Analysis of high purity Cu using high sensitivity LA-ICP-Q-MS K. Warnken, Thermo Fisher Scientific, Lanham, USA. J.D. Wills, L. Rottmann, Thermo Fisher Scientific, Bremen, Germany. Application Note 43142 Key Words Laser ablation, copper, ICP-MS, 5N Goal To illustrate the use of a new quadrupole ICP-MS system for the determination of trace metals in >5N Copper by laser ablation ICP-MS. Introduction Of all the elements in the periodic table, Copper (Cu) is mined and used on a global scale at a rate behind that of only Aluminium and Iron. Copper is sought for its high electrical and thermal conductivities and is used in all types of wiring applications. Copper is produced at different purity levels, e.g. the standard grade of 99.9% purity all the way up 99.999999% (known as 8N Cu), which is very limited in application because of the expense required to purify it. The world’s Cu suppliers currently use analytical techniques such as Arc-Spark OES and XRF, as well as solution-based conventional ICP-MS to control impurity levels. However, these techniques do not meet the ppb detection limit requirements currently required by Cu consumers. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) has become more appealing as a method for the analysis of impurities in Cu over other bulk techniques, which simply do not have the detection capability to match ICP-MS. The new Thermo Scientific ™ iCAP ™ Q ICP-MS, with its excellent sensitivity and background levels, coupled to a laser ablation, is thus ideally suited for the measurement of metal contaminants in high purity Cu. Quantitative analysis by Laser Ablation ICP-MS is largely dependent on the availability of calibration standards while this is less of a concern with GD-MS due to the rather small matrix dependence of the applied relative sensitivity factors (RSF) tables. While this has long been a relative weakness for LA-ICP-MS, the increasing availability of solid standards in a variety of matrices is making the technique more widespread with the eventual goal of meeting the demands of the production laboratory. Compared with solution aspiration, sample introduction via laser ablation is faster, cleaner and less costly as the acid digestion step and its environmental impact are eliminated. Methods Sample analysis Samples were analyzed for eleven analytes: 56 Fe, 60 Ni, 68 Zn 75 As, 78 Se, 107 Ag, 118 Sn, 121 Sb, 125 Te, 208 Pb and 209 Bi, using the iCAP Q ICP-MS with the New Wave Research NWR213 laser ablation system. Calibration was carried out using standards from CopperSpec ™ , Inc., at the following concentrations: 0.1, 0.5, 3.0 and 5.0 ppm. The method was validated by measurement of the European Reference Materials (ERM) EB383 and EB384. Each standard and reference standard was measured in duplicate on consecutive days. ICP-MS settings The iCAP Q ICP-MS was operated in KED mode (using 100% He in the QCell) and instrument set-up was performed using an Autotune on NIST 612 glass with a defined limit of ThO + of <0.3% (STD mode). The instrument was configured with a 2.5 mm quartz injector and a 3.5 mm skimmer cone insert.
Transcript
Analysis of high purity Cu using high sensitivity LA-ICP-Q-MS K. Warnken, Thermo Fisher Scientific, Lanham, USA. J.D. Wills, L. Rottmann, Thermo Fisher Scientific, Bremen, Germany.
Ap
plica
tion
No
te 4
31
42
Key WordsLaser ablation, copper, ICP-MS, 5N
GoalTo illustrate the use of a new quadrupole ICP-MS system for the determination of trace metals in >5N Copper by laser ablation ICP-MS.
IntroductionOf all the elements in the periodic table, Copper (Cu) is mined and used on a global scale at a rate behind that of only Aluminium and Iron. Copper is sought for its high electrical and thermal conductivities and is used in all types of wiring applications. Copper is produced at different purity levels, e.g. the standard grade of 99.9% purity all the way up 99.999999% (known as 8N Cu), which is very limited in application because of the expense required to purify it. The world’s Cu suppliers currently use analytical techniques such as Arc-Spark OES and XRF, as well as solution-based conventional ICP-MS to control impurity levels. However, these techniques do not meet the ppb detection limit requirements currently required by Cu consumers.
Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) has become more appealing as a method for the analysis of impurities in Cu over other bulk techniques, which simply do not have the detection capability to match ICP-MS. The new Thermo Scientific™ iCAP™ Q ICP-MS, with its excellent sensitivity and background levels, coupled to a laser ablation, is thus ideally suited for the measurement of metal contaminants in high purity Cu. Quantitative analysis by Laser Ablation ICP-MS is largely dependent on the availability of calibration standards while this is less of a concern with GD-MS due to the rather small matrix dependence of the applied relative sensitivity factors (RSF) tables. While this has long been a relative weakness for LA-ICP-MS, the increasing availability of solid standards in a variety of matrices is making the technique more widespread with the eventual goal of meeting the demands of the production laboratory. Compared with solution aspiration, sample introduction via laser ablation is faster, cleaner and less costly as the acid digestion step and its environmental impact are eliminated.
Methods Sample analysisSamples were analyzed for eleven analytes: 56Fe, 60Ni, 68Zn 75As, 78Se, 107Ag, 118Sn, 121Sb, 125Te, 208Pb and 209Bi, using the iCAP Q ICP-MS with the New Wave Research NWR213 laser ablation system. Calibration was carried out using standards from CopperSpec™, Inc., at the following concentrations: 0.1, 0.5, 3.0 and 5.0 ppm. The method was validated by measurement of the European Reference Materials (ERM) EB383 and EB384. Each standard and reference standard was measured in duplicate on consecutive days.
ICP-MS settingsThe iCAP Q ICP-MS was operated in KED mode (using 100% He in the QCell) and instrument set-up was performed using an Autotune on NIST 612 glass with a defined limit of ThO+ of <0.3% (STD mode). The instrument was configured with a 2.5 mm quartz injector and a 3.5 mm skimmer cone insert.
Figure 1. ESI NWR213 laser ablation system and the Thermo Scientific iCAP Q ICP-MS
Results Method detection limits were determined from repeat analyses of the 0.1 ppm Cu standard (n=6; 1 min scans). The analytical figures of merit are given in Table 3. With the exception of Fe and Se, which showed detection limits of 0.1 and 0.46 ppm respectively, limits of detection of <100 ppb were achieved. Elements such as Sb, Pb and Bi show single digit ppb detection limits.
2 Table 1. iCAP Q instrument parameters.
Parameter Value
Forward Power (W) 1550
Sampling Depth (mm) 5.0
Nebulizer Flow (mL/min) 790
(Laser cell) He Flow (mL/min) 800
(QCell) He Flow Rate (mL/min) 5.20
KED Voltage Step (V) 4
Laser Ablation Instrument SettingsThe NWR213 is a frequency quintupled 213 Nd:YAG laser, which is capable of an energy of ~3.5 mJ pulse-1. The sample chamber is a two volume large format cell, with a sampling size of 100 mm x 100 mm. Helium was introduced into the laser cell using the on-board mass flow controller at a rate of 800 mL/min and mixed with Argon just prior to the torch. A 60s ablation line was positioned on each of the four standards and two reference materials. Pre-ablation of the surface was carried out, due to severe contamination of Fe and Zn. A total of three line analyses were made at each sample; the first line was used for pre-ablation and only data from the two final passes was used for subsequent quantification.
Table 2. NWR213 instrument parameters.
Parameter Value
Energy (mJ) 3.7
Repetition Rate (Hz) 20
Spot Size (µm) 250 (Focussed Beam)
Scan Rate (µm/s) 15
Analyte Dwell Time (sec) Resolution R
valueBEC
(ppb)MDL (ppb)
56Fe 0.050 Normal 0.9983 170 10065Cu 0.050 High - - -60Ni 0.050 Normal 0.9999 36 2668Zn 0.050 Normal 0.9983 74 4375As 0.050 Normal 0.9998 92 6978Se 0.050 Normal 0.9947 300 460
107Ag 0.050 Normal 0.9999 0 13118Sn 0.050 Normal 0.9999 40 40121Sb 0.050 Normal 0.9998 0 6.0125Te 0.050 Normal 0.9992 23 78208Pb 0.050 Normal 0.9994 0 4.0209Bi 0.050 Normal 0.9998 0 7.0
Table 3. Analytical figures of merit for the determination of trace elements in solid Cu by laser ablation ICP-MS. The MDL is calculated as three times the standard deviation of two runs conducted on three consecutive days.
3The percentage recovery of Cu, used as the internal standard to track the ablation process over the course of the analyses, is shown in Figure 2. Example calibration curves are shown in Figure 3 for the elements As, Ag and Bi.
Figure 2. The percent recovery for Cu as an internal standard.
Figure 3. Calibration curves for the elements As, Ag and Bi.
Time-resolved scans of Bi in the 0.1 ppm standard are shown as overlaid plots in Figure 4. Scan regions were set up to include a gas blank region from 0 to 20 seconds, followed by a quant region from 35 to 75 seconds, using the new Thermo Scientific™ Qtegra™ software. The fully quantitative results for the reference standards BAM 383 and BAM 384 are given in Tables 4 and 5, respectively.
Table 5. Fully quantitative results for the standard reference material BAM 384.
ConclusionFull quantitative analysis of eleven trace elements in a solid Cu matrix by Laser Ablation ICP-MS has been demonstrated using commercially available calibration standards and standard reference materials. The high sensitivity of the Thermo Scientific iCAP Q ICP-MS in KED mode, with its proprietary Flatapole technology makes the detection of sub-ppm levels of contaminants in solid Cu easily achievable. The larger ablation two-volume cell of New Wave’s NWR213 Laser system is suited for a high-volume operation allowing a batch analysis of any number of samples that fit inside a 100x100 mm cell space. The seamless interface between the laser and the ICPMS systems allows the analyst the convenience to perform the operation and collect data directly from one computer screen.
