maca ( lepidium meyenii walp . ) is an endemic highland crop of the central andes which is grown from central peru to bolivia and northwestern argentina [ 1 , 2 ] .
this plant has great potential as an adaptogen and appears to be promising as a nutraceutical in the prevention of several diseases .
maca roots have been traditionally used to increase the rate of fertility in both humans and livestock . over the past 20 years ,
commercial maca products have gained popularity as dietary supplements for aphrodisiac purposes and for increasing fertility and stamina .
recently , maca industry develops fast in yunnan province , china . in yunnan , until the end of 2010 , maca growing and promotion areas reached 175  hm and maca yield achieved 780  t , taking up to 90% and 93% , nationwide .
mineral elements in food are very important because the quality of many functional foods and medicines depends on the content and type of minerals . in the us ,
national surveys show that micronutrient inadequacies are widespread and mineral supplement helps fulfill micronutrient requirements in adults and children . up to now
, only limited studies on selected elements in maca from different origins have been carried out [ 10 , 11 ] . moreover , in some studies , no reference material had been certified for elemental analysis , so there has been doubt about accuracy of the determination . in the present study , inductively
coupled plasma optical emission spectroscopy ( icp - oes ) was used to determine the contents of eight elements ( b , co , cr , cu , li , na , ni , and zn ) in maca samples , and a comparison was made between the samples from china and peru .
standard sample solutions of b , co , cr , cu , li , na , ni , and zn obtained from standard material center of china were used to make a mixed calibration curve in the range of 0400  g  ml .
ten maca samples were collected from four places of yunnan , china , and four samples were from peru .
these samples were washed with deionized water thoroughly , dried to a constant weight , grounded into powder using an agate mortar , passed through a 60-mesh sieve , and stored in the plastic bags .
500  mg of each maca sample was weighed into an acid washed teflon digestion tube .
8  ml of hno3 , 2  ml of h2o2 , and 1  ml ultrapure water were added to the vessel .
samples were digested in a microwave dissolver ( ethos one , milestone , italy ) equipped with ptfe vessels .
the extract was transferred into a cuvette and made up to 25  ml with ultrapure water .
simultaneous multielement detection of b , co , cr , cu , li , na , ni , and zn was performed with icp - oes ( icpe-9000 , shimazu , japan ) . the optimal instrumental conditions for icp - oes are shown in table 2 .
blank experiments were prepared in the same way . to ensure the precision of the experiment , the certified reference material gbw10028 ( dried herb powder astragalus membranaceus ) was used for validation of the method ( table 4 ) . the relative standard deviation ( rsd )
was found to be below 8% , and the recoveries range from 92% to 109% , which proved that this method was accurate and precise .
contents of b , co , cr , cu , li , na , ni , and zn in maca samples are shown in table 5 .
boron affects fat and lipid metabolism , minerals and mineral metabolism , vitamin d , and bone development .
our b values in maca from china and peru were 8.121  mg  kg  dw and 6.612  mg  kg  dw , respectively , which were in agreement with that reported in the literature ( 8.8  mg  kg  dw ) .
cobalt is an essential micronutrient in the form of vitamin b12 , but cobalt is toxic in larger doses or long - term exposure at a low level .
the adverse effects of cobalt relate to various organs and tissues and may include a possible carcinogenic potential .
the contents ( mg  kg  dw ) of co , cr , and li were , respectively , < 0.023 , < 1.13.5 , and 0.0200.17 for the samples from china and < 0.023 , < 1.12.3 , and 0.0350.063 from peru .
up to now , there was no other report on the contents of co , cr , and li in maca .
its compounds show vast array of biological actions , such as anti - inflammatory , antiproliferative , and biocidal activities .
cu contents in the samples from china ( 2.531  mg  kg  dw ) were higher than the samples from peru ( < 2.1  mg  kg  dw ) . published data available on cu in maca from china were 4.032  mg  kg  dw [ 10 , 11 , 13 , 18 ] , while those from peru were 1.562  mg  kg  dw [ 10 , 11 , 1922 ] .
302600  mg  kg  dw which is similar to the value ( 672400  mg  kg 
dw ) in maca from china in literatures [ 11 , 13 , 18 ] .
however , our data on na in the samples from peru ( < 3041  mg  kg  dw ) are lower than the values reported ( 110190  mg  kg  dw ) in the literatures [ 11 , 1922 ] .
the contents of ni in the samples were 0.0854.5  mg  kg  dw from china and 0.681.7  mg  kg  dw from peru
. however , higher value ( 11.3  mg  kg  dw ) was found in the literature on the maca from china .
zinc is essential for a number of physiological functions and plays a significant role in many enzyme actions in the living systems .
zn contents in samples were found to be 1939  mg  kg  dw from china and 2739  mg  kg  dw from peru , which were in accordance with the values for maca in literature available ( 2589  mg  kg  dw from china and
1658  mg  kg  dw from peru ) [ 10 , 11 , 13 , 1822 ] .
cu contents in all of the maca samples from china , as well as na contents in two samples from china , were remarkably higher than those values in other samples .
 contents of eight mineral elements in maca ( lepidium meyenii walp . ) from china and peru were determined by inductively coupled plasma optical emission spectroscopy . 
 cu contents in maca samples from china ( 2.531  mg  kg1 dry weight , dw ) were higher than the samples from peru ( < 2.1  mg  kg1  dw ) . 
 na in two samples from china was found to be significantly of high content ( 2400 and 2600  mg  kg1  dw ) . 
 the contents ( mg  kg1  dw ) of b , co , cr , li , ni , and zn were , respectively , 8.121 , < 0.023 , < 1.1~3.5 , 0.0200.17 , 0.0854.5 , and 1039 for the samples from china , while being 6.612 , < 0.023 , < 1.1~2.3 , 0.0350.063 , 0.681.7 , and 2739 for the samples from peru . 
1. Introduction
2. Materials and Methods
3. Results and Discussion
4. Conclusions