ENVIRONMENTAL analysis A routine method for the Quantitative Measurement of trace metals in WATER Samples compliant with the WATER Quality Standard EN ISO 17294 on the Agilent 7000 Series ICP-MS. Solutions for Your Analytical Business Markets and Applications Programs Authors Roberto Riccio, Vincenzo Misticoni Enzo Trivellone P Paolo Scardina Agilent Technologies, Italy. INTRODUCTION This paper describes the development of a method for the routine measurement of trace level metals in water samples, compliant to the requirements of the Water Quality Standard EN ISO 17294 using an Agilent Technologies 7000 series ICP-MS. This note accompanies a two-day training program where the following points are addressed: 1. Summary of Water Quality Standard EN ISO 17294 2. Setting up the operating procedure 3. Definition of the tests requiring implementation 1. SUMMARY OF WATER QUALITY STANDARD UNI EN ISO 17294-1 The measurement contents and points in the regulatory documents are addressed with the following points. Principles of operation of the ICP-MS General description of the instrument configuration and accessories used. Problem of spectral and non-spectral interferences along with possible analytical approaches to their resolution and control Instrument optimization and calibration Method configuration Definition of analysis and monitoring The general principles of ICP-MS operation, with particular reference to the Agilent 7000 series, are covered during instrument training to bring the users to the required level of competency. One major topic covered defines the methodology that needs to be implemented for management of spectral and non-spectral interferences.
2. SETTING UP THE OPERATING PROCEDURE Method configuration consists of three basic steps: PREPARATION STEP DEFINITION OF A ROUTINE SEQUENCE DETAILED DESCRIPTION OF BLOCKS PREPARATION STEP Choose the elements and isotopes of interest, and set integration times Select and optimize the instrumental parameters Define the calibration ranges Choose the internal standard Choose the Interference Check Solution (ICS) necessary for monitoring of interferences in routine sequences and for determining the LDM. ELEMENTS, ISOTOPES AND INTEGRATION TIMES The elements of interest, isotopes and typical integration times are shown in the table below. The system automatically suggests the isotopes and the recommended exposure times for each element. The final optimization is made during method development. ELEMENT ISOTOPE FIRST/SECOND/THIRD INTEGRATION TIME [s] Ag 107 / 109 1 Al 27 0.5 As 75 1 B 10 / 11 0.3 Ba 137 / 138 0.3 Be 9 1 Cd 111 / 114 1 Co 59 0.3 Cr 52 0.5 Cu 63 / 65 0.3 Fe 56 0.3 Hg 202 / 201 1 Mn 55 0.3 Mo 95 / 98 0.5 Ni 58 / 60 0.3 Pb 208 / 206 / 207 0.3 Sb 121 / 123 1 Se 78 1 Sn 118 / 120 0.3 Tl 205 / 203 0.3 V 51 0.5 Zn 66 / 64 0.3 2
Corrections equation can be needed in case of alternate isotopes as described in the regulation. Selection and Optimization of Instrumental Parameters Auto-tune tools will optimize all instrument parameters (X, Y, Z, gas flows, forward power, etc.) SELECTION CORRECT INTERNAL STANDARDS In Inductively Coupled Plasma Mass Spectrometry (ICP-MS), the overall analytical responses of the elements of interest can be influenced by a number of parameters including: The degree of ionization in the plasma Nebulization and sample transport efficiency Choice of ICS (Interference Check Solutions) Removal control of molecular (polyatomic) interferences are important factors in ICP-MS analysis and regardless of the mode of removal, ICS solutions are chosen to simulate the worst analytical operating conditions thereby ensuring effective and reliable performance under normal operating conditions. The following two stock solutions are used to prepare the two interference checks solutions, ICS1 and ICS2. 6020 Interference Check Solution A (ICS A) Cl 20000 ppm Ca 3000 ppm Fe/Na 2500 ppm C 2000 ppm Al/Mg/P/K/S 1000 ppm Ti/Mo 20 ppm HNO3 5% 6020 Interference Check Solution B (ICS B) Co/Cr/Cu/Mn/Ni/V 20 ppm As/Cd/Se/Zn 10 ppm Ag 5 ppm HNO3 5% 3
Definition of a Routine Sequence According to requirements, a standard operating sequence would be as follows: Calibration Block CB: Calibration Blank CS1-n: Calibration Solution 1... n Initial Verification Block ICB: Initial Calibration Blank (memory effect after calibration block) ICV: Initial Calibration Verification (verification of one of the points of the calibration curve prepared from a different stock solution) CRM: Certified Reference Material (Analysis of a certified reference material [NIST 1643e] for verification of the calibration curve) Intenference Check Block ICS 1: Interference Check Solution 1 (verification of formation rate of interferences) ICS 2: Interference Check Solution 2 (verification of the percent recovery of known spike) Sample Block 1 10 to 20 unknown samples in which to determine the analytes of interest Continuous Verification Block CCB: Continuous Calibration Blank (memory effect after sample block) CCV: Continuous Calibration Verification (verification of one of the calibration points prepared from a different stock solution) Sample Block... n 10 to 20 unknown samples in which to determine the analytes of interest Final Verification Block CCB: Continuous Calibration Blank (memory effect after sample block) CCV: Continuous Calibration Verification (verification of one of the calibration points prepared from a different stock solution) Final Interference Check Block ICS 1: Interference Check Solution 1 (verification of formation rate of interferences) ICS 2: Interference Check Solution 2 (verification of the percent recovery of known spike) 4
Initial Verification Block ICB: Initial Calibration Blank - prepared in the same way as the Calibration Blank using the same acid matrix and dilution water. The response for each analyte, measured in counts per second (cps), must be less than that of the Calibration Blank multiplied by ten: cps (ICB) < 10 x cps (CB). ICV: Initial Calibration Verification - verification of one of the calibration points, typically in the middle of the calibration (STD IV recommended). The observed concentration value for this control standard must be within ± 20% of the expected value. CRM: Certified Reference Material (such as the NIST 1640 for waters). Depending on the concentration of the specific metal in the CRM, recovery values should be within ± 30% Interference and Final Interference Check Block Using the stock solutions, ICS A and ICS B, the two Interference Check Solutions, ICS 1 and ICS 2, were prepared. Continuous and Final Verification Blocks CCB: Continuous Calibration Blank - prepared in the same way as the Calibration Blank using the same acid matrix and dilution water. The response for each analyte, measured in counts per second (cps), must be less than that of the Calibration Blank multiplied by ten: cps (CCB) < 10 x cps (CB). CCV: Continuous Calibration Verification - verification of one of the calibration points, typically in the middle of the calibration (STD IV recommended). The observed concentration value for this control standard must be within ± 20% of the theoretical value expected. 3 - DEFINITION OF TESTS REQUIRING IMPLEMENTATION Once the methodology and configuration have been checked and verified the final method should prove robust provided the routine optimization and checks are adhered to as outlined herein. The fundamental parameters that should be verified and optimized are: Selection of Internal Standards LDI Instrumental Detection Limits LDM Method Detection Limits Precision of the Method Testing the Operating Sequence Internal Standards / LDI / LDM The control and optimization of Internal Standards, together with the calculation of LDI, LDM, can be made using the following sequence: 5
CALIBRATION BLOCK CB: Calibration Blank CS1-n : Calibration Solution 1... n INITIAL VERIFICATION BLOCK ICB: Initial Calibration Blank ICV: Initial Calibration Verification CRM: Certified Reference Material LDI BLOCK Blank 1 Blank 10 INTERNAL STANDARD BLOCK 1 (NO MATRIX) CCV 1 CCV 10 LDM BLOCK ICS 1.1 ICS 1.10 INTERNAL STANDARD BLOCK 2 (MATRIX) ICS 2.1 ICS 2.10 FINAL CHECK BLOCK CCB: CCV: Continuous Calibration Blank Continuous Calibration Verification From the data collected in this sequence, Internal Standard responses can be monitored with varying concentrations of analytes and matrix. Data collected in the two blocks, LDI BLOCK and LDM BLOCK, allows the Instrumental (LDI) and Method (LDM) Limits of Detection to be calculated by applying the following formula: A more conservative LDM can be calculated by measuring the sample solution ICS 1 over 10 consecutive days, and applying the following formula: 6
Values for each analyte are read from the respective calibration curves and the values of LDI and LDM are expressed in the same concentration units. Testing the Standard Operating Sequence The second day of testing is dedicated to operating sequence verification. In order to evaluate recoveries and the repeatability over the course of a complete sequence, three unknown water samples A, B and C are spiked. These samples along with a certified reference material (e.g. CRM NIST 1640) are then analyzed using the routine sequence previously described. 7
APPENDIX: STANDARDS AND REAGENTS Ultrapure H2O according to ASTM Type I 18.2 Mohm Superpure grade HNO3 (Ultrapure if possible) Superpure grade HCl (Ultrapure if possible) Hg Standard (concentration of 10 ppm or higher) Multi-element standard containing all analytes of interest (concentration of 10 ppm or higher) REFERENCES 1. EN ISO 17294-1:2007 Water Quality Application of Inductively Coupled Plasma Mass Spectrometry (ICP- MS) Part 1: General Guidelines 2. EN ISO 17294-2:2005 Water quality -- Application of inductively coupled plasma mass spectrometry (ICP-MS) -- Part 2: Determination of 62 elements Single standards of Al, Fe, Cu, B, Zn (concentration of 1000 ppm) Single standards and multi-element standards containing internal standards (Li-6, Ge-73, Rh-104, In-115, Ir-193) (concentration of 10 ppm or higher) Stock interference check solutions - ICS A and ICS B (supplied by Agilent) CRM (Certified Reference Material) NIST 1640 3 unknown water samples that are typically analyzed in the laboratory (at least 500 ml per sample) Information, descriptions and specifications in this publication are subject to change without notice. Solutions for your analytical business Markets & Applications Programs www.solutions-to-win.com Agilent Technologies, Inc. 2014 Published in USA, November 10, 2014 5991-5320EN