Nitropyrene in Some Source Emissions

Một phần của tài liệu current practice of gas chromatography mass spectrometry (Trang 214 - 218)

2. AMBIENT AIR AND HUMAN BREATH ANALYSIS

2.1. Nitropyrene in Some Source Emissions

Nitro-substituted polycyclic aromatic hydrocarbons (nitro-PAHs) are formed dur- ing the combustion of fossil fuels at high temperatures with a vast supply of combustion air. In this reaction, conversion of nitrite (NO2) to nitric acid is an important intermediate step. Another source of nitro-PAHs is the photochemical radical–mediated conversions of parent PAHs to nitro-derivatives. Combustion at high temperatures with a vast supply of combustion air may lead to the forma- tion of 1-nitropyrene (1-NP), whereas photochemical conversion of pyrene gives rise to 2- and 4-nitropyrene [24,25].

Recovery of nitro-PAH compounds from the filter surface and particles can be achieved in a one-step extraction with a suitable organic solvent, e.g., acetone or methylene chloride, by sonication, Soxhlet extraction, or supercritical fluid extraction. The organic solvent can be removed by a gentle flow of inert gas, e.g., nitrogen. To speed up evaporation, the extracts can be placed in a thermo- static water bath. Some (semi) volatile compounds may be lost easily at the point of complete dryness, which must be prevented by ceasing evaporation or (more practical) addition of a small volume of a stayer. Any losses during this and other steps can be monitored and corrected for by using a suitable internal standard, added just before commencing extraction. The use of deuterated analogs of the analytes is state-of-the-art. For the analysis of small quantities of nitro-PAHs that are associated with combustion particles, extensive pretreatment may be required.

In order to prevent loading of the analytical column with a substantial amount of nonpolar organic compounds such as the parent PAHs, the slightly polar nitro- PAHs can be easily isolated using silica solid-phase cartridges [26]. Nitro-PAHs do not separate nicely on GC. Their volatility can be improved by reduction to their amino analogs and subsequent derivatization with heptafluorobutyric anhy- dride (Fig. 1). Conditions for GC–MS analysis of nitro-PAHs are given in Table 1.

2.2.2. Road Vehicle Emissions

The 1-NP content was analyzed in particulate matter collected from the exhaust of more than 20 diesel-powered road vehicles during the Dutch emission compliance program for passenger cars (TNO Road-Vehicles Research Institute) in 1996.

Particulate matter was collected on polytetrafluoroethylene (PTFE)-coated glass fiber filters according to a European standard procedure (91/542/EC), during a simulated driving cycle on a chassis dynamometer. These fresh exhaust samples contained typically more volatile organic compounds than ambient air samples.

Health Risk Assessment 203

Figure 1 GC–MS–MS analysis of 1-aminopyrene derivatized with HFBA (mass spec- trum in insert). For system description and analysis conditions see Table 1. (From Ref.

xiii in Table 6.)

The 1-NP content of the particles ranges over two orders of magnitude.

Interestingly, Japanese cars produce particles with much higher 1-NP content compared with the exhaust from the cars of European manufacture (Table 2).

There is also a tendency for most cars of increasing 1-NP content when compar- ing the driving conditions from left to right: UDC⫾ UDC-hot⬍ EUDC, and FTP-cold⬍FTP-stab⬍FTP-hot (cf. Table 2). This difference can be explained by the rise in temperature of the engine and the combustion mixture during the preceding driving cycles. In the FTP driving pattern, with the engine preheated during a 9-minute transient cycle (FTP-cold), followed by a 15-minute stabilized cycle (FTP-stab) and 10-minute stationary phase (FTP-hot), the production of oxides of nitrogen (NOx) is gradually increasing due to an increase in combustion temperature. A higher emission of NOxis also observed in the extended extra urban driving cycle (EUDC) with the speed going up to 120 km/hr in simulated highway driving. Because of an overall increase of the NOxproduction, a higher rate of formation of 1-NP is observed in the last part of the driving cycle (Table 3).

2.2.2. Tobacco Smoke

Active and passive smoking is one of the most important sources of coexposure in inhalation exposure assessment. Therefore, it is important to verify if active

204 Scheepers et al.

Table 1 Description of System and Conditions Used During the Analysis of Nitro- PAH

GC Varian 3400 CX

MS Varian Saturn 4D Ion Trap

Pre-column 5 m⫻0.53 mm ID deactivated fused silica ‘‘retention gap’’

Analytical column 30 m⫻0.25 mm ID capillary fused silica DB-5MS column with film thickness of 0.25àm (J & W Scientific, Folsom, CA)

Injection rate 2.0àl/sec Hot needle time 0.1 min Injector temperature 200°C Transfer line 290°C

Carrier gas He at column head pressure of 14 psi GC programme Initial temperature 110°C, 10°C/min to 300°C

MS type ion trap

MS settings EI mode/EI mode/selective reaction monitoring/ nonresonant collision induced mode

Ionization energy 70 eV Isolation of m/z 413, 422

Window m/z 1

Excitation RF 120 amu

Excitation voltage 94 V (noncollision-induced dissociation) Background mass m/z 99

Mass range m/z 180–430

Scan speed 0.6 sec/scan

smoking contributes to 1-NP exposure. So far, 1-NP has not been detected as a constituent of cigarette smoke condensate in MS analysis, presumably because the tobacco smoke mixture is a reductive mixture resulting in the appearance of amino compounds rather than their nitro analogs. It was not observed at 1 ng per cigarette by El-Bayoumy et al. [27], and not at a limit of detection of 10 pg on-column by Williams et al. [28]. The occurrence of 1-NP was verified in tar samples derived from some of the most popular cigarette types in the Netherlands.

The precleaning of the tar extracts by silicon dioxide (SiO2) solid-phase fraction- ation appeared insufficient for a sensitive analysis. To prevent loading of the analytical column with substantial organic debris, a GC-liner was placed before the analytical column (Alltech Applied Science Group, Emmen, The Nether- lands), thus providing scavenging of most of the contamination. In Caballero Plain (13.1 mg tar/ cigarette), Camel Filter (12.8 mg tar/cigarette), Marlboro Filter (12.7 mg tar/cigarette), Marlboro Light (7.9 mg tar/cigarette), and Barclay

Health Risk Assessment 205

Table 2 1-NP Analyzed in Samples of Particulate Matter Collected from Diluted Tailpipe Exhaust of Diesel-Powered Passenger Vehicles Tested on a Chassis Dynamometer

1-Nitropyrene (àg/g) Odometer

Car (km) UDCa UDC-hotb EUDCc

Citroen BX 1.9 TZD 188513 4.3 7.0 12.3

Citroen BX 1.9 TZD 168484 2.1 7.2 11.9

Peugeot 106 11514 0.3 2.9 15.5

Peugeot 106 27136 1.1 5.1 11.1

Peugeot 205 131367 1.4 3.8 8.0

Renault Safrane 53480 4.5 5.1 7.7

Renault Safrane 25541 1.8 4.3 6.5

Opel Astra 5436 1.7 2.3 3.5

Opel Astra 4906 2.6 3.1 4.1

Opel Corsa 18095 2.2 3.1 6.5

Opel Corsa 32444 3.3 4.4 15.6

Mazda 626 CX 30111 22.7 17.6 63.0

Mazda 626 CX 31782 21.2 15.5 67.7

Mazda 626 CX 33344 19.8 31.0 143.4

Chrysler Voyager 96560 6.7 8.1 33.5

FTP- FTP- FTP-

coldd Stabe Hotf

Nissan Primera 41902 16.5 6.6 29.5

Nissan Primera 31418 20.3 33.6 41.4

Nissan Primera 11222 20.4g 10.4g 30.3g

Nissan Primera 11222 25.3g 15.4g 33.3g

Nissan Primera 66516 59.4 26.5 90.0

Mercedes C 200 D 16260 1.7 8.2 29.4

Mercedes C 200 D 40473 7.5 12.7 22.0

Mercedes C 200 D 8958 8.7 29.3 33.2

aUDC, urban driving cycle.

bUDC-hot, UDC hot start.

cEUDC, extra urban driving cycle (0–400 sec).

dFTP-cold, federal testing procedure—cold transition period (0–505 sec).

eFTP-stab, federal testing procedure–stabilized period (505–1372 sec).

fFTP-hot, federal test procedure–hot transition period (1372 -1877 sec).

gCollection and analysis of particulate matter in duplicate.

206 Scheepers et al.

Table 3 Determination of the Content of 1-NP (pg/m3) in Samples of Airborne Particulate Matter According to Two Different Nitro-Reduction Pretreatment Steps and Ion-Trap MS and High-Resolution MS (Both in EI Mode)

Reduction pretreatment On-line zinc NaSH

System Ion-trap MS Ion-trap MS NaSH

Varian Varian High-resolution MS Saturn 1 Saturn 1 VG Autospec Q

Mode EI EI EI

Ionisation energy (eV) 70 70 35

Scanning rate (scan/s) 1 1 3

Emission sourcea Air volume (m3) Outdoor ambient air:

Background 427 NDb ND 1.7

Lawn mower 215 ND ND 6.6

Military vehicles 345 ND ND 12

Passing traffic 420 ND 34 36

River boat 385 93 ND 31

Airport vehicles 260 ND ND 42

Indoor workplace atmosphere:

Trucks 340 110 86 80

Forklift trucks 465 150 88 71

Train engines 345 390 160 280

Forklift trucks 200 780 1,600 1,200

aDiesel-powered combustion source dominating the air quality.

bND, not detected.

(4.4 mg tar/cigarette), 1-NP and 1-aminopyrene (1-AP) were not detected at a limit of determination of 30 pg per cigarette.

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