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 KClO(4) 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.

Rapid analytical method for the determination of organic and inorganic species in tomato samples through HPLC-ICP-AES coupling.

A HPLC-inductively coupled plasma atomic emission spectrometer (ICP-AES) hyphenation technique was used to determine the concentration of some organic (i.e., carbohydrates, carboxylic acids) as well as inorganic (metals and anions) compounds in tomato samples. A high efficiency nebulizer (HEN) coupled to a low inner volume cyclonic spray chamber (Cinnabar) was used to interface both techniques. The HPLC-ICP-AES chromatograms for organic compounds were obtained by plotting the 193.03nm carbon emission intensity versus time. In the present work, it was also possible to obtain information about the concentration of several metals in foodstuffs. Finally, by registering the intensity at the sulphur and phosphorous emission wavelengths, the content of anions such as sulphate and phosphate was determined. In general terms, the results obtained with HPLC-ICP-AES did not differ significantly from those found with a refractive index detector. Due to the huge amount of information provided by this hyphenation, it was possible to apply it to the discrimination among different samples of native tomato cultivars.

A new continuous calibration method for inductively coupled plasma spectrometry.

A new calibration method was developed and applied to inductively coupled plasma atomic emission spectrometry. External calibration was performed as follows. A container was filled with a given volume of deionized (V(p)) water. Then a concentrated standard was introduced at a controlled rate (Q(e)) into the tank by means of a peristaltic pump. The resulting solution was stirred throughout the experiment. Simultaneously, the solution inside the tank was pumped from the vessel to the plasma at a given rate (Q(s)). The signal was continuously recorded. The variation of the concentration of the solution leaving the tank with time was determined by applying a basic equation of stirred tanks. The representation of the emission intensity versus the time and the further conversion of the time scale into a concentration scale gave rise to the calibration line. The best results in terms of linearity were achieved for V(p)=15 cm3, Q(e)=0.6-0.75 ml min(-1) and Q(s)=1-1.2 ml min(-1). Graphs with more than 40 standards were obtained within about 10 min. The results found were not statistically different from those afforded by the conventional calibration method. In addition, the new method was faster and supplied better linearity and precision than the conventional one. Another advantage of the stirred tank was that procedures such as dynamic calibration and standard additions could be easily and quickly applied, thus shortening the analysis time. A complete analysis following these procedures based on the measurement of 30 standards took about 5 min. Several synthetic as well as certified samples (i.e., bovine liver, mussel tissue and powdered milk) were analyzed with the stirred tank by applying four different calibration methodologies (i.e., external calibration, internal calibration, standard additions and a combination of internal standardization and standard additions), with the combination of internal standardization and standard additions being the method that provided the best results. The element concentrations obtained were not significantly different from the actual or certified values.

Evaluation of several pneumatic micronebulizers with different designs for use in ICP-AES and ICP-MS. Future directions for further improvement.

This paper reports characterization of the behavior of five pneumatic micronebulizers based on slightly different designs in inductively coupled plasma atomic-emission spectrometry and mass spectrometry (ICP-AES and ICP-MS). Two nebulizers were used as reference nebulizers, a high-efficiency nebulizer (HEN) and a micromist (MM). They were compared with a commercially available PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) nebulizer and with two new prototypes called the polymeric pneumatic concentric nebulizer (PMN) and the high-solids micronebulizer (HSM). The dimensions of the nebulizers, the gas back-pressure, and the free liquid uptake rates were measured. The study also included tertiary aerosol drop-size distributions, analyte transport rate, and analytical figures of merit, i.e. sensitivities and limits of detection, both in ICP-AES and ICP-MS. Recoveries for two food solid reference materials were also determined. Overall, the results indicated that the PFA and the HEN nebulizers provided the best results. These two nebulizers delivered a higher mass of analyte to the plasma and showed better sensitivies giving lower limits of detection than the PMN, HSM and MM. The results revealed that the liquid prefilming effect occurring before aerosol production in the PFA nebulizer promoted more efficient interaction of liquid and gas, thus affording good results even though gas back-pressure values could be maintained below 3 bar. In contrast, the HEN had to be operated at about 7 bar under the same conditions. Nebulizer design did not have a relevant effect on the recovery, which confirmed that the spray chamber plays an important role in terms of non-spectroscopic interferences.

A system for the direct determination of the nonvolatile organic carbon, dissolved organic carbon, and inorganic carbon in water samples through inductively coupled plasma atomic emission spectrometry.

A new system has been developed for the determination of total organic carbon (TOC) and inorganic carbon (IC) or total inorganic carbon (TIC) in waters. Only nonvolatile organic compounds can be detected through the present method. The system presented in this work is based on the measurement of the carbon atomic emission intensity in inductively coupled plasma atomic emission spectrometry (ICP-AES). This way, the organic matter does not undergo any preoxidation step. A semiautomatic accessory connected to the spectrometer separates the different carbon fractions (i.e., organic and inorganic). Because most of the solutions used in the present work did not contain suspended solid particles, the actual parameter that was determined was the dissolved organic carbon (DOC). The present system exhibits good sensitivities compared to those provided by conventional TOC and IC determination methods. The limits of detection obtained in the present work have been 0.07 and 0.0007 mg/L C in terms of TOC and IC, respectively. Furthermore, the system is able to handle high-salt-content solutions. This fact suggests that it would be possible to analyze seawater samples, avoiding some of the problems encountered with conventional methods, such as system blocking or interferences. The TOC and IC values found for natural samples are very close to those measured using conventional methods. The ICP-AES method has been successfully used in two interesting applications: (i) monitoring the efficiency of a water treatment plant and (ii) determining the contents of dissolved carbon dioxide, on one hand, and that of carbonate and bicarbonate, on the other, in the same sample.