IMPORTANCE OF SAMPLE HANDLING FOR ACCURATE ANALYSIS OF TRACE ELEMENTS: BIOLOGICAL SPECIMENS

Authors: GALLAGHER, SANDRA - UNIVERSITY OF NORTH DAKOT

Submitted to: American Association of Clinical Chemistry
Publication Type: Other
Publication Acceptance Date: 5/15/2005
Publication Date: 7/11/2005
Citation: Gallagher, S. 2005. Importance of sample handling for accurate analysis of trace elements: biological specimens. American Association of Clinical Chemistry Nutrition Division Newsletter. Summer 2005 edition.

Interpretive Summary: Much of the information presented in this article is taken from the Quality Control manual of the Mineral Analysis Laboratory and references for this information may be obtained on request. Contact Sandy Gallagher at [e-mail] for more information. The primary analytical problem encountered in trace mineral analysis is EXTERNAL CONTAMINATION. Many trace elements are present in the laboratory in microgram and even nanogram amounts, hence, contamination may contribute substantially to an analytical value for a trace mineral unless extraordinary measures are taken. A laboratory contemplating trace mineral analysis must be prepared to take precautions to the point of fanaticism; through all sampling, preparation, and analytical procedures to ensure that contamination is minimized. Common sources of trace mineral contamination include rubber stoppers, wood applicators, paper products, metal surfaces, dust, skin, dandruff, and hair. Plastic, borosilicate glass (do not use for boron or silicon) and stainless steel equipment (do not use for chromium) are best suited for trace mineral analysis.

Technical Abstract: Much of the information presented in this article is taken from the Quality Control manual of the Mineral Analysis Laboratory and references for this information may be obtained on request. Contact Sandy Gallagher at [e-mail] for more information. The primary analytical problem encountered in trace mineral analysis is EXTERNAL CONTAMINATION. Many trace elements are present in the laboratory in microgram and even nanogram amounts, hence, contamination may contribute substantially to an analytical value for a trace mineral unless extraordinary measures are taken. A laboratory contemplating trace mineral analysis must be prepared to take precautions to the point of fanaticism; through all sampling, preparation, and analytical procedures to ensure that contamination is minimized. Common sources of trace mineral contamination include rubber stoppers, wood applicators, paper products, metal surfaces, dust, skin, dandruff, and hair. Plastic, borosilicate glass (do not use for boron or silicon) and stainless steel equipment (do not use for chromium) are best suited for trace mineral analysis. Phlebotomy Only plastic disposable syringes with stainless steel needles (siliconized needles are needed for chromium and nickel draws) should be used for blood collection. Evacuated blood collection tubes specified for trace mineral analysis are also suitable if the tops are removed after collection and the sample is not allowed to come in contact with the stopper. Leaching of metals from the stoppers of these and other types of tubes may contaminate the specimen. Other materials involved in sample collection or processing, such as clotting aids or gel serum separators, should be avoided. The amount of trace mineral contamination should be checked in all anticoagulants, tubes, syringes and reagents that are used. When new lot numbers are used, tubes and equipment can be checked for contamination by allowing the equipment to come into contact with a dilute acid solution for one hour and analyzing this solution. This ensures that all equipment is as low in trace minerals as is possible. Common laboratory practices that can contribute to contamination include the use of wooden applicator sticks to ring blood clots of tube walls, the wiping of pipette tips with paper tissues, and the mixing or storing of samples in rubber stoppered tubes. Skin contact with any surface that will be exposed to samples or solution must be avoided. Tubes must be covered at all times. Sample Many things affect the integrity of the sample when reporting a value for trace minerals such as hemolysis, icteric, lipemic, loss of element in the tube, heterogeneity, mixing, contamination during processing, fasting, hemostatsis, posture, exercise, and use of supplements. Physiological conditions should be standardized to minimize these possible sources of sampling variation. Distribution of water depends on posture: standing up leads to a loss of plasma water, and to an apparent increase of approximately 10% in the concentration of nondiffusible blood constituents such as proteins or cells. Similar changes in water distribution take place locally, for example, when a tourniquet is used for blood specimen collection. Most trace minerals are transported in the blood bound to proteins or cells. Changes in posture and application of a tourniquet will therefore change apparent concentrations. Exercise, even of short duration, causes changes in blood serum constituents, possibly caused by leakage of intracellular components. Continuous physical training may cause hemodilution; which may in turn falsely reduce values. Changes caused by physical strain may even be seen in urinary excretion of trace minerals. Evaporation, adsorption on container walls, and precipitation may be sources of variability in biological samples. Adsorption of mineral