UDC 546.271.2:546.49

On a Rapid Method for Determining Low Concentrations of Mercury Vapor in Air

A. B. Belozovsky, Candidate of Technical Sciences; E. V. Zhuravlev, Candidate of Chemical Sciences; V. I. Tarasov; Yu. V. Subbotin

Perm University, named after A. M. Gorky

This paper presents the results of tests of the portable IKRP-450U mercury gas analyzer, developed by the Tsvetmetavtomatika design bureau and described in a special manual. The instrument operates on the principle of absorption by mercury vapor of ultraviolet radiation with a wavelength of 253.7 nm, with the absorption measured by a vacuum photocell.

Conventional analytical methods cannot verify the instrument’s calibration with sufficient accuracy, especially at low concentrations, and therefore cannot establish its accuracy with a specified level of confidence. The reliability of the instrument’s readings was assessed by comparing the mercury vapor concentration in the same sample measured with this instrument and by a radiometric method. The latter consisted in the quantitative determination of the unstable mercury isotope \(\mathrm{Hg}^{203}\) using a single-channel \(\gamma\)-ray spectrometer.

The mercury vapor concentration in the stream entering the instrument was varied by changing the height of the bed of activated-carbon-based charge in dynamic tubes. By exploiting the advantages of the radiochemical method, it was possible to obtain reliable, readily comparable results, since measurements with the instrument and by the radiometric method were performed in parallel.

The results were statistically analyzed under the following conditions: four parallel measurements, a confidence coefficient of 0.95, and a Student’s coefficient of 3.18. Instrument error was not considered separately but was included in the total measurement error. The confidence interval was determined from the root-mean-square error and Student’s coefficient by the method described by O. N. Kassandrova and V. V. Lebedev. The reliability of the results is supported by the radiometric measurements, which generally fall well within the corresponding confidence intervals of the measurement results.

The study showed that the instrument has a reasonably high degree of accuracy and reliability. It should be emphasized, however, that measurements with the instrument require a constant mercury–air flow through the adsorption cell—that is, strict quantitative control of the flow at the rate for which the instrument was calibrated. Otherwise, measurement error will result. Mercury is prone to

…to adsorption on solid surfaces. Consequently, when the instrument is in use, the question inevitably arises as to how long it can be operated without contaminating the cell to an extent that affects the measurement results. To resolve this question, mercury adsorption on glass was investigated as a function of time. Traces of mercury (\(10^{-7}\ \mathrm{mg/m^2}\)) appeared on the glass only after a mercury–air stream with a mercury concentration of \(100\ \mathrm{mg/m^3}\) had been passed through continuously for 2 hours, whereas a concentration measurement with the instrument takes 1–2 minutes. Subsequently passing clean air through the cell completely cleans it.

From the foregoing, it may be concluded that, under suitable conditions, the IKRP-450u instrument can be used successfully for rapid determination of mercury vapor concentrations in air in the range \(1.6\cdot10^{-2}\)–\(2.2\cdot10^{-3}\ \mathrm{mg/m^3}\), with a relative determination error of 6–17%.

References

Methodological Guidelines No. 197 for Testing Instruments That Analyze Mercury Vapor in Air. Moscow, 1966. — Kasandrova, O. N., and Lebedev, V. V. Processing of Observation Results. Moscow, 1970.

Received March 10, 1971.