Determination Of Trace Metal Elements By Dispersive Liquid-liquid Microextraction Combined With Continuum Source-graphite Furnace Atomic Absorption Spectrometry

A new method of dispersive liquid–liquid microextraction prior continuum source-graphite furnace atomic absorption spectrometry with many advantages,such as highefficiency, high recovery, low consumption, low pollution was used to determine tracechromium(VI), lead (II),cobalt(II) in environmental water samples. Dispersiveliqμid–liqμid microextraction factors were optimized, and it is applied to the determinationof the actual water samples under optimal test conditionsThe main content of the article includes the following sections:1.the sources and hazards of heavy metal elements in water,and the advances onmonitoring of metals using different extraction methods of sample pretreatment are brieflydescribed. In particular, DLLME, as a new micro-extraction technology is emphasized,andits role theory, impact factors and application in the analysis of trace elements aredetailed described.2. Ashing temperature and atomization temperature of continuum source-graphitefurnace atomic absorption spectrometry (CS-GFASS) were optimized through standardsolution of chromium(VI) and got the best conditions:1300℃and2400℃. Dispersiveliquid-liquid microextraction separate and enrich trace chromium (VI) complexes withammonium pyrrolidine dithiocarbamate(APDC) and then can be extracted into carbontetrachloride droplets formed by injecting the binary solution of carbon tetrachloride(extraction solvent) and Ethanol (dispersive solvent) into the sample solution. Factors ofDLLME have been discussed and the results is as follows: pH is2.0,temperature is35℃and the volume of chelating,extraction agent and dispersants is0.12g/L,30μL and0.5mLrespectively, extraction time is5minutes. The detection limit of chromium(VI) in watersamples is0.005μg/L and the linear range is0.05~2.00μg/L. when the concentrations of0.20μg/L,1.00μg/L Cr (VI) standard solution were measured10times， the relativestandard deviation is0.3%and2.4%. In order to simulate the actual water samples,available interfering ions were added to standard samples and the results show that therelative standard deviations were less than10%, indicating that the method has a strongselectivity and anti-interference ability.This method is low cost, easy fast, high sensitivity,and environment-friendly.3. A new method for the determination of trace lead in environmental samples wasdeveloped by dispersive liquid-liquid microextraction separation and continuum source-graphite furnace atomic absorption spectrometry (CS-GFASS) was used to determinetrace lead（II）in environmental samples with ammonium pyrrolidine dithiocarbamate(APDC) as chelating agents, carbon tetrachloride as extraction solvent and ethanol as dispersant. Factors (pH, extraction time, temperature and salinity, etc.) have beendiscussed.The results showed that the optimum conditions for the extraction of5mLsamples is as follows：pH is7.0,temperature is55℃,the concentration of the chelatingagent is0.12g/L, and the volume of extraction agent and dispersants is30uL and0.5mLrespectively. Under the optimum conditions, the detection limit of lead in water samples is0.15ug/L and the linear range is1.00~40.00μg/L. When the concentrations of5.00ug/L,20.0μg/L Pb2+standard solution were measured10times,the relative standarddeviation is4.1%and2.6%. This method is applied to the analysis of tap and river,andthe recoveries is between96.8%~104.6%and the result is satisfying.4. The method of dispersive liquid–liquid microextraction prior continuum source-graphite furnace atomic absorption spectrometry was used to determine trace cobalt（II）in environmental samples with ammonium pyrrolidine dithiocarbamate (APDC) aschelating agents, tetrachloroethylene as extraction solvent and ethanol as dispersant，andthe conditions such as pH, extraction time, temperature and salinity impacting DLLMEhave been detailedly discussed.The results showed that the optimum conditions for theextraction of cobalt in5mL samples is as follows：pH is3.0,temperature is40℃,theconcentration of the chelating agent is0.12g/L respectively,and the volume oftetrachloroethylene and ethanol is25μL and0.5mL. Under the optimum conditions, Thedetection limit of cobalt（II）in water samples is0.003μg/L and the linear range is0.05~4.00μg/L. when the concentrations of0.50μg/L,2.00μg/L Cr (VI) standard solution weremeasured10times，the relative standard deviation is2.3%and1.7%. The method hasbeen used for the determination of cobalt（II）in actual samples, such as tap, river and lakeand the result is satisfying.