Required section · Section 2 of 6
Match the matrix and method to the question
The matrix is part of the measurement. EDTA whole blood is the standard specimen for blood lead confirmation and is also used for whole-blood cadmium. Whole blood or red blood cells are more informative for methylmercury, while timed or creatinine-corrected urine is more informative for elemental mercury vapor or inorganic mercury salts.
A total element method answers how much of an element is present in the prepared specimen. ICP-MS without chromatographic separation cannot identify chemical species. For urine arsenic, HPLC or ion chromatography coupled to ICP-MS separates inorganic arsenite and arsenate, methylated metabolites, and seafood-derived organic species.
A spot urine concentration is hydration-dependent. Timing alone does not remove that dilution dependence: a complete timed collection permits calculation of the total amount excreted over the collection interval, whereas a spot result may be normalized to creatinine or specific gravity according to local procedure. A normalized result, an uncorrected concentration, and timed excretion require their own matched interpretation limits.
Name the exposure form and timing before selecting blood, urine, hair, or a total-element method.
| Question | Matrix | Limit |
|---|---|---|
| Lead confirmation | Trace-element-free EDTA whole blood | Capillary screens need venous confirmation when elevated. |
| Methylmercury | Whole blood or RBC, ideally speciated | Urine alone does not establish methylmercury. |
| Elemental or inorganic mercury | Complete timed urine collection or creatinine-corrected spot urine | Timed excretion is a total amount over the validated interval; a spot concentration remains hydration-dependent. |
| Arsenic exposure | Timed urine with speciation when feasible | Total arsenic can be increased by seafood-derived arsenobetaine. |
Choose a defensible trace-element result path
State the exposure question
Specify analyte, suspected form, exposure timing, and intended use.
Select matrix and collection device
Match the question to the validated matrix, additive, and metal-free materials.
Control contamination
Use clean technique and preserve the approved transport and processing pathway.
Match result to method
Determine whether total concentration or chromatographic speciation is required.
Interpret in context
Use the report's matched interval or applicable guidance and state uncertainty.
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