EPA Method 1638

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EPA Method 1638:
Determination of Trace Elements in Ambient Waters by ICPMS. Official Name: Determination of Trace Elements in Ambient Waters by Inductively Coupled Plasma-Mass Spectrometry

A sample is acidified and solubilized by gentle refluxing (if total recoverable elements are desired). The digested sample is introduced into a radiofrequency plasma where energy transfer processes cause desolvation, atomization, and ionization. The ions are extracted from the plasma through a differentially pumped vacuum interface and separated on the basis of their mass-to-charge ratio (m/z) by a mass spectrometer having a minimum resolution capability of 1 amu peak width at 5% peak height at m/z 300. Ions transmitted through the mass analyzer are detected by an electron multiplier or Faraday detector and the resulting current is processed by a data handling system.

This method determines dissolved elements in ambient waters at EPA water quality criteria (WQC) levels. It may also be used for determination of total recoverable element concentrations in these waters.

EPA Method Guidance CD-ROM (includes MCAWW Methods, and most current EPA Methods)

(A) Contamination by carryover: To reduce carryover, the sample introduction system may be rinsed between samples with dilute acid and reagent water.(B) Contamination by samples: Significant laboratory or instrument contamination may result when untreated effluents, in-process waters, landfill leachates, and other samples containing high concentrations of inorganic substances are processed and analyzed.(C) Contamination by indirect contact: It is imperative that every piece of the apparatus that is directly or indirectly used in the collection, processing, and analysis of ambient water samples be cleaned.(D) Contamination by airborne particulate matter: Samples may be contaminated by airborne dust, dirt, particles, or vapors from unfiltered air supplies; nearby corroded or rusted pipes, wires, or other fixtures; or metal-containing paint.(E) Isobaric interferences: Isobaric elemental interferences are caused by isotopes of different elements that form singly or doubly charged ions of the same nominal m/z and that cannot be resolved by the mass spectrometer.(F) Wing overlap: Abundance sensitivity is affected by ion energy and quadruple operating pressure. Wing overlap interferences may result when a small m/z peak is being measured adjacent to a large one.(G) Isobaric interference (polyatomic): Isobaric polyatomic ion interferences are caused by ions consisting of more than one atom which have the same nominal mass-to-charge ratio as the isotope of interest, and which cannot be resolved by the mass spectrometer in use.(H) Physical: Physical interferences are associated with sample transport.(I) Memory effect: Memory interferences result when isotopes of elements in a previous sample contribute to the signals measured in a new sample. Memory effects can result from sample deposition the sampler and skimmer cones, and from the buildup of sample material in the plasma torch and spray chamber.

QC Requirements:
The minimum requirements consist of an initial demonstration of laboratory capability, analysis of samples spiked with metals of interest to evaluate and document data quality, and analysis of standards and blanks as tests of continued performance.

Maximum Holding Time:
6 months (after preservation)



Not Available.

Sample Prep:


MDL as determined by 40 CFR Part 136, Appendix B.

Revision Number: