Sample preparation and storage can change arsenic speciation in human urine.
Author(s): Feldmann J, Lai VW, Cullen WR, Ma M, Lu X, Le XC
Publication: Clin Chem, 1999, Vol. 45, Page 1988-97
PubMed ID: 10545070 PubMed Review Paper? No
Suggested by: ISBER
Purpose of Paper
The purpose of this paper was to asses the stability of arsenic species in urine during storage.
Conclusion of Paper
The stability of arsenic species was dependent on the urine source. Arsenic species were relatively stable in volunteer urine for up to 8 months at 4 degrees C, but approximately 30% of the arsenate was reduced after storage for 4 months at 4 degrees C when commercially purchased urine stabilized with sodium azide (standard urine) was used. Volunteer urine specimens showed the greatest stability when stored at 4 degrees C. Regardless of source, monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and arsenobentaine (AsB) were more stable than arsenate which tended to be reduced to arsenite. Reducing urine pH to 4.5 prior to storage at 4 degrees C, or preservation with hydrochloric acid, sodium azide, benzoic acid, benzyltrimethyammonium chloride, methanol, or cetylpyridinium chloride had no beneficial effects.
Studies
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Study Purpose
The purpose of this study was to determine the effects of storage duration and temperature and the addition of preservatives on the stability of arsenic species in urine. Volunteer urine and freeze-dried or sodium azide preserved urine specimens obtained from commercial sources were spiked with arsenic species. Urine was also obtained from a study population exposed to arsenic through drinking water.
Summary of Findings:
AsB was relatively stable with a maximum of 6% being converted to DMA and 2% to MMA after storage of urine for 8 months. The other arsenic species were relatively stable for up to 8 months at 4 degrees C in urine from volunteers or from environmentally exposed individuals, but less stable in standard urine. In standard urine, 30% of the arsenate was reduced to arsenite after 4 months at 4 degrees C. After storage at -20 degrees C, some volunteer urine specimens showed a substantial reduction in arsenic species, but the ratios were unaffected. Storage of volunteer urine at 25 degrees C for 1 month led to substantial increases in arsenite and reductions in MMA and arsenate. Reducing urine pH to 4.5 prior to storage at 4 degrees C had no effect on arsenic species. Preservation of the volunteer, but not standard urine with hydrochloric acid led to substantial conversion of arsenate to arsenite and a decrease in MMA and DMA recovery, regardless of storage temperature. While none of the other tested preservatives in volunteer urine led to a significant decrease in arsenic species stability, no increase in stability was noted either.
Biospecimens
Preservative Types
- Frozen
- Other Preservative
Diagnoses:
- Not specified
- Normal
Platform:
Analyte Technology Platform Electrolyte/Metal Atomic absorption spectroscopy Electrolyte/Metal HPLC-MS Electrolyte/Metal Inductively coupled plasma mass spectrometry Pre-analytical Factors:
Classification Pre-analytical Factor Value(s) Storage Storage temperature 25 degrees C
4 degrees C
-20 degrees C
Storage Storage duration 1 month
2 months
4 months
8 months
Storage Storage conditions In the dark
Biospecimen Preservation Type of fixation/preservation Hydrochloric acid
Sodium azide
Lyophilized
Benzoic acid
Benzyltrimethyammonium chloride
Cetylpyridinium chloride
Methanol