Air Monitoring 47 the agreement of the Certification Committee.
To demonstrate the accuracy of the instruments, Chromatotec® required other VOCs to be tested by carrying out the same procedures defined for benzene. Similar performance characteristics and performance criteria were applied to 12 additional species which are all as critical as benzene for environmental and health issues (Figure 1). 12 peaks are observed, corresponding to 13 components. The determinands m-xylene and p-xylene were analysed as one chromatographic peak and the results were reported as the sum of the two. For example, the certification range for the type-approval tests was 0 µg.m-3
to 50 µg.m-3 (standardised
at 101.3 kPa and 293 K) for benzene, or 0 parts per billion (ppb) to 15.4 ppb where 1 ppb is equivalent to 1
nmol.mol-1. The certification range of the other determinands in the test programme was also defined as 15.4 ppb.
The laboratory test criteria carried out on all compounds were repeatable, short-term drift, dependence on sample gas pressure, lack of fit (linearity), carry over (memory effect), dependence on voltage, dependence on surrounding air temperature, cross interference with ozone, cross interference with water (relative humidity test), and cross interference with organic compounds. The performance criteria were met for benzene covering all the requirements listed above in strict compliance with the current MCERTS and European standard EN 14662-3.
The cross interference with organic compounds, which evaluates the influence of the interference from the sum of possible interfering VOCs at the span concentration value (between 70% and 90% of the certification range) was below 5% for 10 tested interferring compounds for all the four analysers. It is important to highlight that all potential organic cross interferents listed in the EN-14662-3 (methylcyclopentane, 2,2,3-trimethylbutane, 2,4-dimethylpentane, tetrachloromethane, cyclohexane, 2,3-dimethylpentane, 2-methylhexane, 3-ethylpentane, trichloroethylene, n-heptane) were tested.
Among the superior results obtained during laboratory tests, the repeatability at 0.5 µg.m-3 0.02 µg.m-3
and 0.06 µg.m-3 .
for benzene was found to be as low as for airTOXIC (PID) and airmoVOC (FID)
respectively. To be compliant with the standard method EN 14662- 3, the repeatability value must be less than ± 0.3 µg.m-3
Chromatotec’s analysers operate continuously in industry and may encounter interference from an unstable surrounding environment. Therefore, the sensitivity coefficients for the influence of voltage and ambient pressure, as well as temperature were tested. These stress tests on the analysers show that they are ideally suited for continuous analysis of industrial ambient air.
In cooperation with airmotec/Chromatotec®, NPL also proposed a
Field Test Programme, which was approved by Sira Environmental Limited. The field tests were conducted in accordance with UKAS- accredited NPL Test Procedure QPAS/B/528b, using appropriately calibrated equipment. The tests were performed at the Automatic Urban Rural Network (AURN) monitoring site in Marylebone Road, London W1 (central London). During three months of tests, the maintenance requirements specified by Chromatotec®
were
followed. The field tests carried out included operational requirements, long term drift, maintenance interval, availability, and reproducibility standard deviation under field conditions.
Long term drift was determined at the span value (between 70% and 90% of certification range) of Benzene, namely 45 µg.m-3
(13.9
ppb), over 14 days. All other determinands involved in the test had concentrations of nominally 13.9 ppb. A total of four valid determinand sample injections were employed at the start and end of each drift period, resulting in six sets of data. The CAMS sampled ambient air at all other times when span measurements were not being carried out. The largest value of the drift complied with the requirements: d14d < ± 10 %. Tests on the four different analysers successfully passed or exceeded requirements for benzene and for the additional VOCs species.
Concerning the maintenance interval, Chromatotec® demonstrated
the robustness of its analysers by showing that maintenance was not necessary on the instruments, in contrast to the MCERTS scheme which envisaged maintenance every two weeks during the field test period: the performance criteria were met without maintenance. Another parameter tested was the availability, a parameter that weighs the elapsed time of analysis with the ability to give validated results. Results are given in percentage and must be greater than or equal to 90%. For benzene specifically, 99.8% and 100% were obtained with airmoVOC (FID) and airTOXIC (PID) respectively. Once again, these results demonstrate the excellence of Chromatotec®
analyser in meeting the performance criteria. The reproducibility standard deviation test was carried out by
Figure 1: Typical chromatograph obtained during the tests carried out by the NPL. The 13 analyzed compounds are: N-Hexane; Benzene; 2,2,4-Triethyl pentane (i-octane); N-Heptane; Toluene; N-Octane; Ethyl-Benzene; m&p-Xylene; o-Xylene; 1,3,5-Trimethylbenzene; 1,2,4- Trimethylbenzene; 1,2,3-Trimethylbenzene.
Performance characteristic Laboratory tests
Performance criterion
Lack of fit, largest residual < ± 5 % Repeatability at 0.5 µg m-3
interference from ozone
Influence of the interference from sum of possible interfering organic compounds at span value
Influence of the
interference from relative humidity
Sensitivity coefficient for the influence of
surrounding temperature at span value
Sensitivity coefficient for the influence of ambient pressure at span value
Sensitivity coefficient for the influence of voltage a span value
Short term drift (24 hours) at span value
Carry over
Performance characteristic Field tests
Long term drift at span value (14 days)
Maintenance interval Availability
< ± 4 % < ± 0.2 % K-1 < ± 1 % kPa-1 < ± 0.2 % V-1 < ± 5 %
< 10 % of limit value for second analysis (=0.5µg m-3
)
Performance criterion
Reproducibility standard deviation < ± 0.25 µg m-3
< ± 10 %
> 14 days > 90 %
Test result (airmoVOC Serial number 20190309)
0.24 µg m-3 1.54 %
90 days 96.3 %
comparing the ambient measurement data between pairs of CAMs of the same type throughout the three month trial. It did not include measurements of span gases or down time for maintenance. The values 0.24 µg m-3 µg.m-3
airmoVOC (FID) and 0.08 airTOXIC (PID) respectively obtained for benzene
measurements were in compliance with the required standard: sRF < ± 0.25 µg.m-3
. Furthermore, the value of the expanded
uncertainty for each CAMS may not exceed the requirements of the Directive 2009/69/EC of the European Parliament and of the Council of 16th November 2000 relating to limit values for benzene and carbon monoxide in ambient air: Abl. Nr. L313, p.12. This standard permits for benzene a maximum value of ±25% for the expanded uncertainty for continuous measurements. The total uncertainty was determined for each CAM using the relevant performance characteristics determined in the laboratory and field tests for the determinand benzene. The results were 12.1% and 15.0% for PID (Model A73022) and FID (Model A21022) respectively, comfortably meeting the requirements of the European Directive.
Test result
(airmoVOC serial number 20730509)
0.24 µg m-3 4.42 %
90 days 99.7 %
Test result (airTOXIC serial number 20430309)
0.08 µg m-3 7.52 %
90 days 100 %
Test result (airTOXIC serial number 20720509)
0.08 µg m-3 4.68 %
90 days 99.9 %
The NPL, is known worldwide for being at the edge of technology for air quality monitoring and type testing, performed in the laboratory and in the field. Their conclusion is that Chromatotec® analysers met the requirements for continuous monitoring of ambient air both indoors and outdoors. The results obtained in the different tests frequently surpassed the limit criteria defined in the standard method EN 14662-3. Chromatotec®
instruments on the market which have been tested successfully for 13 VOCs in accordance with MCERTS performance standards and EN 14662-3.
An audit of airmotec/Chromatotec® by Sira was carried out at the
end of 2012 in accordance with EN 15267-1 . The company completely fulfilled the requirements of the norm EN 15267-2 relative to air quality: Certification of automated measuring systems Part 2: Initial assessment of the AMS manufacturer's quality management system and post certification surveillance for the manufacturing process.
0.001 % 0.03 % K-1 0.18 % kPa-1 0.022 % V-1 1.82 % 0.36 µg m-3 0.001 % 0.08 % K-1 0.10 % kPa-1 0.010 % V-1 0.15 % 0.41 µg m-3 0.78 % 0.16 % K-1 0.26 % kPa-1 0.031 % V-1 0.96 % 0.35 µg m-3 1.16 % 0.10 % K-1 0.15 % kPa-1 0.027 % V-1 0.79 % 0.37 µg m-3 < ± 5 % < ± 5 %
Test result (airmoVOC Serial number 20190309)
2.12 % < ± 0.3 µg m-3
Repeatability at limit value < ± 5 % Influence of the
0.06 µg m-3 1.84 %
1.19 % 3.87 % Test result
(airmoVOC serial number 20730509)
2.54 %
0.20 µg m-3 1.42 %
1.25 % 4.58 % Test result
(airTOXIC serial number 20430309)
4.60 %
0.02 µg m-3 3.74 %
0.87 % 1.81 % Test result
(airTOXIC serial number 20720509)
4.42 %
0.03 µg m-3 1.34 %
1.00 % 2.81 %
analysers are the only
www.envirotech-online.com IET Annual Buyers’ Guide 2013
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