Establishment And Application Of Pentafluorophenyl Hydrazine Derivatization-thermal Desorption-gas Chromatography/Mass Spectrometry For Determination Of Airborne Carbonyl Compounds

Carbonyls (aldehydes and ketones) are an important class of volatile organiccompounds in the atmosphere. They continue to receive more and more attention astheir important role in atmospheric photochemical reaction and having variousadverse effects on human health. However, the concentrations of carbonyls in theatmospheric environment are relatively low (ppb level or lower ppb level) and mostof them have strong polarity, volatility and reactivity. It is easy to volatilize,decompose or oxidize for the carbonyls in the collection and analysis. Therefore, theanalytical method for airborne carbonyls has been a challenging problem all the time.Now, the common methods for determination of airborne carbonyls were to collectthem onto solid sorbents coated with a derivatizing agent, desorb with solvent andanalyze using high-pressure liquid chromatography/ultraviolet detection (HPLC/UV)or gas chromatography/mass spectrometric detection (GC/MS). These approachescan show higher sensitivities and meet the analytical requirement, but were all relianton complicated pretreatment of solvent desorption which was time-consuming andmanually intensive. What is worse, these methods suffered from reduced sensitivityas only a few percent of the eluent was analyzed. In comparison with solventdesorption, thermal desorption was a good alternative for the sample pretreatment. Inthe thermal desorption, it was organic solvent-free, convenient for automaticoperation, rapid and simple to run, on-line coupled with analytical system whichavoided the outside interference, and to obtain enhanced sensitivity because of thewhole sample being used for analysis. Thus, to establish an analytical method by thepretreatment of thermal desorption has an important significance for measuring thetrace carbonyls in the time-varying atmospheric environment.In this work, with the thermal desorption coupled with GC/MS andpentafluorophenyl hydrazine (PFPH) acted as the derivatizing agent, a simpleapproach with great sensitivity and reproducibility was developed for thesimultaneous determination of various carbonyls in the atmosphere, which was the method of PFPH derivatization–thermal desorption–GC/MS. In this method,carbonyls in the ambient air were collected onto Tenax TA coated with PFPH thatreacted with carbonyls to form thermo-stable PFPH derivatives, followed bythermally desorbing the derivatives from the sorbents and re-focusing them, and thenpromptly releasing them into GC/MS for separation and analysis. The conditions ofthermal desorption, including tube desorbing flow rate, time and trap desorbing flowrate, time, were optimized in this paper. When the tube desorbing flow rate, time andtrap desorbing flow rate and time were10mL min-1,8min and5mL min-1,8min,respectively, the recoveries of all the target carbony-PFPH derivatives were higher.In this study, the calibration curves were established by external standard method.The correlation coefficient of the calibration curves (R2), calibrating ranges, methodprecision (relative standard deviations (RSD), n=6)of the tested13carbonylcompounds were in the range of0.990～0.998,5～150ng tube-1and6.9～12.6%,respectively. The limits of detection (LODs) of the tested carbonyls were in the rangeof0.44～1.23ng tube1or0.004～0.029nmol tube1, which were lower thanPFPH–solvent desorption–GC/MS method and PFPH–in-injection port thermaldesorption–GC/MS method. As an assumption sampling volume of9L, the LODswould be about0.049～0.137μg m3. The collection efficiencies of sampling tube,with a coating amount of500nmol PFPH per50mg Tenax TA and operated at asampling fow rate of50mL min1for3h, were above86%for all detectedcarbonyls. Lastly, compared with the established PFPH–solvent desorption–GC/MSmethod in the field test, the proposed method showed lower LODs and detectedmore carbonyls of low concentration. In addition, there has been a good agreementbetween the two methods with the deviations below15%, especially for thecarbonyls of high concentration in the ambient air.The characteristics of carbonyl compounds including their concentrations,diurnal variations and C1/C2, C2/C3were investigated in the hazy days and clear daysof Shanghai using the proposed method. The results showed that formaldehyde and acetaldehyde were the two most abundant carbonyls in the hazy days and clear days.We found that the total carbonyl concentrations in the hazy days were much higherthan those in clear days, which demonstrated that the more serious pollution ofcarbonyls existed in the hazy days. In addition, the comparison of the trends ofdiurnal variation and C1/C2, C2/C3in the hazy days and clear days showed that thespecial meteorological condition was one important reason resulting in carbonylaccumulation.