Use of an ICP-MS for direct analysis of multiple elements in a sample matrix > 0.4% dissolved solids using uhmi. Fred Fryer Agilent Technologies

Transcription

1 Use of an ICP-MS for direct analysis of multiple elements in a sample matrix > 0.4% dissolved solids using uhmi Fred Fryer Agilent Technologies July 8,

2 Challenges of measuring samples Weakly acidified water is our ideal and difference in response compared to the ideal is undesirable or needs to be compensated for. Differences observed are: Element signal suppression or enhancement (per sample) Longer term upward or downward change in signal (drift). The change is seen once the dissolved solid content of a sample excedes 0.2% w/v and can have a few causes.

3 Effects of the sample matrix cones Nebulization Desolvation Vaporization, Atomization, Ionization Sample density, surface tension, viscosity affects nebulisation Intractable material deposits on the cooler interface and changes the performance of the vacuum interface (cones) and is seen as drift. The major element composition in the plasma affects degree of ionisation eg: sodium suppresses, carbon enhances, at about 0.5% or more. The composition of the ion beam affects mass balance due to space charge. Confidentiality Label July 8,

4 The Sample Matrix typical seawater Element Atomic Weight 1 st Ionization Potential Concentration (mg/l) Sodium (Na) ,800 Chlorine (Cl) ,400 Magnesuim (Mg) ,290 Sulfur(S) Potassium (K) Calcium (Ca) Bromine (Br) Causes Ionization suppression Forms polyatomic interferences False response due to polyatomic molecules are greater with heavier matrix. Agilent and ICP-MS August 2007

5 Seawater The suppression and drift is caused by the amount of sample matrix dilution puts less sample matrix into the ICP-MS, giving tolerance Undiluted Seawater Initial calibration CCVs and s Cal Blank Cal Blank 1/10 Seawater replicates (n=10) / 25 5 / / Blank 1000 ppm Na Check ICSAB + 1ppb + 1ppb + 1ppb + 1ppb + 1ppb CCV + 1ppb + 1ppb + 1ppb + 1ppb + 1ppb CCV + 1ppb + 1ppb + 1ppb + 1ppb + 1ppb CCV + 1ppb + 1ppb + 1ppb + 1ppb + 1ppb CCV Li / 6 [#3] Sc / 45 [#1] Sc / 45 [#2] Sc / 45 [#3] Ge / 72 [#1] Ge / 72 [#2] Ge / 72 [#3] In / 115 [#3] Tb / 159 [#3] Bi / 209 [#3] Approximately 10% upward drift in sensitivity over 14 hours of continuous analysis of 1/10 seawater Agilent and ICP-MS August 2007

6 Challenges of Measuring High TDS samples Robustness > Design the sample introduction such that the sample change doesn t have such an impact High solids nebuliser, low flow sample introduction system, wide torch injector diammeter, High RF power, long residence time in the plasma. Many challenges- How can these be addressed? Use a collision cell capable of dealing with the polatomic molecules Helium collision for single quad or QqQ reaction Dilution > Reduce the matrix back to the ideal (< 0.2% tds)

7 Dilution Offline LOR is increased by dilution factor Online Solution based dilution online has a few limitations Slow Varies with varying matrix, if using peripumps the dilution ratio changes over time Aerosol dilution The nebuliser aerosol is reduced but the total gas flow to the plasma is maintained - aerosol is diluted into argon High Matrix Introduction system Confidentiality Label July 8,

8 Aerosol dilution Normal sample uptake rate ~0.4 ml min -1 Sample aerosol is diluted by addition of gas after the spray chamber Makeup (Dilution) gas in Carrier gas in to torch Carrier gas 0.23 L min -1 Makeup gas 0.72 L min -1 Total gas flow = 0.95 L min -1 to drain Agilent and ICP-MS August 2007

9 Combining aerosol suppression and ion diffusion -highly robust conditions -excellent stability for undiluted seawater raw counts (normalized) long-term stability for undiluted seawater (50ppb/5ppm spiked) (repeated measurements of seawater for 15 hours) measurement # 9 Be (He) 25Mg (He) 27Al (He) 39K (He) 43Ca (H2) 44Ca (H2) 51V (He) 52Cr (He) 55Mn (H2) 56Fe (H2) 58Ni (He) 59Co (He) 60Ni (He) 63Cu (He) 65Cu (He) 66Zn (He) 75As (He) 78Se(H2) 88Sr (He) 88Sr (H2) 95Mo (He) 107Ag (He) 111Cd (He) 114Cd (114) 121Sb (He) 137Ba (He) 208Pb (He) 232Th (He) 238U (He) Agilent and ICP-MS August 2007

10 New revision HMI = uhmi (Ultra HMI) Increased dilution range to x100 even higher matrix capability Less matrix loading to interface, so better long-term stability uhmi maintains high carrier gas flow through spray chamber, so faster gas replacement and washout HMI-4 (HMI-L) HMI-8 (HMI-M) HMI-25 (HMI-H) Carrier gas flow (L/min) 7700 HMI 7900 UHMI HMI-50 N.A Total gas flow UHMI Dilution Port HMI-100 N.A

11 Other sample introduction considerations Agilent Ar gas humidifier Assists when measuring high salt solutions Uses a hollow fiber membrane tubing to wet the aerosol Helps to reduce salt build-up in the interface and at the nebuliser tip. 2 channels in one body for Carrier gas and Dilution gas

12 Brine Analysis: Chemicals and Samples Actual samples of nearly saturated salt water are not easy to obtain. In this experiment, artificial salt water was prepared from commercial table salts. 30g of pure sodium chloride (Kanto Chemicals, Japan) dissolved in 100g of UPW was used for preliminary experiment (23%). Calibration standards were prepared by spiking to this solution. Samples for analysis were purchased in Japan and USA

13 Brine Analysis: Results and Discussion The recovery rates were calculated by spiking to the actual salt water with various concentration. Very good recoveries could be obtained over a wide ( ppb) concentration range. Fig 2: Spiked concentrations Fig. 3. Recovery rates

14 Detection limits Table 3. Detection Limits in ppb (ug/l) Detection limits were calculated from 3 standard deviations of calibration blank counts from the mean. (3 sigma DL) Internal standard was added online so the counts are normalised to internal standard signal. 7 Li Cu Cd Mg Zn Sn Al Ga Sb S As Te K Se I Ca Br Cs Ti Rb Ba V Sr W Cr Zr Au Mn Mo Hg Fe Ag Pb

15 Normalized concentration of analyte Long term stability test 140% 130% 120% Fig. 4: 5 hours stability 7Li/6Li Nogas 39K/45Sc H2 48Ti/45Sc HEHe 65Cu/45Sc He 79Br/115In HEHe 88Sr/103Rh HEHe 138Ba/159Tb HEHe 26Mg/45Sc H2 44Ca/45Sc H2 55Mn/45Sc H2 79Br/115In H2 85Rb/103Rh He 133Cs/159Tb Nogas 208Pb/209Bi He 110% 100% 90% 80% 70% 60% 0:00:00 1:00:00 2:00:00 3:00:00 4:00:00 5:00:01 Elapsed time The long term stability of analyte concentration was examined by using one of the salt sample solutions The stability graphs show that ISTD works very well. There was no need to clean the lenses after analysis

16 Analysis of various type of table salts K Mg Ca S Zr Ga Cs W Salt samples #1-15: Sea or Rock salt from Japan, Mexico, Germany, South Africa, USA, Pakistan, Mongolia Covers concentration range from <0.01 ppb to >1,000 ppm in Brine.

17 Excellent detection capability with He collision Spectral interference from the major component (Cl) of salt water was almost completely eliminated by He mode. 51 V (ClO interference) and 75 As (ArCl interference) were detected at low concentrations in 23% NaCl. V BEC: 0.06 ppb As BEC: 0.2 ppb

18 Other productivity tools for the 7900 Integrated Sample Introduction System (ISIS 3) Increase the sample thru-put, and save on Ar costs Close-coupled valve very short tube length so minimal stabilization/rinse delay Easier tubing setup by color coding Piston pump for faster sample uptake 3-way valve to switch between online ISTD or tune solution ISIS is compatible with Startup autooptimization functions and full autotune 7 port valve (incl. online ISTD port) Piston pump 3-way valve

19 Summary 7900 ICP-MS with UHMI makes it possible to analyze even saturated salt water. Good stability Low detection limit Wide measurement range from ppt to >1,000 ppm Expands ICP-MS into fields where only AAS, ICP-OES or XRF have previously been available. Low sample preparation NPT SAPK, Agilent Restricted January