be analyzed, solid-sampling techniques have been used for flame AA, ICP, and the furnace. These opportunities deserve greater attention. Slurries are sometimes satisfactory samples for flame AA, ICP, or the furnace if they are not allowed to settle. Ultrasonic agitation of the autosampler table is useful for automated sampling. For the ICP the Babbington nebulizer is helpful for viscous samples or slurries. The graphite furnace is particularly useful for solid sampling in situations in which a few hundred micrograms provides a homogeneous representation of the sample. The modern furnace technology permits such samples to be calibrated by solution working curves. Hydride methods. Metals such as As, Se, Sb, Bi, and others can be readily converted to their metal hydrides, which are gaseous at room temperatures. This permits relatively large samples—10 to 50 mL—to be extracted with minimal sample handling and quantitated by thermal decomposition of the hydride in flame AA instruments. Designs are now available that extend the signals over sufficient time to permit ICP analysis in rapid sequential systems. Furnaces have also been used for the hydride technique. By now, hydride methods provide parts-per-billion sensitivity for As and Se in simple matrices such as environmental waters and plant and animal fluids and tissues. All chemical forms of the element of interest must be converted to a single valence state prior to hydride generation, and some interferences persist. The relative sensitivity (ppb) of hydride methods is similar to that of the furnace, and the hydride equipment is less expensive. Modern furnace methods have fewer interferences for As and Se. Nonspectroscopic techniques There are techniques other than spectroscopy that are used for the determination of metals both at major and at trace levels. Some of these techniques have advantages in certain situations. Others are quite general and are recommended by their supporters. Using my own judgment, I will try to put them into perspective compared with spectroscopic techniques. Electroanalytical techniques. Electrochemical methods are probably the most widely used competition for spectroscopy in trace metal determinations. Of these methods, anodic stripping voltammetry is the most widely used. The technique predates AA, and flame AA took over many analytical problems previously solved by electroanalytical means. However, electroanalytical techniques have been greatly improved in recent years. The
availability of sophisticated electronics at low cost has stimulated further interest in the field. For many metals, electroanalytical methods are about equally sensitive to flame AA or ICP. They are generally less sensitive than furnace AAS. It is usually necessary to pretreat a sample prior to electroanalytical measurement to put all of the analyte metal into the same chemical form. In other words, interferences occur as a result of differences in the chemical state of the analyte metals. This can sometimes be turned to advantage. For instance, in seawater analysis, the free ionic metal is sometimes preferred over total metal, which includes the metal adsorbed to particles. Electroanalytical techniques will distinguish between these two states of the metal, whereas the spectroscopic techniques measure total metal. X-ray fluorescence. X-ray fluorescence has been used for many years to measure major metal content of many classes of samples, especially alloys. X-ray fluorescence provides high precision, often 0.1% or 0.2% RSD. Standardization requires reasonably close matching of standard and sample. In recent years improvements have been made in the sensitivity of X-ray fluorescence so that the technique is now also applied to trace metals. However, it seems to me that modern flame AA and ICP are simpler to use (except for very routine analyses), somewhat less expensive, and can achieve equal precision and accuracy—and usually better sensitivity. Mass spectroscopy. Isotope dilution mass spectroscopy (IDMS) has been highly recommended by many workers who are trying to reach the very lowest detection levels in unknown and complex matrices. IDMS is the only technique permitted by the National Bureau of Standards for establishing reference values on standard reference materials. The technique requires considerable handling of the sample and a great deal of time for each sample. Also, the equipment is very expensive. Only those with specialized skills can obtain good results. The new technique of ICP-mass spectroscopy (ICP-MS) can be used effectively in some IDMS applications. The ICP is an ideal ion source for the mass spectrometer. It is still a little early to assess the eventual success of ICP-MS, although it is likely to become a highly useful technique. Neutron activation analysis. Neutron activation analysis (NAA) has been used for a long time for trace metal determinations. Neutron activation can be accomplished by a pile or by instrumental techniques, and the choice between these two options will determine the sensitivity and the cost. I ANALYTICAL
Microelectronics Processing Inorganic Materials Characterization
L.A. Casper, Editor Honeywell, Inc. Highlights leading-edge research in the field of materials development. Provides a thorough overview of techniques used in analyzing and characterizing inorganic materials in integrated circuits. Covers all major aspects of materials science, along with applications to a wide variety of high-technology areas. Includes extensive discussion on the role of chemistry in high-technology materials. CONTENTS Analytical Approaches and Expert Systems · Electrical Characterization of Semiconductor Materials · Dopant Profiles by the Spreading Resistance Technique · Semiconductor Materials Characterized by S E M · Semiconductor Materials Defect Diagnostics · Microelectronic Materials Characterized by SIMS · Applications of AES in Microelectronics · X-ray Photoelectron Spectroscopy · NDP Applied to Microelectronic Materials Processing · Thermal-Wave Measurement of Thin-Film Thickness · Optical Reflectance and Ellipsometric Techniques · Oxygen and Carbon Content of Silicon Wafers · Raman Microprobe Applied to Analytical Problems · Characterization of GaAs · Thermal-Wave Imaging in an SEM · Microelectronics Service Laboratory · Elemental and Isotopic Analysis · Activation Analysis of Electronics Materials · Trace Element Survey Analysis · Plasma Phosphorous-Doped Oxides · Vacuum-Deposited Nickel-Chromium · SpinOn Glass Film as a Planarizing Dielectric · Silicon-Wafer Cleaning · Monitoring Gas Particles · Microelectronics Processing Problem Solving Based on a symposium sponsored by the Division of Industrial and Engineering Chemistry of the American Chemical Society ACS Symposium Series No. 295 440 pages (1985) Clothbound LC 85-30648 ISBN 0-8412-0934-0 US & Canada $79.95 Export $95.95 Order from: American Chemical Society Distribution Dept. 95 1155 Sixteenth St., N.W. Washington, DC 20036 or CALL TOLL FREE 800-424-6747 and use your credit card!
C H E M I S T R Y', V O L . 5 8 , N O . 4 , A P R I L
1986
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Reverse Osmosis and Ultrafiltration
S. Sou ri raja η and Takeshi Matsuura, Editors National Research Council of Canada Reports significant advances in the technological improvement and funda mental understanding of reverse-osmosis-ultrafiltration membranes and pro cesses. Features topics such as new studies in gas separations and pervaporation by RO membranes, fundamental studies in membrane formation and membranes transport, progress in development and industrial use of inorganic membranes, and more. CONTENTS Materials Science of Reverse-Osmosis-Ultrafiltration Membranes · Polyethersulfone Ultrafiltration Membranes · Nature of Dynamically Formed Ultrafiltration Membranes · Polyblend Membranes in Hyperfiltration of Electrolyte Solutions · Structure, Permeability, and Separation Characteristics of Porous Alumina Membranes · Plasma-Polymerized Membranes of 4-Vinylpyridine · Gamma RayInduced Enhancement Effect on Salt Rejection Properties of Irradiated Membranes · Polyether Composite-1000 Spiral-Wound Membrane Element · Transport in Pressure-Drive η Membrane Separation Process · Physicochemical Interpretation of Behav ior of Pressure-Driven Membrane Separation Process · Effect of Hydrolysis on Cellulose Acetate RO Transport Coefficients · Application of Multicomponent Membrane Transport Model to RO Separation Processes · Predictability of Membrane Perform ance in RO Systems Involving Mixed Ionized Solutes in Aqueous Solutions · Solute Separation and Transport Characteristics Through Polyether Com posite-1000 RO Membranes · Hydrodynamic Properties of Skin and Bulk of Asymmetric RO Membranes · Limiting Flux in Ultrafiltration of Macromolecular Solutions · Mineral Ultrafiltration Membranes in Industry · Membrane Bioreactors for High-Performance Fermentation · Single-Stage Seawater Desalting with Thin-Film Composite Membrane Elements · Boiler-Feed Quality Water from Bitumen-Heavy Oil-Oil-in-Water Emulsions · Treatment of Paper-Plant Wastewater by Ultrafiltra tion · Concentration and Recovery of e-Caprolactam from Process Waste Stream · Sanitary Design RO Systems for Pharmaceutical Industry · UInfiltrative Solute Rejection Behavior of Black Liquor · RO and Ultrafiltration Applied to Processing of Fruit Juices · Halogen Interaction with Polyamide RO Membranes · RO Membrane Fouling at Yuma Desalting Test Facility · Fluid Mechanics of Dilute Solutions · RO and Ultrafiltration Membrane Compaction and Fouling Studies Using Ultrafiltration Pretreatment · Gel Volume Deposits on Ultrafiltration Membranes · Pretreatment, Fouling, and Cleaning in Membrane Processing of Industrial Effluents · Gas Permeability of Polypeptide Membranes · SolventExchange Drying of Cellulose Acetate Membranes for Separation ofHydrogen-Methane Gas Mixtures · Pervaporation Membranes · Dehydration of AlcoholWater Mixtures Through Composite Membranes by Pervaporation Based on a symposium sponsored by the Division of Industrial and Engineering Chemistry of the American Chemical Society ACS Symposium Series No. 281 501 pages (1985) Clothbound LC 85-0921-9 ISBN 0-8412-0921-9 U.S. & Canada $89.95 Export $107.95 Order from: American Chemical Society Distribution Office Dept. 36 1155 Sixteenth St., N.W. Washington, DC 20036 or CALL TOLL FREE 800-424-6747 and use your credit card.
Either way, NAA is less sensitive for most metals than furnace AAS. Never theless, workers experienced with the technique generally believe that it is more accurate than the several spec troscopic techniques. Although the judgment is personal, I have not understood why IDMS or NAA should be considered superior to furnace AAS for reference methods. With any of these methods, the most frequent analytical problem results from contamination, which is equally difficult to control in any of the meth ods. Workers who must determine Pb, Cd, Zn, etc., at levels below 1 Mg/L must take considerable precautions to use reagents that have been specially purified and to keep dust from set tling on the samples. If care is taken in the control of contamination, graphite furnace AAS will provide results that are at least as accurate as NAA or IDMS. For most elements, furnace AAS is more sensitive, thus requiring less sample handling. Chromatography. Over the years, gas chromatography (GC) has been used by some workers to determine trace metals in complex organic mix tures. Because GC separates com pounds, the different metallic species are determined. For those compounds for which the technology is appropri ate, very sensitive measurements can be made. However, the technique re quires specialized skills. In the past several years ion chro matography has been developed as an offshoot from modern liquid chroma tography. When ion chromatography is used for metal determination, the metallic compounds are separated and an appropriate detector is used to quantitate the compounds. The tech nique is particularly convenient for anions that are not easily determined by spectroscopic methods (for exam ple, halides, sulfate, and phosphate). Groups of metals can be separated by ion chromatography and detected at levels that begin to be competitive with flame AA or ICP. However, sam ples must be treated so that appropri ate compounds are formed. Ion chro matography is unlikely to be as specif ic as spectroscopic methods, but the cost for equipment is likely to be simi lar to the simplest flame AA instru ments and, of course, the anions can be determined. Choosing a technique Flame AA. Given all of these con siderations, how do you choose an ap propriate technique? If your primary requirements relate to a limited num ber of metals at higher levels, you will almost always be best off with flame AA. If an analyst is new to metal anal ysis or if an experienced spectroscopist is not available to run the lab, I
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think flame AA is the technique to choose. And don't let a plasma zealot con vince you that the ICP has no interfer ences and is, thus, easier to use than flame AA. It is free of some of the AA chemical interferences, but it has many more of its own. Certainly, I don't claim the platform Zeeman fur nace is free of interference; otherwise, why have we spent so much time find ing appropriate matrix modifiers? Flame AA is the easiest and most trouble-free metal determination technique. This probably will change gradually with respect to ICP, but it is certainly true today and will be for several years to come. Compared with ICP, flame AA is a much less expensive way to use spec troscopy for metal analysis. Flame AA costs from $10,000 to $40,000, depend ing on the level of automation. The ICP costs from $60,000 to $150,000, depending on speed and automation. A new laboratory not yet using spec troscopic methods for metal analysis can expect to be operational much more rapidly using flame AA. ICP. If you have a well-equipped AA lab, you may want to expand this capability to additional analytes: B, V, P, Zr, W, Nb, Ta, S, and some others. Sequential ICP is the way to do it. It is versatile and flexible. The routine wa ter test lab that determines a large number of elements on each sample and analyzes many samples will be better off with the ICP than with flame AA because the simple matrix of natural waters is easy to handle on the ICP. But the ICP requires more skill than does flame AA. Furnace AA. However, if the most important activity for which new in strumentation is being obtained is to determine metals at ultratrace levels, especially in inorganic or partly inor ganic materials, furnace AAS is called for. The Zeeman system provides ma jor advantages for furnace analysis in almost every case in which real sam ples are being analyzed. Note that the furnace should no longer be considered an accessory to a flame AA instrument. It is a complete ly independent analytical technique requiring optimized instrumentation. In practice, every well-equipped lab doing metal analysis is frequently re quired to reach the low levels in diffi cult matrices that demand the Zeeman platform furnace system. The Zeeman platform furnace A A, technique is ap propriate for every well-equipped metal analysis lab. It has properties that make it unique. The single overriding complaint about the furnace, which curtailed its growth for many years, was that it was greatly error prone because of inter ferences. There are many comments in
