Trace Chemical Analysis Research Articles

Specification-Based Modified Control Limits in Quality Control of Trace Chemical Analyses

Abstract Shewhart X and R charts were used to maintain and validate data quality of percent recovery estimates for 8 analytes determined by 4 procedures used routinely in 4 commercial laboratories over a 2-year period. However, because range (R) estimates of uncertainty did not Include lot-to-lot calibration variability, approximately 24% of the lots were "out-of-control." We extracted pooled standard deviations for So (repeatability within lot), SL (calibration variability), and SR (reproducibility), which represents the total variability. Values of So and SL were generally similar In size although there were some substantial differences between analytes and between laboratories for a given analyte. When control limits were based on reproducibility rather than repeatability, only about 6% of the lots were "out-of-control." However, these limits are less convenient to compute at the bench, wlthln-lot precision estimates are still required, and there Is still no Information on data acceptability. Capability estimates from the grand mean ±3 SR were surprisingly consistent for the 8 analytes. These values coupled with data quality objectives suggested the 82-115% range as the specifications for acceptable individual recoveries. A combination of repeatability limits plus modified limits anchored to specifications retains the simplicity of range computations while offering substantial administrative advantages. Examples are given to illustrate these points.

An Improved Raindrop Chemistry Spectrometer

Abstract A spectrometer allowing size-fractional chemical analysis of raindrops has been described previously by the authors. Modifications to this raindrop chemistry spectrometer now allow improved performance in windy conditions. Instrument verifications show that drop-size distribution parameters can be estimated to 2%, and pH versus drop-size spectra can be obtained to 0.02 pH units in wind speeds up to 3 m s−1. Improved resolution will allow trace chemical analysis for comparison with detailed rain chemistry models.

Ultralow Detection Limit of a Near-Infrared Dye by Diode-Laser-Induced Fluorescence in a Flowing Stream

Diode lasers are compact, highly efficient, temperature-tunable, long-lived, low-noise, simple-to-operate, and relatively inexpensive solid-state lasers that are rapidly becoming more useful in spectrochemical studies. Recently, Imasaka and Ishibashi reviewed the uses of diode lasers in trace chemical analyses. Due to the virtual elimination of background fluorescence from sample impurities, and the large wavelength shift of the Raman scatter from the solvent at red and near-infrared excitation wavelengths, the rather powerful diode lasers are very useful in laser-induced fluorescence (LIF) detection of very small amounts of red and near-infrared fluorophors. To our knowledge, the lowest detection limit obtained of a fluorescent species with the use of diode laser excitation is 46,000 molecules in a 56-nL volume of the laser dye IR-140 flowing in a liquid jet emanating from a capillary. With some simple improvements upon that system, the detection limit has been lowered to 3000 molecules of IR-140 in a 250-pL volume.

Some applications of microanalytical techniques in very large scale integrated circuits fabrication

The trend in technology development for the fabrication of very large scale integrated circuits (IC’s) continues in the direction of increased density of components with smaller dimensions. Devices with submicron dimension are currently either in manufacture or in development stage. The scaling down of device dimensions, both laterally and in depth, has resulted in new challenges and developments in material and process technologies. The successful implementation of these technologies in the fabrication of reliable devices is critically dependent on the proper understanding of the material properties, the processes, and their interactions. The need for analytical tools with high spatial resolution (∼nm range), depth resolution, and ultralow detectable limits (≪parts per 109) continues. The characterization efforts have been aided by the emergence and maturing of a variety of sophisticated analytical techniques aimed at physical, chemical, and electrical characterization. The physical and chemical methods include various microscopy techniques, surface, interface, and bulk compositional analysis, and trace chemical analysis tools each with its own strengths and weaknesses. Usually multiple techniques are necessary and are used in a synergistic manner for a comprehensive analysis. The application of a particular technique varies based on the emphasis on material, process development, process monitoring, yield enhancement, or device failure analysis. Typical examples of application of various microanalytical techniques to process development for IC fabrication are presented and some of the current challenges facing analysts are identified.

Accuracy in Trace Analysis Accomplishments, Goals, Challenges September 28 - October 1, 1987 Gaithersburg, MD

As the national reference laboratory for compositional measurements, NBS plays a major role in establishing the accuracy base for the chemical measurement system in the United States. It accomplishes this role through the issuance of Standard Reference Materials, the development of measurement methodology, and the provision of quality assurance services. In accomplishing our mission, we have a keen interest in understanding the accuracy achieved, and needed, in the ever-growing and ever-more-demanding area of trace chemical analysis. It has been almost a decade since a conference was held, at NBS, with the specific aim of reviewing the state of the art of this important measurement technology. A decade ago, trace analysis was largely focused on environmental analyses and some health-related measurements. Since then, trace analysis has grown dramatically in number of analyses performed annually and in scope. Trace analysis has grown into a major industry in the United States, covering a broad spectrum of needs in both the private and public sectors. The applications of trace analyses have increased in areas of health and nutrition, and blossomed in the area of industrial quality assurance. The role of trace analysis in industry is certain to continue to grow as we better understand the relationships between chemical composition and product performance. Feedstock characterization, and in-line process control and quality assurance will increasingly replace after-the-fact product performance evaluation. The use of computers in trace chemical analyses has also undergone a dramatic transformation in the past decade. Ten years ago, computers were used almost exclusively for data accumulation and evaluation. Today, computers are being used in measurement protocol design and optimization; this use will expand in the future. We will also see computers increasingly incorporated into measurement feedback loops and expert system control of measurement processes. With the transformations in technology that have occurred in the past 10 years and with the potential for the future, it was an appropriate time to review the accomplishments of the past decade, assess the current state of knowledge in trace chemical analyses, and project future needs and directions for this area of measurement science. The papers in this issue of the Journal of Research provide a unique picture of a measurement science that is growing, is in great current demand, and is of vital importance to future technology and product quality in the United States and the world.

Importance of chemical blanks and chemical-yields in accurate trace chemical-analysis

[1] Date, A. R., Preparation of Trace Element Reference Materials by a Co-precipitated Gel Technique, Report No. 101, Institute of Geological Sciences, London, March 1977. [2] Vanskii, L., Rosenberg, R. J., and Pitkinen, V., Nucl. Instrum. Methods 213, 343 (1983). [3] Rosenberg, R. J., and Viinskii, L., STOAV84, a Computer Program for an Automatic Gamma Spectrometer for Activation Analysis, Technical Research Centre of Finland, Research Notes 415, Espoo, 1985. [4) Rosenberg, R. I., Kaistila, M., and Zilliacus, R., J. Radioanal. Chem. 71, 419 (1982). Importance of Chemical Blanks and Chemical Yields in Accurate Trace Chemical Analysis

Chemical analyses of geothermal waters and strategic petroleum reserve brines for metals of economic importance

Waters from seven hydrothermal-geothermal, one geopressured-geothermal, and six Strategic Petroleum Reserve wells have been surveyed for 12 metals of economic importance using trace chemical analysis techniques. The elements sought were Cr, Co, Mn, Ta, Sn, V, Nb, Li, Sr, Pt, Au and Ag. Platinum was found at a concentration of ∼50 ppb in a brine from the Salton Sea geothermal area. Brine from this region, as has been known from previous studies, is also rich in Li, Sr and Mn. Higher concentrations (∼900 ppm) of Sr are found in the high-salinity geopressured brines. None of the fluids contained interesting concentrations of the other metals. Good recovery of precious metals at sub-ppm concentrations from synthetic high salinity brines was achieved using Amborane reductive resin, but similar recovery in the laboratory using real brines could not be demonstrated. Several analytical techniques were compared in sensitivity for the determination of the precious metals; neutron activation analysis with carrier separation is the best for gold and platinum in geothermal brines.

Today’s Chemical Realities

Abstract The difficulty with current food safety laws arises from the apparent inability of the toxicologist to determine the biological significance of the extremely low concentrations that the chemist can currently measure. In discussions of this technical ability, however, the practical limitations of chemical measurement science are rarely mentioned. Some of these limitations are: (1) The reliability of identification and quantitation decreases exponentially as concentration decreases; (2) at very low concentrations baseline effects become the limiting factor; and (3) the cost of the analysis becomes exorbitant. The practical reality of trace chemical analysis in the interlaboratory environment must answer the question: When does the cost of the analysis exceed the value of the information gained as to the identity and amount of the material present, considering also the uncertainties associated with the analysis itself and with the biological effect of that concentration? The current practical limit of measurement is in the low parts per billion, e.g., aflatoxin contamination. 2,3,7,8-Tetrachlorodibenzodioxin can be determined in fish at the moderate parts per trillion level, but at an estimated cost in salaries and expenses of roughly $1000 per individual value reported, without capitalizing our $2,000,000 mass spectrometry laboratory.

Trace chemical analysis of high-purity glass

Trace-element impurities in high-purity silica (Corning Code 7940 fused silica and J. T. Baker Ultrex silicon dioxide), 96% silica glass (Corning Code 7913), borosilicate glasses (Corning Code 7740 and Owens-Illinois KG-33) and doped optical waveguide glass have been determined by spark-source mass-spectrometry, optical-emission spectrography, neutron-activation analysis, atomic-absorption and plasma emission spectrometry, spectrophotometry, voltammetry and chemical methods. Particular care was taken to prepare samples and carry out analyses in a clean environment with ultrapure reagents. In most cases some 30 elements as well as water were determined by two or more of the techniques indicated. The impurity level for many elements in the high-purity silica and optical waveguide glass is in the ng/g range and in theμg/g range for the other glasses. Spark-source mass-spectrometry and neutron-activation analyses were carried out not only on samples prepared by a hydrofluoric acid dissolution-evaporation procedure but also on undissolved samples for volatile elements such as B, P, S, As and Hg. Results obtained are discussed with respect to application of the materials as well as to the analytical methods developed.