| Objective Nickel is an essential trace element for the human body,but excessive intake can inhibit the activity of certain enzymes in the body and produce toxic effects,such as delayed allergy,allergic dermatitis,lung cancer,nasopharyngeal cancer,sinus cancer and so on.It is widely used in the chemical,metallurgy,construction and other industries,which can easily cause physical damage to exposed personnel.Nickel is ingested and absorbed through the human respiratory tract in the form of dust,smoke and carbonyl vapor.About 90%of nickel is excreted in feces and 10%in urine.Therefore,the concentration of urinary nickel can be used as a biomarker for occupational contacts.The BAR of urine nickel is 3μg/L in Germany.But the biological exposure limit for it has not yet been established in our country.WS/T44-1996《Graphite Furnace Atomic Absorption Spectrometry Method for the Determination of Nickel in Urine》specifies the method for the determination of nickel in urine.Its minimum detection concentration is 1.43μg/L,which has a high detection limit and can easily be affected by urine matrix composition.Meanwhile the method has not been updated for more than 20 years.In recent years,the method of dispersive liquid-liquid microextraction has the advantages of high extraction efficiency,simple operation,high speed,and good reproducibility.It has become an environmentally friendly sample pretreatment technology.Under the action of dispersant,ionic liquid can be uniformly dispersed and insoluble in the water phase,completing the extraction of the target substance quickly.This research aims to establish an ultrasonic-assisted ionic liquid dispersion-liquid microextraction-graphite furnace atomic absorption spectrometry method for the determination of nickel in urine,so as to realize the determination of low-concentration nickel in urine.Methods Use ultrasonic-assisted ionic liquid microextraction-graphite furnace atomic absorption spectrometry to determine nickel in urine.Use single factor rotation experiment to determine the type and amount of chelating agent,dispersant and extractant,extraction time,p H and other conditions in the experiment.（1）Methanol as dispersant,ammonium pyrrolidine dithioformate as chelating agent,and[Hmim][PF6]as extractant are used to extract nickel in urine,then 600μL p H=9 buffer solution is added,sonicated for 10 minutes in water bath at 30℃,centrifuge and discard the supernatant,150μL methanol and 30 g/L vitamin C 50μL are added,vortex to dissolve for 2 min,15μL for injection is taken and measured with GFAAS7000.（2）Single factor rotation experiment is used to optimizate the type and amount of chelating agent,dispersant and extractant,extraction p H,water bath temperature,ultrasonic time,graphite tube types,graphite furnace temperature program and other conditions in the experiment.Finally the best conditions of ultrasonic-assisted ionic liquid microextraction-graphite furnace atomic absorption spectrometry for the determination of nickel in urine are determined.（3）Experimental research and discussion is conducted on methodological performance indicators such as detection limit,precision,accuracy and sample stability.（4）This method is applied to determinate urine samples of college student volunteers,and feed the SD rats with nickel solution of 500μg/L,collect rat urine,then determinate nickel content,so as to further verify the accuracy,precision and practicability of the method.（5）The uncertainty introduced during the experiment is evaluated to determine the key links that affect the results.Result（1）The best conditions are explored and the graphite furnace atomic absorption spectrophotometer is adjusted to the best state:wavelength 232 nm,spectrum width 0.2 nm,lamp current 12 m A,deuterium lamp background correction,injection volume 15μL,ashing temperature 800°C and atomization temperature2500℃.（2）Extraction conditions:anhydrous methanol as the dispersant,APDC as the chelating agent,[Hmim][PF6]as the extractant,the dosages are 500μL of anhydrous methanol,60μL of ionic liquid,10mg of APDC,p H=9,50μL of Vitamin C,sonicate for 10 minutes in water bath at 30℃.（3）The concentration of urinary nickel has a good linear relationship with its absorbance in the range of 0～10μg/L.The equation is Y=0.0466x+0.0214,r=0.996.After pretreatment,the absorbance of the blank was measured 20 times in succession on the working curve,and the concentration corresponding to 3 times the SD of the absorbance value was used as the detection limit,and the detection limit was 0.43μg/L,the RSD is between2.53%and 4.82%,the recovery rate of standard addition is between 95.6%and103.7%.（4）According to the method,the urine nickel concentration of 50 college student volunteers range from 0.50μg/L to 6.34μg/L,and the urine nickel concentration of experimental rats range from 3.49μg/L to 17.51μg/L.Conclusion（1）A new method of ultrasonic-assisted ionic liquid micro-extraction-graphite furnace atomic absorption of nickel in urine using methanol as dispersant,APDC as chelating agent,and[Hmim][PF6]as extractant was established.This method is environmentally friendly and simple operation,has high enrichment efficiency and sensitivity,the results are accurate and reliable.（2）The established new method has a low detection limit and realizes the determination of low-concentration nickel in urine,which can be applied to the determination of nickel in urine of occupationally exposed and non-occupational populations.（3）The performance of the developed method meet the standard requirements of《Guidelines for the Establishment of Occupational Health Standards Part 5:Methods for Determination of Chemical Substances in Biological Materials》.（4）The feasibility and practical value of the method are verified by testing the metabolic urine samples of rats and the urine samples of volunteers for nickel. |
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