Study On Solid Phase Extraction Of Trace Elements From Food Grade FeSO₄·7H₂O And Determination By Atomic Spectrometry

The paper reviewed the methods for determination of trace elements in iron matrix and the application of solid phase extraction techniques to separation and enrichment of trace elements in inorganic samples.The methods for detecting trace elements in food grade FeSO4·7H2O by combining ion exchange fiber solid phase extraction with atomic spectrometry was established.1.A method for detecting trace manganese in food grade FeSO4·7H2O by combining solid phase extraction with atomic spectrometry was established.The research showed that when coexistent amount of iron was greater than or equal to 100 times of manganese,the relative error of direct determination of manganese by FAAS was greater than or equal to+5%.The separation principle of this method is Mn2+ions can be absorbed by SACEF but Fe3+ ions can’t be absorbed in EDTA and HNO3 medium when pH is 1.5.Because under this condition,Fe3+ ions can react wilil EDTA to form complex anion.Firstly,Fe2+ions were oxidized to Fe3+ by HN03.Fe3+ions were masked by 5.00 mL 0.1 mol·L-1 EDTA in HN03 medium when pH was 1.5.Mn2+ ions were then adsorbed by 0.0200 g strong acid cation exchange fiber(SACEF)for 10 min and eluted by 10.00 mL 2.5 mol·L-1 HNO3 for 15 min.Extract liquid was detected by FAAS.The coexistent amount of iron was only 2 times of manganese after separation and the interference was eliminated.Under the optimum conditions,the adsorption capacity of SACEF to Mn2+ ions were attained to be 9.27 mg·g-1.The method’s detection limit of manganese was found to be 0.115μg·mL-1.The proposed method was used for determination of manganese in synthetic mixtures and food grade FeSI4·7H2O.The research showed that the both measured results of manganese by FAAS and ICP-AES were basically consistent.The recoveries were in the range of 96.1%～103%and RSDs(n=5)were less than 3.0%.The contents of manganese in three batches of FeSO4·7H2O samples were 325 μg·g-1,823 μg·g-1,772 μg·g-1 respectively.The quality of FeSO4·7H2O samples all reached the requirements of Chinese Pharmacopoeia(The contents of manganese must be less than 0.1%).2.Solid phase extraction(SPE)as a per-treatment technique for ICP-AES and FAAS,the method for separation and enrichment of trace zinc in food grade FeSO4·7H2O samples by using strong base anion exchange fiber(SBAEF)as sorbent was studied.The research showed that when coexistent amount of iron was greater than or equal to 60 times of zinc and coexistent amount of manganese was greater than or equal to 20 times of zinc,the relative error of direct determination of zinc by FAAS was greater than or equal to+5%.The separation principle of this method is Zn2+ions can be absorbed by SBAEF in 1.5 mol·L-1 HC1 medium because Zn2+ ions can react with Cl-1 to form complex anion under this condition.Fe3+ ions and Mn2+ ions can’t react with Cl-1 to form stable complex anion under this condition.So they can’t be absorbed.Firstly,Fe2+ions were oxidized to Fe3+ions by HNO3.Zn2+ions were adsorbed by 0.3000 g SBAEF for 20 min and eluted by 15.00 mL HNO3 with pH value was 1.5 for 10 min.Extract liquid was detected by FAAS.The coexistent amount of iron was only 13 times of zinc after separation and the interference was eliminated.Under the optimum conditions,the adsorption capacity of SBAEF to Zn2+ ions was attained to be 26.4 mg·g-1.The method’s detection limit of zinc was found to be 0.011μg·mL-1.The proposed method was used for determination of zinc in synthetic mixtures and food grade FeSO4·7H2O.The research showed that the both measured results of zinc by FAAS and ICP-AES were basically consistent.The recoveries were in the range of 95.0%～106%and RSDs(n=5)were less than 6.0%.The contents of zinc in three batches of FeSO4-7H2O samples were 26.4 μg·g-1,21.9 μg·g-1,39.6 μg·g-1 respectively.The quality of FeSO4-7H2O samples all reached the requirements of Chinese Pharmacopoeia(The contents of zinc must be less than 0.05%).3.A method for detecting trace cobalt,manganese and nickel in food grade FeSO4-7H2O by combining solid phase extraction with atomic spectrometry was established.The research showed that when coexistent amount of iron was greater than or equal to 1000 times of manganese,4300 times of cobalt and 700 times of nickel,the relative error of direct determination of manganese,cobalt and nickel by ICP-AES was greater than or equal to+5%.The separation principle of this method is that complex stability constant of Co2+-Cl-1,Mn2+-Cl-1 and Ni2+-Cl-1 are smaller than Fe3+-Cl-1 complex stability constant.Fe3+-Cl-1 complex anion can be absorbed by SBAEF but Co2+,Mn2+and Ni2+can’t be absorbed.Firstly,Fe2+ions were oxidized to Fe3+by HNO3.The method of determination cobalt and manganese:Fe3+ions was adsorbed by 0.3000 g SBAEF for 30 min in 2.0 mol·L-1 HCl medium.Extract liquid was detected by ICP-AES.The method of determination nickel:Fe3+ions were adsorbed by 0.4000 g SBAEF for 30 min in 12.0 mol·L-1 HCl medium.Extract liquid was detected by ICP-AES.The coexistent amount of iron was only 181 times of manganese,3620 times of cobalt and 300 times of nickel after separation and the interference was eliminated.Under the optimum conditions,the adsorption capacity of SBAEF to Fe3+ions was attained to be 41.2 mg·g-1.The method’s detection limit of cobalt,manganese and nickel was found to be 0.06pμg·mL-1,0.0092 μg·m-1 and 0.0034 μg·mL-1.The proposed method was used for determination of cobalt,manganese and nickel in synthetic mixtures and food grade FeS04-7H20.The recoveries were in the range of 90.7%～101%and RSDs(n=5)were less than 7.0%.The contents of manganese in two batches of FeSO4·7H2O samples were 312 μg·g-1,808 μg·g-1 The contents of cobalt in two batches of FeSO4·7H2O samples were 16.3μg·g-1，15.5μg·g-1.The contents of nickel in two batches of FeS04-7H20 samples were 1.65 μg·g-1,1.43 μg·g-1.4.Solid phase extraction(SPE)as a per-treatment technique for ICP-AES,the method for separation and enrichment of trace arsenic in food grade FeSO4·7H2O samples by using strong acid cation exchange fiber(SACEF)as sorbent was studied.The research showed that when coexistent amount of iron was greater than or equal to 400 times of arsenic,the relative error of direct determination of arsenic by ICP-AES was greater than or equal to+5%.The separation principle of this method is arsenic can’t be absorbed by SACEF,but Fe3+ions can be absorbed when pH of medium is 2.0.Because most of arsenic exist in the form of arsenate under this condition.Firstly，Fe2+ ions was oxidized to Fe3+ ions by HNO3.Fe3+ ions was adsorbed by 1.0000 g SACEF for 20 min in pH=2.0 HNO3 medium.Extract liquid was detected by ICP-AES.The coexistent amount of iron was only 7 times of arsenic after separation and the interference was eliminated.Under the optimum conditions,the adsorption capacity of SACEF to arsenic was attained to be 48.5 mg·g-1.The method’s detection limit of arsenic was found to be 0.027 μg·mL-1.The proposed method was used for determination of arsenic in synthetic mixtures and FeSO4·7H2O samples.The recoveries were 99.6%and RSD(n=5)was 1.6%.The content of arsenic was zero in FeSO4-7H2O samples.