were used as chemical modifiers for the determination of the Pb, Cd, Cr, Cu, and Ni levels. The reagents were of analytical grade, and all solutions were prepared using deionized water (18.2 MΩ/cm) produced using a PureLab Prime system (PALL, Washington, NY, USA). All containers and glassware were cleaned by soaking in the 5 mol/L HNO3 for at least 24 hours and rinsed three times with deionized water prior to use.
ซื้อจากศูนย์วิจัยแห่งชาติที่ได้รับการรับรองอ้างอิงวัสดุของจีน(Beijing, China) ส่วน working standard solutions เตรียมทุกวันโดย stepwise dilution of the standard stock solutions ใช้ 0.5% (v/v) nitric acid (HNO3), ammonium phosphate monobasic (NH4H2PO4), and magnesium nitrate [Mg(NO3)2]