Evaluation of Major and Trace Elements in Medicinal Plants

This study presents the elemental concentration results obtained from 59 medicinal plants used in Brazil, determined by instrumental neutron activation analysis (INAA), inductively coupled plasma-optical emission spectrometry (ICP OES) and cold vapor atomic absorption spectrometry (CV AAS). The selected plant species were chosen from the Brazilian National Agency for Sanitary Vigilance (ANVISA) list of herbs recommended for utilization by the Public System of Health in Brazil (SUS). The results showed that high levels of foreign matter were found in almost 50% of the analyzed samples. The concentration of the elements varied in a wide range, although, generally in accordance with values found in literature. High concentrations of Ba, Cr, Fe, Hg, Se and Ni were found in some samples. The enrichment factor indicated that potentially hazardous elements can be accumulated mainly in the bark of the plants, possibly indicating an anthropogenic contribution.


Introduction
3][4][5] The growing interest in this type of health care has also been accompanied by effectiveness, availability, preservation, quality, safety and regulation concerns.Therefore, the World Health Organization has also set out the need for quality control standards of medicinal plants including classification, botanical identification, active compounds determination and contaminant identification, following the recommendation of the World Health Assembly. 6As a global strategy for traditional and complementary medicine, the WHO has stimulated the State Members to develop public policies in order to include herbal medicines and phytotherapics in their public health system. 1 Besides being used for the treatment of diseases, the medicinal plants are also used as dietary supplements once they are found to be rich in one or more elements.
Elemental content in medicinal plants can vary in a wide range, depending on factors such as soil geochemical characteristics, atmospheric deposition and the ability of each plant species to selectively accumulate some of them. 7,8Nevertheless, medicinal herbs can be easily contaminated during growth, development and processing.
The determination of major, minor and trace elements in medicinal plants and their impacts on human health are also of great importance due to the growth of environmental pollution that directly affects the plants and, therefore, their phytotherapics.][11] Brazil possesses one of the greatest vegetal genetic diversity of the world, accounting for approximately 20% of all known living species globally; 12 over one thousand species of plants are estimated to be used as medicine by the population.However, to be used by the Public System of Health, the National Agency for Sanitary Vigilance establishes that toxicological risks and the absence of toxic chemical substances must be within safe proven limits.
Despite the richness of the Brazilian flora, the extensive use of medicinal plants by the population and the importance exerted by trace elements in the human metabolism 13 lead to a consensus that scientific studies on elemental concentrations in medicinal plants are insufficient in view of the importance of these results, considering individual and social consequences.
Therefore, the objective of this paper was to determine the content of inorganic constituents in herbal medicines: moisture, ash, insoluble acid ash and the element concentrations of As, Ba, Br, Ca, Cl, Co, Cr, Cs, Fe, Hf, K, Na, Mg, Mn, Rb, Sb, Sc, Se, Ti, V and Zn, by instrumental neutron activation analysis (INAA); Cd, Cu, Ni and Pb by inductively coupled plasma-optical emission spectrometry (ICP OES) and Hg by cold vapor atomic absorption spectrometry (CV AAS).The results were used to verify the quality of the products, the range of concentrations found in plants commonly used in folk medicine and whether these concentrations are within the safe limits stated by reference standards of intake, when existent.To verify the distribution pattern of the elemental concentrations, statistical analysis (correlation coefficient, cluster analysis and principal component analysis) was also applied to the results.As far as we know, the concentration of the elements proposed to be determined in this study has not been determined before, for the majority of the plants.

Experimental
Plant species were chosen from a list of 66 herbs recommended by the Brazilian National Agency for Sanitary Vigilance (ANVISA) to be used in the Public Health System.From this list, 59 species, in the form of dried material, were found in specialized pharmacies and drugstores.The plant names, used parts and medicinal applications are listed on Table 1.

Search for foreign matter
Foreign matter, as defined by WHO, is any part of the medicinal plant material or materials other than those named with the limits specified for the plant material concerned; any organism, part or product of an organism, other than that named in the specification and description of the plant material concerned or; any mineral admixtures not adhering to the medicinal plant materials, such as soil, stones, sand, and dust. 14or foreign matter determination, the whole sample pack, after being precisely weighed, was spread above a white and clean surface and any strange material was removed.Particles of soil, stone, sand, insects or parts of insects, as well as any part of the plant other than that indicated for use was considered foreign matter.Signs of mould, abnormal odor, discoloration, slime and deterioration were, also, searched. 14

Moisture determination
For moisture determination, approximately 10 g of each sample was weighed in analytical balance and let to stand in an oven at temperature varying from 100 to 105 ºC, until constant weight, being weighed after cooling in a desiccator. 14

Ash
The inorganic ash determination was done by calcinating the sample used in the moisture determination in a muffle, at 900 ºC, for 2 hours.The residue was allowed to cool in a desiccator and weighed.

Insoluble acid ash
The residue obtained in the inorganic ash determination was then treated with 25 mL of ultrapure concentrated HNO 3 , filtered in paper filter.The paper was washed with 5 mL of ultra-pure water and let to dry in a ventilated furnace oven.The insoluble acid ash amount was determined by the difference in the filter paper weigh before and after the filtration.

INAA measurement
][17] For the INAA determinations, the raw plant samples were dried in a ventilated furnace oven at 40 to 45 ºC and then powdered to a grain size lower than 0.150 mm.Approximately 150 mg of the powdered samples and 100 mg of powdered reference materials (United States Geological Survey-USGS-Rhyolite, Glass Mountain, RGM-2 and Syenite, Table Mountain, STM-2) were sealed in pre-cleaned polyethylene bags.Synthetic standards were also prepared by pipetting convenient aliquots of standard solutions (SPEX Certiprep Inc., USA) using Milli-Q water 18.2 MΩ cm at 25 °C (Millipore Corporation, USA), onto small filter paper sheets.The plant samples, reference materials and synthetic standards were irradiated for 8 h, in the IEA-R1 nuclear reactor at IPEN (Instituto de Pesquisas Energéticas e Nucleares, Brazil), for As, Ba, Br, Ca, Co, Cr, Cs, Fe, Hf, K, Na, Rb, Sb, Sc, Se, and Zn determination and for 20 s for Cl, Mg, Mn, Ti and V determination under a thermal neutron flux of 1-5 × 10 12 cm -2 s -1 .The counting was done at different time frames, depending on the radionuclide half-live produced during the irradiation: this process was performed by Gamma Spectrometry, using an EG&G Ortec Ge Highpure Gamma Spectrometer detector (AMETEK Inc., USA) and associated electronics, with a resolution of 0.88 and 1.90 keV for 57 Co and 60 Co, respectively.The analysis of the data was done by using an in-house gamma ray software, VISPECT program, to identify the gamma-ray peaks.The methodology precision and accuracy were verified by using, as Standard Reference Materials (SRM) from the National Institute of Standards and Technology (NIST), apple leaves (NIST SRM 1515), peach leaves (NIST SRM1547) and tomato leaves (NIST SRM1573a).

ICP OES and CV AAS measurement
For the determination of Cd, Cu, Ni and Pb, approximately, 300 mg of each dried and powdered sample were dissolved with a mixture of concentrated acids (HNO 3 , HCl, HClO 4 ) and H 2 O 2 ; all reagents were of analytical grade, and digested in a MARS 5 (CEM Corporation, USA) microwave closed system.After the digestion process, the samples were allowed to cool and filtered.The concentrations were determined by using a Spectro Flame M120E ICP OES (AMETEK Inc., USA).For the determination of Hg by CV AAS, the same digested samples were measured by using a PerkinElmer AANALYST 800 instrument.The methodology precision and accuracy were verified by using the reference materials apple leave (NIST SRM 1515) and peach leave (NIST SRM1547).The detailed methodology for ICP OES and CV AAS measurements, as well as the calibration curves used for the concentrations in all the samples are presented in the literature. 18

Results
Table 2 shows the percentages of foreign matter, moisture, ash, insoluble acid ash and the permitted amounts of these parameters, according to the Brazilian Pharmacopeia. 19nless specified elsewhere, the total permitted foreign matter is 2% in the dried raw material.Among the analyzed samples, 47% showed foreign matter content above the recommended levels, with the highest values over 60%  2. Foreign matter quantities (FM), permitted foreign matter (PFM), moisture (M), permitted moisture, permitted moisture (PM) total ash (TA), permitted total ash (PTA) insoluble acid ash (IAA) and permitted insoluble acid ash (PIAA) (cont.) and the main foreign matter found was represented by parts of the plant other than what was indicated for use.Soil particles were, also, detected, but in small amounts.Moisture was found varying from 4 to 12% and only three samples showed values above the permitted levels: Allium sativum, Citrus auranrium and Illicium verum.However, it was noted that the majority of the samples had moisture contents close to the recommended.High moisture percentage may favor the appearance of mould, slime and plant deterioration.The amount limit of permitted ash was not found in the Brazilian Pharmacopeia, for all of the analyzed plants and among those which presented it, only four possess ash content higher than the limits: Arctium lappa, Cinnamomum verum, Illicium verum and Taraxacum officinalles.Just a few plants showed the permitted values for insoluble acid ash and only in Passiflora alata and Peumus boldus the measured values were higher.
The amount of ash is related to the physiological and non-physiological inorganic material content.The obtained inorganic ash indicates the presence of non-physiological inorganic material that can be related to inorganic waste contaminants.
The precision and accuracy of the method evaluated by analyzing certified reference material are shown in Table 3, for the results obtained by INAA, and in Table 4, for the results obtained by ICP OES and CV AAS for quality measurement and control purposes.It can be seen that the relative errors are generally less than 20%, for most of the elements.Exceptions are K in peach leaves and Co in tomato leaves.Nevertheless, the general results were considered satisfactory regarding the low levels of concentrations normally observed in plant material.Cadmium concentrations in these reference materials was below the detection limit for ICP OES applied methodology (0.06 mg kg -1 ).The results obtained for the element concentrations in the samples, all in dry basis, are shown in Table 5. Blanks in Table 5 mean values below the limit of detection (LOD), presented by Francisconi. 18t can be noted, from the data in Table 5 that the concentration in the medicinal plant samples varies in a wide range for almost all the elements.The main reason for this variation certainly must be the fact that different species and different plant parts were analyzed.Furthermore, water sources, climatic conditions and environmental pollution must also contribute for the variation. 20

Discussion
Good quality control of medicinal plants is important, since they are normally consumed without any limitation.It is almost a consensus that, being a natural product, they do not pose any harm to health.Concerning the element concentrations present in medicinal plants, besides the essential elements, they also may contain toxic and non-toxic elements, but, in concentrations above the permissible levels.
In fact, among the elements determined in this paper, only As, Cd and Pb has been limited by WHO 14

Scientific name
Pb / (mg kg -1 ) Rb / (mg kg -1 ) Se / (mg kg -1 ) Ti / (mg kg -1 ) V / (mg kg -1 ) Zn / (mg kg -1 ) A. montana 0.5 ± 0. used as raw material, in concentrations of 1.0, 0.3 and 10 mg kg -1 .Observing the data in Table 5, it can be noted that this value exceeded by 15% of the samples for Pb, by 5% of the samples for Cd and in no sample for As.Mentha pulegium showed the highest concentrations for the elements Co, Fe, Sc and Ti and relatively high concentrations for the elements Ba, Cr, Cs, Hf, Na, Sb, V, Zn; Taraxacum officinale showed the highest concentration for As and relatively high concentrations for Ba, Br, Co, Cs, Fe, Hf, Hg, Rb, Sc, Ti, V, Zn; Salvia officinalis showed the highest concentrations for the elements Cu, Hf and V and relatively high concentrations for Ca, Co, Cs, Fe, Hf, Mg, Ni, Sb, Sc, Ti, Zn; Agerantum conyzoides showed the highest concentrations for Mg and relatively high concentrations for Ba, Br, Co, Fe, Na, Sb, Sc, Ti, V; the highest concentration of Cd, Pb and Hg was observed in the samples of Vernonia polyanthes, Eugenia uniflora and Eucalyptus globulus, respectively.High concentrations were also observed in Malva sylvestris for Ba, Br, Cr, Fe, Hf, K, Mg, Sc, Ti, V and Zn and in Passiflora incarnate, for Br, Cr, Cs, Fe, Hf, Hg, Sb, Sc, Se, Mn and Zn.

Major elements
Calcium is an essential element for plants and its content varied from 0.035 to 2.4% in the samples of Allium sativum and Caesalpinia ferrea, respectively.Low Ca concentrations were also found in the literature for Allium sativum 21 and high concentrations, varying from 1.5 to 2.0%, 7,22 have been found in Glycyrrhiza glabra and Malva sylvestris.Compared with our results, the highest values are in the same order of magnitude and the lowest are well below the reported figures.Potassium, an essential element that is generally supplied to plants by means of fertilization processes also showed a wide variation with a higher value found in Echinodorus macrophyllus.In the plants with this element, the concentrations determined ranged from 0.16 to 7.4%.Magnesium, besides being a chlorophyll component is also an enzyme co-factor. 23ts concentration varied from below LOD up to 1.14% in the sample of Agerantum conyzoides and these values are in good agreement with the literature, registering concentrations which vary from 0.0004 to 2.3% in Melissa officinales and Matricaria recutita samples, respectively. 22,24Another essential element for plants, Cl concentrations varied from below LOD up to 1.8% in the Equisetum arvense sample.

Minor elements
Iron and manganese are essential elements for plant protein synthesis. 25Allium sativum was the sample with the lowest Fe value, while the highest was registered in the Mentha pulegium sample: the range of variation for this element was from 26 to 12259 mg kg -1 , respectively.The range of Fe concentrations, found in the literature, 26,27 vary from 6.7 to 1787 mg kg -1 , considering the same plant species included in this study.Manganese concentrations varied from 2.4 to 1046 mg kg -1 in Punica granatum and Mikania glomerata, respectively.
Copper is a micronutrient and an essential enzymatic element for normal plant growth and development, but it can be toxic at excessive levels and it is a harmful element for human health. 28The concentrations here obtained varied from 1.88 to 24.5 mg kg -1 in samples of Rhamnus purshiana and Salvia officinalis, respectively.These values are in well agreement with those found in the literature, which vary from 0.1 mg kg -1 in Zingirber officinale up to 27.4 mg kg -1 in Plantago major, 29,30 although higher concentrations, up to 177 mg kg -1 , had been reported for Aesculus hippocastanum leaves. 31Ni concentrations varied from 0.4 mg kg -1 in Allium sativum to 53 µg kg -1 in Momordica charantia samples.It was observed that the concentration of this element, for most of the species, were in agreement with values found in the literature, 32,33 varying from 0.32 to 6.7 µg kg -1 in samples of Cinnamomum verum and Anacardium occidentales, respectively, although approximately one quarter of the samples showed an enrichment for this metal.Zinc is an essential element for plants and animals whose biological functions can be catalytic, structural or regulatory.In this study, Zn concentrations varied from 7.4 mg kg -1 in Rhamnus purshiana to 169 mg kg -1 in Equisetum arvense samples.The literature 34,35 reported values showing variations ranging from 0.86 to 168 mg kg -1 in Aesculus hippocastanum and Bidens pilosa, respectively.

Other trace elements
Barium was found in the range of 2 to 390 mg kg -1 in Cinnamomum verum and Schinus terebinthifolia, respectively.Reported concentrations 32,36 vary from 2 to 100 mg kg -1 , indicating that some of the herbs here analyzed are enriched with this element.Enrichment in some herbs can also be observed for Br.For this reported concentrations 37,38 vary from 2 to 45 mg kg -1 and, in the samples analyzed in this study, varied from 0.7 to 168 mg kg -1 , for Illicium verum and Echinodorus macrophyllus, respectively.The values found for Se in the literature 33,37 range from 76 to 500 µg kg -1 , in samples of Anacardium occidentale and Curcuma longa, while the values obtained in this study ranged from 31 to 1100 µg kg -1 in Eugenia uniflora and Senna alexandrina, also, indicating a Se enrichment in the present samples.
Concentrations of Co varying from 69 to 9100 µg kg -1 were found in our samples, with the lowest values in Passiflora alata and the highest in Mentha pulegium while reported values ranges from 17 to 1200 µg kg -1 in Allium sativum and Malva sylvestris, respectively. 22,37hromium(VI), which is a by-product of numerous industrial processes, is recognized as a carcinogen when inhaled and Cr III is the most stable oxidation state and, presumably, the form that is present in food supply, due to the presence of reducing substances. 39he levels of Cr in our samples ranged from 0.5 to 256 mg kg -1 in the samples of Paulinia cupana and Aesculus hippocastanum, respectively: some samples showed higher values than those found in the literature, 33,40 which ranged from 0.012 to 115 mg kg -1 in samples of Anacardium occidentale and Casearia sylvestris, respectively.
Very few values have been reported in the literature for Cs, Hf, Rb, Sb, Sc, Ti and V in the same species here analyzed.
The elements Rb, Sc and Sb were found in the range of 2.6 to 229, 1.2 to 3660 and 5 to 90 µg kg -1 , respectively.The reported values in the literature are 2 to 80, 41,40 0.14 to 10.3 25,40 and 0.4 to 20000 µg kg -1 , 33,34 respectively.The plants with higher concentrations for these elements, observed in this study, were Equisetum arvense for Rb and Sb and Mentha pulegium for Sc.As to the values found in the literature, Casearia sylvestris showed the highest concentration of Rb and Sc 40 and Equisetum arvense of Sb. 35 Vanadium concentrations were found varying between below LOD up to 8.2 µg kg -1 in the sample of Salvia officinalis, what was consistent with those values found in the literature.The results obtained for Ti showed enrichment in some of the medicinal plants here analyzed with concentrations reaching values up to 644 µg kg 1 , once a range varying from 1.4 to 57 µg kg -1 was verified for plants of the same species. 22,25esium was found in values up to 1.19 mg kg -1 in Curcuma longa 37 and compared to our samples about half of the plants, in which this element was measured, contain higher levels of this element.A concentration of 53 µg kg -1 is registered for Hf in Anacardium occidentale and this value is much lower than that encountered in almost all the herbs here analyzed.

Potentially hazardous elements
Arsenic was measured only in a small number of samples with concentrations varying from 0.05 µg kg -1 , in Psidium guajava, to 0.59 µg kg -1 in Taraxacum officinalles species, respectively.
The chronic toxicity of Cd to humans has been documented with cases of poisoning from herbal products in India, China, Brazil, Argentina and Mexico. 42Short term effects include nausea, vomiting, diarrhea and cramps. 43In the present samples, Cd concentrations varied from below LOD up to 0.55 µg g -1 , in the sample of Vernonia polyanthes.Low level of this element was found 44 in Curcuma longa, 0.004 µg g -1 , and the highest amount was found 45 in Taraxacum officinalles, 7.24 µg g -1 , considering the plants included in this paper.
Very few data about Hg are found in medicinal plants and values from 0.065 up to 54 µg kg -1 were reported 29,46 for Salvia officinalis and Momordica charantia, respectively.Among the samples analyzed in this work, almost all of them showed measurable amounts of this element and the concentrations varied from 2.5 to 434 µg kg -1 , in Aesculus hippocastanum and Eucalyptus globulus samples, respectively, indicating an one order of magnitude enrichment for this element, when compared to that found in foods other than fish products that, generally, varies between 1 and 50 µg kg -1 .
Lead is a non-essential element, but it is found widespread in the environment.In the present samples, its concentration varied from below LOD to 76.9 mg kg -1 in the Eugenia uniflora sample.The literature registers values up to 1544 mg kg -1 for this element in plants belonging to the same set of those here analyzed. 42It is worth noting that nine of our samples showed values higher than the permitted by WHO for this element.

Elemental distribution pattern
In Figure 1, the mean concentration distribution, according to the part of the plant used as medicine, is shown.The elements were distributed in the figure according to their magnitude.It can be seen that shoots showed high concentrations for the elements Br, Cl, Co, Cr, Cs, Fe, Hf, Mg, Mn, Na, Rb, Sb, Sc, Ti, V, Zn and for the potentially toxic Cd.When the whole plant was analyzed high concentrations was verified for the elements Ba, Br, Fe, Hf, K, Rb, Sc, Ti, V, Zn and Cu and for the potentially toxic As and Hg.It can also be verified that seeds showed high concentrations for the elements Ba, Co, Cr, Cu, Ni and Pb; rhizome samples showed high concentrations for the elements As, Mn and Se and inflorescence, for the Vol.27, No. 12, 2016 elements Ca, Cl, Mg, Na and Cu; fruits showed high values of mean concentrations for Se, Hg and Ni; leaves showed high concentrations for Hg and Pb; flowers, for Cr and Cd; beans, for Ca and Zn and, finally, barks showed higher Cd concentrations.
The role of essential and non elements in the plant parts analyzed in this study is beyond the scope of this paper but the distribution pattern observed must be related to the plant metabolism and the availability of these elements for transfer from soil to plant. 47Also, it is increasingly recognized that the availability of a given micronutrient or contaminant varies substantially in relation to the different chemical species present, 48,49 being this elemental speciation, among other factors, a function of soil mineralogy, pH and redox potential. 50Another possible contribution source is the pollution of air, soil, and water that arose from the industrial growth and from the agricultural practices that have caused the environmental dispersion of these elements, including the potentially toxic ones, resulting in their entry into food chains, including the medicinal plants. 51A remarkable challenge in this field is, therefore, to estimate the anthropogenic contribution for the observed concentrations.
Since the concentration of all the elements varies widely in the analyzed parts of the plants, the main implication of this variation must be that their bioavailability will also vary for consumption depending on the solvent and preparation mode.

Enrichment factor
Enrichment factor (EF) analysis is generally used to assess anthropogenic contribution to the environment. 52,53F represents the ratio between a given element (E i ) and a conservative element (E r ) in the sample normalized by the same ration, in a geological reference.Generally, the upper continental crust (UCC) is used as the geological reference and the formula is given as EF = (E i /E r ) sample/(E i /E r ) UCC .Magnesium was chosen as the conservative element, since it is both ubiquitous and an essential element for plants.The calculated EF values for the present samples showed a large variation, ranging from 0.01 up to 500 and were categorized in three groups: (i) EF < 1: As, Ba, Co, Cs, Fe, Hf, Na, Sb, Sc, Ti, V and Ni; (ii) 1 < EF < 10: Ca, Cr, K, Mn, Rb, Zn, Cu and Pb; (iii) EF > 10: Br, Cl, Se, Hg, and Cd.
The first group is composed, mainly, by non-essential trace elements, that are generally transferred to plants in amounts smaller than the essential ones.The presence of Fe, as well as of V, in this group can be explained because they are major components of the soil. 54Most of the essential elements for plants were categorized in the second group, that also include the potentially toxic, Pb.These elements tend to be enriched in the plants up to two orders of magnitude related to the non-essential elements. 55,56lthough being a non-essential element Rb was included in this group possibly due to its ionic radius close to the K radius. 54The third group contains, besides the halogens, the potentially hazardous elements Se, Hg and Cd.
It was, also, verified that high EF values, for the majority of the elements, were observed, mainly, in the roots and bark, while the potentially toxic elements are mainly enriched in barks.This enrichment for the elements of the third group may possibly reflect some anthropogenic contribution, since they are not essential elements and their mean EF values were up to three orders of magnitude greater than the values obtained for the elements of the other groups and also that its own values obtained in other parts of the plants.

Conclusions
This study presents the results obtained for 59 medicinal plants commonly used in Brazil.Impurities were found in 50% of the samples, most of them in parts of plants not used for medicinal purposes; moisture levels varied up to 12%.The elemental concentrations varied in a wide range for almost all the determined elements, with a variation coefficient ranging from 50 to 245%.The species in which relatively high concentrations were measured were Mentha pulegium, Taraxacum officinale, Malva sylvestris, Salvia officinalis, Passiflora incarnateand, Agerantum conyzoides, while low concentrations were found in the Allium sativum, Calendula officinalis, Casearia sylvestris, Cinnamomum verum, Citrus auranrium, Glycyrrhiza glaba, Illicium verum, Maytenus ilicifolia, Psidium guajava and Punica granatum samples.
Good agreement was found between the results obtained in this work and the level of elements reported in the literature, although higher values for some elements such as Ba, Cr, Fe, Hg, Se and Ni were found in some samples.
It was observed that the pattern of elemental distribution varies according to the part of the plant analyzed.Nonessential elements tend to show a low enrichment factor, generally, inferior to 1, while essential elements show EF between 1 and 10.Higher EF values include the potentially hazardous elements Hg and Cd, mainly, in the bark of the plants, possibly indicating anthropogenic contribution.

Table 1 .
Plants, scientific name (Brazilian popular name), used part to extract preparation, medicinal indication, dosage and mode of preparation according to ANVISA

Table 1 .
Plants, scientific name (popular name), used part to extract preparation, medicinal indication, dosage and mode of preparation according to ANVISA (cont.)

Table 3 .
Results obtained for the certificate reference materials apple, peach and tomato leaves, in mg kg -1 , excepted where indicated with %, mean value (n = 5), standard deviation and relative error MV: measured value; TV: true value; RE: relative error.

Table 4 .
Results of the Certificate Reference Materials apple and peach leaves obtained by ICP OES and CV AAS, in mg kg -1 , mean value (n = 5), standard deviation and relative error

Table 5 .
Concentrations and expanded uncertainty (K = 2) obtained in the analyzed samples

Table 5 .
Concentrations and expanded uncertainty (K = 2) obtained in the analyzed samples (cont.)

Table 5 .
Concentrations and expanded uncertainty (K = 2) obtained in the analyzed samples (cont.)