NUPRO Valves and Filters foi Analytical Applications
SHUT OFF
Compact valves for reliable flow regulation and shut off • stem threads removed from system fluid • compact designs • ball tip or regulating stems
NUPRO Valves and Filters offer these design and performance choices: • End Connections: SWAGELOK® Tube Fittings, NPT, Tube Stub, Weld, CAJON VCO e & VCR® • Service Ratings: vacuum to 6000 psi; temperatures to 900 °F STOCKED FOR IMMEDIATE DELIVERY BY AUTHORIZED SALES AND SERVICE REPRESENTATIVES. NUPRO COMPANY
NUPRO
4800 East 345th Street Willoughby, OH 44094
METERING METERING
• quick-acting, 1/4 turn • full flow • easy maintenance
Valves for precise flow control in laboratory and instrument systems • accurate, repeatable flow adjustment with no initial surge • compact, low dead space • stem threads removed from system
FILTRATION Inline and tee type filters to protect instruments by removing hard particle contamination from fluid lines • choice of sintered and wire mesh elements from 0.5 to 440 microns • compact designs • all metal construction SWAGEL0K - TM Crawford Fining Company CAJON, VCO S VCR - TM Cajon Company β 1986 SWAGEL0K Co., all rights reserved N-5
FOCUS NAA and ICP, which have coarser tem poral resolutions, says Ernest Bondietti, a soil chemist at Oak Ridge Na tional Laboratory in Tennessee. Be cause trees transport water in a number of their outermost growth rings—collectively called the sapwood—some dissolved materials will migrate between rings. This greatly re duces the utility of studies with yearto-year resolution, Bondietti argues. Using ICP analysis, he recently showed that the 90Sr from bomb testing during the 1950s and 1960s is well re flected in the tree rings. The Sr signals begin to show in rings formed during the 1940s, which still were part of the sapwood when the bomb tests be gan. Currently Bondietti is following up on pollution studies reported earlier by Oak Ridge colleagues Sandy McLaugh lin and Charles Baes. The earlier work—also using ICP—focused on the effects of pollution from Tennessee copper smelters on trees in the Great Smoky Mountains National Park be tween 1863 and 1912. This was a period when emissions were mostly unregulat ed. In a pivotal study published several years ago in Science, these researchers reported that growth rings from shortleaf pine trees in the park show sup pressed growth and increased iron con tent. McLaughlin and Baes uncovered similar patterns, including increases in other metals, in rings during the past 25 years, "a period when regional fossil fuel combustion emissions increased about 200 percent." The researchers have since examined how elemental concentrations vary in cores taken from trees growing at different eleva tions. Specifically, they are interested in the Ca/Al ratio because it relates to the overall health of the trees. Prelimi nary studies indicate that the ratio has been decreasing, a trend that fits the prevailing theory that acid deposition from atmospheric sulfate and nitrate pollution is liberating soil aluminum, which ends up gumming up roots and depositing in the rings. "This is poten tially very powerful evidence that the environment in which these trees have been growing has been chemically changed [by acidic depositions]," McLaughlin says.
Wrinkles in reading the rings It is one thing to find out which ele ments are in which rings. It is quite another to infer what this means in terms of plant physiology or environ mental events. "These are high-risk studies with high potential payoffs" ac cording to Yanosky. Bondietti of Oak CIRCLE 112 ON READER SERVICE CARD
1106 A · ANALYTICAL CHEMISTRY, VOL. 60, NO. 19, OCTOBER 1, 1988
