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ANALYTICAL CURRENTS Real-time personal ozone monitor
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13
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7 1. Sample air inlet 2. Filter holder 3. Nafion dryer
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4. Sensor housing 5.Orifice flow control
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6. Pump
3 25 cm
Despite the number of ozone monitors available, detailed knowledge of human exposure to ozone is still lacking. Ozone concentrations are typically measured outdoors, where people spend only an estimated 10% of their time, and current badge monitors, which are designed for personal use, must integrate measurements over relatively long time scales. To address these limitations, Robert A. Harley and colleagues at the University of California–Berkeley and Aerosol Dynamics have developed a portable, real-time ozone monitor, which is based on a piezoelectric quartz crystal detector. The new monitor is a 25 3 35 3 13 cm unit that weighs 5 kg. Data are recorded with a time resolution of 10 min as changes in the crystal’s oscillation frequency. These frequency changes are caused by the reaction
7. Sample air exhaust 8. Power cord 9. Power supply 10. Pump power switch
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5 11
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11. Battery 12. Datalogger 13. Datalogger connector
35 cm Schematic of portable ozone monitor.
of ozone with a polybutadiene coating on the crystal, which changes the mass on the surface of the crystal. The researchers report a sensitivity of 3 ppb ozone and a useful lifetime of ~20 h at an average ozone concentra-
tion of 50 ppb, and they suggest that, after miniaturization and other modifications, the device may be used as a personal, real-time ozone monitor. (Environ. Sci. Technol. 2000, 34, 3031– 3040)
Post-PCR purification in microcolumns Reversed-phase (RP) HPLC offers very
tion “cocktail”. Now, Scott McWhorter
columns as UV detection does. The de-
high recoveries in the separation of am-
and Steven A. Soper at Louisiana State
tector is made from a quartz micro-T, in
plified DNA products from a PCR reac-
University describe a conductivity de-
which two platinum electrodes, spaced
tector designed to detect PCR products
60 µm apart, intersect with a 360-µm-i.d.
that have been separated using micro-
fused-silica capillary.
Platinum electrode
B
Fused-silica capillary
column RP-HPLC.
The researchers report the efficient
A
The researchers chose conductivity A = 75 µm B = 60 µm C = 360 µm
Quartz micro-T C
Schematic of the conductivity cell. (Adapted with permission. Copyright 2000 Elsevier Science.)
574 A
separation of a double-stranded, 500-
detection because it does not require
base pair PCR product from the reaction
the labeling of DNA products as fluores-
reagents in
