Determination of Chromium and Zinc in Soil by Microwave Digestion and Flame Atomic AbsorPtion SPectrometry

Tianshun WANG，Yu YA，Jie HE，Leixing MO，Bo LlN，Song Ll，Junjie ZHP*

1.Research lnstitute of Agro-products QualitY SafetY and Testing TechnologY，Guangxi AcademY of Agriculture Sciences/QualitY Supervision and Testing Center for Sugarcane，China NinistrY of Agriculture，Nanning 530007，China；

2.Sugarcane Research lnstitute，Guangxi AcademY of Agriculture Sciences，Nanning 53007，China

Determination of Chromium and Zinc in Soil by Microwave Digestion and Flame Atomic AbsorPtion SPectrometry

Tianshun WANG1，Yu YA1，Jie HE1，Leixing MO1，Bo LlN1，Song Ll2，Junjie ZHP1*

1.Research lnstitute of Agro-products QualitY SafetY and Testing TechnologY，Guangxi AcademY of Agriculture Sciences/QualitY Supervision and Testing Center for Sugarcane，China NinistrY of Agriculture，Nanning 530007，China；

2.Sugarcane Research lnstitute，Guangxi AcademY of Agriculture Sciences，Nanning 53007，China

［Objective］The aim was to develop a rapid，simple method for determination of chromium and zinc in soil samples bY flame atomic absorption spectrometrY.［Method］The method for determination of Cr and Zn in soil bY combined flame atomic absorption spectrometrY and microwave digestion was used. ［Result］The concentration curve was linear within the range of 0-0.8 mg/L for Cr and 0-0.8 mg/L for Zn，the detection limits of Cr and Zn was 0.0025 mg/L and 0.002 3 mg/L，respectivelY.Recoveries of 102.4%-103.2%for Cr and 97.7%-98.3%for Zn were obtained for there soil samples.［Conclusion］The proposed method has the advantages of simple operation，high sensitivitY，and high efficiencY；it was successfullY used for determination of Cr and Zn in soil samples.

Nicrowave digestion；Flame Atomic absorption spectrometrY；Chromium；Zinc；Soil

S oil，as an important part of the environment，has been increasinglY paid attention to the impact on human health.The determination of toxic metals in soil has become a matter of wide interest as a means of assessing their influence in the environment process，with the social progress as well as the enhancement of environmental protection.Soil is easilY sampled and provides a useful indicator of exposure to toxic and heavY metals.lt is also known that these elements and their compounds can be toxic if their concentrations exceed certain limits.Thus，the determination of chromium and zinc in soil appears to be much more important. There are manY methods［1-12］to determine the levelofCrand Zn. Some of them emploY standard addition method，and some include sample pre-procession，such as drY or wet or microwave digestion or graphite digestion.

The aim of the wok discussed in this paper was to develop a rapid，simple method for determination of Cr and Zn in soil samples bY FAAS.The validitY of the method for real sample analYsis was tested bY successful determination of Cr and Zn in three soil samples and two certified reference materials. The characteristics of method are its simplicitY，sensitivitY and efficiencY.

ExPeriments

APParatus

Varian AA240 flame atomic absorption spectrometrY，including uncode Hollow Cathode Lamp；was purchased from America Varian Corporation.Speedwave NWS-2 Nicrowave Digestion SYstem with Built-in，Non-ContactTemperatureNeasurement was purchased from BERGHOF Products+instruments GNBH，Ger

manY.UPH-Ⅱ-20T UP Water Purification sYstem was purchased Cheng-du ultra pure science and technologY Co.，LTD，China.

Reagents and materials

All reagents are of highest available puritY or at least analYtical grade. Ultra-pure water obtained from UP Water Purification sYstem was used throughout.Blended Standard working solutions of Cr （10.0 mg/L）and Zn（10.0 mg/L）were prepared bY stepwise dilution of a standard stock solution of Cr and Zn （1 000 mg/L Cr and 1 000 mg/L Zn；supplied bY the National Center for Standard Naterials，Beijing，China）with 1%（V/V）HNO3just before use.Nitric acid solution，1%（V/V），was prepared bY dissolving the reagents in ultra-pure water.Soil samples were picked from chewing cane field.

All the glass and plastic wares were soaked in 20%（V/V）nitric solution for 24 hours，and then rinsed bY ultra-pure water，finallY dried in a dustfree environment.After these steps the Cr and Zn contents of blank solutions were negligible.

The Processing of the soil

The collected soil sample was airdried and quartered after removing stones，animal and plant debris and other foreign matter，then soil sample was picked up and grinded with agate stick.SubsequentlY，sieved through a 2mm nYlon sieve and mixed，the soil sample was further grinded with agate mortar，and then sieved through a 100 mesh sieve.

SamPle PreParation

The 0.250 0 g soil sample and certified reference materialsample were placed in PTFE vessels，respectivelY.After adding 5 ml HNO3，1 ml H2O2，3 ml HCl and 1 ml HF，the vessels were sealed and placed in the microwave digestion oven.The digestion program consisted of three stages，stage 1（160℃，10 min，90%of power），stage 2 （200℃，20 min，90%of power）and stage 3（100℃，10 min，40%of power）.After digesting and cooling room temperature，the solution in a vessel was transferred into a 50 ml calibrated flask for further test.At the same time，a blank sample was prepared.

Analytic Procedures

0，1.0，2.0，3.0，4.0ml of the blended standard solution 10.0 mg/L Cr and 0，0.5，1.0，2.0，4.0 ml of the blended standard solution 10.0 mg/L Zn were put in 5 calibrated flasks of 100ml，then diluted to scale with nitric acid solution （1%，v/v），respectivelY. The total solution volume in each flask was 50ml，the Cr concentrations in different flasks were 0，0.20，0.40，0.60，0.80 mg/L and Zn concentrations in different flasks were 0，0.10，0.20，0.40 and 0.80 mg/L.Then the contents of Cr and Zn in each sample were determined bY FAAS.The Cr and Zn level of soil sample were obtained from standard calibration curve bY sample absorbance after blank solution correction.Operation conditions of FAAS are listed in Table 1.

Table 1 Working parameters of flame atomic absorption spectrophotometer

Table 2 Calibration function，detection limits，and precision

Table 3 Result from determination of Cr and Zn in the CRN

Table 4 Result from determination of Cr and Zn in the soil samples

Result and Discussion

Effect of matrix modifier

As the vulnerable elements，Cr and Zn are easilY disturbed in the determination process.ln the nitric acid medium （1%，v/v），the contents of Cr and Zn were determined with matrix modifier，including LaNO3，NH4Cl，and NH4NO3.The experiment showed that the intensitY of the atomic absorption for Cr is strong and stable enough to measure with NH4Cl as matrix modifier，and for Zn with LaNO3as matrix modifier.

Analytical Performance

The analYtical characteristics of the proposed method were satisfactorY（Table 2）.lt should be noted that the methods for determination Cr and Zn are reliable and calibration graphs were verY good linearitY.The detection limits （DL）for both elements were evaluated on the basis of the standard deviation （SD）of signals measured（11times）for the bland solution，and theY were calculated from the formula DL=（3SD）K-1，where K is the slope of the calibration graph.The precision（RSD）was examined in terms of repeatabilitY of the analYtical results.

To demonstrate the accuracY of the method，it was used for determination of Cr and Zn in GBW07403 and GBW07408.Results from determination of Cr and Zn in the GBW07403 and GBW07408 are shown in Table 3.lt can be seen that the value determinedbYmethodswereingood agreement with the certified values.

The methods were also successfullY applied to the determination of Cr and Zn in three soil samples.The results are shown in Table 4.With recoveries bY adding standard analYte solutions to digests，the concentrations added the analYtes were similar to half of the original value.

Conclusion

After digesting，determination of Cr and Zn in soil bY flame atomic absorption spectrometer is fast and simple.The determination of the standard reference material was within the permissible error range.The method can meet the requirement of determination of Cr and Zn in soil samples.

Reference

［1］PENG JR（彭靖茹），GAN ZY（甘志勇），NONG YJ（农耀京）.Continuous determination of available Cu，Fe，Zn and Nn in soil bY ultrasonic extraction-flame atomic absorption spectrometrY（超声波提取-火焰原子吸收光谱法连续测定土壤中有效铜铁锌锰）［J］，Journal of analYtical science（分析科学学报），2011，27（2）:261-263.

［2］GAO XL（高筱玲），WANG RF（王瑞芬），ZHAO ZY （赵智勇）.Determination of Cu，Zn，Ni，Cr in soil bY inductivelY coupled plasma optical emission spectrometrY using electric heating-graphite digestion（电热石墨消解lCP-OES测定土壤中铜锌镍铬）［J］.Chemical analYsis and meterage（化学分析计量），2013，22（3）:54-56.

［3］PENG N（彭萌），ZHU K（诸堃），CHEN LH（陈莲红），et al.lCPNS determination of Cr，Cd，Ni，Cu，Pb and Zn in atmo

spheric dust fall（电感耦合等离子体质谱法测定大气降尘中铬、镉、镍、铜、铅和锌）［J］.PhYsical testing and chemical analYsis:part B chemical analYsis（理化检验-化学分册），2012，48（9）:1039-1041.

［4］HE LZ（和丽忠），DU LJ（杜丽娟），YAN HN （严红梅），et al.Determination of Pb，Cd，As，Cu，Zn and Cr in blank fungus bY lCP-NS with microwave digestion（微波消解-电感耦合等离子体-质谱法测定黑木耳中铅、镉、砷、铜、锌和铬）［J］. Chinese journal of spectroscopY laboratorY（光谱实验室），2012，29（1）:435-438.

［5］Ll CL（李昌丽），JlANG XG（蒋晓光），ZHANG YF（张彦甫），et al.Determination of copper，zinc and chrome content in laterite nickel ores bY flame atomic absorption spectrometrY（火焰原子吸收光谱法测定红土镍矿中铜、锌、铬含量）［J］.Chemical analYsis and meterage（化学分析计量），2012，21（3）:44-27.

［6］HU XJ（胡晓静），ZENG Z（曾泽），WANG CW （王长文），et al.lnductivelY coupled plasma atomic emission spectrometric determination of acid-soluble metal elements chromium，manganese，zinc and copper in talcum power（电感耦合等离子体原子发射光谱法测定滑石粉中酸溶金属元素铬锰锌铜）［J］.Netallurgical analYsis（冶金分析），2011，31（9）:7-10.

［7］WU YL（吴育廉）.Digestion with high pressure airproof pot-determined of Fe and Zn in babY formula bY using flame atomic absorption spectrometrY（高压密封湿法消解-火焰原子吸收光谱法测定婴儿配方奶粉中铁锌）［J］.Studies of trace elements and health（微量元素与健康研究），2011，28（3）:49-50.

［8］WEl SH（魏淑红），GUO JC（郭晋川），WANG J（王吉），et al.Determination of lead and zinc with high content bY inductivelY coupled plasma optical emission spectrometrY（电感耦合等离子体发射光谱法测定矿石中的高含量铅和锌）［J］.Chinese journal of spectroscopY laboratorY（光谱实验室），2013，30（6）: 3268-3272.

［9］DeivY Wilson，Juan Nanuel Gutiérrez，Salvador Alegret，et al.Simultaneous Determination of Zn（ll），Cu（ll），Cd（ll）and Pb（ll）in Soil Samples EmploYing an ArraY of Potentiometric Sensors and an Artificial Neural Network Nodel［J］. ElectroanalYsis，2012，24（12）:2249-2256.

［10］WU JW，TAN YF，WANG YQ，et al. Toxic metal contamination in Artemisia annua L.herbal preparations from different commercial sources in China［J］.JournalofNaturalNedicines. 2011，65（3-4）:656-661.

［11］CHEN SJ，ZHANG XS，YU LY，et al. Simultaneous determination of Cr（lll）and Cr（Vl）in tannerY wastewater using low pressure ion chromatographY combined with flow injection spectrophotometrY［J］.Spectrochimica acta Part A:molecular and biomolecular spectroscopY.2012，88:49-55.

［12］ALENA NANOVA，SONA HUNENlKOVA，NlLAN STRELEC，et al.Determination of chromium （Vl）and total chromium in water bY in-electrode coulometric titration in a porous glassY carbon electrode［J］.Nicrochimica Acta.2007，159（1-2）:41-47.

ResPonsible editor：Xiaoxue WANG

ResPonsible Proofreader：Xiaoyan WP

微波消解-火焰原子吸收测定土壤中的铬和锌

王天顺1，牙禹1，何洁1，莫磊兴1，林波1，李松2，朱俊杰1*（1.广西农业科学院农产品质量安全与检测技术研究所/农业部甘蔗品质监督检验测试中心，广西南宁 53007；2.广西农业科学院甘蔗研究所，广西南宁 530007）

［目的］探索一种简单快捷的利用原子吸收光谱法测定土壤中的铬和锌的方法。［方法］利用微波消解样品，建立了原子吸收光谱法测定土壤中的铬和锌的方法。［结果］铬在0～0.8 mg/L浓度范围内和锌0～0.8 mg/L浓度范围内的校正曲线呈线性，检出限分别为0.002 5 mg/L和0.002 3 mg/L。3个土壤样品铬和锌的加标回收率分别为102.4%～103.2%、97.7%～98.3%。［结论］该方法操作简单、灵敏度高、高效，适合土壤样品中铬和锌的测定。

微波消解；火焰原子吸收光谱；铬；锌；土壤

广西农科院基本科研业务专项重点项目（桂农科2014JZ01）；广西农科院基本科研业务专项重点项目（桂农科2013YZ07）。

王天顺（1980-），男，河南项城人，助理研究员，硕士，主要从事农产品质量安全及产地环境研究。*通讯作者，E-mail：xcdike2325@163.com。

2015-07-06

Supported bY KeY Fund of Guangxi AcademY of Agricultural Sciences（2014JZ01 and 2013YZ07）.

*Corresponding author.E-mail:xcdike2325@163.com

Received:JulY 6，2015 Accepted:August 16，2015

修回日期 2015-08-16