Determination Of Cadmium In Urine By Dispersive Ionic Liquid-liquid Microextraction-Graphite Furnace Atomic Absorption Spectrophotometry

Objective Cadmium is a highly toxic heavy metal element widely used in the manufacture of pigments,plastic stabilizers,?TV image tube?phosphors,insecticides,fungicides,paints,batteries and other fields.Cadmium can be quickly absorbed by the body through the respiratory tract,digestive tract,etc.Among which,cadmium absorbed through the respiratory tract accounts for 25%to 40%of the total cadmium intake.60%of cadmium in human body is enriched in the liver and kidney,and excreted in the urine and bile by metabolism.Sore throat,fever and other symptoms could be resulted from a large amount of cadmium oxide exposed in a short period of time.In severe cases,toxic pulmonary edema and chemical pneumonia could occur.And long-term exposed has bad influences on the body's immune system,urinary system,bones,nervous system,and reproductive system.With the widespread use of cadmium in industry,the cadmium content in occupational and natural environments has been increasing,the health problems caused of which have became increasingly significant.There is a significant linear relationship between urinary cadmium emission and cadmium content in the body,so that urinary cadmium can be used as a good bio-monitoring indicator of cadmium content in the body,depend of which,the damage caused by cadmium could be indirectly judge.The5?g/g creatinine?in the urine?of cadmium was stipulated as biological exposure limit?index?by China's WS/T 113-1999 and the American Association of Governmental Industrial Physicians?ACGIH?.A national standard method GBZ/T 307.1-2018 has been established for the determination of cadmium in urine in China,a matrix improver was used to directly dilute the sample and then measurement was carried out in this method.Actually,the measurement results could be greatly affected by the matrix of the urine sample,which resulting in a large error in the determination when the content of elements to be tested is in a low level.It is only suitable for the determination of urinary cadmium in occupational exposed populations,but isn't suitable for urinary cadmium in non-occupational exposed populations,and the method is prone to double peaks during the detection process,which causes interference to quantitative detection.In view of the above problems,an ionic liquid dispersion liquid-liquid microextraction-graphite furnace atomic absorption spectrometer for detecting cadmium in urine was established,This method utilizes liquid-liquid microextraction and acid solution elution process to separate and purify cadmium in urine,thereby greatly reducing the influence of substrate components on the detection process,depend on which,the method could provide a methodological basis for the detection of urinary cadmium in occupational and non-occupational exposed populations.Methods The pre-treatment technology of ionic liquid dispersion liquid microextraction was adopted.0.50 ml of urine sample was take into a 10 ml centrifuge tube,0.50 ml NH₃-NH₄Cl buffer solution was added,and then pure water was added to 3ml,through the above steps,the pH was adjusted to 9.560?l[Hmim][PF₆]-APDC-ethanol mixed system solution was injected into the tube,5 min later in 45°C water bath,centrifugation was conducted at 3500r/min for 5 min,then the upper solution was removed.After which,200?l 10%nitric acid was used to back stripping.2 minutes later,centrifugation at 3 500r/min for 5 min.100?l of the supernatant was accurately aspirated using a calibrated pipette after stratification,50?l of 0.03 g/ml vitamin C matrix modifier was added to make a final volume of 0.15 ml,10?l of which was finally injected for detection.The concentrations of cadmium and the corresponding absorbance values were choosed as abscissa and ordinate,respectively.The conditions of impregnated graphite tube type,the type and amount chelating agent and dispersing agent,amount of extracting agent,extraction pH,extraction temperature,extraction time,eluent dosage,eluent time and graphite furnace parameters were investigated through single factor rotation test.On the basis of the single factor rotation experiment,three factors beside chelating agent APDC,dispersant ethanol and[Hmim][PF₆],which have great influence on DLLME,were selected and tested by orthogonal table design to attain the optimal DLLME conditions.The method was applied to urine samples of college students and cadmium occupational exposure population,and the accuracy,precision and practicability of the method were also further verified.In addition,the uncertainty introduced during the experiment was assessed to determine the key aspects of uncertainty.Results The experimental results showed that the high density graphite tube impregnated with cerium nitrate can effectively reduce the substrate effect and improve the sensitivity of the sample.With 60?l of extractant[Hmim][PF₆],0.50 ml of dispersant ethanol,0.2 mg of chelating agent APDC added to 3.0 ml of the diluted sample,extraction for 5 min at pH=9,45°C water bath can effectively increase the extraction rate of urinary cadmium.After extracted,the supernatant was removed by centrifugation,and 200?l of10%nitric acid was used to elute for 2 min to obtain a good elution effect.Adding0.03g/ml of vitamin C matrix modifier 50?l to the supernatant of the eluate can effectively eliminated the double peak and reduced matrix interference.Under the operational conditions of a high-density graphite tube impregnated with cerium nitrate,with an ashing temperature of 800°C,and an atomization temperature of 2000°C for the graphite furnace atomic absorption spectrometer,the cadmium standard solution showed a good linear relationship with the absorbance value in the range of 1.00²0.0?g/l.The standard curve equation y=0.0243x+0.0089,the correlation coefficient r=0.9992,the detection limit of the method was 1.3pg?0.078?g/L?.The Spike recovery were95.2%¹07.5%,the relative standard deviation were 1.66%³.98%.The measured value of cadmium in freeze-dried human cadmium control sample?No.ZK018-1?was 5.47?g/L,which met the requirements of the standard value 5.1±0.9?g/L,the urinary cadmium range of college students were 0.12?g/l².85?g/L,and the range of cadmium exposed workers were 2.67⁹.88?g/L.A 5.0?g/L urine sample was assessed with an extended uncertainty of 0.4?g/L.Conclusions Cadmium in urine was determined by dispersion liquid-liquid microextraction-graphite furnace atomic absorption spectrometry,ionic liquid was selected as extractant,ethanol as dispersant,APDC as chelating agent,the best extraction and elution condition was explored by single factor rotation and orthogonal test.The method can selectively enrich the urine cadmium,remove the matrix which has great influence on the detection result,and has the advantages of low detection limit,high sensitivity,with no harm to the human body,and accurate and reliable detection result for the low concentration sample.The indicators of this method were in line with the standard requirements of the“Guidelines for the establishment of occupational health standards,Part 5:Methods for determination of chemical substances in biological materials”?GBZ/T210.5-2008?.The method was applied to the determination of actual urinary cadmium content in college students and cadmium occupational exposure populations,which verified the feasibility of the method.It was suitable for the detection of urinary cadmium in occupational and non-occupational exposure populations.It has practical value and can provide technical support for the determination of urinary cadmium content.