Potential matrix interferences were compensated for using the method of additions for calibration. Although quantitative recovery of these elements was earlier reported when the digests were analyzed by graphite furnace atomic absorption spectrometry GF AAS , 3 it was evident that complete solubilization of the matrix is not achieved without the additional heating step. Since the digests were filtered prior to analysis in this study, whereas they were directly sampled for determination by GF AAS by Scriver et al.
Selenium, mainly present as selenocysteine and selenomethionine amino acids in tissue samples, 16 may be difficult to recover with use of formic acid unless elevated temperatures are used 17 , 18 and thus recovery of Se is not satisfactory if undigested proteins are removed by filtration prior to analysis of unheated mixtures.
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The presence of a residue requiring filtration leads to the conclusion that even with the addition of the heating step, extraction, rather than solubilization, is achieved. The desirability function is a popular and established methodology for system optimization based on multiple input responses; the approach modified by Deringer and Suich 19 described the relationship between response and dependent variables utilizing a desirability function which identifies the optimal compromise conditions.
The response Y in a desired individual function d can range from 0 representing a completely undesirable value to 1 representing an ideal response value. It is evident that there is a large increase in the desirability 0. US time.
On the other hand, recovery of Mn, Ni, Pb and V was readily achieved by following the simplified digestion procedure. The optimized compromised response for all elements was obtained using the following formic acid extraction procedure: 0. Table 2 summarizes estimated limits of quantification LOQ calculated as fold the standard deviation of 10 replicate measurements of the blank divided by the slope of the analytical calibration curve and multiplied by the sample dilution factor.
The LOQs for Al, As and Ba improved from 6- to 8-fold with formic acid extraction; Mn and Ni improved 5-fold and even Se presented a 3-fold better LOQ using this approach compared to analysis following microwave-assisted digestion with nitric acid. Measurement sensitivity increased for all elements in the formic acid medium. Whole and defatted Brazil nut samples were processed with HCOOH using the optimized procedure identified by the experimental design.
The presence of carbon in the plasma may affect response as a consequence of both spectral and matrix interferences. Reports of concentrations of Se and Ba in Brazil nuts reveal substantial variability; 12 - 15 , 23 there is consensus that levels of Se in the nut kernels may vary with geographic location and soil characteristics in which they have been grown. Naozuka et al. Selenium content was not measured, probably due to an insufficient LOQ available with the inductively coupled plasma optical emission spectrometry ICP-OES detection method used. Parekh et al. These authors encountered a range of 0.
In the present work, concentrations of Ba averaging mg kg -1 were obtained in the whole Brazil nuts.
In the same manner, the concentrations summarized in Table 3 for other micronutrients in the Brazil nuts studied here, such as Mn and Zn, are comparable to those reported by Naozuka et al. Results for the analysis of solutions prepared by microwave-assisted nitric acid digestion of these samples were compared to those obtained by formic acid extraction so as to calculate recoveries using the latter procedure. However, low recoveries are evident for Al in both the whole and defatted samples of the nut.
This aspect needs further study. Freeze-dried whole and defatted fractions of babassu coconut samples were also extracted with HCOOH using the earlier established optimized procedure. Results obtained for the determination of the trace elements are summarized in Tables 5 and 6. As the microwave-assisted acid digestion methodology was previously validated Table 1 , such results were used as reference values for calculation of recoveries of elements subjected to the formic acid extraction procedure. It is important to emphasize that the concentration levels of the elements found in such almonds can be different and are dependent on the plant physiology as well as characteristics of the soil in which they are grown.
Each species has its own capacity to uptake and accumulate various elements, 1 , 22 despite their being harvested from the same geographic region of Brazil, i. In contrast to the Brazil nuts, concentrations of Se and Ba present in babassu coconut are much lower, 0. Babassu coconut presents concentrations of Al and Zn comparable to those reported by Naozuka et al. Formic acid extraction of the elements from the oil fractions derived from the samples was not efficient. However, microwave-assisted digestions of this fraction allowed quantitation of the trace elements by ICP-MS.
Table 7 summarizes the trace element content in the oil fraction derived from both materials. These trends compliment results reported by Welna et al. Although babassu oil is widely used in the manufacture of cosmetics and is used in foods, there are unfortunately no published studies concerning the composition of trace elements in this nut sample. As solutions obtained following the described ultrasound and heating steps using formic acid required filtering prior to analysis, it is clear that this process is equivalent to an "extraction", rather than a complete solubilization or digestion.
Filtration precluded any problems with particles clogging the nebulizer; obviously, this does not impact the analysis of such preparations when determinations are performed by GF AAS, in which case the process may be considered to be a solubilization. Nevertheless, a formic acid extraction approach provides a greener, simpler and less expensive alternative to acid digestions for sample preparation for the subsequent determination of trace elements in such samples.https://tolucalrutus.cf
Routine Maintenance in ICP-MS: Critical When Monitoring Elemental Impurities in Complex Samples
Moreover, the resultant digests may be suitable for direct use of photochemical vapor generation for a number of these elements 25 to enhance sample introduction efficiency and improve LOQs. Optimization of the extraction procedure using chemometric tools allows mapping the entire experimental domain studied. Thus it may be inferred that some elements Mn, Ni, Pb, Sr and V are readily extracted following the simplified procedure as described in the literature.
Treatment of the oil fractions with formic acid in an attempt to extract them was unsuccessful. More studies are needed to thoroughly investigate this approach. The relatively high fractions of elements such as Cr and Ni remaining in the lipid phase may be of interest from the perspective of speciation of these elements. To date, only speciation of Se has been studied. Acta, Part B , 61 , Acta, Part B , 65 , Acta , , 1.
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