Fast Determination of Toxic Arsenic Species in Food Samples Using Narrow-bore High-Performance Liquid-Chromatography Inductively Coupled Plasma Mass Spectrometry.

A new method for the speciation analysis of arsenic in food using narrow-bore high-performance liquid-chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) has been developed. Fast separation of arsenite, arsenate, monomethylarsonic acid and dimethylarsinic acid was carried out in 7 min using an anion-exchange narrow-bore Nucleosil 100 SB column and 12 mM ammonium dihydrogen phosphate of pH 5.2 as the mobile phase, at a flow rate of 0.3 mL min(-1). A PFA-ST micronebulizer jointed to a cyclonic spray chamber was used for HPLC-ICP-MS coupling. Compared with standard-bore HPLC-ICP-MS, the new method has provided higher sensitivity, reduced mobile-phase consumption, a lower matrix plasma load and a shorter analysis time. The achieved instrumental limits of detection were in the 0.3 - 0.4 ng As mL(-1) range, and the precision was better than 3%. The arsenic compounds were efficiently (>80%) extracted from various food samples using a 1:5 methanol/water solution, with additional ultrasonic treatment for rice products. The applicability of this method was demonstrated by the analysis of several samples, such as seafood (fish, mussels, shrimps, edible algae) and rice-based products (Jasmine and Arborio rice, spaghetti, flour, crackers), including three certified reference materials.

High temperature liquid chromatography-inductively coupled plasma mass spectrometry for the determination of arsenosugars in biological samples.

The potential of high temperature liquid chromatography (HTLC) with detection by inductively coupled plasma mass spectrometry (ICP-MS) for the determination of arsenosugars in marine organisms was examined for the first time. The retention behavior of four naturally occurring dimethylarsinoylribosides was studied on a graphite column using plain water as mobile phase. An aqueous solution of pH 8, ionic strength 13.8mM and containing 2% (v/v) of methanol, along with a column temperature of 120°C and a liquid flow rate of 1.0 mL/min, were selected as the optimal conditions, as they allowed the separation of the four arsenosugars in less than 18 min, without any interferences due to other common arsenic species (arsenite, arsenate, dimethylarsinate, methylarsonate and arsenobetaine). The run time could be further decreased to 12 min by working at 1.5 mL/min, although with a 3-4 times loss of sensitivity. The procedural limits of detection were 0.03-0.04 µg As/g dry mass, and the precision of the procedure ranged from 4% for arsenosugar glycerol to 18% for arsenosugar sulfate (RSD%, n=5). The developed method was applied to a number of representative biological samples, such as algae and crustaceans, providing results consistent with previous studies. In the red algae samples, the most of extracted arsenic was as arsenosugars (81-97%), mainly arsenosugar phosphate (56-94%). On the other hand, lower concentrations of these compounds were found in the crustacean, accounting for about 15% of the extracted arsenic.

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.

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.

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).