The Application Of Surface-enhanced Raman Spectroscopy In Detection Of Heavy Metal Ions In Water

Surface-enhanced Raman spectroscopy(SERS)is a method based on molecular vibration for trace analysis.This method has high sensitivity and is often applied to detect environmental,food,drugs and other aspects.There are many reports on the synthesis of silver nanoparticles(Ag NPs)that as a widely substrate for SERS.The shape and size of the Ag NPs and the properties of the reducing and protecting agent have a certain influence on the SERS signal intensity.In this paper,sodium alginate and sodium citrate were used as reducing and protecting agents for synthesis Ag NPs,and the heavy metal ions Cr(VI)and Hg(II)in water were quantitatively detected.An easily manipulated method was developed to synthesize Ag NPs by using sodium alginate(SA)to perform the dual role of reducing and protecting agent.The particle size of SA-protected Ag NPs is about 27 nm.Using SA-protected Ag NPs as substrates,a simple and ultra-sensitive surface-enhanced Raman scattering(SERS)method was established for the determination of Cr(VI)in water.The method is based on redox reaction of carbimazole with Cr(VI).In the presence of Cr(VI),the SERS signal of carbimazole decreases with the increase of Cr(VI)concentration,so as to achieve the purpose of indirect determination of Cr(VI).The volume of Ag NPs,the acidity of the system and the concentration of Na Cl solution were optimized.Under optimum conditions,a good linearity(r = 0.993)in the range of 1.71–171 × 10-9 mol L-1 was obtained and the limits of detection(LOD)is 1.01 × 10-9 mol L-1.The method was applied to the determination of Cr(VI)in water,with recoveries between 97.9–104.0% and with relative standard deviations of < 4.0%(n = 5).AgNPs was synthesized by using sodium citrate as a reducing and protecting agent,which was based on a slight adjustment of the method of Lee and Meisel.Acriflavine can absorb on the surface of Ag NPs through electrostatic interaction or Ag-N band which can produce a SERS signal of acriflavine.In the presence of Hg(II),citrate ion attached to the surface of Ag NPs could reduce Hg(II)to Hg,and then formed the Hg-Ag alloys on the surface of Ag NPs.It prevents the interaction of acriflavine with Ag NPs and leads to a decrease of SERS signal.Hg(II)is determined indirectly by using acriflavine as a SERS probe.The volume of Ag NPs,p H,and the concentration of Na Cl were optimized.Under the optimal conditions,there was a good linear relationship when the concentration of Hg(II)in the range of 0.1-8.0×10-7 mol L-1,and the correlation coefficient was 0.996.The limit of detection(LOD)and limit of quantitation(LOQ)were 2.8 nmol L-1 and 9.4 nmol L-1,respectively.The recovery of Hg(II)in the actual sample was 92.55%-102.38%.