Detection of explosives as negative ions directly from surfaces using a miniature mass spectrometer.

A miniature mass spectrometer was modified by incorporating a conversion dynode detector system and the appropriate electronics to allow the detection of negatively charged ions. The system was fitted with a discontinuous atmospheric pressure interface to allow external ionization by desorption electrospray ionization (DESI). It was used to identify the explosives 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenyl-N-methylnitramine (Tetryl), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) present in trace amounts on surfaces (500 pg/cm(2) to 1 microg/cm(2)) both individually and as components of mixtures. Detection of explosives was demonstrated in the presence of an interfering matrix. A large surface (5 cm x15 cm) on which 1 microg/cm(2) samples of TNT, Tetryl, and HMX had been spotted randomly was interrogated in 22 s in the full scan mode, and signals characteristic of each of the explosives were observed in the DESI mass spectrum.

Hand-held mass spectrometer for environmentally relevant analytes using a variety of sampling and ionization methods.

A recently developed hand-held, rectilinear ion trap mass spectrometer, capable of performing in situ analysis, has been evaluated for a variety of environmentally relevant analytes. Different sampling and ionization methods were implemented, demonstrating the considerable versatility of this instrument. A discontinuous (viz. pulsed) atmospheric pressure inlet (DAPI) was used to introduce externally-generated analyte ions. Nitro compounds were ionized by electrosonic spray ionization (ESSI) yielding the protonated and sodiated forms of the molecular ion, as well as fragment ions. The amines 2,2,6,6-tetramethylpiperidine, triethylamine and 2,6-diphenylpyridine showed low parts per billion (ppb) detection limits. Vapor phase external ionization was used to examine the chemical warfare simulant dimethyl methylphosphonate and the insect repellant N,N-diethyl-m-toluamide. Membrane introduction mass spectrometry (MIMS) was used as the introduction system for hydrophobic analytes using a selectively permeable (polydimethylsiloxane) membrane placed within the vacuum manifold with subsequent ionization of the thermally desorbed neutral compounds inside the ion trap. MIMS allowed the quantitation of trace levels (a few ppb) of fluorinated compounds in the vapor phase. MIMS was also applied to the quantitation of aqueous polycyclic aromatic hydrocarbons (PAH's) with limits of detection again in the low ppb range for naphthalene, acenaphthene, anthracene and phenanthrene.

Direct detection of benzene, toluene, and ethylbenzene at trace levels in ambient air by atmospheric pressure chemical ionization using a handheld mass spectrometer.

The capabilities of a portable mass spectrometer for real-time monitoring of trace levels of benzene, toluene, and ethylbenzene in air are illustrated. An atmospheric pressure interface was built to implement atmospheric pressure chemical ionization for direct analysis of gas-phase samples on a previously described miniature mass spectrometer (Gao et al. Anal. Chem.2006, 78, 5994-6002). Linear dynamic ranges, limits of detection and other analytical figures of merit were evaluated: for benzene, a limit of detection of 0.2 parts-per-billion was achieved for air samples without any sample preconcentration. The corresponding limits of detection for toluene and ethylbenzene were 0.5 parts-per-billion and 0.7 parts-per-billion, respectively. These detection limits are well below the compounds' permissible exposure levels, even in the presence of added complex mixtures of organics at levels exceeding the parts-per-million level. The linear dynamic ranges of benzene, toluene, and ethylbenzene are limited to approximately two orders of magnitude by saturation of the detection electronics.

Direct monitoring of toxic compounds in air using a portable mass spectrometer.

A portable tandem mass spectrometer, capable of performing atmospheric pressure chemical ionization (APCI) using a direct atmospheric inlet, is applied to the real-time monitoring of toxic compounds in air. Analytes of interest include dimethyl methylphosphonate, arsine, benzene, toluene, pyridine and vinyl acetate. The detection, identification and quantification of organic and inorganic compounds in air is demonstrated using short analysis times (<5 seconds) with detection limits in the low ppb (v/v) levels and linear dynamic ranges of several orders of magnitude. Highly specific detection and identification is achieved, even when the analyte is a trace component in a complex mixture including such interferents as fuels, lubricants, and cleaners. The effects of environmental conditions, including temperature and humidity, are delineated. Receiver operating characteristic (ROC) curves are presented to show the trade-off between false positive and false negative detection rates. Tandem mass spectrometry based both on collision-induced dissociation and on selective atmospheric pressure ion/molecule reactions is also used to increase selectivity and sensitivity.

Analysis of gaseous toxic industrial compounds and chemical warfare agent simulants by atmospheric pressure ionization mass spectrometry.

The suitability of atmospheric pressure chemical ionization mass spectrometry as sensing instrumentation for the real-time monitoring of low levels of toxic compounds is assessed, especially with respect to public safety applications. Gaseous samples of nine toxic industrial compounds, NH3, H2S, Cl2, CS2, SO2, C2H4O, HBr, C6H6 and AsH3, and two chemical warfare agent simulants, dimethyl methylphosphonate (DMMP) and methyl salicylate (MeS), were studied. API-MS proves highly suited to this application, with speedy analysis times (<30 seconds), high sensitivity, high selectivity towards analytes, good precision, dynamic range and accuracy. Tandem MS methods were implemented in selected cases for improved selectivity, sensitivity, and limits of detection. Limits of detection in the parts-per-billion and parts-per-trillion range were achieved for this set of analytes. In all cases detection limits were well below the compounds' permissible exposure limits (PELs), even in the presence of added complex mixtures of alkanes. Linear responses, up to several orders of magnitude, were obtained over the concentration ranges studied (sub-ppb to ppm), with relative standard deviations less than 3%, regardless of the presence of alkane interferents. Receiver operating characteristic (ROC) curves are presented to show the performance trade-off between sensitivity, probability of correct detection, and false positive rate. A dynamic sample preparation system for the production of gas phase analyte concentrations ranging from 100 pptr to 100 ppm and capable of admixing gaseous matrix compounds and control of relative humidity and temperature is also described.