Atomic absorption (AA) has been known since the 19th century, but it was not until the 1950s, thanks to efforts by Alan Walsh at Australia’s CSIRO research center, that use of AA spectrometers became routine for metals analysis.
AA measures ultraviolet light absorbed by hot, atomized metals. The absorbance wavelength is unique to every metal, but the signal intensity varies by concentration. Instrumentation is straightforward, consisting of a light source, atomizer and detector. Atomizers are traditionally hightemperature flames, but graphite furnaces and various plasma sources are also used. Light sources include hollow cathode lamps (most common) and diode lasers. Detectors are most usually photomultiplier tubes. AA could be considered for nearly any application that requires the identification and/or quantification of metals, including environmental analysis, forensics, archeology, mining, agriculture and quality control for contaminant, ingredient, or trace metal in foods, drugs, personal care products, paper, materials, and other products.
Chuck Schneider, business unit manager for PerkinElmer’s (Shelton, Conn.) inorganic analysis products, breaks AA instrumentation down into three categories: flame, graphite furnace, and dedicated analyzers. PerkinElmer further delineates these into entry-level systems and higher-end systems with more extensive automation, software, data handling, and the ability to switch back and forth from flame to graphite furnace operation.
Graphite furnace AA spectrometers are significantly slower than flame-atomizer instruments, but they provide several benefits. Because they concentrate the cloud of atomized metals, graphite furnace instruments require less sample than flame AA spectrophotometers—20 μl vs. up to 5 ml. Sensitivity (ppb vs. ppm) is also higher in graphite furnace models.
PerkinElmer has recently completed a large survey of inorganic analysis customers and found that the top two factors entering into purchase decisions are customer service (including the salesperson’s knowledge and service support) and ease of use and setup for hardware and software. The third factor is the vendor’s reputation. Price is “fifth or sixth on the list,” Mr. Schneider says. “AA has got to be dead simple to use, because instruments are used by a lot of different people who may not have specific training in the technique. Years ago a lab might have had five people operating six or seven instruments. The number of techniques has remained the same, but the number of analysts might be down to two. Lab workers need to be generalists.”
With more or less the same hardware technology accessible to all manufacturers, Yong Xie, AA product manager at Aurora Biomed (Vancouver, BC), believes that some vendors err in focusing on the hardware and automation alone and not enough on the ease of use—a factor noted in the PerkinElmer study. “The computer industry has made huge progress in both hardware and software,” he says, as have advances in automation, autosampling, and unattended operation. Since these advances won’t help with detection limits or other fundamental performance factors, “they are best applied to enhancing the user experience, to provide the most convenient environment for operating the instrument and achieving desired objectives.”
• Features an Eberl mount monochromator and user-selectable bandwith for flexibility
• D2 lamp emits radiation from far-UV region (<190 nm to approximately 350 nm)
• Three-lamp turret has individual controls for alignment and stay warm/operating facilities for each lamp
• Features a solid-state detector for increased analytical performance over entire AA wavelength range
• THGA tube design eliminates most interferences
• Features longitudinal Zeeman-effect correction for improved accuracy and detection levels
• Includes automated flame and furnace atomizer
• Features quick auto-switch between Flame and GF atomizers
• Fast wavelength scan takes 30 seconds to scan from 190-900 nm
• Automatic acetylene flow rate control ensures hands-free operation
• Features a built-in camera in the GF system for efficient method development
• Combines flame, hydride and graphite furnace in one device
• HR-CS AAS technique closes the methodological gap between AAS and ICP OES
• Features High-Resolution Continuum Source Technology for trace and ultra-trace analysis using atomic absorption with a graphite furnace