E N V I R O N M E N TA L application note SIMULTANEOUS DETERMINATION of Pb, Cd, Cr, Ni, and Cu in PLANTS using microwave digestion and graphite furnace AAS Introduction The determination of lead, cadmium, chromium, nickel, and copper in plants is part of several biological monitoring programs. Monitoring these elements is important in order to observe and document the damage on plants caused by environmental pollution. The samples consist of leaves and needles collected from different types of trees. These trees are selected species monitored over a long period of time. The method described shows how Pb, Cd, Cr, Ni, and Cu can be measured simultaneously using electrothermal atomic absorption spectrometry (ETAAS). The following standard refenence materials were used to verify the method: NBS reference material: NIST 1571 (Orchard Leaves) NIST 1572 (Citrus Leaves) NIST 1575 (Pine Needles) BCR reference material: CRM 60 (lagarosiphon major) CRM 62 (olive leaves) Experimental A standard PerkinElmer SIMAA™ 6100 simultaneous atomic aborption spectrometer with transversely heated graphite furnace and Zeemaneffect background correction was employed. An electrodeless discharge lamp (EDL) was used for Cd, whereas hollow cathode lamps (HCL) were used for Pb, Ni, Cr, and Cu. The concentration of the palladium-magnesium nitrate matrix modifier was 5 µg Pd and 3 µg Mg(NO3)2 per analysis. The PerkinElmer multielement standard (Part Number N930-0244) was used to prepare the reference solutions. All reference solutions and samples were acidified using 0.2% (v/v) ultrapure HNO3. The samples were collected from reference trees using the seventh verticil from the top. The needle samples from conifers were collected during the winter pause of vegetation growth and the leaves from deciduous trees were collected during foliation. Microwave Sample Digestion The decompositions were performed in a PerkinElmer Multiwave Microwave Digestion System: • The plant samples were first dried at 105°C for 6 to 8 hours. • The standard reference materials (NIST and CRM) were dried at 80°C for 2 hours. • 0.5 gram of the dry material was decomposed in a quartz vessel using 1 mL HCl and 4 mL HNO3. • The digested samples were made up to 25-mL volume using deionized water. Multiwave Program Step 1 2 3 Power from to 100 W 800 W cool 500 W 800 W cool Time 5 min 15 min 15 min Instrument Parameter Element Wavelength (nm) Lamp Lamp current (mA) Integration time (s) Std 1 (µ g/L) Std 2 (µ g/L) Std 3 (µ g/L) Technique Signal processing Modifier (10 µ L) Replicates Modifier (10µ L) Pb Cd Cr Ni Cu 283.3 228.8 357.9 232.0 324.8 HCL EDL HCL HCL HCL 10 200 25 25 25 3.5 2.5 5.0 5.0 4.0 60 3 12 30 30 120 6 24 60 60 200 10 40 100 100 – – – – – – – – – – – – AA-BG – – – – – – – – – – – – – – – – – – – – – – – – – – – Peak Area – – – – – – – – – – – – – – – 5 µ g Pd + 3 µ g Mg (NO3)2 3 5 % Pd (NO3)2 + 0.5% Mg (NO3)2 Lagarosiphon Major (CRM 60) THGA Program Step Temp Ramp Hold Internal Gas Read flow type (°C) time time (s) (s) (mL/min) 1 2 3 4 5 110 130 400 2300 2450 1 25 10 0 1 30 30 20 5 5 250 250 250 0 250 Ar Ar Ar Ar Ar Analyte Pb Cd Cr Ni Cu X Precision and Recoveries The results of the analyses of the microwave-digested plant reference materials are shown in the following tables. Orchard Leaves (NIST 1571) Analyte Certified Average value results (mg/kg) (mg/kg) Pb Cd Cr Ni Cu 45 ± 3 0.1 ± 0.01 2.6 ± 0.3 1.3 ± 0.2 12 ± 1 40.75 0.10 2.32 1.37 11.90 SD 0.408 0.002 0.005 0.025 0.037 Citrus Leaves (NIST 1572) Analyte Certified value (mg/kg) Pb Cd Cr Ni Cu 13.3 ± 2.4 0.03 ± 0.01 0.8 ± 0.2 0.6 ± 0.6 16.5 ± 1.0 Average results (mg/kg) 12.41 0.04 0.74 0.61 16.57 0.273 0.002 0.009 0.029 0.116 Pine Needles (NIST 1575) Analyte Certified value (mg/kg) Pb Cd Cr Ni Cu 10.8 ± 0.5 < 0.50 2.60 ± 0.2 (3.50) 3.00 ± 0.3 Average results (mg/kg) 9.34 0.2 2.58 2.36 2.91 SD SD 0.037 0.004 0.021 0.054 0.020 83.8 92.1 98.9 99.0 91.2 Analyte Certified Recovery value (mg/kg) Pb Cd Cr Ni 101.4 99.0 98.9 102.9 101.7 RSD Recovery (%) (%) 0.4 2.1 0.8 2.3 0.7 87.9 107.4 92.2 96.4 112.7 65.50 2.27 25.15 40.77 57.72 25.0 ± 1.5 0.10 ± 0.02 nn (8) SD 0.196 0.029 0.151 0.367 0.404 RSD Recovery (%) (%) 0.3 1.3 0.6 0.9 0.7 91.0 101.4 98.9 102.2 93.9 Average SD RSD (%) (%) 25.96 0.08 1.63 3.16 0.649 0.006 0.030 0.231 2.5 6.1 1.8 7.3 87.9 87.2 98.0 101.1 results (mg/kg) Pine Needles (Real Sample) Cu 46.6 ± 1.8 145.95 Analyte Results SD (mg/kg) RSD Recovery (%) (%) 2.2 4.6 1.2 4.9 0.7 63.8 ± 3.2 2.20 ± 0.10 nn (40) 51.2 ± 1.9 Olive Leaves (CRM 62) RSD Recovery (%) (%) 1.0 1.7 0.2 1.8 0.3 Certified Average value results (mg/kg) (mg/kg) Pb Cd Cr Ni 29.07 0.42 6.70 5.79 0.486 0.009 0.070 0.218 Cu 52.10 0.374 Summary 0.229 0.5 101.2 RSD Recovery (%) (%) 1.7 2.1 1.0 3.7 101.5 100.5 100.2 96.1 0.7 94.3 The method described is applicable for the determination of low (ppb) levels of metals in digests of plant samples. Standard THGA graphite tubes were used. The methodology and results presented demonstrate the potential of simultaneous graphite furnace AAS for the accurate determination of trace metals in plants. In addition, there is significant time savings using fast microwave sample digestion, followed by the simultaneous atomic absorption determination of five elements. PerkinElmer Life and Analytical Sciences 710 Bridgeport Avenue Shelton, CT 06484-4794 USA Phone: 800-762-4000 (+1) 203-925-4600 www.perkinelmer.com © 2003 PerkinElmer, Inc. All rights reserved. PerkinElmer is a trademark of PerkinElmer, Inc. and AAnalyst and SIMAA are trademarks of PerkinElmer Instruments LLC. PerkinElmer reserves the right to change this brochure at any time and disclaims liability for editorial, pictorial, or typographical errors. Order No. D-5930B KG0103XX Printed in USA.