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Comparison of three methods of digestion for trace metal analysis in surface

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 Nature and Science 2012;10(10) http://www.sciencepub.net/nature

Comparison of Three Methods of Digestion for Trace Metal Analysis in Surface Dust Collected from an E-
waste Recycling Site

Ehi-Eromosele C.O.1,*Adaramodu A.A.2 , Anake W.U.1, Ajanaku C.O.1, Edobor-Osoh, A.1

1
Department of Chemistry, Covenant University, P.M.B. 1023 Ota, Nigeria
2
Department of Chemistry, University of Lagos, Nigeria
cyril_720@yahoo.com

Abstract: The recycling of e-waste materials potentially contaminates the environment with heavy metals.
Analysing the exact contents of heavy metal in e-waste products is germane for the routine monitoring, risk
assessment and regulation of the environment. Therefore, the efficiency of three methods of digestion was evaluated
for Cd, Fe, Pb, Cr and Zn by AAS in surface dust from an e-waste recycling site and to recommend the most
efficient digestion method. The digestion methods were aqua regia, dry ashing followed by aqua regia and nitric acid
digestion followed by extraction with HCl. Analysis of variance, Student’s t-test and F-test were performed
separately for the indoor, outdoor and control dust samples analytical result. Analytical results indicated that the
nitric acid digestion followed by extraction with HCl was the most efficient in recovering Pb and Fe based on
recovery efficiency. Aqua regia was found to be an alternative method for recovering Pb and Fe based on cost and
time effectiveness. Aqua regia was the most efficient in recovering Zn while aqua regia and nitric acid digestion
followed by extraction with HCl were satisfactory for the recovery of Cd. Dry ashing followed by aqua regia was
found unsuitable for the analysis of these metals in the samples because it recovers relatively little heavy metals and
more analysis time.
[Ehi-Eromosele Cyril Osereme, Adaramodu Adebayo Abraham, Anake Winifred Uduak, Ajanaku Christina,
Edobor-Osoh Abiola. Comparison of Three Methods of Digestion for Trace Metal Analysis in Surface Dust
Collected From an E-waste Recycling Site. Nat Sci 2012;10(10):42-47]. (ISSN: 1545-0740).
http://www.sciencepub.net/nature. 7

Keywords: Digestion methods; Dust; e-waste; Heavy metals

1. Introduction choosing the procedure for the digestion of the

Electronic waste or e-waste products contain examined samples remains a fundamental one in spite
intricate blends of plastics and chemicals, which when of the huge amount of work done to develop accurate
not properly handled can be harmful to people and the methods for the determination of trace metals in
environment (Leung et al., 2006). The composition of different materials (Maria, 2002). The effect of the
e-waste is very diverse and differs in products across sample preparation steps on the quality of the
different categories. It contains more than 1000 analytical result is universally recognized. The
different substances, which fall under ‘hazardous’ and application of an appropriate digestion procedure and
‘non-hazardous’ categories. The presence of elements its effective combination with the separation and
like lead, mercury, arsenic, cadmium, selenium and detection methods are of major importance in the
hexavalent chromium and flame retardants beyond analysis of trace metals samples (Maria, 2002).
threshold quantities in e-waste classifies them as Many techniques employed for elemental
hazardous waste (http:// www.cpcb.nic.in). analysis require the conversion of the sample matrix
Consequently, exactly analyzing the contents of heavy into a solution form (Twyman, 2005). The ultimate
metal in e-waste is very important for the routine choice of decomposition method is influenced by the
monitoring and risk assessment and regulation of amount of sample available, the nature of the sample,
environment. The level of heavy metal concentration the sample matrix and the analysis time available
in e-waste may be evaluated from the level of dust (Adeloju, 1989). The approaches for destroying
deposition per unit area and metal concentrations in organic material and dissolving heavy metals fall into
the deposit (Krolak, 2000). This is because most e- two groups-wet digestion by acid mixtures prior to
wastes often contain dust particles embedded within elemental analysis and dry ashing, followed by acid
their various components and as such poses health dissolution of the ash (Zarcinas et al., 1987; Hseu,
risks when dismantled and piled up in stores without 2004). Concentrated acids such as HNO3, HCl, H2SO4,
proper disposal. and HClO4 as well as dual or triple mixtures of them
Low concentrations of trace metals, particularly with or without other oxidants (e.g. H2O2) have been
in geological and environmental samples require pre- used extensively for such purposes (Maria, 2002;
concentration prior to detection. The problem of Hseu, 2004; Zachariadis et al., 1995; Ming and Lena,

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 Nature and Science 2012;10(10) http://www.sciencepub.net/nature

1998; USEPA, 1996). Also, many efficient dry ashing heavy metal contribution from e-waste is likely not to
methods have been developed and applied to soil be present. The samples were homogenized and
sample analysis. These sample preparation techniques mixed. This was used as the control sample. Each
for total metal analysis can require several hours, or representative sample was stored in polyethylene bags
even several days, to complete. They use acid which had been previously treated overnight with
digestion and thermal decomposition steps, which can dilute HNO3. They were then placed in dessicators to
result in analyte losses, incomplete recoveries, and/or get rid of moisture and ground into fine powder. Dry
sample contamination (Smith, 1994; Smith and samples were sieved with 0.125mm sieve and
Arsenault, 1996). These limitations are well known to homogenized. This particle size range was chosen to
the analytical community and to end users of these facilitate comparison of heavy metal concentration
methods (Binstock, 1991). with soil guidelines.
Though a lot of digestion methods have been
published for trace metal analysis in soil samples, no 2.3. Digestion Methods
one method has been found to be efficient in 2.3.1. Method A: Hot Plate Aqua-regia Digestion
recovering all the heavy metals. Analytical 1g of a well homogenized sample obtained from
Laboratories are particularly interested in reproducible sample preparation procedure above was weighed into
and absolutely efficient digestion techniques for a Kjeldahl flask and 12ml of freshly prepared aqua
sample treatment prior to analysis (Zachariadiset al., regia (3ml HNO3 + 9ml HCl i.e. ratio 1:3) was added.
1995). Hence, over the years, research has been The beaker was covered and the contents heated for 2
geared towards finding efficient digestion techniques hours on the medium heat of a hot plate. The mixture
for different sample types. This has been mainly was allowed to cool and then filtered through a
achieved by modifying existing digestion techniques. Whatman No. 42 filter paper into a 50ml standard
Therefore, the aims of this study are to (1) evaluate volumetric flask. The filtrate was diluted to 50ml with
the contents of Cd, Cr, Fe, Pb and Zn in surface dust de-ionized distilled water. Blank solutions were also
from an e-waste site using different digestion prepared.
methods; and (2) recommend the most appropriate
digestion method for determining the five heavy 2.3.2.Method B: Dry Ashing Followed By Aqua-
metals in surface dust from an e-waste site. regia Digestion
1g of each dust samples were accurately
2. Material and Methods weighed into different crucibles and placed inside a
2.1. Study Area Vecstar Furnace (serial No. F191600, model- LF3,
Westminster Electronic Market is situated in 250V, 13A, 3000W) and ashed at 460 c for 12 hours.
Apapa Local Government Area of Lagos, Nigeria, The ash was digested in a 12ml freshly prepared aqua
close to the Lagos Tincan Island Port. Its location has regia solution on a hot plate within a fume cupboard
made it an attractive point for disembarking and for 2 hours. The digests were transferred into clean
selling Used Electrical and Electronic Equipment centrifuge bottles and placed inside a centrifuge which
(UEEE). The market has about 300 outlets where all was set at 3000 revolutions per minute for 15 minutes.
types of UEEE are sold. Additionally, the market also The mixture was finally transferred into a 50ml
has large storing facilities, which make it a big hub for standard volumetric flask and filtered through a
storing UEEE before being redistributed to other Whatman No. 42 filter paper. The filtrate was made
markets or exported to neighbouring countries up to mark with 10% HNO3. The procedure was
(Odeyingbo, 2011). repeated and blank was also prepared.
2.2. Sample Collection and Preparation
Three categories of dust samples were randomly 2.3.3.Method C: Digestion with HNO3 followed by
collected between November 2010 and January 2011 Extraction with HCl
during the dry season, when the prevalence of dust 1g of each dust sample was accurately weighed
was expected to be high. Dust samples were collected into a 250ml Kjeldahl flask and 3ml of concentrated
from the surfaces of printed circuit boards, plastic Nitric acid was added. It was evaporated to dryness
casings, cathode ray tubes and other internal and without allowing it to boil. After cooling, another 3ml
external components of e-waste across different stores of nitric acid was added and placed on a hot plate with
within the market by careful brushing with plastic the flask covered with a wash glass. The temperature
brushes into plastic containers. This was tagged indoor was increased until a gentle reflux action was taking
dust. Surface dust was collected randomly from bare place. Heating was continued until the digestion was
ground across the market area outside the workshops. complete which is indicated by a light coloured
This was tagged Outdoor dust. Surface dust was also residue. 15ml of 1:1 HCl/Nitric acid was added and
collected 100 meters away from the market area where the beaker again gently heated for 15 minutes. The

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 Nature and Science 2012;10(10) http://www.sciencepub.net/nature

wash glass and flask were washed down with de- recoveries with dry ashing in comparison with other
ionized water into a Whatman No. 42 filter paper and methods of digestion. Method B also gave the lowest
filtered into a 50ml volumetric flask. The filtrate was precision of the three digestion methods used;
made up to mark with de-ionized water. Blank signaling it’s unsuitability for the analysis of these
solutions were also prepared. heavy metals in the samples studied.

2.4. Heavy Metal Analysis 3.1. Statistical Analysis

The concentrations of Pb, Cd, Fe, Cr and Zn in Significant differences between concentrations
the final solutions after the digestions of the indoor, of heavy metals, following different digestion
outdoor and control dust samples were determined by methods were analyzed by ANOVA (table 2).
an atomic absorption spectrometer (AAS) (Perkin Statistical significance was defined as p < 0:05. The
Elmer 1100). one-way ANOVA showed sufficient evidence to
conclude at the 95% confidence level that the means
3. Results of the three digestion methods for the three samples
Table 1 illustrates the mean concentration (from analysed were not equal except for Cr in the outdoor
four sub-samples) of the elements determined in sample. However, results of the Student’s t-test for the
indoor dust, outdoor dust and control dust samples significance of differences of the mean values
expressed in mgKg-1. The mean heavy metal obtained between methods A and B, and methods C
concentrations in indoor dusts were higher than that of and A at a probability level of 95% (tcritical = 3.18)
dust collected from the outdoor environment and showed no difference for most metals analysed in the
control dust. This is due to the interaction between e- three samples. Table 3 lists the mean values obtained
waste and dust deposited on them over time from methods C and B, the pooled standard deviation
(Adaramodu, et al., 2011). The results of the three of both of them, the calculated texperiment, and the result
methods of digestion showed large standard deviations of the t-test against tcritical = 3.18 (95% probability
indicating the highly heterogeneous nature of the dust level). In comparison with method B, method C gave
samples. Generally, concentrations of heavy metals in significantly higher recoveries in cases of lead, iron
control dust were relatively lower than the rest (indoor and zinc in both the indoor and control samples. Only
and outdoor) with the three methods of digestion, for cadmium in indoor sample; iron, chromium and
indicating less impact of heavy metal pollution zinc in outdoor sample; and zinc in control sample the
activities within the area. Method B gave the lowest results didn’t differ significantly at this probability
results for all the heavy metals analysed in the three level. Table 4(a – c) shows the comparison of the
samples except for chromium in outdoor dust sample. precision of the three methods using F-test (one-sided
Dry ashing may cause some elements to be lost by the test) at 95% probability level. In comparison with
volatilization or adsorption of elements on the walls of method B and C, method A gave better precision for
the furnace, such that As, Cr and Pb may be lost at most of the metals analysed in the three samples while
ashing temperatures of 500–550oC (Azcue and method B gave the lowest.
Mudroch, 1994). Katz et al (1981) obtained low

Table 1: Results of the concentration of Pb, Cd, Fe, Cr and Zn in mgKg-1 found in indoor, outdoor and control
dust samples using the three different methods of digestion. The results are the mean values calculated from four
replicate measurement of each sample for the different metals.
INDOOR DUST OUTDOOR DUST CONTROL DUST
Methods
A B C A B C A B C
Pb 22.5 9.3 27 15.9 6.4 21.3 9.4 4.7 10.5
Cd 1.8 0.5 1.25 1.9 ND* 1.9 ND ND ND
Fe 108 103.3 131 103.3 74.7 106.5 62 12.3 65
Cr 0.35 ND ND 0.1 2 0.3 ND ND ND
Zn 295.5 231 63.5 213 142.5 184 78 63.5 63.5
* Not Detected

Table 2 indicated a one-way analysis of the variances (ANOVA) for comparing methods A, B and C for the
heavy metals analysed in the three samples. The between-treatment (BT) represents the three different digestion
methods while the within-treatment (WT) represents the replicate measurements of each method. The F-
experimental values should be compared to F-critical values for 2x9 degrees of freedom. The F-critical values for P
= 0.05 (95%) is 4.26 and the result of the hypothesis if the variations differ significantly is expressed by yes or no.

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 Nature and Science 2012;10(10) http://www.sciencepub.net/nature

Table 2. A one-way analysis of the variances (ANOVA) for comparing methods A, B and C for the heavy metals
analysed in the three samples.
Metal Source of Indoor Dust F- 95% Outdoor Dust F- 95% Control Dust F- 95%
Variation Experimental value Experimental value Experimental value
Pb BT/WT 56.99 yes 42.71 yes 12.65 yes
Cd BT/WT 9.47 yes - - -
Fe BT/WT 10.45 yes 5.39 yes 375.59 yes
Cr BT/WT - yes 2.91 No -
Zn BT/WT 129.77 yes 120.15 yes 52.9 yes

Table 3. Results of the Student’s t-test for the significance of differences of the mean values between methods C
and B at a probability level of 95% (tcritical = 3.18)
Element Mean of Mean of Pooled s t-value Significant
Method Method difference
CMg/kg BMg/kg
Pb 27 9.3 1.77 14.14 Yes
Dust sample Dust sample Dust sample

Cd 1.25 0.5 0.72 1.47 No

Indoor

Fe 131 103.3 11.18 3.50 Yes

Cr - - - - -
Zn 63.5 231 25.74 86.44 Yes
Pb 21.3 6.4 5.93 3.55 Yes
Cd - - - - -
Outdoor

Fe 106.5 74.7 14.21 3.16 No

Cr 0.3 2.0 1.58 1.52 No
Zn 184 142.5 54.71 1.07 No
Pb 10.5 4.7 1.12 7.32 Yes
Control

Cd - - - -
Fe 65 12.3 8.25 9.03 Yes
Cr - - - - -
Zn 63.5 63.5 7.91 0 No

Table 4(a-c). The comparison of the precision of the three methods using F-test (one-sided test) at 95% probability
level. The F-experimental values should be compared to the F-critical values for 3x3 degrees of freedom. The F-
critical values for P = 0.05 (95%) is 9.28 and the result of the hypothesis if the variances differ significantly is
expressed by yes or no.

(a) INDOOR DUST SAMPLE

Method 95% Comment Method 95% Comment Method 95% Comment
AxB BxC AxC
F-value F-value F-value
Pb 5.14 No - 1.78 No - 2.89 No -
Cd 25 Yes Method A 25 Yes Method C 1 No -
more precise more precise
Fe 11.11 Yes Method A 9 No - 100 Yes Method A
more precise more precise
Cr - - - - - - - - -
Zn 1225 Yes Method A 12.25 Yes Method C 100 Yes Method A
more precise more precise more precise

(b) OUTDOOR DUST SAMPLE

Method 95% Comment Method 95% Comment Method 95% Comment
AxB BxC AxC
F-value F-value F-value

Pb 4.84 No - 10.24 Yes Method B 2.12 No -

more precise

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 Nature and Science 2012;10(10) http://www.sciencepub.net/nature

Cd - - - - - - 2.25 No -
Fe 178 Yes Method A 100 Yes Method C 1.78 No -
more precise more precise
Cr 1.78 No - 4 No - 2.25 No -
Zn 10.30 Yes Method A 3.89 No - 2.65 No -
more precise

(c) CONTROL DUST SAMPLE

Method 95% Comment Method 95% Comment Method 95% Comment
AxB BxC AxC
F-value F-value F-value

Pb 21.78 Yes Method B 9 No - 196 Yes Method C

more precise more precise
Cd - - - - - - - -
Fe 1.83 No 1.13 No - 2.07 No -
Cr - - - - - - - - -
Zn 100 Yes Method A 4 No - 25 Yes Method A
more precise more precise

3.2. Comparison of the Digestion Methods no significant difference (p < 0.05) in mean
Method C showed higher mean lead concentrations of Fe in the three samples using
concentration than method A for the three samples methods A and C. There was also no significant
analysed. The Student’s t-test showed no significant difference in their variances except for the indoor
difference (p < 0.05) in terms of the recovery of lead dust sample where method A was found to be more
from the three samples using both methods. The precise.
comparison of the precision of both methods in the The mean Cr concentration in the samples was
analysis of the three samples also showed no generally low and was undetected in the control dust
significant difference in their variances except for the sample with the three digestion methods and in the
control dust sample where method C was found to be indoor dust sample with method B and C. This might
more precise than method A. Hence, Digestion with be due to the fact that Cr is present in small amount
nitric acid followed by Extraction with HCl (method in e-waste and also in nature. There was no
C) was found most suitable for the analysis of lead in significant difference in mean concentrations of Cr
the three samples. Sastre et al. (2002) stated that and in their variances in the outdoor dust sample
nitric acid digestion was an optimum method for using methods A and C. Method B gave the highest
estimating heavy metal content in soil samples with mean Cr concentration in the outdoor dust sample.
high organic matter content, being superior to Zeng-Yei Hseu (2004) reported the highest Cr
microwave-assisted and aqua regia digestions. recovery by dry ashing method for different composts
The higher mean cadmium concentration when compared with other methods. It is worthy to
(1.9mg/kg) recorded in outdoor dust indicates a high note that the duration of the ashing used was far less
contamination of cadmium outside the stores. This than the one used in this experiment. Morales et al.
might be due to e-waste dumping and dismantling (1989) obtained greater values for Cr by USEPA
within the environment. Cadmium wasn’t detected in method 3051 than by the dry ashing method for
the control dust sample. In comparison with method sewage sludge samples. Further Cr analysis in these
C, method A recorded higher mean cadmium samples is required.
concentration in the indoor dust but gave the same Zn was the most abundant of the heavy metals
mean concentration in the outdoor dust sample. There in the dust samples. This might be due to the
was a significant difference (p < 0.05) in terms of the presence of Zn in metal casings and also because of
recovery of cadmium in the indoor dust sample the low melting point of Zinc. Overall, method A
between methods A and C and no significant gave highest recoveries of Zn. There was a
difference in the outdoor dust sample. The significant difference in mean concentrations of Zn in
comparison of the precision of both methods in the the indoor and control dust samples using methods A
analysis of the three samples for cadmium also and C. In comparison with method B and C, method
showed no significant difference in their variances. A gave better precision for Zn in all three samples.
Method C gave the highest recovery for Fe than
the other two methods in the three samples. The high 4.0. Conclusion
concentration of Fe in the samples maybe due to the Digestion with nitric acid followed by
huge amount of Fe found in electronics. There was Extraction with HCl (method C) was found most

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 Nature and Science 2012;10(10) http://www.sciencepub.net/nature

suitable for the analysis of lead and iron in the three for the determination of metals in sewage sludges by
samples. Aqua regia (method A) could also be used flame atomic absorption spectrometry, International
reproducibly for these metals in the samples. Journal of Environmental Analytical Chemistry, 9(3)
Methods A and C could be used reproducibly for the 209-220 (1981).
7. Krolak E., Heavy metals in fallen dust in Eastern
efficient recovery of Cd in the samples. Method A Maziwiekie province, Polish Journal of environmental
was the most efficient method for recovering Zn in studies, (2000) Vol. 9, No. 6, pp 517- 522.
the samples. Dry ashing followed by aqua regia 8. Leung A.O., Cai Z.W. and Wong M.H.,
digestion gave the lowest recovery for all the heavy Environmental Contamination from Electronic Waste
metals analysed except for Cr in outdoor dust sample. Recycling at Guiyu, southeast China. Journal of
Further investigation would be carried out with the Material Cycles Waste Management (2006) 8(1):21-
dry ashing method mostly in the area of reducing the 33.
ashing period. In summary, method C is 9. Maria B. Sample digestion methods for the
recommended as the method for digesting surface determination of traces of precious metals by
spectrometric techniques, Japan Society for Analytical
dust in the recovery of Pb and Fe from e-waste site Chemistry, (2002) vol. 18, 737-750
based on recovery efficiency. Method A with 10. Ming C. and Lena Q.M. Comparison of four USEPA
comparable cost and time effectiveness with method digestion methods for trace metal analysis using
C can be used as an alternative in the pretreatment certified and Florida soils. Journal of Environmental
analysis of Pb and Fe. Method A is recommended as Quality, vol. 27, no. 6 (1998).
the method for recovering Zn in these samples while 11. Morales A., Pomares F., de la Guardia M. and
methods A and C are the recommended methods for Salvador A. Determination of cadmium, copper, iron,
the recovery of Cd in the samples. Method B is not manganese, lead and zinc in sewage sludge with prior
recommended for the analysis of these heavy metals acid digestion in a microwave oven and slurry
introduction. J. Anal. Atomic Spectrom. 4:329-332
in the samples because of its little recovery and (1989).
longer analysis time. 12. Odeyingbo O.O. Assessment of the flow and driving
forces of used electrical and electronic equipment into
Corresponding Author: and within Nigeria, M.Sc Thesis submitted to BTU,
Ehi-Eromosele C.O Cottbus, Germany. 2011.
Department of Chemistry 13. Sastre J., Sahuquillo A., Vidal M. and Rauret G.
Covenant University Determination of Cd, Cu, Pb and Zn in environmental
P.MB. 1023, Ota, Nigeria samples: microwave-assisted total digestion versus
E-mail: cyril_720@yahoo.com aqua regia and nitric acid extraction. Anal. Chim. Acta
462, 59–72. 2002.
14. Smith F.E. and Arsenault E.A. Microwave-assisted
References sample preparation in analytical chemistry, Talanta
1. Adeloju S.B. Comparison of some wet digestion and 43:1207-1268 (1996).
dry ashing methods for voltammetric trace element 15. Smith R. Handbook of environmental analysis, 2nd ed.
analysis. Analyst, 1989, 114, 455-461. Genium Publishing Corp., Schenetacdy, N.Y (1994)
2. Adaramodu A.A., Osuntogun A.O. and Ehi-Eromosele 16. Twyman R.M. Sample dissolution for elemental
C.O. Heavy metal concentration of surface dust analysis/wet digestion, University of York, York, UK,
present in e-waste components: The Westminister (2005) pp 146-153, Elsevier Ltd.
electronic market, Lagos case study, Resources and 17. U.S. Environmental Protection Agency. Soil screening
Environment, 1(1):1-5 (2011). guidance: Technical background document. USEPA
3. Azcue J. and Mudroch A. Comparison of different Rep. 540/R-95/128. U.S. Gov. Print. Office,
washing, ashing and digestion methods for the Washington D.C. (1996).
analysis of trace elements in vegetation. Int. J. 18. Available from: http:// www.cpcb.nic.in/ Electronic%
Environ. Anal. Chem. 12, 211–221. (1994) 20Waste/Chapter1-2.html.
4. Binstock D.A., Grohse P.M., Gaskill A. Jr., Sellers C., 19. Zachariadis G. A., Stratis J.A., Kaniou I. and Kalligas
Luk K.K. H.M. Kingston and Jassie L.B. G. Critical comparison of wet and dry digestion
Development and validation of a method for procedures for trace metal analysis of meat and fish
determining elements in solid waste by microwave tissues. Mikrochim. Acta 119, 191-198 (1995)
digestion, Anal. Chem. 74:360-366 (1991). 20. Zarcinas B.A., Cartwright B. and Spouncer L.R. Nitric
5. Hseu Z.-Y., Evaluating heavy metal contents in nine acid digestion and multi-element analysis of plant
composts using four digestion methods. Bioresource material by inductively coupled plasma spectrometry.
Technology 95 (2004) 53-59.
Commun. Soil Sci. Plant Anal. 18, 131–146, 1987.
6. Katz S.A., Jenniss S.W., Mount T., Tout R.E. and
Chatt A. Comparison of sample preparation methods

7/13/2012

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