Table 1.

An evaluation of M²⁺ interference-correction approaches on m/z 75 in reagent and regional tap water matrices fortified with Nd and Sm

Reagent Water Fortified with Low and High Rare Earth Spikes	m/z 75, No Correction1,2	m/z 75, No Correction1,3	m/z 75, External Correction1,3,4	m/z 75, In-Sample Correction5	m/z 91, 8800 ICP-MS6	High Resolution ICP-MS7
	4.5mL He ([ppb] ± 2σ)	2.5mL He ([ppb] ± 2σ)	2.5mL He ([ppb] ± 2σ)	2.5mL He ([ppb] ± 2σ)	75→91 As [O2] ([ppb] ± 2σ)	75As ([ppb] ± 2σ)
2 ppb Nd	0.05 ± 0.03	0.04 ± 0.04	0.00 ± 0.04	0.00 ± 0.04	−0.002 ± 0.001	−0.012 ± 0.002
2 ppb Nd + spike8	0.10 ± 0.06	0.10 ± 0.03	0.06 ± 0.03	0.05 ± 0.07	0.05 ± 0.01	0.043 ± 0.005
50 ppb Nd	1.44 ± 0.21	0.84 ± 0.13	−0.02 ± 0.12	0.06 ± 0.22	0.000 ± 0.001	−0.0111 ± 0.0004
50 ppb Nd +spike8	1.51 ± 0.12	0.92 ± 0.18	0.06 ± 0.18	0.05 ± 0.22	0.05 ± 0.01	0.045 ± 0.009
2 ppb Sm	0.06 ± 0.04	0.03 ± 0.02	0.00 ± 0.02	0.01 ± 0.05	0.003 ± 0.002	−0.009 ± 0.001
2 ppb Sm + spike8	0.09 ± 0.04	0.09 ± 0.06	0.05 ± 0.07	0.07 ± 0.06	0.05 ± 0.01	0.044 ± 0.001
50 ppb Sm	1.36 ± 0.16	0.79 ± 0.13	−0.07 ± 0.12	−0.03 ± 0.20	0.000 ± 0.001	−0.01 ± 0.01
50 ppb Sm + spike8	1.45 ± 0.14	0.84 ± 0.12	−0.01 ± 0.11	0.05 ± 0.11	0.05 ± 0.01	0.034 ± 0.007
Regional tap waters9
Water A + 50 ppb Gd, Nd, Sm	3.01 ± 0.31	1.74 ± 0.22	−0.22 ± 0.24	0.52 ± 0.46	0.45 ± 0.02	0.48 ± 0.14
Water B + 50 ppb Gd, Nd, Sm	2.47 ± 0.34	1.27 ± 0.27	−0.73 ± 0.29	0.08 ± 0.25	0.18 ± 0.01	0.15 ± 0.05
Water C + 50 ppb Gd, Nd, Sm	4.85 ± 0.47	3.38 ± 0.51	1.60 ± 0.54	2.27 ± 0.47	2.03 ± 0.03	2.11 ± 0.48
Water D + 50 ppb Gd, Nd, Sm	2.83 ± 0.65	1.53 ± 0.34	−0.46 ± 0.40	0.20 ± 0.33	0.23 ± 0.02	0.17 ± 0.05
Water E + 50 ppb Gd, Nd, Sm	2.77 ± 0.32	1.44 ± 0.40	−0.62 ± 0.46	0.10 ± 0.52	0.11 ± 0.01	0.07 ± 0.02
Water F + 50 ppb Gd, Nd, Sm	2.91 ± 0.52	1.53 ± 0.15	−0.51 ± 0.15	0.29 ± 0.28	0.35 ± 0.02	0.32 ± 0.06

^1.Data were collected in normal resolution mode (0.8 amu at 10% peak height) using In as an internal standard with a 0.3-sec/amu integration time in selective ion monitoring mode. All estimates are based on 10 instrument replicates.

^2.The calibration blank and 50 ppt standard associated with the analysis of reagent waters (4.5 mL He) produced 3 cps and 45 cps, respectively. The calibration blank and 100 ppt standard associated with the regional waters (4.5 mL He) produced 6 cps and 60 cps, respectively.

^3.The calibration blank and 50 ppt standard associated with the analysis of reagent waters (2.5 mL He) produced 6 cps and 41 cps, respectively. The calibration blank and 100 ppt standard associated with the regional waters (2.5 mL He) produced 12 cps and 56 cps respectively.

^4.The M²⁺ correction factors were estimated in narrow resolution mode (0.4 amu at 10% peak height) using an external rare earth standard and applied as a fixed correction factor to all samples. This correction also incorporated a narrow to normal conversion factor (see Figure 5). No additional correction was required for the ⁴⁰Ar³⁵Cl interference.

^5.Data were collected in narrow resolution mode (0.4 amu at 10% peak height) using In as an internal standard with a 0.3-sec/amu integration time in selective ion monitoring mode. All estimates are based on 10 instrument replicates. The M²⁺ correction factors were estimated in each sample. The solutions fortified with 2 ppb rare earth produced about 30 cps at the corresponding half-mass with percent relative standard deviation (RSD) across the 10 replicates of about 25%. The solutions fortified with 50 ppb rare earth produced about 300–500 cps at the corresponding half-mass with %RSD across the 10 replicates of about 12%. A 50 ppt As standard in narrow resolution mode using 2.5 mL He produces 25 cps with a 3 cps blank. All in-sample M²⁺ estimates required manual abundance-sensitivity evaluations at the adjacent masses to the M²⁺ ion. No additional correction was required for the ⁴⁰Ar³⁵Cl interference.

^6.Data were collected at m/z 91 in oxygen mode using 0.5 mL/min with a 0.99-sec/amu integration time in selective ion monitoring mode. All estimates are based on n = 5 using Y as an internal standard (YO⁺, 89→105). The calibration blank and 50 ppt standard produced 6 cps and 465 cps, respectively.

^7.Arsenic data used a mass range of 74.916–94.926 amu, 40 samples per peak, 0.200 sampling time, and 30% search and 60% integration windows over 3 runs and 2 passes (n = 6). All data were collected in high-resolution mode, and concentrations were determined relative to the ¹¹⁵In internal standard. The Auto Lock Mass feature was active during analysis.

^8.This sample was fortified with 0.050 ppb As and 1 ppb Se.

^9.All regional waters were prepared to reflect the 0.4% HCl concentration that results from an acid digestion according to Method 200.8.