537 Bulgarian Journal of Agricultural Science, 12 (2006), 537-551 National Centre for Agrarian Sciences AAS and ICP Determination of Heavy Metal Content in Tobacco P. S. ZAPRJANOVA 1 , V. R. ANGELOVA 2 , G. L. BEKJAROV 3 and K. I. IVANOV 2 1 Institute of Tobacco and Tobacco Products, BG - 4108 Plovdiv, Bulgaria 2 University of Agriculture, Dept. of Chemistry, BG - 4000 Plovdiv, Bulgaria 3 Gardering and Canning Institute, BG - 4000 Plovdiv, Bulgaria Abstract ZAPRJANOVA, P. S., V. R. ANGELOVA, G. L. BEKJAROV and K. I. IVANOV, 2006. AAS and ICP determination of heavy metal content in tobacco. Bulg. J. Agric. Sci., 12: 537-551 There has been carried out a comparative study of the standard methods (dry ashing, acid digestion and microwave digestion) and analysis (ICP - OES and AAS) of tobacco leaves of Burley and Virginia varieties for the determination of Fe, Mn, Cu, Zn, Pb, Cd and Ni. It can be concluded, that both measurement methods (ICP-OES and AAS) provide comparable results with a good agreement and the results of this study are affected in greater extent by the decom- position procedure than by measurement techniques. A careful choice of suitable digestion procedures is critical step in ensuring correct results because even very similar material may exhibit different behavior during the digestion. The use of HNO 3 alone does not provide us with good results even with the microwave digestion of tobacco samples. To achieve total decompo- sition of sample matrices and dissolution of elements, combination of HNO 3 and HCI, HF, HCIO 4 or H 2 O 2 have to be used. A careful approach should be applied when using dry ashing for sample preparation. The lower temperatures (400 - 450 o C) and the longer heat treatment favor the obtaining of correct results. Taking into consideration the good detection limits, large linear dynamic range and simultaneous multi-element capability it seems that the combination of ICP with microwave digestion procedure is a very rapid and accurate method for analyzing plant materials. Key words: tobacco leaves, sample preparation, heavy metals, AAS, ICP-OES Introduction Tobacco is a main agricultural crop for many countries, including Bulgaria. Be- cause of its large use in the cigarette in- dustry, it is very important regarding hu- man health, especially considering its ca- pacity to accumulate heavy metals (Adamu et al., 1989; Bell et al., 1992). It is known that the content of metals
Transcript
537
Bulgarian Journal of Agricultural Science, 12 (2006), 537-551National Centre for Agrarian Sciences
AAS and ICP Determination of Heavy Metal Contentin TobaccoP. S. ZAPRJANOVA1, V. R. ANGELOVA2, G. L. BEKJAROV3 and K. I. IVANOV2
1 Institute of Tobacco and Tobacco Products, BG - 4108 Plovdiv, Bulgaria2 University of Agriculture, Dept. of Chemistry, BG - 4000 Plovdiv, Bulgaria3 Gardering and Canning Institute, BG - 4000 Plovdiv, Bulgaria
Abstract
ZAPRJANOVA, P. S., V. R. ANGELOVA, G. L. BEKJAROV and K. I. IVANOV,2006. AAS and ICP determination of heavy metal content in tobacco. Bulg. J. Agric.Sci., 12: 537-551
There has been carried out a comparative study of the standard methods (dry ashing, aciddigestion and microwave digestion) and analysis (ICP - OES and AAS) of tobacco leaves ofBurley and Virginia varieties for the determination of Fe, Mn, Cu, Zn, Pb, Cd and Ni. It can beconcluded, that both measurement methods (ICP-OES and AAS) provide comparable resultswith a good agreement and the results of this study are affected in greater extent by the decom-position procedure than by measurement techniques. A careful choice of suitable digestionprocedures is critical step in ensuring correct results because even very similar material mayexhibit different behavior during the digestion. The use of HNO3 alone does not provide us withgood results even with the microwave digestion of tobacco samples. To achieve total decompo-sition of sample matrices and dissolution of elements, combination of HNO3 and HCI, HF, HCIO4or H2O2 have to be used. A careful approach should be applied when using dry ashing for samplepreparation. The lower temperatures (400 - 450 oC) and the longer heat treatment favor theobtaining of correct results. Taking into consideration the good detection limits, large lineardynamic range and simultaneous multi-element capability it seems that the combination of ICPwith microwave digestion procedure is a very rapid and accurate method for analyzing plantmaterials.Key words: tobacco leaves, sample preparation, heavy metals, AAS, ICP-OES
Introduction
Tobacco is a main agricultural crop formany countries, including Bulgaria. Be-cause of its large use in the cigarette in-
dustry, it is very important regarding hu-man health, especially considering its ca-pacity to accumulate heavy metals(Adamu et al., 1989; Bell et al., 1992).
It is known that the content of metals
538
in tobacco varies a lot and it depends onseveral factors such as soil type and pHgenotype, use of a metal-containing pesti-cides, fertilizers, etc. Some of the metalssuch as iron, manganese, zinc and copperare important micronutrients and they arealso very important for plant growth andyield. However, other metals such as lead,cadmium and nickel are not important forthe plant growth, but they can cause seri-ous health and ecological problems. In bothcases, we need to pay attention to theirright determination, which will allow us toundertake due correcting operations withserious economic consequences. It isknown that the latter depends on the rightselection of a method for test sampling andsuitable measuring equipment. Although,a number of investigations have been car-ried out on heavy metal concentration intobacco leaves (Golia et al., 2003;Zaprjanova and Boshinova, 2004), only afew studies have been done concerningmethods and techniques for samplespreparation and heavy metals determina-tion. This made us consider performing acomparative study of the basic methodsfor samples mineralization (dry ashing, aciddigestion and microwave digestion) andanalysis (ICP - OES and AAS) of tobaccosamples, through which we could assessthe advantages and disadvantages for de-termining the most important elements forthe mineral nutrition and the market quali-ties of tobacco.
A lot of publications are dedicated tothe evaluation of various mineralizationmethods and measurement techniques fortrace element analysis of different mate-rials. Curdova et al. (1998) has comparedthree decomposition methods (microwavedigestion, classical dry ashing and dryashing in a mixture of oxidizing gases) for
six plant materials and three measurementtechniques (ICP - MS, FAAS andETAAS) for the determination of Cd, Cu,Pb and Zn. According to the statisticalevaluation, no significant differences be-tween analytical methods are found. It'sconcluded that the results obtained areaffected to a greater extent by the decom-position procedure than by measurementtechniques. On the contrary, Pyle et al.(1996) have registered a significant differ-ence in cadmium determination of 50 soilsamples by four techniques (ICP - AES,AAS, PSA and XRF). Analyzing the re-sults of the laboratories participating inFood Analysis Performance AssessmentScheme (FAPAS) in the period 1991 - 2000Rose et al. (2001) reported that percent-age of satisfactory results are in the rangeof 34 to 100 depending on the material,sample digestion and detection techniques.According to these authors, ICP-relatedtechniques produce better results thanAAS. Comparing five methods for sampledigestion they indicate that pressure ves-sel is consistently associated with goodanalytical performance. The same wasconcluded by Poykio et al. (2000) on thebasis of a comparison of dissolution meth-ods for multi-element analysis of somereference plant materials. According tothese authors, microwave dissolution, com-bined with ICP-AES or ICP-MS determi-nation is a very rapid and accurate methodfor analyzing botanical materials.
It can be summarized that a carefulchoice of suitable digestion procedure anddetection techniques are of great impor-tance for the ensuring of correct results.This is especially important for the deter-mination of plant materials because, as arule, plant material is not homogeneous andusually contains variable matrices.
P. S. Zaprjanova, V. R. Angelova, G. L. Bekjarov and K. I. Ivanov
539AAS and ICP Determination of Heavy Metal Content in Tobacco
Material and Methods
InstrumentationTwo detection methods most frequently
used for heavy metals determination inplant materials ware compared:
• ICP - OES. An ICP spectrometerSpectroflame-D (Spectro Analytical In-struments, Kleve, Germany), equippedwith two monochromators: (i) spectralrange 160 - 460 nm with nitrogen purgedoptics and (ii) spectral range 240 - 790 nmwith air purged optics, was used. The ana-lytical operational parameters were opti-mized with the aim to achieve the lowestpossible limit of detection for the determi-nation of led. For all elements, with theexception of Cu and Zn, a backgroundcorrection was performed. The wave-lengths of the analytical lines and wave-lengths used for background correctionare listed in Table 1.
• AAS. Specter AA-220 (Varian, Aus-tralia) atomic absorption spectrometer wasused in flame mode. The working wave
lengths were as follows: Fe - 248.3 nm;Mn - 279.5 nm; Cu - 324.8 nm; Zn - 213.9nm; Pb - 217.0 nm; Cd - 328.8 nm and Ni- 224.8 nm.
Reagents and standardsThe acids, including nitric acid, hydro-
chloric acid, perchloric acid and hydrof-luoric acid, as well as H2O2 were obtainedfrom E. Merck Company (Germany).
The calibration was performed usingfive or six aqueous standard solutions in2 % v/v HNO3. A commercial multi-ele-ment standard solution with concentration100 mg/l for ICP and individual standardsolution with concentration 1000 mg/l forAAS were used as a stock solution. Thecalibration standard solutions had the fold-ing concentrations: 0. 0.2; 0.5; 2.0 and 5.0mg/l for ICP calibration and 0; 0.2; 0.4;0.6; 0.8 and 1.0 mg/l (Zn, Cu, Mn and Cd)and 0; 1.0; 2.0; 3.0; 4.0 and 5.0 mg/l (Fe,Ni and Pb) for AAS calibration.
MaterialsTwo samples of tobacco leaves from
the tobacco varieties, which are of great-est importance for the Bulgarian econom-ics - Burley and Virginia, were used. Sam-pling procedures followed Bulgarian stan-dard 17728-91, including representativesamples collection, washing, drying andgrounding.
Digestion proceduresThree various sample digestion proce-
dures were applied as follows:• Procedure for dry ashing at 525 o C in
muffle furnace, following Bulgarian stan-dard 17365-94 was used. Samples (0.5 g)were weighed in 50 ml glass beakers.charged on a hot plate with stepwise in-creasing temperature up to 350o C for 4hours and finally ashed in a muffle fur-
Table 1
ElementAnalytical line,
nm
Backgroundcorrection line,
nmFe 259.94 259.54
Mn 257.61 257.21
Cu 327.754 *
Zn 206.19 *
Pb 220.353 220.313
Cd 226.502 226.543
Ni 231.604 231.655
Analytical lines and wavelengths used for background
*Background correction not performed
540
nace at 525o C for 1 hour. After cooling,ashes were dissolved in 20 ml of 1.5 %HNO3.
• Procedure for acid digestion, follow-ing Bulgarian standard 11708 - 93, includ-ing mineralization of the tobacco sampleby a mixture consisting of nitric and per-chloric acid, was used.
• Procedure for microwave digestionwith different acid mixtures, following EPAMETHOD 3051, suitable for flame AASand ICP - OES determination of heavymetals, was used. A microwave digestionsystem (Milestone 1200 MEGA, Italy)with 10 MRD 300 rotor with 10 positionsmaxes. pressure of 30 bar and max. power1000 W was used. A homogenized sampleof 0.5 g dry substance was weighed onassay balance into a teflon bomb and 10ml of concentrated nitric acid were added.The microwave mineralization programcomprised of tree stages: (i) 5 min nonpulsed 250 W microwave irradiation; (ii)5 min 400 W pulsed microwave irradia-tion and (iii) 5 min 600 W pulsed micro-wave irradiation. After a ventilation of oneminute the sample was cooled and dilutedto 50 ml.
Statistical evaluation of resultsStatistical evaluation of the results was
performed by using of SPSS program(Analysis of Variance, IndependentSamples T Test). The mean difference issignificant at the 0.05 level.
Results and Discussion
The most important elements for to-bacco growth, yield and quality - Cu, Zn,Fe, Mn, Pb, Cd and Ni, were object of ourinvestigation.
• Copper and zincCopper and zinc are essential metals
for tobacco growth and yield and their con-centrations in tobacco leaves according toGolia et al. (2003) are as follows: Burley -1.1 - 34.5 mg/kg Cu; 6.8 - 165.5 mg/kg Znand Virginia -1.1 - 68.8 mg/kg Cu; 4.8 -108.8 mg/kg Zn. The addition of Cu wassuggested to be related to the increasingof nicotine content and decreasing of cit-ric acid in tobacco leaves (Voss and Nicol,1960). Zinc stimulates germination andprobably activates the enzymatic processesof mobilizing the food reserves of seeds.
The results of Cu and Zn in tobaccovarieties Virginia and Burley, obtained byvarious digestion methods and measure-ment techniques together with standard de-viation (SD) and relative standard devia-tion (RSD) are presented in Table 2.
As it can be seen from the table, thevalues obtained for copper and zinc con-tent by means of the different digestionmethods vary in narrow limits. With theVirginia variety they are 13.7-16.9 mg/kgfor the copper and 34.2-37.9 mg/kg forthe zinc. Apparently, the Burley varietyaccumulates greater amounts of coppercontent - 19.3-23.9 mg/kg. This differenceis well specified with the zinc, which val-ues reach 63.0-69.4 mg/kg.
The results obtained show that all meth-ods used for preparation of the samplesare appropriate for determining the cop-per and zinc content in tobacco samples.This conclusion is confirmed by the resultsof the statistic data processing, presentedin Tables 3 and 4. In any case, the ob-served significance level s exceeds thesignificance level (0.05).
The comparison of the detection meth-ods does not show significant differences
P. S. Zaprjanova, V. R. Angelova, G. L. Bekjarov and K. I. Ivanov
№ Type of Samples tobacco preparation AAS ICP AAS ICP
Table 2Comparison of results for Cu and Zn content of tobacco leaves obtained by different digestion methods and measurements techniques.* average value (mg/kg); **SD; **RSD
541AAS and ICP Determination of Heavy Metal Content in Tobacco
∆ ∆ ∆ ∆
542
in the results, obtained by ICP and AAS(Table 4). In all cases the observed levelof significance s (0.05). The relative stan-dard deviations are low and do not ex-ceed 2.7 % for AAS and 3.8 % for ICP.
• Iron and manganeseIron and manganese are essential met-
als for tobacco growth and yield too, andtheir concentrations in tobacco leaves areas follows (Golia et al., 2003; Zaprjanovaand Boshinova, 2004): Burley - 90.0 - 232.0mg/kg Fe; 16.7 - 662.5 mg/kg Mn and Vir-ginia - 1.1-68.8 mg/kg Fe; 4.1-897.5mg/kg Mn. Manganese is important forplant metabolism and tobacco plants re-quire Mn for growth, but are sensitive totoxicity.
The results of Fe and Mn in tobaccovarieties Virginia and Burley, obtained byvarious digestion methods and measure-ments techniques together with standard
deviation (SD) and relative standard de-viation (RSD) are presented in Table 5.
As it can be seen from the table, thevalues obtained for iron and manganesecontent at the different digestion methodsvary in large limits. With Virginia variety,they are 44.8-68.1 mg/kg for iron and 22.2-35.3 mg/kg for manganese. In this casethe Burley variety accumulates significantlylarger quantity from the two elements aswell - the iron is from 72.2 to 94.8 mg/kg.and the manganese - from 60.2 to 85.9mg/kg.
The results of the statistic data process-ing show that in any case, the observedsignificance level αs does not exceed thesignificance level (0.05), which means thatthe differences of the values, obtainedthrough the different methods are statisti-cally significant. The only exception oc-curs with the comparison of microwaveand wet digestion for manganese content
P. S. Zaprjanova, V. R. Angelova, G. L. Bekjarov and K. I. Ivanov
Ni Virg in ia DD-M D* 0.875 0.306 0.009DD-W D* -0.838 0.306 0.012M D-W D* -1.713 0.306 0.000
Bu rley DD-M D* 2.025 0.703 0.009DD-W D -0.913 0.703 0.208
M D-W D* -1.725 0.703 0.000
Table 3Statistical evaluation of the relationship between digestion methods at ααααα (0.05)DD – dry digestion, 5250 C; MD – micro wave digestion; WD – wet digestion; * αααααs < ααααα
AAS and ICP Determination of Heavy Metal Content in Tobacco 543
αs
in Virginia variety, where αs = 0.920. Themost significant losses are observed withthe dry digestion method, and the fullestextraction is with the wet digestion.
The comparison of the detection meth-ods does not show significant differencesin the results, obtained by ICP and AASand αs >α (0.05). The relative standard de-viations are also low and do not exceed2.0 % for AAS and 2.9 % for ICP.
• Lead, cadmium and nickelLead, cadmium and nickel are not es-
sential metals for tobacco growth and yield(Voss and Nicol, 1960). However, theircontent in tobacco is of great importancefor reducing the risks for smokers' health,especially, having in mind their capacity toaccumulate in tobacco leaves.
Nickel is important as a regulator ofthe oxidation process occurring in plants.
Their concentrations in tobacco leavesusually are as follows (Golia et al., 2003;Zaprjanova and Boshinova, 2004): Burley- 0.04-9.1 mg/kg Pb; 0.04-3.6 mg/kg; 0.04-.6 mg/kg Cd, 6.8-165.5 mg/kg Ni and Vir-ginia - 0.01-10.2 mg/kg Pb; 0.01-3.4mg/kg Cd, 0.7-4.7 mg/kg Ni.
The results of Pb, Cd and Ni in tobaccovarieties Virginia and Burley, obtained byvarious digestion methods and measure-ments techniques together with standarddeviation (SD) and relative standard de-viation (RSD) are presented in Table 6.
As it can be seen from the table, thevalues obtained for lead, cadmium andmanganese content at the different diges-tion methods vary in large limits. With Vir-ginia variety they are 1.1-2.6 mg/kg forlead, 0.28-1.25 mg/kg for cadmium and1.6-4.7 mg/kg for nickel. In this case aswell the Burley variety accumulates sig-
Table 4Statistical evaluation of the relationship between detection methods at α α α α α (0.05) * αααααs< ααααα
Element TobaccoFe Virginia -0.414 22 0.683 -1.3667 3.3003
Table 5Comparison of results for Fe and Mn content of tobacco leaves obtained by different digestionmethods and measurements techniques. * average value (mg/kg); **SD; **RSD
∆ ∆ ∆ ∆
AAS and ICP Determination of Heavy Metal Content in Tobacco 545
nificantly larger amounts of the three ele-ments as lead is from 0.8 to 3.4 mg/kg,cadmium - from 0.8 to 3.5 mg/kg andnickel - from 2.8 to 7.7 mg/kg.
Here, just as it was with the copperand manganese, the largest losses of Pband Cd are observed with the dry diges-tion method, and the fullest extraction iswith the wet digestion. Only with the nickel,the results of the dry digestion are com-mensurable with these of the wet diges-tion.
The comparison of the detection meth-ods does not show significant differencesin the results, obtained by ICP and AASfor most of the elements. Only with thelead, the observed significance level isαs<α (0.05). In this case the relative stan-dard deviations are also high (up to 50%),which reduces to a large extent the cor-rectness of the obtained results.
The analysis of the results shown inTables 2 - 6 show that the results obtainedby the dry digestion method and micro-
wave mineralization do not provide us withappropriate results for most of the testedelements. Other authors have also ob-served lowered results for the content ofheavy metals with dry digestion of thesamples on studying other materials (Soonand Bates, 1982). However, in most of thecases, the microwave mineralization isconsidered the most appropriate methodfor preparation of the samples, especiallywith the easily volatile elements. Mostprobably, the reason for the differencesobserved is the need of specific workingconditions, in dependence with the com-position and the properties of the exam-ined material. To make this problem clear,we changed some of the basic parametersof the digestion process - we reduced thetemperature and increased the calcinatingtime of the dry mineralization and we usedstronger oxidizing mixtures with the mi-crowave mineralization.The results ob-tained are shown in Table 7.
P. S. Zaprjanova, V. R. Angelova, G. L. Bekjarov and K. I. Ivanov546
AAS and ICP Determination of Heavy Metal Content in Tobacco 547
№T
ype
of
Sam
ples
toba
cco
prep
arat
ion
AA
SIC
PA
AS
ICP
AA
SIC
P
X*
+
**
X +
X +
X +
X +
X +
12
34
56
78
91
Virg
inia
Dry
dig
estio
n2.
0 +
0.3
1.5
+ 0.
50.
35 +
0.0
40.
31 +
0.0
43.
4 +
0.4
2.9
+ 1.
052
5o C, 1
h15
.0**
*30
11.4
12.9
11.8
34.5
1.7
+ 0.
41.
1 +
0.5
0.35
+ 0
.05
0.30
+ 0
.11
4.2
+ 0.
63.
4 +
1.0
23.5
45.5
14.3
36.7
14.3
29.4
1.5
+ 0.
21.
6 +
0.4
0.35
+ 0
.05
0.32
+ 0
.14
3.7
+ 0.
33.
0 +
1.1
13.3
2514
.343
.88.
136
.6B
urle
y1.
6 +
0.2
1.9
+ 0.
30.
30 +
0.0
60.
28 +
0.1
14.
1 +
1.1
3.6
+ 1.
112
.515
.820
39.3
26.8
30.6
Dry
dig
estio
n3.
0 +
0.3
1.5
+ 0.
20.
80 +
0.0
60.
82 +
0.1
17.
0 +
0.3
6.5
+ 0.
452
5o C, 1
h10
13.3
7.5
13.4
4.3
6.2
2.9
+ 0.
31.
3 +
0.2
1.1
0 +
0.07
1.10
+ 0
.03
7.6
+ 0.
47.
0 +
0.3
10.3
15.3
6.3
2.7
5.3
4.3
2.5
+ 0.
4 2
.0 +
0.2
1.20
+ 0
.06
1.2
+ 0
.09
7.2
+ 0.
7 6
.4 +
0.4
1610
57.
59.
76.
23.
1 +
0.3
1.6
+ 0.
2 1
.05
+ 0.
051.
00 +
0.0
86.
8 +
0.8
6.3
+ 0.
49.
712
.54.
88.
011
.86.
32
Virg
inia
Mic
row
ave
2.5
+ 0.
51.
4 +
0.1
1.15
+ 0
.04
0.92
+ 0
.06
3.5
+ 0.
71.
6 +
1.2
dige
stio
n20
7.1
3.5
6.5
2075
10 m
l HN
O3
2.1
+ 0.
61.
6 +
0.3
1.10
+ 0
.05
0.91
+ 0
.08
2.9
+ 1.
21.
6 +
1.0
28.6
18.8
4.6
8.8
41.3
62.5
2.5
+ 0.
42.
3 +
0.2
1.15
+ 0
.04
0.95
+ 0
.06
3.5
+ 0.
62.
0 +
1.0
168.
73.
56.
317
.150
Con
tent
of N
i, m
g/kg
Con
tent
of P
b, m
g/kg
Con
tent
of C
d, m
g/kg
P. S. Zaprjanova, V. R. Angelova, G. L. Bekjarov and K. I. Ivanov5481
23
45
67
89
Bur
ley
2.2
+ 0
.31.
3 +
0.3
1.25
+ 0
.06
0.90
+ 0
.07
3.9
+ 0
.22.
3 +
1.0
13.6
23.1
4.8
7.8
5.1
43.5
Mic
row
ave
2.5
+ 0.
4 1
.0 +
0.5
3.30
+ 0
.05
2.72
+ 0
.09
5.2
+ 0.
43.
8 +
1.1
Dig
estio
n16
.050
.01.
53.
37.
728
.910
ml H
NO
32.
1 +
0.3
1.4
+ 0.
23.
35 +
0.6
2.73
+ 0
.08
4.5
+ 0.
23.
9 +
1.1
14.0
14.3
1.8
2.9
4.4
28.2
2.0
+ 0.
3 0
.8 +
0.4
3.10
+ 0
.04
2.68
+ 0
.07
4.1
+ 0.
7 2
.8 +
0.3
15.0
50.0
1.3
2.6
17.1
10.7
2.6
+ 0.
42.
3 +
0.2
3.10
+ 0
.06
2.74
+ 0
.09
4.2
+ 0.
33.
1 +
0.4
15.4
8.9
1.9
3.3
7.1
12.9
3V
irgin
iaW
et d
iges
tion
2.5
+ 0.
5*2.
0 +
0.5
1.15
+ 0
.06
1.22
+ 0
.06
4.2
+ 0.
64.
7 +
0.7
HN
O3 +
HC
IO4
20.0
**25
.0**
5.2*
*4.
9**
14.3
**14
.9**
2.3
+ 0.
62.
2 +
0.7
1.15
+ 0
.08
1.11
+ 0
.05
4.3
+ 0.
54.
7 +
0.7
26.1
31.8
7.0
4.5
11.6
14.9
2.5
+ 1.
22.
2 +
1.2
1.05
+ 0
.07
1.03
+ 0
.05
3.9
+ 0.
44.
5 +
0 .5
48.0
55.0
0.7
4.9
10.2
11.1
Bur
ley
2.6
+ 0.
92.
0 +
0.9
1.05
+ 0
.09
1.05
+ 0
.05
4.2
+ 0.
74.
5 +
0 .5
Wet
dig
estio
n34
.645
.02.
64.
816
.711
.1H
NO
3 +
HC
IO4
3.0
+ 0.
93.
3 +
083.
4 +
0.08
3.27
+ 0
.04
6.2
+ 0.
87.
7 +
1.2
30.0
24.2
2.4
1.2
2.0
15.6
3.2
+ 0.
83.
4 +
0.7
3.4
+ 0.
073.
04 +
0.0
75.
9 +
0.3
7.6
+ 1.
225
20.6
2.1
2.3
5.1
15.6
3.0
+ 0.
83.
1 +
0.9
3.5
+ 0.
093.
44 +
0.0
66.
5 +
0.6
7.5
+ 0.
826
.729
2.6
1.7
9.3
10.7
2.9
+ 0.
73.
0 +
0.8
3.2
+ 0.
083.
23 +
0.0
86.
3 +
0.9
7.4
+ 0
.824
.126
.72.
52.
514
.310
.8
Tabl
e 6
cont
inue
Tabl
e 7C
ompa
riso
n of
resu
lts fo
r Cu,
Zn,
Fe,
Mn,
Pb,
Cd
and
Ni c
onte
nt of
toba
cco l
eave
s obt
aine
d by
diff
eren
t dig
estio
n*a
vera
ge v
alue
, mg/
kg; *
*SD
; ***
RSD
№Ty
pe o
f Sa
mpl
es
toba
cco
prep
arat
ion
FeM
nCu
ZnPb
CdN
i
1Vi
rgin
iaD
ry d
iges
tion.
66.0
+ 0
.933
.4 +
0.5
13. +
0.2
32.2
+ 0
.52.
2 +
0.8
0.73
+ 0
.04
3.6
+ 0.
3
450o C
, 3 h
1.4*
**1.
51.
51.
636
.45.
48.
3Bu
rley
94.2
+ 1
.179
.0 +
0.4
20.8
+ 0
.370
.0 +
0.3
3.0
+ 0.
8 2
.62
+ 0.
036.
3 +
0.5
1.2
0.5
1.4
0.4
26.7
1.1
7.9
2Vi
rgin
iaD
ry d
iges
tion.
62.1
+ 1
.232
.2 +
0.2
13.9
+ 0
.332
.0 +
0.3
2.3
+ 0.
80.
80 +
0.0
23.
3 +
0.5
400o C
, 12
h1.
90.
62.
20.
934
.82.
515
.2Bu
rley
94.1
+ 1
.180
.2 +
1.2
20.3
+ 0
.169
.0 +
0.5
2.9
+ 0.
92.
80 +
0.0
36.
0 +
0.6
1.2
1.5
0.5
0.7
311.
110
3Vi
rgin
ia60
.8 +
0.4
34.6
+ 0
.215
.1 +
0.3
36.8
+ 0
.22.
5 +
1.0
0.92
+ 0
.04
4.8
+ 0.
50.
70.
50.
40.
540
4.3
10.4
Burle
y97
.4 +
2.1
77.7
+ 0
.422
.9 +
0.2
68.4
+ 0
.33.
2 +
1.0
3.2
+ 0.
038.
9 +
0.9
2.2
0.5
0.9
0.4
31.3
0.9
10.1
4Vi
rgin
ia63
.4 +
1.7
33.8
+ 0
.314
.5 +
0.3
36.8
+ 0
.32.
4 +
0.8
1.02
+ 0
.01
4.6
+ 0.
42.
70.
92.
10.
833
.31
8.7
Burle
y94
.2 +
1.2
81.2
+ 0
.523
.1 +
0.3
67.2
+ 0
.43.
0 +
0.9
3.31
+ 0
.04
8.0
+ 0.
61.
30.
61.
40.
630
1.2
7.5
Cont
ent o
f Fe
, Mn,
Cu,
Zn,
Pb,
Cd
and
Ni,
mg/
kg,
X*
+
Mic
row
ave
dige
stio
n.9
ml H
NO
3 + 2
ml H
F +
2 m
l H2O
2
Mic
row
ave
dige
stio
n.9
ml H
NO
3 +
2 m
l HCI
+
2 m
l H2O
2
AAS and ICP Determination of Heavy Metal Content in Tobacco 549
The results presented in show that re-ducing of the temperatures and increas-ing the calcinating time of the dry diges-tion and the use of H2O2 and HF with themicrowave mineralization are favorable forthe complete extraction of the elementsand make the results obtained completelycomparable.
Conclusions
• It can be concluded, that both mea-surement methods (ICP-OES and AAS)provide comparable results with a goodagreement and the results of this study areaffected in greater extent by the decom-position procedure than by measurementtechniques. A careful choice of suitabledigestion procedures is critical step in en-suring correct results because even verysimilar material may exhibit different be-havior during the digestion.
• The use of HNO3 alone does not pro-vide us with good results even with themicrowave digestion of tobacco samples.To achieve total decomposition of samplematrices and dissolution of elements, com-bination of HNO3 and HCI, HF, HCIO4or H2O2 have to be used.
• A careful approach should be appliedwhen using dry ashing for sample prepa-ration. The lower temperatures (400 -450îÑ) and the longer heat treatment fa-vor the obtaining of correct results.
• Taking into consideration the gooddetection limits, large linear dynamic rangeand simultaneous multi-element capabilityit seems that the combination of ICP withmicrowave digestion procedure is a veryrapid and accurate method for analyzingplant materials.
References
Adamu, C. A., C. L. Mulchi and P. F. Bell,1989. Relationships between soil pH, clay,organic matter and CEC [cation exchangecapacity] and heavy metal concentrationsin soils and tobacco. Tob. Sci., 33: 96-100.
Bell, P. F., C. L. Mulchi and R. L. Chaney,1992. Microelement concentration in Mary-land air-cured tobacco. Commun. Soil. Sci.Plant Anal., 23 (13&14): 1617-1628.
Bulgarian standard 17728-91. Fruits veg-etables and derived products. Meat andmeat vegetable cans. Mineralization of or-ganic content determination. Acidicmethod.
Bulgarian standard 17365-94. Tobacco andtobacco products.
Bulgarian standard 11708-93. Fruits veg-etables and derived products. Meat andmeat vegetable cans. Mineralization of or-ganic content determination. Method ofdry mineralization.
Curdova, E., J. Szakova, D. Miholova, O.Mestek and M. Suchanek, 1998. Evalua-tion of various mineralization methods andmeasurement techniques for trace elementanalysis of plant materials. Analusis, 26:116-121.
Golia, E. E, I. K. Mitsios and C. D. Tsadilas,2003. Concentration of heavy metals in to-bacco leaves (Burley, Virginia and Orien-tal) in Thessaly region. Central Greece. 8thInternational symposium on soil and plantanalysis. 2003, January, 13-17, 2003, CapeTown, South Africa.
Poykio, R., H. Torvela, P. Peramaki, T.Koukkanen and T. Ronkkomaki, 2000.
P. S. Zaprjanova, V. R. Angelova, G. L. Bekjarov and K. I. Ivanov550
Comparison of dissolution methods formulti-element analysis of some plant mate-rials used as bioindicator of sulphur andheavy metal deposition determined by ICP-AES and ICP-MS. Analusis, 28: 850-854.
Pyle. S., J. Nocerino, S. Deming, J. A.Palasota, J. M. Palasota, E. Miller, D.Hillman, M. Watson and K. Nicholas, 1996.Comparison of AAS, ICP-AES, PSA andXRF in determining lead and cadmium insoil. Environ. Sci. Technol., 30: 204-213.
Rose, M., M. Knaggs, L. Owen and M. Baxter,2001. A review of analytical methods for
lead, cadmium, mercury, arsenic and tindetermination used in proficiency testing.JAAS, 16: 1101-1106.
Soon, Y. K. and T. E. Bates, 1982. Chemicalpools of cadmium, nickel, and zinc in pol-luted soils and some preliminary indica-tions of their availability to plants. J. SoilSci., 33: 477-488.
Voss, R. C. and N. Nicol, 1960. Metallic traceelements in tobacco. Lancet, 2: 435-458.
Zaprjanova, P. and R. Boshinova, 2004. HeavyMetal Content in Virginia and Burley To-bacco. Ecology and Future, 3: 25-29.
AAS and ICP Determination of Heavy Metal Content in Tobacco 551
Received March, 23, 2006; accepted June, 14, 2006.
