The 5 Most Common Questions About ICP-MS

1. The test results do not meet expectations and are either too high or too low. Where do the errors come from?

Assuming there are no issues in the overall testing process, it is normal to have some degree of variation. Every test has a certain level of uncertainty, so some differences in the data are to be expected.

As long as these differences are not significant, they are considered normal. If the discrepancies are large, the causes should be analyzed from two perspectives.

First, the testing party should analyze whether improper operations in any steps could lead to significant data deviations, such as uneven sampling, whether the selected digestion method is appropriate, or whether the dilution factor is too high.

Second, the sample itself should be examined to determine if there are issues such as non-uniformity, susceptibility to moisture absorption, water loss, or oxidation, which could alter the physical and chemical properties of the sample.

2. Why should the digested samples to be tested not contain organic matter, solid impurities, F-, etc.?

The presence of organic matter and solid impurities can clog the instrument's sample introduction tube, leading to instrument failure and damage. Additionally, it can cause measurement errors. The presence of F- and alkaline substances can corrode internal components of the instrument, resulting in malfunctions and damage.

3. How effective is ICP-MS in measuring Hg? What is the detectable concentration range?

(1) ICP-MS can measure Hg down to the ppt level; however, sample preparation and the medium are crucial, as errors and memory effects can be significant. Measuring Hg is challenging, mainly due to memory effects, and alkaline solutions are most effective for cleaning.

(2) Generally, it is more accurate to measure concentrations around or below 10 ppb, due to the significant memory effect, which requires extensive cleaning afterward. Diluted solutions and alkaline washing are recommended.

4. How should samples be prepared for measuring heavy metals in seawater using ICP-MS?

This includes sample dilution, mass selection, etc.

(1) Acidification and filtration. Ensure that nitric acid and containers are clean, preferably using redistilled nitric acid. Typically, a tenfold dilution method is employed.

(2) Since you're measuring heavy metals, ORS, DRC, and CCT are not particularly effective. The reaction cell works better for mass numbers below 85. Cd111 may be interfered with by MOZr and other oxides, so correction equations should be edited. For Pb, use 206+207+208, and for Hg, use 202.

5. What are some of the quicker sample preparation methods for environmental samples using ICP-MS?

(1) Use a high-pressure microwave digestion system, such as MILLSTONE or CEM.

(2) Microwave digestion or acid leaching, depending on the sample and element. For isotopic abundance analysis, leaching may suffice.

(3) The method depends on the type of environmental sample. Acid fixation is sufficient for water samples. Soil samples are more challenging and can be prepared with microwave digestion, using different speeds and methods based on the elements being analyzed.