The PerkinElmer Elan 6100 DRC ICP-MS has a Dynamic Reaction Cell (DRC), which can be used to help reduce certain interferences. Basically, the cell is a low resolution quadrupole inside a metal can that normally acts as an ion beam transfer lens. In DRC mode a small amount of gas is bled into the can, which chemically reacts with polyatomic ions in the ion beam. Our lab uses ammonia gas (NH3). The gas reacts with different species in the ion beam in different ways. Some species, such as Ar+ and ArO+, react rapidly and are almost quantitatively lost from the ion beam. If the interfering species reacts faster than the species you are trying to measure (e.g., ArO+ interfering with 56Fe), then reduction in the interference can result in drastically improved detection limits.

Optimization solutions

  1. Stock stock element solution: to a 1000 ml volumetric flask add 0.01 ml of each of the single element solutions you are interested in, 14 ml of high-purity HNO3, and dilute to volume. Element concentration is 10 ppb.
  2. Blank: to a 100 ml volumetric flask add 1.4 ml of high-purity HNO3, and dilute to volume.
  3. Chloride blank: to a 100 ml volumetric flask add 0.28 ml of high-purity HCl, 1.4 ml of high-purity HNO3, and dilute to volume. Cl concentration is ~1000 ppm.
Here are the results of an optimization, done at standard operating conditions with the non-cooled spray chamber.

  Abundance, % Best NH3 flow, ml/minute Acceptable NH3 flow, ml/minute "Detection limits, ppb" DRC of value Comments
27Al 100 0.5 0.45 0.4-0.55 0.3-0.65 0.001 0.001 Yes Reduces background by only ~50%.
28Si 92.23 0 0 0 0 <1 <1 No Large N2 interference, recommend no HNO3 in any analytical solutions (DI water only).
31P 100 0   0.1-0.2   1   No  
39K 93.26 0.1   0.1-0.5   0.3   Yes DRC reduces the tail of 40Ar, but doesn't have much effect on whatever interference is sitting directly under 39K
40Ca 96.94 0.45   0.3-1.0   0.1   Yes  
44Ca 2.09 0   0.1-1.0   1   No  
45Sc 100 0 0 0.25-0.4 0.25-0.4 0.003 0.003 No  
51V 99.76 0.4 0.35 0.25-0.6 0.25-0.4 0.0002 0.0015 Yes ClO+ interference
52Cr 83.76 0.3 0.4 0.25-0.4 0.35-0.5 0.0003 0.0003 Yes  
53Cr 9.55 0.45 0.6 0.3-0.5 0.5-0.9 0.001 0.002 Yes ClO+ interference
55Mn 100 0.6 0.65 0.5-0.8 0.45-0.8 0.002 0.001 Yes Low NH3 flow yields poor results
54Fe 5.82 0.5 0.5 0.3-0.55 0.4-0.55 0.002 0.002 Yes Best Fe mass for most natural water samples; 56Fe signal is unnecessarily large.
56Fe 91.66 0.4 0.4 0.3-0.5 0.3-0.5 0.0005 0.0005 Yes CaO+ interference
57Fe 2.19 0.3 0.35 0.25-0.45 0.25-0.4 0.01 0.015 Yes CaO+ interference
59Co 100 0 0 0.25-0.4 0.25-0.45 0.0003 0.0003 No  
58Ni 68.27 0 0.3 0.25-0.45 0.25-0.4 0.001 0.001 If Cl-rich Minor CaO+ interference
60Ni 26.10 0 0 0.25-0.45 0.25-0.35 0.001 0.001 No Minor CaO+ interference
64Zn 48.89 0 0.3 0.25-0.4 0.25-0.45 0.001 0.001 If Cl-rich TiO+, minor CaO+ interference
66Zn 27.81 0 0 0.25-0.4 0.25-0.5 0.001 0.001 No TiO+ interference
68Zn 18.57 0.7 0.7 0.5-0.8 0.55-0.75 0.005 0.005 Yes  
63Cu 69.09 0 0 0.25-0.45 0.25-0.4 0.0005 0.0005 No TiO+, NaAr+ interference
65Cu 30.91 0 0 0.25-0.45 0.25-0.45 0.001 0.005 No TiO+ interference
69Ga 60.4 0 0 All All 0.0003 0.0003 No  
71Ga 39.6 0 0 All All 0.0003 0.0003 No  
75As 100 0 0 0.25-0.4 0.25-0.4 0.003 0.003 No Ammonia DRC gas has no benefit for ArCl+ interference.
76Se 9.02 0.6 0.7 0.55-0.75 0.5-0.75 0.02 0.02 Yes  
77Se 7.58 0 0 0.25-0.55 0.25-0.4 0.01 0.01 No Used for ArCl+ correction on As+.
78Se 23.52 0.45 0.45 0.25-0.55 0.25-0.55 0.02 0.02 Yes  
82Se 9.19 0 0 0.25-0.45 0.25-0.35 0.03 0.03 No  
Blue areas are results for a 1% HNO3 blank.
Green areas are results for a 1% HNO3 blank with 1000 ppm Cl.
Preferred isotope.
"Detection limits" just based on peak/background count rates, actual detection limits will be poorer.

 

The end result is that the following elements are best analyzed (in water samples) at the following DRC cell gas flows:

 

Elements NH3 gas flow Suggested internal standard elements
Sc, Co, Ni, Zn, Cu, Ga, As, Se None Sc, Co, Ga
K (best) 0.1 ml/minute Ga
K, Ca, Al, V, Cr, Fe 0.40 ml/minute Ga
Mn 0.60 ml/minute Ga

 

Kurt Hollocher

Geology Department

Union College

Schenectady, NY  12308

U.S.A.