USGS Test Method I-2020-05


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Source:
USGS

Method Name:
Elements (filtered) in water by cICP-MS. Official Name: Determination of Elements in Natural-water, Biota, Sediment, and Soil Samples using Collision/Reaction Cell Inductively-Coupled Plasma-Mass Spectrometry

Description:
The inductively coupled plasma operating characteristics used in this method are typical of those used in earlier methods. However, there are substantial differences in the sample introduction and ion optics in conjunction with the use of the collision/reaction cell. A pneumatic concentric nebulizer is used to introduce samples at a flow rate of 0.2 to 0.3 mL/min into a thermostatically controlled spray chamber. This introduction system minimizes sample volume requirements, increases sample introduction efficiency, reduces instrumental drift, and reduces oxide and hydroxide molecular ions. The internal standards are introduced automatically through a junction tee. Most of the lens potentials and pole biases are similar regardless of whether a collision gas is introduced; notable differences are the cell entrance and exit potentials and the quadrupole (QP) and octapole (OctP) biases. Nominal hydrogen and helium flow rate in the gas cell is about 4 mL/min. Previous ICP-MS methods used substantially different sample-introduction systems (nebulizer and spray chamber) and ion optics.Minor changes were required for determining the distribution of arsenic species using high-performance liquid chromatography (HPLC) in combination with cICP-MS instrumentation. An Agilent 1100 HPLC was used to separate the arsenic species with various anion exchange columns and mobile phases as described in the original methods. No changes were needed for arsenic speciation methods that use hydride generation for sample introduction. However, there was a mismatch in flow rates between the HPLC (about 1 mL/min) and the microflow nebulizer (about 0.3 mL/min) for other arsenic speciation methods. The mismatch required using the junction tee that is usually used for introducing the internal standard to reduce flow into the nebulizer. Differences in data-acquisition characteristics, nebulizer flow rate, spray-chamber volume, and transfer-line lengths had negligible effects on the chromatograph

Scope:
The method described in this report can be used to determine a wide range of elements in filtered water. The collision/reaction gas is used when determining As (speciated and unspeciated), Ca, Co, Cr, Cu, Fe, K, Mg, Na, Ni, Se, Si, V, W, and Zn.

Citation:
Garbarino, J.R., Kanagy, L.K., and Cree, M.E., 2006, Determination of elements in natural-water, biota, sediment, and soil samples using collision/reaction cell inductively coupled plasma-mass spectrometry, U.S. Geological Survey Techniques and Methods Book 5, Ch. B1

Interferences:
Spectral interferences associated with isobaric ions and molecular ions can affect the accuracy of elemental analysis using ICP-MS. Molecular ion interferences evolve from the argon plasma and elements composing the sample matrix. Such interferences are greatly reduced or eliminated for ICP-MS instruments that use a collision/reaction cell without using correction equations. By introducing a gas into the cell, either He or H2 in this method, an interfering molecular ion is isolated from the analyte ion through collisional or reactional interactions, thereby improving the accuracy of the determination of selected elements.Interferences also may be associated with aqueous sample introduction and ionization processes. Dissolved-solid concentrations affect nebulization efficiency and suppress ionization. Typical limitations for dissolved-solid concentration for most pneumatic nebulizers range from 0.1 to 0.3 percent; some high dissolved-solid nebulizers do not have this limitation but also have higher sample flow rates. High dissolved solid concentrations associated with easily ionized cations like sodium affect the ionization of analyte ions. Dissolved-solid concentrations of 0.1 to 0.3% translate into estimated specific conductances of between 4,000 and 6,000 uS/cm in natural water These test-sample results suggest that samples having specific conductances less than 7,500 uS/cm can be analyzed directly with acceptable bias and variability. In previous ICP-MS methods, samples with specific conductances greater than 2,500 uS/cm required dilution.

QC Requirements:
A minimum of one laboratory reagent blank is analyzed for every 10 analytical samples. A minimum of one laboratory control samples is analyzed for every 10 analytical samples.

Maximum Holding Time:
6 months for acid-preserved samples stored in tightly capped polyethylene bottles

Media:
WATER

Subcategory:
Inorganic

Concentration:
Variable based on analyte.

Sample Prep:
See http://pubs.water.usgs.gov/twri9A/,

Precision:
Bias and variability were determined at 2 to 4 spike-concentration levels in reagent-water, ground-water, and surface-water matrices. Reagent water was spiked at 4 concentrations; 2 levels were in the lower one-third of the normal calibration range, 1 at roughly one-third and 1 at roughly two-thirds of the normal calibration range. Ground-water and surface-water matrices were spiked at roughly one-third and two-thirds of the normal calibration range. The number of measurements at each concentration was between 16 and 33 for each matrix determined over several days.

Detection:
Most method detection limits are lower or relatively unchanged compared to earlier methods except for Co, K, Mg, Ni, SiO2, and Tl, which are less than a factor of 2 higher. Other elements (Ag, Al, B, Ba, Be, Cd, Li, Mn, Mo, Pb, Sb, Sr, Tl, and U) that have been determined using previous ICP-MS methods can be determined with similar performance using this method.

Revision Number:
2006

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