with Celiac Disease: A Review with a Systematic Approach.

Celiac disease (CD) is an immunological disorder that mainly affects the small intestine, generating an inflammatory process in response to the presence of gluten (a protein). Autoimmune diseases are part of a group of diseases that are difficult to diagnose without a specific protocol or consensus to detect them due to the number of symptoms and diseases with which it has a relationship. Therefore, the aim of this review was to analyze the diagnostic tools of CD used in middle-aged women, to compare the use and effectiveness of the different tools, and to propose a strategy for the use of the tools based on the results found in the literature. The present research followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. The search was conducted in the following databases: Scielo, PubMed, Web of Science, and Worldwide Science org. In the initial literature search, 2004 titles and relevant abstracts were found. Among them, 687 were duplicates, leaving 1130 articles. Based on the inclusion criteria, only 41 articles passed the selection process; 4 main types of analyses appear in the studies: blood tests, questionnaires, clinical history, and biopsy. It can be said that none of the analyses have a 100% reliability since most of them can present false negatives; therefore, the best way to diagnose celiac disease up to now is through a combination of different tests (Immunoglobulin A and small intestinal biopsy).

Alcohol and metal determination in alcoholic beverages through high-temperature liquid-chromatography coupled to an inductively coupled plasma atomic emission spectrometer.

In the present work, an inductively coupled plasma atomic emission spectrometry (ICP-AES) system was used as a high temperature liquid chromatography (HTLC) detector for the determination of alcohols and metals in beverages. For the sake of comparison, a refractive index (RI) detector was also employed for the first time to detect alcohols with HTLC. The organic compounds studied were methanol, ethanol, propan-1-ol and butan-1-ol (in the 10-125 mg/L concentration range) and the elements tested were magnesium, aluminum, copper, manganese and barium at concentrations included between roughly 0.01 and 80 mg/L. Column heating temperatures ranged from 80 to 175 °C and the optimum ones in terms of peak resolution, sensitivity and column lifetime were 125 and 100 °C for the HTLC-RI and HTLC-ICP-AES couplings, respectively. The HTLC-ICP-AES interface design (i.e., spray chamber design and nebulizer type used) was studied and it was found that a single pass spray chamber provided about 2 times higher sensitivities than a cyclonic conventional design. Comparatively speaking, limits of detection for alcohols were of the same order for the two evaluated detection systems (from 5 to 25 mg/L). In contrast, unlike RI, ICP-AES provided information about the content of both organic and inorganic species. Furthermore, temperature programming was applied to shorten the analysis time and it was verified that ICP-AES was less sensitive to temperature changes and modifications in the analyte chemical nature than the RI detector. Both detectors were successfully applied to the determination of short chain alcohols in several beverages such as muscatel, pacharan, punch, vermouth and two different brands of whiskeys (from 10 to 40 g of ethanol/100 g of sample). The results of the inorganic elements studied by HTLC-ICP-AES were compared with those obtained using inductively coupled plasma mass spectrometry (ICP-MS) obtaining good agreement between them. Recoveries found for spiked samples were close to 100% for both, inorganic elements (with both HLTC-ICP-AES and ICP-MS) and alcohols (with both HTLC-ICP-AES and HTLC-RI hyphenations).

High-temperature liquid chromatography inductively coupled plasma atomic emission spectrometry hyphenation for the combined organic and inorganic analysis of foodstuffs.

The coupling of a High-Temperature Liquid Chromatography system (HTLC) with an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) is reported for the first time. This hyphenation combines the separation efficiency of HTLC with the detection power of a simultaneous ICP-AES system and allows the combined determination of organic compound and metals. The effluents of the column were introduced into the spectrometer and the chromatograms for organic compounds were obtained by plotting the carbon emission signal at a characteristic wavelength versus time. As regards metals, they were determined by injecting a small sample volume between the exit of the column and the spectrometer and taking the emission intensity for each one of the elements simultaneously. Provided that in HTLC the effluents emerged at high temperatures, an aerosol was easily generated at the exit of the column. Therefore, the use of a pneumatic nebulizer as a component of a liquid sample introduction system in the ICP-AES could be avoided, thus reducing the peak dispersion and limits of detection by a factor of two. The fact that a hot liquid stream was nebulized made it necessary to use a thermostated spray chamber so as to avoid the plasma cooling as a cause of the excessive mass of solvent delivered to it. Due to the similarity in sample introduction, an Evaporative Light Scattering Detector (ELSD) was taken as a reference. Comparatively speaking, limits of detection were of the same order for both HTLC-ICP-AES and HTLC-ELSD, although the latter provided better results for some compounds (from 10 to 20 mg L(-1) and 5-10 mg L(-1), respectively). In contrast, the dynamic range for the new hyphenation was about two orders of magnitude wider. More importantly, HTLC-ICP-AES provided information about the content of both organic (glucose, sucrose, maltose and lactose at concentrations from roughly 10 to 400 mg L(-1)) as well as inorganic (magnesium, calcium, sodium, zinc, potassium and boron at levels included within the 6-3000 mg L(-1)) species. The new development was applied to the analysis of several food samples such as milk, cream, candy, isotonic beverage and beer. Good correlation was found between the data obtained for the two detectors used (i.e., ICP-AES and ELSD).

Simultaneous determination of carbohydrates, carboxylic acids, alcohols, and metals in foods by high-performance liquid chromatography inductively coupled plasma atomic emission spectrometry.

The applicability of the HPLC-ICP-AES coupling for the simultaneous determination of carbohydrates, carboxylic acids, alcohols, and metals in a single chromatographic run has been demonstrated in the present work. Five saccharides, glucose, fructose, sucrose, sorbitol, and lactose; five carboxylic acids, citric, tartaric, malic, lactic, and acetic; and three alcohols, glycerol, ethanol, and methanol, have been determined. A H+ cation exchange column has been used to separate these compounds. The chromatograms have been obtained by monitoring the carbon emission signal at 193.09 nm. The results obtained by HPLC-ICP-AES have been compared against those found with conventional detection systems (i.e., refractive index, UV, and photodyode array detectors). The HPLC-ICP-AES method has shown the following features: (i) organic compounds and metals can be simultaneously determined; (ii) the detection method is universal; (iii) for nonvolatile organic compounds, a complete calibration line can be obtained from a single injection; and (iv) it provides absolute limits of detection similar to or lower than those found with conventional detection systems (i.e., on the order of several tens of nanograms of organic compound). The methodology has been validated through the analysis of food samples such as juices, isotonic beverages, wines, and a certified nonfat milk powder sample.