Amanda Terol

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.

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).

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 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.

Influence of chemical species on the determination of arsenic using inductively coupled plasma mass spectrometry at a low liquid flow rate

The effect of common arsenic species on the ICP-MS signal working at a low liquid flow rate was investigated, taking into account the influence of the analytical concentration and of the matrix, comparing various sample introduction systems. Significant decrease (up to 65%) in the relative sensitivity of arsenite compared to arsenate was found, while methylarsonate, dimethylarsinate and arsenobetaine gave the same response (within 6%) as arsenate, throughout the 20–1000 μL min−1 liquid flow rate range. The effect was independent of the analytical concentration in the 1–100 μg L−1 range, and it was ascribed to processes related to both the sample introduction system and the ion generation and transport. Ion defocussing due to dissimilar kinetic energy of the arsenic ions generated from arsenite and arsenate was ruled out. Results obtained by various micronebulizer/spray chamber configurations showed that the temperature of the spray chamber is relevant in determining the relative responses of the arsenic species: heating the spray chamber at 60 °C caused a decrease in relative sensitivity of arsenite and dimethylarsinate compared to arsenate, while the arsenite-to-arsenate signal ratio was improved by cooling at 4 °C. The relative response of arsenite and arsenate was also significantly influenced by the presence of ammonium phosphate, which mitigated the difference between the species using conventional sample introduction devices. The influence of the chemical species on the ICP-MS signal was also investigated for species of other elements, finding significant differences in sensitivity for Hg, Se and Sn compounds when working at a low liquid flow rate. The results proved to have an effect on the accurate quantification of total concentration, as well as for arsenic speciation analysis by μHPLC/ICP-MS.

Simple and rapid analytical method for the simultaneous determination of cetrimonium chloride and alkyl alcohols in hair conditioners

A simple method for the simultaneous determination of a cationic surfactant (cetrimonium chloride) and four non‐ionic surfactants (1‐tetradecanol, 1‐hexadecanol, 1‐octadecanol and 1‐eicosanol) has been developed. Direct extraction of the analytes from the sample with methanol and a subsequent separation using reversed‐phase high‐performance liquid chromatography with refractive index detection are the steps followed in the procedure. The column used was a Luna C18 and the mobile phase consisted of a 0.1 M KClO4 solution prepared on a 95:5 mixture of methanol and water. This solution was adjusted to pH 2.8 with phosphoric acid. Recoveries close to 100% were obtained in spiked commercial hair conditioner samples for the surfactants assayed using this method. Limits of detection were 10.4, 16.7 and 22.9 mg kg−1 of cetrimonium chloride, 1‐hexadecanol, 1‐hexadecanol and 1‐1‐octadecanol respectively. The methodology was successfully applied to nine commercial hair conditioners of several types and different brands. All hair conditioners but one contained at least two of the surfactants included in this study.

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.

CHAPTER 25:Determination of Maltose in Food Samples by High-temperature Liquid Chromatography Coupled to ICP-AES

In this chapter, we will discuss the use of High Temperature Liquid Chromatography (HTLC) to carry out food analysis. Attention will be paid to the coupling of this separation technique to an Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). As regards the determination of maltose, it has been traditionally carried out through High Performance Liquid Chromatography (HPLC) coupled to several detectors such as refractometric index (RI) and Visible-Ultraviolet detector (VIS-UV). Additional detectors have been applied to the sugar determination such as the Evaporative Light Scattering Detector (ELSD), with good results. Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES) has been used as a HPLC detector providing information of both organic as well as inorganic compounds in food samples. The High Temperature Liquid Chromatography Inductively Coupled Plasma Atomic Emission Spectrometer (HTLC-ICP-AES) hyphenation is thus interesting because of the shortening in retention times, with the concomitant reduction in the cost of the analysis. All these points are commented in the present chapter together with selected applications in which maltose has been determined in food samples.