IMPROVEMENT OF THE EC REFERENCE METHOD FOR THE DETERMINATION OF SULFUR DIOXIDE
The ECC Council Directive no 80/779 on limiting values of atmospheric SO-2 requests the use of the colorimetric p-rosaniline (TCM) method. As described, it refers to a 30 minutes' sampling period and has a precision of +- 4 % (rel) at 530 mug/m**3 5200 ppb SO-2 and +- 15 % below 130 mug/m**3 (50 ppb SO-2). In order to respond to certain requirements of the Directive, the method has to be adapted for 24 h sampling by reducing the air flow (0.2 l/min) and increasing the TCM solution (50 ml), the precision remaining basically unchanged. For sufficient stability, the disulfitomercurate complex formed with SO-2 must be kept at 20 degrees C for maximum storage time of 24 h (or at 5 degrees C for 20 days) and the photometric measurement must be made at constant temperature (+- 1 degrees ). The improved TCM method correlates well with flame photometric data between 18 - 600 mug/m**3 SO-2 17 - 230 ppb).Test sources were permeation devices, synthetic air - SO-2 mixtures from gas cylinders and PFTE bags. Out of the 7 commercial p-rosanilines only two and only after purification corresponded to the specifications given in the Directive (maximum absorbtion at 540 nm, blank absorption: 0.10, slope of the calibration curve + z < 0,030 unit absorbtion/mug SO-2). Purification was made by four extractions with 1-butanol - HCl; the recommended recrystallisation is inefficient. The recommended scrubbing of H-2S is unnecessary for ambient concentrations and would moreover impair the reliability of the method by partial SO-2 absorption.
Bibliographic Reference: WORKSHOP ON MONITORING SO-2, BLACK SMOKE AND TOTAL SUSPENDED PARTICULATES, BILTHOVEN (THE NETHERLANDS), NOV. 5-7, 1984 WRITE TO CEC LUXEMBOURG, DG XIII/A2, POB 1907 MENTIONING PAPER E 31688 ORA
Availability: Can be ordered online
Record Number: 1989123026400 / Last updated on: 1987-01-01
Available languages: en