Instruments for Clinical Chemistry A
dvances in instrumentation are having a dramatic impact on the quality of work performed in the nation's clinical chemistry laboratories. New or improved instruments are making it possible for clinical labs to obtain data more rapidly, more accurately, and more reproducibly. In some cases, new instruments are providing scientific information never before available. All this is proving of enormous value to the medical profession. It is giving physicians far more reliable laboratory data—vital in diagnosing and treating disease. Many of the instruments used in clinical chemistry labs are the same types found in conventional analytical labs—colorimeters, spectrophotometers, flame photometers, fluorometers, pH meters, gas chromatographs, radiation counters. More and more, however, they are instruments designed specifically for the clinical laboratory. Also, as is true of analytical laboratories in general, some clinical labs are now using instruments that only a few years ago were considered suitable only for the more esoteric forms of research. The overwhelming trend in lab112
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DEC. 16, 196 3
Labs
oratory instruments today is to more and more automation. Yet, despite the surging interest in automation, the work horse in many clinical chemistry laboratories continues to be the manually operated colorimeter. The vast majority of clinical chemistry analyses are done colorimetrically. Such analyses are usually much simpler and faster to carry out than tests done gravimetrically or titrimetrically. Also, colorimetric methods can offer
greater sensitivity—important in determining the small amounts of materials present in clinical samples. Hence, there is a great demand for simple, rugged colorimeters, which are found in virtually all clinical chemistry labs. These photoelectric instruments, also known as filter photometers, use optical filters to select the desired visible wave lengths. Ever since these instruments were introduced in
special report
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Second
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series
#llll§JCOMMON BECOMES ROUTINE
ANALYSIS.
Formerly used
almost entirely in research, spectrophotofluorometers becoming
are
increasingly
popular for routine clinical analysis.
This unit,
produced
by American Instrument,
is
used by Lancaster B. Knott of Georgetown University to measure the
Hospital
concentration
of hydrocortisone in plasma
the mid-1930's, they have found important use in clinical labs. They are used to determine glucose, urea nitrogen, bilirubin, creatinine, phosphatase, amylase, cholesterol, hemoglobin, and many other substances in body fluids. Made by American Instrument, Bausch & Lomb, Central Scientific, Coleman, Fisher, Klett Mfg., Leitz, Photovolt, Zeiss, and more than 20 other companies, colorimeters have undergone gradual improvement in recent years. Some are now available with recorder attachments, more sensitive photodetector cells, or other refinements. In September, Fisher introduced two special-purpose colorimeters for the clinical lab. One is designed to determine glucose in blood; the other to measure urea nitrogen. These instruments, which give the results directly in milligrams per 100 ml., can be obtained with a series of accessories designed to make the analysis semiautomatic. Spectrophotometers Years ago, only the larger, better equipped clinical chemistry labs
owned anything so elegant as a spectrophotometer. Now most clinical labs have at least one of these instruments, usually covering both the visible and ultraviolet ranges. First in the field was Beckman's DU spectrophotometer, which continues to be one of the company's best known instruments. In many clinical labs, spectrophotometers are being called upon to do tests formerly carried out by colorimeters. For many types of chemical analysis, a spectrophotometer can give greater accuracy and precision than a colorimeter. In addition, a spectrophotometer can operate over a much broader range of the spectrum— the ultraviolet, visible, and infrared— and thus offer greater versatility. Although visible-UV spectrophotometers can do everything a colorimeter can do, clinical laboratories seldom use them for such routine analyses as glucose and urea nitrogen. The reason is that spectrophotometers are generally less convenient to operate than colorimeters and cost too much to be used unnecessarily. In many labs, spectrophotometers are being put to work determining cholesterol, creDEC.
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113
INFRARED
EQUIPMENT.
trophotometers.
Workers at Perkin-Elmer
IR instruments
check the operation of infrared spec-
are of special value because they can identify
stances more specifically than can either an ultraviolet or visible
FLAME
PHOTOMETER.
Available
since
many
sub-
instrument
about
1945, flame photometers found almost immediate acceptance in clinical laboratories. a new flame photometer measure sodium and
A technician
made by Baird-Atomic
Counters or Tape Some of the newer spectrophotometers give their results on digital counters or on printed or punched tape. A few months ago, Coleman Instruments introduced its Autoset C&EN
to
potassium
atinine, phosphatase, inorganic phosphorus, and many other substances. The UV part of the spectrum is particularly valuable in measuring barbiturates, sulfa drugs, steroids, enzymes, and vitamins. Spectrophotometers are made by American Instrument, Applied Physics, Baird-Atomic, Bausch & Lomb, Beckman, Coleman, Perkin-Elmer, Research Specialties, Zeiss, and many other companies. Since their introduction in the early 1940's, visible-UV spectrophotometers have been modified to give improved accuracy, better methods of recording, and wider spectral range. In addition, simplified instruments have been made available for the routine user who doesn't need all the refinements required by the man in research.
114
uses
DEC. 16, 196 3
spectrophotometer, which indicates either per cent transmittance or absorbance units directly on a digital counter. This instrument, selling for about $2500, operates in the near-UV, visible, and near-IR ranges. This year, Research Specialties brought out a fully automated spectrophotometer system that indicates the results in optical density, per cent transmittance, milligram per cent, or milliequivalents per liter on a digital print-out device. The system includes a turntable that automatically presents up to 52 samples at a time to the instrument. Price of the system: about $4500. Early this year, Perkin-Elmer began marketing an infrared spectro-
photometer system that records its output on a punched tape that can be fed directly into a computer. For infrared analysis, IR spectrophotometers have been available commercially since the late 1940's. They began to be used in clinical labs about 1950 but have not made rapid headway in this area. Their use continues to be mainly in research. The big advantage of infrared spectrophotometers is their ability to identify many substances more specifically than can either a UV or visible instrument. IR methods, however, have two major shortcomings. They are less sensitive than UV methods. In addition, a sample for IR analysis
Fluorometers can measure as little as 0.1 part per billion •. •
COLORIMETER the new colorimeter
ASSEMBLY.
A technician
operates
system made by Fisher Scientific
measure urea nitrogen in blood.
to Fluorometers
It includes various ac-
cessories that make the analysis semiautomatic. system is available for determining
In 1960, Technicon introduced a fully automatic instrument for measuring sodium and potassium in body fluids; it consists of its AutoAnalyzer with a flame photometer attachment.
A similar
glucose
must be free of water, which absorbs strongly in the infrared. This is a particular drawback in clinical labs, where most specimens are aqueous solutions. Nevertheless, the use of IR in clinical labs is expected to grow, especially as more sensitive instruments are developed. Today, infrared spectrophotometers are being used to identify and measure such materials as barbiturates, tranquilizers, and steroids in blood. They are also being used in place of conventional wet-chemical methods to analyze kidney and gall bladder stones to help distinguish between various disease states. Among the compounds determined in kidney stones, for example, are uric acid (a high concentration may suggest the presence of gout), calcium oxalate and calcium phosphate (may suggest hyperparathyroidism ), and xanthine (may indicate improper oxidation of purines). Information of this type may be of value to the physician in deciding whether the patient needs a change of diet, surgery, or other treatment.
Testing with Flame
Photometers
Before flame photometers became available about 1945, if a clinical laboratory ran an analysis for sodium or potassium (a chore it seldom tackled), the job might have taken several hours by the old gravimetric methods. With a flame photometer, the determination can be completed in a minute or so. Flame photometers won almost immediate acceptance in clinical labs. The importance of the flame photometer can be judged by the fact that it handles about 10% of the work load of the average clinical chemistry lab. The instrument is used primarily to measure sodium and potassium. Although some labs also use it to measure calcium, most clinical labs determine calcium titrimetrically. More than 20 companies make flame photometers, among them Baird-Atomic, Beckman, Coleman, Jarrell-Ash, Technicon, and Zeiss. Coleman says its Model 21 flame photometer is used today in about 80% of the nation's clinical laboratories.
Are Highly
Sensitive
Fluorometers, which have been on the market since the early 1940\s, have gradually found widespread use in clinical chemistry labs. Their prime virtue is their high sensitivity. A fluorometer can measure as little as 0.1 part per billion. With a colorimeter, few substances can be measured unless their concentration is at least 0.1 part per million. The need for fluorometers is growing as clinical labs are being called upon more and more to monitor the blood of patients taking such drugs as reserpine, cortisones, antimalarials, and antibiotics. Fluorometers are also being used to determine porphyrins, adrenaline, noradrenaline, cholesterol, estrogens, phenylalanine, and vitamins, as well as calcium and magnesium. Measurement of phenylalanine, for example, is useful in testing for phenylketonuria, a hereditary metabolic disorder that causes mental retardation. Some observers predict that, within the next decade, a test for phenylalanine will be run routinely on almost every newborn baby in the U.S. Among the leading manufacturers of fluorometers are American Instrument, Beckman, Coleman, Farrand Optical, Jarrell-Ash, Klett Mfg., Photovolt, G. K. Turner Associates, and Zeiss. Some of these firms also make spectrophotofluorometers, which seDEC. 16, 196 3 C&EN
115
Demand for blood-gas analyzers is expected to rise sharply . . .
BLOOD
GASES.
New
chromato-
graphic blood-gas analyzers use devices that admit precisely amounts ment.
measured
of blood into the instruThey also provide
temperature tectors.
This
manufactured
improved
control and better deis the by
instrument
Beckman
lect the desired wave lengths with gratings or prisms instead of filters. A recent improvement in spectrophotofluorometers has been the use of higher intensity sources of UV radiation, such as xenon lamps, in place of conventional mercury-vapor lamps. Van Slyke
Apparatus
Among the oldest and most valuable instruments in clinical chemistry labs is the apparatus developed by Dr. Donald D. Van Slyke, clinical chemist, for measuring blood gases. In 1917, he introduced a volumetric instrument that is used today in many clinical labs. Also widely used is the more accurate manometric instrument he introduced in 1924. Over the years, the manometric Van Slyke unit has remained the most accurate instrument available for determining carbon dioxide (both dissolved and chemically combined), as well as oxygen, anesthetic gases, and other gases in blood. The Van Slyke apparatus, made by Arthur H. Thomas, Fisher, Macalaster Bicknell, Sargent, and others, has undergone gradual modification. Arthur H. Thomas, for example, offers a microchamber adapter that permits the use of a much smaller sample—0.1 ml., compared to 1 ml. for the standard Van Slyke instrument. Another 116
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advance has been the revised miniaturized Van Slyke instrument, the microgasometer, developed by Dr. Samuel Natelson of New York's Roosevelt Hospital. This device, placed on the market by Scientific Industries in 1952, requires a sample of only 0.02 ml. This smaller sample size can be a major advantage when many tests must be run on a single blood sample or when tests must be done on infants, who have relatively little blood to spare. Widely used in clinical labs, the Natelson instrument, with built-in pipet, has speeded up the manometric determination of blood gases. Although highly accurate, the conventional manometric Van Slyke method has some basic shortcomings. It is relatively slow. It is exacting and requires well-trained technicians. Also, it involves a great deal of hand operation. For a quicker, simpler way of measuring carbon dioxide in blood, a growing number of clinical labs have been turning to the automatic colorimetric method of the Auto Analyzer. This instrument, using a 0.3-ml. sample, can determine carbon dioxide content at a rate of 40 samples an hour, compared to about 10 an hour to measure carbon dioxide by the Van Slyke method. On the other hand, no sat-
isfactory method has yet been worked out for using the AutoAnalyzer to measure the oxygen content of blood, a determination that physicians are asking for increasingly. Blood-Gas
Chromatographs
The growing demand for oxygen determinations accounts, in part, for the mounting interest in chromatographic blood-gas analyzers or, as they are sometimes known more simply, blood-gas analyzers. These instruments can measure oxygen, carbon dioxide, carbon monoxide, and anesthetic gases such as nitrous oxide. In the past two years, Fisher, F & M Scientific, Perkin-Elmer, Beckman, and R. L. Faley have introduced versions of this instrument. Industry spokesmen believe these chromatographic units are just on the threshold of rapidly expanding use in clinical chemistry labs. F & M Scientific estimates that, although perhaps no more than about 200 chromatographic blood-gas analyzers are currently in operation in the U.S., this figure will soar to over 1000 in the next two years. "Within 10 years," says Howard L. Ashmead, research supervisor at F & M, "just about every mediumsized and larger hospital in the country will have one/'
MANOMETRIC. nologist, William
A medical R. Wittman,
erates a manometric
techop-
Van Shjke ap-
paratus
made
Thomas.
A manometric Van Slyke
instrument equipment
is the
by
Arthur most
available for
H.
CHROMATOGRAPHY.
Automatic
amino acid
ers based on ion exchange chromatography such companies Technicon.
as Beckman,
analyz-
are made by
Research Specialties,
Here, John Deutschlander
of Beckman
and de-
scribes the operation of his company s instrument
accurate measuring
carbon dioxide, oxygen, and various other gases in blood
Chromatographic blood-gas analyzers have a number of compelling advantages over alternate methods: • Speed. They can analyze 12 to 15 samples an hour for both carbon dioxide and oxygen (compared to three or four an hour for measuring both gases by the Van Slyke method). • Smaller sample. They require only 0.1 to 0.2 ml. of blood (compared to 1 ml. by the Van Slyke procedure ). • Automation. Chromatography lends itself to automatic analysis—a major improvement over the laborious manual operations of the manometric Van Slyke method. • Accuracy. The accuracy of the chromatographic method ( ± 1 % ) is better than that of the Auto Analyzer (about ± 4 % ) , although not quite so
good as that of the manometric Van Slyke method ( ± 0 . 5 % ). Despite these inherent virtues, chromatographic blood-gas analysis has had a rocky career in the clinical laboratory in the past few years. The first chromatographic unit to measure blood gases was Fisher Scientific's Clinical Gas Partitioner, introduced in December 1959. The instrument worked so poorly and erratically in the hands of the average user that Fisher agreed in December 1961 to take back the equipment at full refund if the customer wasn't completely satisfied. Of 251 units sold, 103 were returned. In the past year or so, however, the situation has improved. The new chromatographic instruments, including the revamped unit introduced by Fisher late last year, are clearly superior to the original Fisher instrument. Among their chief improvements are special sampling valves or pipets that admit precisely measured amounts of blood into the system. With the early instrument, the sample
was injected with a conventional syringe (only slightly modified), and the operator wasn't always sure of exactly how much blood was added. The new instruments have also been improved by use of better temperature control, better detectors, and modified reaction chambers that permit more effective release of the gases from the sample. Some blood-gas analyzers have been criticized for taking too long to measure carbon dioxide. One instrument takes as long as seven minutes. Says a clinical chemist, "In a large hospital lab where you may have to run 100 or so COL>'s in a few hours, you just can't fool around and wait seven minutes for each determination. What you want is an analysis every minute or two." The new instruments are moving in the direction of higher speed. In some units, oxygen is determined first, then nitrogen, and finally carbon dioxide. However, in F & M's instrument, for example, the carbon dioxide is measured first—after two minDEC. 16, 196 3 C&EN
117
utes. The complete analysis for carbon dioxide and oxygen takes four minutes. Even with their many advantages, chromatographic blood-gas analyzers are not apt to sweep the Van Slyke instruments into oblivion. One reason is that these chromatographic units range in price from about $2000 to $3500, compared to only $300 to $400 for a high-quality manometric Van Slyke instrument and much less for a conventional, less elaborate instrument. Also, chromatographic units are relatively untried. Yet most manufacturers of the new instruments are. confident that gas chromatography shows enormous promise in the clinical laboratory, and not only in determining blood gases. Other Gas
Chromatographs
For the present, gas chromatographs other than blood-gas analyzers are relatively uncommon in clinical chemistry labs—that is, unless the laboratory is also doing research. Clinical chemists fully realize that gas chromatography offers exceptional speed, simplicity, and sensitivity in analyzing complex mixtures. However, one of the chief factors limiting its use is that, although gas chromatography can supply a vast amount of information, the medical significance of much of this information is now only vaguely understood. What is needed is more knowledge about the chemistry of disease and the clinical value of specific chemical determinations. Needless to say, gas chromatography is finding expanding use in the clinical laboratory. It is being called upon to measure such compounds as fatty acids, lipids, steroids (sex hormones, adrenocortical hormones), and drugs (heroin, codeine, amphetamine). Gas chromatographic equipment is made by several dozen U.S. companies. Among these are Barber-Colman, Beckman, Burrell, F & M Scientific, Fisher, Jarrell-Ash, Micro-Tek, Packard Instrument, Perkin-Elmer, Podbielniak, Research Specialties, and Wilkens Instrument & Research. In recent years, companies have improved their equipment by providing for temperature programing and for analysis at unusually high or low temperatures. They have also introduced better detectors, such as flame-ionization detectors, which are more sensitive than 118
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Some of the Instruments Used in COLORIMETERS
A colorimeter (filter photometer) is designed to measure the light absorption of a sample solution in the visible range. The term "colorimeter" as used in clinical laboratories, usually means an instrument that employs a photoelectric device to measure the light intensity. In the past, the term has also been used to mean a device, such as the old Duboscq instrument, in which the colors of an unknown solution and of a standard solution were compared visually. In a colorimeter, a band of visible wave lengths, selected by an optical filter, passes through the test solution. The extent of light absorbance or transmittance is determined photo electrically and indicated on a meter. By this method, the concentration of the absorbing material can be determined. The light absorbance of a material (if it follows Beer's law) is directly proportional to its concentration. The band of wave lengths chosen to measure the absorbance is usually the one at which the material most strongly absorbs since at this point the instrument is most sensitive. However, different wave lengths may be used to avoid interference from other substances in solution that might absorb strongly at nearby wave lengths. SPECTROPHOTOMETERS—UV ? VISIBLE, AND IR
In their basic operation, spectrophotometers are very much like colorimeters. However, instead of using a filter to provide the desired wave lengths, they use a prism or diffraction grating. A spectrophotometer has much greater versatility than a colorimeter. Since it can select any part of a broad band of wave lengths, it can perform the function of numerous filters. Moreover, it can give a narrow wave-length band rather than (as a filter does) a relatively wide band of wave lengths. In many analytical measurements, this can result in greater accuracy. Most spectrophotometers used in clinical labs cover the visible range and part of the ultraviolet. Others operate only in the visible spectrum or the infrared. In some cases, spectrophotometers are provided with strip-chart recorders. F L A M E PHOTOMETERS
In these instruments, the sample is atomized in a flame. The characteristic light radiation produced by a specific element passes through a suitable filter. The light intensity, determined by a photocell or phototube, is a measure of the concentration of the element in the sample. In the clinical laboratory, the instrument is used chiefly to determine sodium (by its yellow radiation) and potassium (violet). FLUOROMETERS
A fluorometer measures substances that fluoresce or can be made to fluoresce (it can also measure substances that destroy fluorescence). In this instrument, the sample is exposed to particular wave lengths of light (usually ultraviolet) that pass through a selected filter. The band of
Clinical Chemistry Laboratories—How They Work wave lengths chosen is the one that gives the sample component the maximum activation. The intensity of the resulting fluorescence is measured at right angles to the activating light. A second filter selects the particular wave lengths at which this fluorescence is measured by a photocell. Most fluorometers in clinical labs use filters. In some of the newer instruments called spectrophotofluorometers, two prisms or diffraction gratings take the place of the two filters in the conventional instrument. The prisms or gratings give more selective wave lengths and also provide greater versatility, which is particularly important in research. V A N SLYKE APPARATUS
In the volumetric Van Slyke instrument, the volumes of the individual gas components in blood are measured at constant pressure. In the manometric instrument, the pressures are measured at constant volume. These instruments are used in clinical labs primarily to measure carbon dioxide and oxygen, which are present in both combined and dissolved forms. In most clinical labs, carbon dioxide and oxygen are determined individually on separate samples, although the analysis can also be done on a single sample. Whenever oxygen is measured, the sample must be whole blood since oxygen is present in blood primarily in the red cells. Normally, only carbon dioxide is measured. In this case, the sample (usually serum) is treated with lactic acid to release the chemically combined carbon dioxide. In addition, a material such as caprylic alcohol is used to prevent foaming. The released carbon dioxide and the previously dissolved carbon dioxide are then measured. To determine oxygen, the sample of whole blood is treated with saponin, potassium ferricyanide, and an antifoam agent. The saponin breaks down the walls of the red cells to free the hemoglobin. The potassium ferricyanide reacts with the hemoglobin, thus releasing the combined oxygen. This oxygen and the small amount of oxygen that was previously dissolved in the sample are then measured. G A S CHROMATOGRAPHS
Gas chromatographs are used to separate components in a gaseous or vaporized sample. The separation is based on differences in the rates with which various components move through the chromatographic column. These differences, in turn, are based on variations in the forces with which the column materials retain each of the components. These may be such forces as adsorption, solubility, polarity, or chemical bonding. In gas chromatography, there is both a moving phase (the sample and the carrier gas) and a stationary phase. The stationary phase may be a solid partitioning agent, in which case the method is called gas-solid chromatography. Or the stationary phase may be a nonvolatile liquid partitioning agent held on a solid support, in which case the method is called gas-liquid chromatography. As the sample moves through the column with the carrier gas (usually helium or argon), the components are sep-
arated. As each component leaves the column, it is measured by a thermal-conductivity detector or other device, such as a flame-ionization, argon-ionization, or gas-density detector. The detector output is recorded on a strip-chart recorder as a series of peaks. The area under each peak (or, if the peak is symmetrical and essentially triangular, the height of each peak) is proportional to the concentration of the related component in the sample. In gas-solid chromatography, the column packing is a material such as activated alumina, activated charcoal, silica gel, or a molecular sieve. Gas-solid chromatography, although widely used, is not as versatile as gas-liquid chromatography because the range of solids that can act as partitioning agents is not as great as the range of usable liquids. In gas-liquid chromatography, the liquid phase may be silicone oil, polyethylene glycol, diethylene glycol succinate, or any one of dozens of other substances. The solid support may be diatomaceous earth, Teflon, or various other materials.
CHROMATOGRAPHIC BLOOD-GAS ANALYZERS
These instruments, based on gas-solid chromatography, are used mainly to determine carbon dioxide and oxygen, although they can also measure a variety of other blood gases. In chromatographic blood-gas analysis, the first step is to release the blood gases. The releasing agents recommended by various instrument companies may differ from the usual mixture employed in the Van Slyke method. One company, for example, recommends sulfuric acid in place of lactic acid, to speed up the reaction. The released gases are swept through the system by a carrier gas, usually helium. The system includes two chromatographic columns and two detectors. The first detector measures the gases leaving the first column; the other detector measures the gases leaving the second column. Both detectors are thermal-conductivity devices. The first column, usually packed with activated charcoal or silica gel, temporarily holds back the carbon dioxide, allowing the oxygen and nitrogen to leave the column rapidly. The oxygen and nitrogen simultaneously pass the first detector and are recorded as a composite peak. They then go to the second column, packed with a molecular sieve. There, the nitrogen is slowed down briefly, while the oxygen immediately passes through. In some chromatographic blood-gas analyzers, the oxygen leaving the second column and passing the second detector is the first gas to be measured separately. Then the nitrogen emerging from the second column is measured. Finally, the carbon dioxide that is retarded in the first column leaves that column and is measured by the first detector. In some instruments, the retention time of carbon dioxide in the first column is reduced sufficiently so that carbon dioxide is the first gas determined after the composite measurement of oxygen and nitrogen. The carbon dioxide, after passing the first detector, either goes to a separate carbon dioxide absorber or to the second chromatographic column, where it is permanently absorbed. The outputs of the two detectors are recorded on a DEC. 16, 196 3 C&EN
119
strip chart. The peaks for the unknowns with those for the standards to determine concentrations.
are compared the blood-gas
ELECTROPHORESIS A P P A R A T U S
Like chromatography, electrophoresis separates components by differences in their rates of movement. In electrophoresis, charged particles in a liquid or other medium migrate under the influence of an electric field. Proteins, for example, can be separated because of characteristic differences in their speed of migration, which depends on differences in their electrical charge. When electrophoresis is carried out in a gel, the mobility is also affected by the size of the panicles. Electrophoresis takes place either in solution or in a supporting medium such as paper. After the components are separated by paper electrophoresis, for example, quantitative results can be obtained by staining the electrophoretic strip and measuring the various color densities with a photoelectric densitometer. Or the individual bands may be dissolved in a solvent and the color intensity of each solution measured with a colorimeter. Another method involves determining the fluorescence with a suitable fluorometer.
conventional thermal-conductivity cells. For measuring amino acids, gas chromatography is generally not too satisfactory, partly because it requires that the nonvolatile amino acids be converted to volatile derivatives. Instead, ion exchange chromatography is frequently used. In the new automatic amino acid analyzers made by Beckman, Research Specialties, Technicon, and others, the chromatographic column is filled with an ion exchange resin. The amino acids are eluted by a series of buffer solutions at varying p H and temperature. Although automatic amino acid analyzers are widely used in research, relatively few are being used routinely in clinical chemistry labs. The demand for this equipment in clinical labs is expected to grow, however, as improved instruments are developed. One needed improvement, * for example, is higher speed (at present, an analysis takes between three and six hours).
AUTOMATIC CHLORIDE TITRATOR
The Cotlove chloride titrator uses two pairs of silver electrodes, both of which are immersed in the sample. A constant direct current flows between one pair of electrodes (the coulometric electrodes), thus releasing a steady stream of silver ions into the sample. The silver ions react with the chloride ions to form insoluble silver chloride. In time, all of the chloride ions combine. At this point, the current across the other pair of electrodes (the amperometric electrodes) rapidly increases. Once this current reaches a predetermined value, the timer that was turned on at the start of the test automatically stops. The elapsed time for the test is a measure of the amount of chloride ion present in the sample.
A T O M I C ABSORPTION SPECTROPHOTOMETERS
In atomic absorption spectrophotometers, the sample is vaporized in a flame. Simultaneously, the flame is irradiated by light from a lamp having a cathode made of the same metal that is being determined. At certain resonance wave lengths, the light striking the atoms of the sample metal in the flame is partially absorbed. The extent of absorption, determined by a photodetector, is a measure of the concentration of the metal in the sample.
X - R A Y SPECTROMETERS
In x-ray spectrometers, the specimen is exposed to a beam of x-rays. This causes the atoms in the sample to give off their own characteristic x-rays. These radiations are picked up and reflected by an analyzing crystal. The rays reflected from this crystal are measured by an x-ray detector and recorded on a strip-chart recorder in terms of angular position and intensity. In this way, the elements present can be identified and measured. 120
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Paper
Chromatography
Other forms of chromatography are finding much wider application. Paper chromatography is being used in clinical labs to identify sugars and to determine cysteine, phenylalanine, and other amino acids in urine. It is also being used to separate cholesterol and other lipids. In the past three or four years, growing interest has centered on thinlayer chromatography, which actually has been used in Europe for the past 10 years or more. In this method, such adsorbents as silica gel or alumina are applied in thin layers to glass plates. These adsorbents, being highly resistant chemically, can be treated with a variety of corrosive reagents that might be much too destructive for use in paper chromatography. In the clinical lab, thin-layer chromatography is being used to separate alkaloids such as heroin and morphine, which are analyzed by treating with strong acids. The thin-layer method is also being put to work identifying and measuring barbiturates, tranquilizers, antihistamines, and other drugs. Among the producers of thin-layer chromatographic instruments are Camag of Switzerland (equipment distributed in the U.S. by Arthur H. Thomas), Desaga of West Germany (distributed by Brinkmann), Shandon
of England (distributed by Colab), Research Specialties, and others. Electrophoretic
Methods
Electrophoresis, introduced into clinical labs on a limited scale in the mid-1940's, has in recent years found extensive use clinically. Today, some form of electrophoresis apparatus is standard equipment in all but the smallest clinical labs. Electrophoresis is used primarily to separate and measure serum proteins (such as albumin and globulins) and hemoglobins. Diseases such as multiple myeloma and hypogammaglobulinemia can be identified by analyzing the electrophoretic patterns of serum proteins. Electrophoresis is also used to separate enzymes, such as fractions of lactic dehydrogenase (useful in diagnosing myocardial infarction, acute hepatitis, and leukemia). Electrophoretic methods are classified under five broad headings: freesolution (or moving-boundary) electrophoresis, paper electrophoresis, membrane electrophoresis, gel electrophoresis, and thin-layer electrophoresis. The first successful electrophoretic method was the free-solution technique, developed by Dr. Arne Tiselius of Uppsala University in Sweden in 1937. He separated various components of serum in a liquid medium. Free-solution electrophoresis instruments, being relatively expensive and inconvenient to operate, have found only limited routine use in clinical labs. These instruments, made by American Instrument, Beckman, Perkin-Elmer, Technicon, and others, are used largely in research. The free-solution technique continues to be developed. In April 1962, for example, Dr. Leonard T. Skeggs and Dr. Harry Hochstrasser of the Veterans Administration Hospital in Cleveland announced a new automatic instrument for separating proteins electrophoretically in a short, steep gradient formed by sucrose solutions of varying concentration. A serum sample of 0.2 ml. is introduced into the electrophoretic cell in a thin band, and the components are rapidly separated. The cell is scanned with ultraviolet light, and the results are recorded on a strip-chart recorder. The commercial instrument, which Technicon began offering in 1962, can produce an electrophoretic pattern every 20 minutes.
In clinical laboratories, the most widely used electrophoresis instruments use filter paper as a supporting medium. Paper electrophoresis has the advantage of being a relatively inexpensive and simple technique. However, like free-solution electrophoresis, it can only separate about five or six protein fractions. Paper electrophoresis equipment is available from about two dozen companies, including Beckman, Buchler Instruments, E-C Apparatus, German In-
lose acetate electrophoresis system, which in only 20 minutes can carry out serum protein separations that would take 16 hours by paper electrophoresis. Recently, Gelman Instrument introduced a microporous cellulose polyacetate called Sepraphore III, which the company especially recommends for separating hemoglobins and enzymes. Among the gels used in electrophoresis equipment are agar, starch, and polyacrylamide. Agar has a resolv-
PAPER ELECTROPHORESIS.
Paper electrophoresis is the most
common form of electrophoresis used in clinical labs.
Dr. Martin
Rubin (left), head of the clinical chemistry lab at Georgetown University Hospital, discusses with Ramakant M. Mhatre the patterns of serum proteins obtained on paper strips
strument, Research Specialties, Scientific Industries, and Arthur H. Thomas. In membrane electrophoresis, the supporting material is usually either cellulose acetate or cellulose polyacetate. Cellulose acetate membranes, introduced in 1960, give better resolution than paper. They can isolate about eight to 10 protein fractions in serum. Cellulose polyacetate gives even better resolution—up to 14 protein fractions. Among the leading U.S. suppliers of cellulose acetate membranes is Colab, which distributes the Oxoid material made by Courtaulds of England. A few months ago, Beckman began marketing its MicroZone cellu-
ing power somewhere between that of paper electrophoresis and membrane electrophoresis. Agar-gel equipment is supplied by such companies as Buchler Instruments, E-C Apparatus, and LKB Instruments. Agar and, to a lesser extent, polyacrylamide are also used in a related technique known as immunoelectrophoresis. In this method, the proteins are separated by conventional gel electrophoresis. The separated proteins are then treated with various known antigens. Since a given antigen will only react with a specific protein, the method is useful in identifying proteins. In 1955, Dr. Oliver Smithies at the DEC. 16, 1963 C&EN
121
University of Toronto (now at the University of Wisconsin) introduced the first of the high-resolution gels, starch gel. It can isolate as many as 30 protein components in serum. This high resolution is possible because the proteins are not only separated on the basis of their electrical charge but also their particle size, because of the sieving effect of the porous gel. Starch-gel electrophoresis, using equipment made by Buchler Instruments, E-C Apparatus, Research Specialties, and others, has aided significantly in the study of multiple forms of enzymes (called isozymes), which are becoming of increasing interest in medical diagnosis. However, the starch-gel method is fairly demanding technically (it's a problem, for example, getting a uniform gel), and the method is used primarily in research. In 1959, Dr. Samuel Raymond and Dr. Lewis Weintraub at the University of Pennsylvania developed a method using another high-resolution gel, polyacrylamide. This material can separate 20 to 25 protein fractions in serum. Since 1960, E-C Apparatus has been supplying polyacrylamide-gel units that, for example, can resolve as many as 10 hemoglobins. The separation and measurement of hemoglobins with such equipment can be of value in detecting sickle-cell anemia and other hemoglobin diseases. Also using polyacrylamide gel, Dr. Leonard Ornstein and Dr. Baruch J. Davis of New York's Mt. Sinai Hospital in 1959 developed the Disc electrophoresis method. With the latest polyacrylamide formulations, this method can separate as many as 40 serum proteins, compared to about 30 previously. In Disc electrophoresis, which uses polyacrylamide gel in the form of a small cylinder, the components are separated in thin wafershaped layers. The method can isolate not only serum proteins but also hemoglobins and enzymes, such as esterases, peptidases, and dehydrogenases. Since 1961, Canal Industrial has been marketing equipment and reagents for Disc electrophoresis, which the company describes as "the most sensitive of all electrophoretic methods available to date." Until recently, gel electrophoresis has found only limited use in clinical chemistry labs. One problem has been the comparative newness of the method and the widespread acceptance of paper electrophoresis. Also, some labs have had difficulty obtain122
C&EN
DEC. 16, 196 3
ing accurate quantitative results with gel electrophoresis. Another problem has been the preparation of a satisfactorily uniform gel, a job that was recently simplified when E-C Apparatus and Canal Industrial began supplying premixed solutions for making polyacrylamide gels. Still another electrophoretic technique is thin-layer electrophoresis, pioneered commercially in the U.S. by Research Specialties. The method uses silica gel, alumina, or other adsorbents similar to those used in thinlayer chromatography. Thin-layer electrophoresis has been recommended, for example, for separating histidine, glycine, aspartic acid, and other amino acids. In one or two hours, it can perform separations that might take 12 hours by paper electrophoresis. Special Electrode
Devices
In recent years, a significant advance has been the introduction of improved electrode instruments for determining the pH of blood. Accurate measurement of blood p H can be vitally important since even slight variations from the normal pH of 7.3 to 7.4 can indicate a serious disturbance in the body's acid-base balance. pH meters covering the full range from 0 to 14 have been on the market since about 1935. In the past few years, a number of companies such as Beckman, Radiometer of Denmark (equipment distributed in the U.S. by London Co.), Metrohm of Switzerland (distributed by Brinkmann), Epsco, and Instrumentation Laboratory have introduced instruments with both regular and expanded scales specifically for measuring blood pH. Radiometer's instrument, for example, provides an enlarged scale from pH 6.8 to 8.2. The instrument can measure the pH of samples as small as 0.025 ml., while a constant-temperature unit maintains the sample at body temperature. A blood p H meter made by Instrumentation Laboratory can handle samples as small as 0.015 ml. In September, Beckman introduced a highsensitivity research p H meter with a relative accuracy of ±0.001 pH. A number of companies such as Beckman, Radiometer, Metrohm, Epsco, Instrumentation Laboratory, and Yellow Springs Instrument supply equipment for determining the partial pressures of dissolved oxygen and carbon dioxide (p02 and p C 0 2 ) in blood.
The newer units are more dependable and accurate and are easier to operate than instruments available previously. Increasingly, physicians are asking for measurements of the blood's p 0 2 and p C 0 2 . Many physicians feel such measurements may provide more useful information than determinations of the total (dissolved and chemically combined) content of each of these gases. Chemists look to the growing use of electrode measurements in the clinical lab. They expect far greater use of electrodes for determining such ions as sodium, potassium, and chloride. Needed but yet to be made available commercially are electrodes for determining calcium, magnesium, and other ions in body fluids. For the past two years, Dr. Alfred H. Truesdell of the U.S. Geological Survey and Dr. Alfred M. Pommer, now at USDA's Human Nutrition Research Division, have been developing electrodes for measuring calcium and magnesium ions. Results so far, they say, look promising. Titrators Go
Automatic
In recent years, companies have been offering an increasing number of
New devices give better measurement of partial pressures . . .
TITRATING.
Among the various types of
titrators available
is this instrument,
made by Fisher Scientific.
BLOOD pH.
Titralyzer,
blood into a constant-temperature
The operator checks
printed tape that automatically ume of liquid used in each
the
automatic the
records the precise vol-
titration
devices that carry out colorimetric, fluorometric, or potentiometric titrations automatically. This equipment, made by American Instrument, Coleman, Fisher, Metrohm, and other companies, has been gradually improved. The new Fisher instrument, the Titralyzer, introduced in May, indicates the volume of liquid titrant both on a digital counter and a printed tape. The instrument can be obtained with a turntable that automatically handles as many as 16 samples at a time. One of the most notable developments in recent years has been the automatic chloride titrator announced in 1958 by Dr. Ernest Cotlove, a research physician and clinical chemist at the National Institutes of Health. This device, supplied by American Instrument and Buchler Instruments, is now being used in hundreds of clinical chemistry labs throughout the U.S. In the Cotlove instrument, the "titrating solution" is actuallv a constant
A laboratory worker draws a sample of
a Beckman pH meter.
device
used
with
A number of companies both in
the U.S. and abroad produce instruments
designed spe-
cifically for measuring blood pH
stream of silver ions produced by a silver ion-generating electrode. The flow of silver ions can be maintained much more uniformly by this electrode method than by using a conventional silver-ion solution. The Cotlove instrument handles samples of about 0.1 ml. and does not require that they be deproteinized. The instrument carries out determinations with high accuracy in about a minute, compared to about 10 to 15 minutes by the older manual methods involving protein precipitation followed by colorimetric titration. Atomic
Absorption
A number of instruments today are somewhere in the borderland between research and routine clinical laboratory use. In some cases where the equipment is being used routinely, the number of clinical labs involved may be fairlv small.
An instrument gradually gaining acceptance for day-to-day clinical analysis is the atomic absorption spectrophotometer. At New York Hospital, Grace-New Haven Hospital, Illinois Masonic Hospital, and elsewhere, it is finding routine use primarily in measuring calcium and magnesium. It can also analyze for sodium and potassium, which are normally determined with a flame photometer. An atomic absorption spectrophotometer can measure zinc, cadmium, chromium, manganese, and copper at very low levels—less than 0.01 microgram per ml. It can also determine such poisons as arsenic, mercury, and selenium. In less than four minutes, it can turn out an analysis that in some cases might take a day or more by wetchemical methods. Compared to flame photometry, atomic absorption analysis is more sensitive and selective. The potential value of atomic absorption methods in chemical analysis DEC. 16f 196 3 C&EN
123
X-ray spectrometers accurately determine a variety of metals . . . was recognized as far back as 1872. However, it wasn't until 1955 that the first successful instrument was developed by Dr. Alan Walsh, an Australian physicist. In the U.S., Jarrell-Ash and Perkin-Elmer began offering their first commercial atomic absorption spectrophotometers in 1961. Among other manufacturers are Hilger & Watts in England, Optica in Italy, and Hitachi in Japan. U.S. instruments currently sell for about $5000. Atomic absorption analysis is still used mainly in research. However, Perkin-Elmer and others predict far greater use routinely in clinical labs as scientists learn more about the role of trace metals in disease. Example: the role of copper in Wilson's disease, a progressive disorder of the nervous system. Says P-E's Walter W. Slavin, "We believe that every large clinical laboratory in the country will own or have access to an atomic absorption instrument within the next five years." X-Ray
Spectrometers
Today, probably less than half a dozen U.S. clinical chemistry laboratories possess x-ray spectrometers. However, as Dr. Natelson, head of the clinical chemistry laboratory at New York's Roosevelt Hospital, and others see it, the use of this instrument in clinical labs will grow markedly in the coming years. Meanwhile, it continues to find widespread laboratory use in the metallurgical and chemical industries. At Roosevelt Hospital, an x-ray spectrometer routinely measures calcium, potassium, sulfur, zinc, and iron. It could also determine chromium, manganese, cobalt, nickel, and copper, as well as such heavy metals as mercury, thallium, and lead. Among the chief advantages of the x-ray method is its high sensitivity (it requires a sample of only 0.01 to 0.05 ml.). Also, the x-ray technique lends itself readily to automation. Using a Philips x-ray spectrometer, Dr. Natelson has developed an automatic method of feeding samples into the machine. He places the liquid samples within standard circular areas on a long filter-paper strip, dries the 124
C&EN
DEC. 16,
1963
strip, and feeds it continuously into the instrument. Readings can be made once every 20 seconds. Philips Electronic Instruments expects to introduce an automatic x-ray spectrometer for clinical labs early next year. One problem with existing x-ray spectrometers, however, is that they cost about $20,000. Development of cheaper sources of x-rays and other improvements, says Dr. Natelson, should eventually lower the price of the instrument to about $8000. Industry spokesmen, however, question whether the price can be reduced much below 815,000. Electron Paramagnetic
Resonance
Spectrometers that measure electron paramagnetic resonance (EPR), also known as electron spin resonance, are for the time being strictly research tools. However, some observers are keenly optimistic about the future use of EPR in the clinical laboratory, especially for measuring free radicals. A growing amount of research, they point out, indicates that free-radical concentrations may be related to the pathological state of tissues. EPR spectrometers, which are involved basically in measuring unpaired electrons, can determine not only free radicals but also transition-element ions and the kinetics of biochemical reactions. One laboratory is testing EPR as a means of monitoring the level of phenothiazine tranquilizers in the serum and urine of mental patients. Early this year, Dr. Jessie L. Ternberg and Dr. Barry Commoner of Washington University in St. Louis, Mo., reported that measurement of the free-radical concentration in liver assays may be a simple and effective way of distinguishing between cases of obstructive and nonobstructive jaundice. Using a specially designed EPR spectrometer built at the university, they found that the free-radical concentration is significantly higher in patients with obstructive jaundice (caused by a mechanical obstruction) than in patients with the nonobstructive disorder—for reasons not yet understood. The importance of this test lies in the fact that, if a patient has
nonobstructive jaundice (for example, the type caused by drugs), the need for surgery may be ruled out. Varian Associates introduced the first commercial EPR spectrometer in 1955, and other companies are now also in the field. Currently, about 175 EPR spectrometers are being used in research laboratories, only a few of which are involved in clinical research. By clinical laboratory standards, these instruments are costly. Varian's research units sell for between $30,000 and $40,000. However, as production of these instruments increases and as better techniques are introduced, the cost of this equipment is expected to decline. Measuring
Radioactivity
Clinical chemistry labs that measure radioactively tagged compounds are equipped with various radioactivity counting devices. These instruments are used in determining thyroid excretion (with iodine-131), pernicious anemia (cobalt-60), liver activity (iodine-131), iron turnover rates (iron-59), and other functions. Says a Baird-Atomic spokesman, "Fifteen years ago, medical radioisotope work was a tentative, experimental, and even suspect procedure. Now it is widely used and also universally recognized for its reliability and versatility in the medical and clinical chemistry fields." More than two dozen companies, including Applied Physics, Baird-Atomic, Nuclear-Chicago, Packard Instrument, Picker, Tracerlab, and Vanguard Instrument make equipment for measuring radioisotopes. Many of these instruments give digital readings directly in counts per minute or counts per second. Some are available with automatic print-outs. Other
Equipment
Clinical laboratories also use a great range of other instruments. Freezing-point osmometers provide data on kidney function, electrolyte-water ratios, and other factors. In some labs, refractometers measure the total protein in blood or serum.
RADIOACTIVITY. radioactivity
Instruments
are finding
Kenneth McCoy (standing), probe used in measuring
for
expanding
determining
use
clinically.
a technician, adjusts the radioactive
radiation counter is made by
iodine.
The
Baird-Atomic
To separate cells, proteins, lipids, and other materials in blood, clinical laboratories may use a variety of centrifuges. Refrigerated, high-speed centrifuges may be given the job of isolating abnormally large proteins that provide valuable information about diseases such as macroglobulinemia. In recent years, various laboratories have attempted to develop automatic centrifuges—but without notable success. Future
CONTINUOUS
READINGS.
At Grasslands Hospital in Valhalla,
N.Y., Dr. Charles Weller starts to take continuous of a patienfs
measurements
blood sugar after obtaining the peaks for the various
standard solutions.
This research uses a Technicon
that analyzes blood taken directly from the patienfs
AutpAnalyzer arm
Advances
Looking to the years ahead, chemists foresee revolutionary changes in the way clinical chemical analyses are performed. "Twenty years from now," says Dr. Raymond Jonnard, laboratory director at Prudential Insurance, "clinical laboratory instrumentation will be radically different. It will involve true automation—using different chemical reactions and different functional principles. New instruments will incorporate greatly improved transducers, physical sensors, and amplifiers. The speed of analysis will be increased several orders of magnitude." Chemists expect far greater clinical use of methods now used only on a limited scale or not at all, such as atomic absorption analysis, x-ray spectrometer measurements, EPR analysis, and the determination of Raman spectra. Some look to the use of laser beams to excite spectral emission in samples—a method that may be especially valuable in analyzing for trace metals in vivo (such as zinc in living brain tissue). Chemists also foresee far greater use of continuous in vivo measurements. Patients in operating rooms and recovery rooms following surgery, they say, will quite literally be "plugged into" special instruments that will monitor their body chemistry continuously. This may involve, for example, the use of in vivo electrode detectors to measure electrolytes and DEC. 16, 196 3 C&EN
125
other materials in blood. Dr. Lyle H. Hamilton of the Veterans Administration Center in Wood, Wis., predicts, "In some cases, samples will be obtained by in-dwelling catheters, with alarms incorporated into the system to warn the medical staff instantly if dangerous trends develop." At the University of Alabama Medical Center in Birmingham, Dr. Leland C. Clark, Jr., is using automatic instruments to measure and record continuously the blood-gas partial pressures, blood-gas contents, electrolytes, pH, glucose, lactic acid, and various enzymes of cardiovascular surgical patients. As part of a National Institutes of Health research project, Dr. Clark and co-workers have carried out such measurements for thousands of hours. The required blood is withdrawn from an artery or vein at a rate of less than 20 ml. an hour. At Grasslands Hospital in Valhalla, N.Y., Dr. Charles Weller and Dr. Morton Linder are using an AutoAnalyzer to determine continuously the glucose content of a patient's blood. The method, which requires the continuous withdrawal of 6 ml. of blood an hour, is being tested as a means of determining the effects of various drugs on a patient's blood glucose. In addition, it is being used experimentally to find out how rapidly a patient is able to metabolize glucose and also to determine how a patient's glucose level is affected by physical or emotional stress. Beckman's Spinco Division makes an instrument that can continuously measure the partial pressure of oxygen in vivo. It uses a platinum-silver electrode fitted into a slender needle that can be inserted directly into the brain, body tissue, spinal fluid, or circulating blood. More than 300 of these in vivo instruments are now in use, primarily in research. Processing Data
Automatically
In the future, a major trend will be the increasing use of computers to process the data obtained in clinical laboratories. Computers will calculate the final results of instrument measurements. They will collate the various results for each patient and automatically print them out on a single report sheet, thus speeding the delivery of laboratory data to the physician. At the same time, information on the types of tests performed will be automatically transmitted to 126
C&EN
DEC. 16, 1963
the hospital's business office for rapid processing by automatic billing machines. Says Dr. Robert L. Dryer, associate professor of biochemistry at the State University of Iowa and national secretary of the American Association of Clinical Chemists, "The slow rate at which laboratory information is transmitted to the physician is one of the chief limiting factors today in many hospitals. Obviously, we are still in the horse-and-buggy stage as far as records handling is concerned. In the future, a central computer in the hospital will automatically relay the laboratory results to ward stations. There, machines will not only print out all current data on the patient but will summarize past data so that trends can be immediately detected." Scientists also believe that computers will find an important place in assisting physicians in making medical diagnoses. The computer will be given perhaps 30 or more variables, such as information on the patient's symptoms, the results of his physical examination and laboratory tests, details on his age, sex, medical history, and so on. The computer may then: • Suggest the various possible diagnoses (only occasionally might it actually pinpoint a diagnosis). • Recommend additional laboratory tests that may help narrow the possibilities. • Indicate the probabilities of success with various alternate methods of treatment. In the years ahead, computers are expected to become vital aids to physicians in making diagnoses on the basis of the rapidly mounting volume of available medical information. So far, this use of computers is still in the research stage. Work is moving ahead at such centers as Tulane University, the University of Cincinnati, Massachusetts General Hospital, and the University of California, Los Angeles, where studies are being financed in large part through the U.S. Public Health Service. Says Dr. Lee B. Lusted, senior scientist at the Oregon Regional Primate Research Center in Beaverton, "I expect that in 10 years a number of leading U.S. hospitals will be using computers on a practical, routine basis as an aid in medical diagnosis. Once two or three pilot projects in large, well-recognized hospitals have demonstrated the effectiveness of computers, their ac-
ceptance by the medical profession will come rapidly." The future will not only bring far greater use of computers but also far greater clinical chemical testing of patients on a routine basis. Now when a patient enters a hospital, he may, as a standard procedure, have his blood tested for glucose and possibly also for urea nitrogen. And that's all —except for the additional tests his physician may specifically order. Clinical chemists look to the day when the hospital will routinely run a set of 10 to 12 tests on all incoming patients. It will be simpler and possibly even cheaper, they believe, to do 12 standard tests fully automatically on all patients than to do, say, four of these tests on one patient and seven on another on the present custom-order basis. Any additional tests, of course, would be performed as needed. This sort of large-scale testing is expected to be extremely valuable medically. It should permit the early detection of diseases that at present may be completely unsuspected. In addition, it will add significantly to the volume of much-needed medical statistics on the over-all population. This advance will require a marked increase in the use of automatic instruments in clinical chemistry laboratories —instruments that will carry out tests quickly and accurately and feed their data directly into computers for processing. Only through the use of efficient automatic instruments will this sort of mass testing meet the ultimate test of economic feasibility. Automation is moving ahead rapidly in clinical chemistry laboratories. Inexorably, the trend is in the direction of vastly more to come.
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