Focus
Gas Monitoring System Improves Control of Anesthesia Some of the most exciting and imp o r t a n t applications of analytical technology appear, quite naturally, in locations far removed from the academic, industrial, and governmental laboratories in which they are developed. T h e struggle for life on the hospital operating table depends to a greater and greater extent today on analytical methodology and instrumentation. At Wishard Memorial, a general hospital affiliated with Indiana University Medical School, such analytical instrumentation includes a PerkinElmer Respiratory Monitoring System (RMS), used to analyze patient breath for oxygen, carbon dioxide, and nitrogen, and to monitor concentrations of anesthetic gases. T h e heart of the system is a mass spectrometer. When one of 16 monitoring stations is selected, a small a m o u n t of gas is drawn from the patient's breath into an inlet selector valve, which delivers the gas to the mass spectrometer analyzer. "We want to make certain t h a t the patient undergoing surgery has the
proper breathing environment," says Gale E. Dryden, Chief of Anesthesiology at the hospital. "This means t h a t he has enough oxygen, t h a t carbon dioxide is properly removed, and t h a t the mixture of oxygen and nitrous oxide is correct. T h e R M S is capable of telling us what these conditions are at the exhaled gas level with great accuracy." In addition to these measurements, Dryden points out t h a t the R M S is also used to measure supplemental quantities of anesthetics administered in conjunction with nitrous oxide, such as halothane and enflurane. T h e gas monitoring system can sequentially monitor as many as 16 patients, with displays of six respiratory and anesthetic gases at a central station and within each operating room. T h e selection of individual stations to be monitored and the setting of alarm levels for concentrations of anesthetic gases t h a t are either too low or too high can be controlled from the central station. T h e system will also sound an alarm if the patient's respiration ceases.
An anesthesiologist scans respiratory monitor for data on patient at Wishard Memorial Hospital in Indianapolis
during
surgery
" W i t h the use of the R M S , " says Dryden, "we were able to replace a number of old-type oxygen monitors. Formerly, gas was wasted at a rate of 6000-8000 cm 3 per minute to ensure adequate oxygen during nitrous oxide anesthesia." Dryden calls this "a costly and unsophisticated procedure." He estimates t h a t the R M S could save enough in gas bills and drug bills to pay for itself within three years.
Monitoring Steam to Combat Corrosion It sounds very heavy-duty: monitoring steam purity for turbine corrosion control. B u t it may be illustrative of the role industrial analytical chemistry will be playing in the future. T h e problem facing Bill Hickam, Jim Bellows, Dave Pensenstadler, and Steve Peterson of the Westinghouse Electric Corporation's Research & Development Center in Pittsburgh was corrosion in power plant turbines. Records showed t h a t the number of turbine corrosion incidents had increased significantly over the last decade. It seemed to be an industry-wide trend—the group at Westinghouse had knowledge of over 45 units t h a t had experienced corrosion distress and failure during the previous three years. T h e central problem of turbine corrosion involves corrosive impurities. Hickam, Bellows, Pensenstadler, and Peterson set up an analytical protocol by which they were able to identify corrosive species in the steam used to drive the turbines. They then measured the concentrations of the corrodants, and studied their sources and sinks throughout the plant steam/ water cycle. Extensive testing and analysis by the Westinghouse researchers showed t h a t the corrodants of primary concern were chlorides, sulfates, caustic (NaOH), and oxygen. "Even at low
ANALYTICAL CHEMISTRY, VOL. 52, NO. 13, NOVEMBER 1980 · 1409 A
thermogravimetric analysis physical adsorption thermomagnetic analysis surface characterization vacuum and pressure work chemisorption magnetic susceptibility particle size distribution surface tension studies corrosion studies. Westinghouse Carson
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concentration levels," they wrote, "these corrodants can cause signifi cant damage to steam turbines." And they do mean low. Drinking quality water would never be accept able for use in a power plant, where the NaCl content of steam, for in stance, must be kept in the 1-5 p p b range, or even lower. T h e investigators found t h a t units t h a t have experi enced corrosion incidents have a high chloride content in turbine deposits, relative to other operating units. In a typical crack in a blade from a turbine t h a t had suffered corrosion attack, for example, high chloride levels were found all through the crack. T o respond to the analytical de mands at hand, Westinghouse devel oped a continuous steam analyzer package. T h e system includes contin uous monitors for sodium, dissolved oxygen, p H , cation conductivity, and specific conductivity; and there are thermocouples to measure steam and condensate temperature. Oxygen and sodium are determined with continu ous on-line electrochemical cells. Of great concern is the absence of an effective chloride monitor in the continuous analyzer, in light of chlo ride's proven role as a major cause of corrosion. T h e problem is the compat ibility of chloride-selective electrodes with power plant cycles. T h e elec trodes are sensitive to damage and characterized by long recovery times when they dry out. " P l a n t s do shut down," explains Bill Hickam. "We can't have people watching electrodes all the time. Ana lyzers have to keep working for several months without being attended t o . " Westinghouse has been working close ly with Orion Research Corporation to develop chloride analyzers with the requisite sensitivity and reliability, and a number of electrodes are pres ently under evaluation. In the meantime, the researchers have found t h a t determining chloride NO. 13, NOVEMBER
1980
system.
W. M. Hickam,
left, and G. L.
in grab samples by ion chromatogra phy is the next best thing to continu ous analysis. T h e ion chromatographic procedure is also used to determine other anions and cations of interest. T h e ion chromatograph employs ion exchange resins to separate ions in so lution. A suppressor column removes the native conductivity of the eluant, leaving only the analyte cations or an ions to be detected conductimetrically against a pure water background. A given analysis is specific for either cat ions or anions, as different sets of resin columns and eluants are used for each ion type. T h e Westinghouse researchers rou tinely tested for sodium, chloride, and sulfate. T h e y were also able to deter mine potassium, ammonium, fluoride, bromide, nitrate, and phosphate with the ion chromatographic procedure. Concentrator columns were used to concentrate the ions from 10 m L of sample, in order to attain detection limits in the p p b range. T h e analytical protocol for continu ous monitoring and grab sampling is used by Westinghouse to monitor power plants to be sure they are oper ating within recommended steam pu rity limits. In addition, the monitoring protocol is useful in diagnostic studies of equipment malfunction. Bill Hickam explains t h a t the need for increased analytical monitoring in power plants is partly due to increases in demand for electrical energy. In 1952, the 200 MW power plant was a new species. Today many convention al power plants are in the 1000 MW range. And the nuclear plants are as large as 1300 MW. Changes such as these, with concomitant increases in capital investment per plant, have in creased the need for careful monitor ing. "Analytical chemistry in power plants," says Hickam, "has become a more visible and recognizable'need t h a n it was 10-15 years ago." Stuart A. Borman
