INSTRUMENTATION
DEVELOPING A CHEMICAL HYGIENE PLAN
Joy A. Young Warren Κ. Kingsley George Η. Wahl,Jr.
PUBLISHED BY THE AMERICAN CHEMICAL SOCIETY
Figure 2. Background correction using EDS.
Developing a Chemical Hygiene Plan
T
his essential "how-to" book tells you what you need to know to comply with the federal regulation known as the "OSHA Laboratory Standard" which requires chemical hygiene plans. Developed by the ACS Committee on Chemical Safety, the guide pre sents hygiene plans that can be modified ac cording to the particulars of individual labora tories. Among the topics covered in this valuable book you'll find • • • • •
application of the OSHA Laboratory Standard history of the OSHA Laboratory Standard standard operating procedures control measures and equipment records and recordkeeping
In addition, several appendices are provided, including employee information and training techniques, exposure assessment procedures, the elements of an emergency procedure plan, the OSHA Laboratory Standard, a list of con tacts for states that have OSHA-approved state plans, and a list of acronyms. This reference is critical to all lab supervi sors who must have in place by January 31. 1991, a chemical hygiene plan that outlines specific work practices and procedures ensur ing employee protection from health hazards associated with hazardous chemicals. by Jay A. Young, Warren K. Kingsley, and George H. Wahl Developed by the Committee on Chemical Safety of the American Chemical Society
Specimen is A l - C u eutectic alloy, (a) AI composi tional map, (b) Cu compositional map, (c) Sc arti fact distribution with constant background correc tion, and (d) elimination of false Sc contrast with formal background correction. Image field width is 44 μπ\. (Adapted from Reference 13.)
quantitative maps (16). Figure 2 illus trates this approach for the Al-Cu eu tectic sample (17). The apparent level of the Sc component in the map pre pared without proper background cor rection is approximately 1% in the Curich phase, as shown in Figure 2c. With background correction, the apparent Sc component is eliminated, as shown in Figure 2d. Only randomly scattered bright points are observed with con trast expansion. Instrumental strategy for compositional mapping
Because the strengths of one comple ment the weaknesses of the other, there are several advantages to employing an instrumental strategy that uses both WDS and EDS (18). WDS offers the advantages of high
sensitivity because of a high S/N and a high limiting count rate. The wave length-dispersive spectrometer also provides high resolution to eliminate spectral overlap, which is particularly important when a minor or trace con stituent is to be measured in the spec tral region of a major constituent. The main problem of WDS is usually the limited number of spectrometers avail able to measure the constituents of a complex specimen. This limitation be comes important when an accurate background correction is necessary for quantitative determination of minor or trace constituents in a complex speci men. Because all of the major constitu ents, and preferably the minor constit uents as well, must be measured to calculate an accurate background cor rection, having an adequate number of spectrometers to measure all trace, mi nor, and major constituents simulta neously is often impossible. When only WDS is available, repeated image scans are often required to measure all con stituents of interest. EDS has the potential to detect all constituents simultaneously, but its poor S/N and low limiting count rate on minor and trace peaks result in a poor detection limit in the mapping mode. Interferences are also a major problem with EDS because of its poor spectral resolution, which can cause worse detection limits when a minor peak is located near a major peak. This is especially true in mapping, where the maximum time available per pixel is a few seconds, resulting in relatively poor counting statistics. Despite these limitations, EDS can be used with WDS in a combined map ping strategy. EDS can simultaneously provide measurements of the major constituents because an adequate counting rate can usually be obtained
72 pages (1990) Paperbound ISBN 0-8412-1876-5 LC 90-46721 $18.95 Ο
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ANALYTICAL
Figure 3. Combined EDS and WDS compositional mapping. Specimen is garnet, (a) Ca, EDS; (b) Mn, WDS; (c) Ti, WDS; (d) Fe, EDS; (e) background channel, EDS; (f) AI, EDS; (g) Mg, WDS; and (h) Si EDS. Contrast chosen for each image is such that b l a c k - w h i t e corre sponds to the range 0 - m a x i m u m concentration. Image field width is 125 μπ\.
CHEMISTRY, VOL. 6 2 , NO. 24, DECEMBER
15,
1990
