Standards are essential for promoting accuracy in measurements pertaining to human health and nutrition.Electrolyte concentrations in the body affect most intra- and inter-cellular processes. Abnormal levels of electrolytes may cause or result from a variety of conditions. Thus, measurement of serum levels of electrolytes is a vital part of health status assessment
NIST announces the addition of reference values for ionized calcium and chloride in its SRM 956a Electrolytes in Human Serum with the revision of its certification of 13 November 1996.The values for these new analytes complement the previously certified values for total calcium, lithium, magnesium, potassium, and sodium in the material, all of which were determined by primary clinical methods. The new chloride values were determined by microcoulometry. The new, ionized calcium values were determined by ion selective electrode potentiometry, the candidate designated comparison method of the NCCLS. The usefulness of SRM 956a as an ionized calcium reference material was established by an interlaboratory study involving 19 industrial and clinical laboratories using various types of commercial instrumentation.
This SRM can be used for standardizing direct-reading ion-selective electrode analyzers and for validating working or secondary reference materials for electrolytes in either diluted or undiluted human serum or plasma.
A unit of SRM 956a consists of six flame-sealed ampoules of frozen human serum: two ampoules each of three different concentration levels. Each ampoule contains approximately 2.00 mL of human serum. The development of this SRM is the result of a cooperative effort between NIST and the NCCLS Subcommittee on Electrolytes.

On Monday, July 29, 2002 a mass stranding of 57 long-finned pilot whales (Globicephala melas) occurred in Dennis, MA on Cape Cod. Strandings of marine mammals occur regularly at Cape Cod; however, a stranding of this magnitude creates considerable activity among the scientific and volunteer personnel of the local stranding networks and aquariums, as well as tourists and the press. Barbara Porter and Rebecca Pugh of the Analytical Chemistry Division of CSTL participated at the stranding site in the collection of tissue specimens from the whales for archival in the NIST National Biomonitoring Specimen Bank (NBSB).

Since 1987, the NIST NBSB has participated in collecting and banking of tissues from marine mammals from U.S. waters of the Atlantic, Gulf of Mexico, and Pacific, including Alaska. The NBSB is designed to cryogenically preserve environmental and biological specimens over long periods of time (decades) for future retrospective analyses. A major activity of the NBSB is the National Marine Mammal Tissue Bank (NMMTB), established by Federal Legislation in 1992, and maintained at the NBSB through partial support from the National Oceanic and Atmospheric Administration (NOAA), National Marine Fisheries Service (NMFS) and the U.S. Geological Survey, Biological Resources Division.

The CSTL scientists worked with scientists and volunteers from the New England Aquarium, the Northeast Stranding Network, the NMFS, and the Woods Hole Oceanographic Institute to obtain samples for inclusion in the NMMTB. Tissue specimens were collected from 11 animals that died on the first day of the stranding. Three late stage pregnancies were found among the 11 whales, and tissue specimens were also removed from the 3 fetuses for a total of 14 animals sampled. Tissue specimens for the NMMTB are collected and processed following rigid standard operating procedures designed to reduce any contamination to the tissue. After processing, the tissue samples were immediately frozen and eventually stored in liquid nitrogen vapor freezers at the NIST NBSB satellite facility located at the Hollings Marine Laboratory in Charleston, SC. These specimens, along with over 2,000 tissue specimens from over 715 other marine mammals already archived in the NBSB, will be used to determine the levels of contaminants not only in marine mammals, but the health of the marine environment as well, and they will be available to scientists for evaluation for many years to come.

The entire suite of NIST cement and clinker Standard Reference Materials (SRMs) have been updated. These SRMs have been essential to laboratories which certify concrete products for performance and evaluate mechanisms for concrete corrosion and failure.

For more information on Cement SRMs, see the Standard Reference Material website: http://ts.nist.gov/ts/htdocs/230/232/232.htm

Date: September 2002

NIST Chemists Define and Refine Properties of Plastic Microsystems
Laurie Locascio, Analytical Chemistry Division, CSTL
David Ross, Process Measurements Division, CSTL
Tim Johnson

There may well be a plastic biochip in your future, thanks in part to the National Institute of Standards and Technology (NIST).
Microfluidics devices, also known as “lab-on-a-chip” systems, are miniaturized chemical and biochemical analyzers that one day may be used for quick, inexpensive tests in physicians’ offices. Most microfluidics devices today are made of glass materials. Cheaper, disposable devices could be made of plastics, but their properties are not yet well understood.
NIST is contributing to the development of these plastic microfluidics. One study looked at how fluids flowed in plastic microchannels by tracking fluorescent dye in the fluids. NIST researchers also developed an easy technique for accurately
measuring fluid temperatures—an important parameter for chemical reactions. A third project spawned a method for concentrating and separating an ionic (charged) substance in solution within microchannels. The technique concentrates the substance as much as 10,000-fold or more, making it easier to detect in ultrasmall quantities (nanoliters—a billionth of a liter—or less).
Finally, NIST staff designed a novel system to overcome the difficult problem of slow mixing in microfluidics devices. The mixer consists of a T-shaped microchannel imprinted in plastic that is modified with a laser to create a series of slanted wells.
The wells speed the mixing of two streams entering the passage.

Date: August 2002

NIST Chocolate Standard Raises the 'Bar' on Accuracy
Katherine S. Sharpless, Analytical Chemistry Division, CSTL

Chocoholics, rejoice. Now there’s a way to know more precisely than ever how much fat (and other constituents) are in chocolate and similar foods. The National Institute of Standards and Technology (NIST) has issued Standard Reference Material (SRM) 2384, Baking Chocolate, which has been characterized with state-of-the-art measurement methods to show how much fat, protein, carbohydrates, individual fatty acids, elements, vitamins and other components it contains. It is part of a series of food-matrix SRMs that can be used by food processors to validate analytical methods and for quality assurance when assigning values to products with similar compositions. The baking chocolate SRM is the first standard to contain a high proportion of fat—more than 50 percent. A high-fat food standard has been identified as a priority by manufacturers. Because of this high fat content, the new SRM can be analyzed by manufacturers of chocolate and by quality assurance labs of companies that produce other types of fatty products, such as black olives and potato chips. This SRM also is the first to have values assigned for catechins (which, as antioxidants, may help protect the body against damage associated with age-related diseases) and caffeine. NIST’s food-matrix SRMs will help manufacturers comply with the Food and Drug Administration labeling requirements.

Date: August 2002

Temperature Gradient Focusing in Microfluidic Channels
David Ross, Process Measurements Division, CSTL
Laurie Locascio, Analytical Chemistry Division, CSTL

Scientists in the Process Measurements and Analytical Chemistry Divisions of CSTL have developed a new method to concentrate and separate chemical species in microfluidic channels. Microfluidic, or "lab-on-a-chip," devices are miniaturized chemical and biochemical analysis systems that one day may replace conventional bench top instruments.
The new technique, temperature gradient focusing, balances the electrophoretic motion of analytes in a microchannel against the bulk flow of buffer solution through the microchannel while applying both an electric field and a temperature gradient along the length of the channel. For buffer solutions having temperature-dependent ionic strength, the applied temperature gradient results in a corresponding gradient in the electrophoretic velocity of a charged analytes in the channel. The bulk flow velocity can then be adjusted so that the total analyte velocity (the sum of the bulk and electrophoretic velocities) is zero at some point along the channel length, and all of the analyte in the channel will be focused, or concentrated, at that point.
The technique gives simultaneous focusing and separation of differently charged analytes in a manner analogous to isoelectric focusing of proteins, but is much simpler to implement than isoelectric focusing and has the additional advantage of working with any charged analyte, rather than just proteins. Temperature gradient focusing has been demonstrated for a variety of different analytes including fluorescent dyes, amino acids, proteins, DNA, and colloidal particles. In addition, it has been shown to be capable of greater than 10,000-fold concentration of a dilute analyte. A description of the technique has been submitted for publication in the journal Analytical Chemistry.

Date: May 2002

After we presented this technique and our results at an ASTM E01 committee meeting in May 2001, we established a collaboration to implement it with Metalor Technologies USA, North Attleboro, Mass., a precious metals and advanced materials supplier. Together, we developed methods for the determination of palladium and platinum in metallic samples. NIST provided software tools to perform the calculations. Less than one year later, this technique was in routine use at Metalor, complementing the gravimetric wet chemical technique used in their labs. According to Arnold Savolainen of Metalor, “This technique has revolutionized our Platinum Group Metals assay lab. Assay completion times which ran 20 to 30 days, now average four to six days. Assay precisions have improved by more than an order of magnitude. Accuracy, as measured by the number of assays sent for umpire laboratory analysis, has improved to the point that we have not had to go to umpire in over three months. I am now setting up the procedure for the determination of gold at major levels.”

Date: May 2002

Return to ACD Home
Return to Top of Document

Date created: May 13, 2002
Last updated: January 15, 2003
Contact: acd_webmaster@nist.gov