The reaction of trimethylamine (TMA) vapor with a polydisperse distribution of ammonium nitrate particles (20-500 nm dia.) was studied in a flow tube reactor with particle analysis by laser desorption (1064 nm) 70 eV electron ionization (EI) in an ion trap time-of-flight (IT-TOF) aerosol mass spectrometer. When the TMA vapor concentration was very high, essentially complete exchange of TMA for ammonia in the particles was achieved. When the TMA vapor concentration was lower ( approximately 500 ppb for a reaction time of 23 s), partial exchange was observed, and the initial reactive uptake coefficient was estimated to be on the order of 2 x 10(-3) at 20% RH. This value suggests that measurable exchange is possible in the atmosphere when particles are exposed to an amine concentration on the order of 1 ppb for a few hours. The effects of particle size, water content, and amine molecular structure on uptake remain to be elucidated.

No abstract

The atmospheric solids probe analysis (ASAP) probe was investigated as a means for conducting desorption electrospray ionization (DESI) using a commercially available ion source. Solid and liquid samples as well as a raw urine sample were placed on individual melting point tubes and were inserted into either a heated gas stream for ASAP analysis or a charged solvent spray for DESI-like experiments. Samples ranged in polarity, volatility, mass, (100-17,000 Da), and concentration (neat to submicromolar). Mass spectra of multiple samples were obtained within a single acquisition on a short time scale (<30 s per sample). The configuration of the ion source also allowed rapid switching (approximately 1 min) between ASAP, electrospray ionization (ESI), and DESI.

Angiotensin II (DRVYIHPF) and two analogs, (DRVYIAPA and DRVAIHPA), were used as model systems to study the ozonolysis of peptides containing tyrosine and histidine residues. The ESI mass spectrum of angiotensin II following exposure to ozone showed the formation of adducts containing one, three, and four oxygen atoms. CID and SID spectra of these adducts were consistent with formation of Tyr ϩ O and His ϩ 3O as expected from previous work with amino acids. However, several fragment ions observed in the CID and SID spectra suggested formation of a rather unexpected adduct, Tyr ϩ 3O, and a small amount of the Phe ϩ O adduct. These findings were confirmed by examining two angiotensin analogs. Exposure of DRVYIAPA to ozone resulted in the addition of either one or three oxygen atoms on Tyr, while DRVAIHPA showed only the addition of three oxygen atoms-all on His. Other noteworthy minor oxidation products were observed from these analogs including Tyr ϩ 34 Da, His ϩ 5 Da, His ϩ 34 Da, and His ϩ 82 Da. The reaction rates of the peptides with ozone were found to be similar: second-order rate coefficients are 274 Ϯ 3, 379 Ϯ 6, and 439 Ϯ 34 M Ϫ1 s Ϫ1 for DRVYIAPA, DRVAIHPA, and angiotensin II, respectively. The relative rates indicate (1) an isolated His residue has a slightly greater ozone reactivity than an isolated Tyr residue, and (2) the reaction rates of isolated residues are not additive when both residues are present in the same

A fluorescence-based chemical sensor for fluorene was created by molecularly imprinting a sol-gel comprising the bridged silsesquioxane, bis(trimethoxysilylethyl)benzene. The template was covalently bound to the sol-gel matrix using a fluorene analogue functionalized silane. After chemical removal of template via cleavage of a carbamate linkage, an amine group was left that provided an attachment site for the environmentally sensitive fluorescent probe 7-nitrobenz-2-oxa-1,3-diazole (NBD). Fluorene binding was detected by a change in NBD fluorescence intensity induced by a difference in the local polarity around the probe when the recognition site is filled. Such an approach eliminated response to nonspecific binding to the matrix. Sensing films deposited on glass slides were shown to have response times of <60 s and detection limits below 10 parts-per-trillion. Binding experiments demonstrated that the materials had good selectivity for fluorene over close structural analogues including naphthalene, fluoranthene, and anthracene. However, the sensing design is limited by a lack of reversibility following fluorene binding.