Performance-Enhanced “Tunable” Capillary Microwave-Induced Plasma Mass Spectrometer for Gas Chromatography Detection

Abstract

Improvements in the stability and performance of a capillary microwave-induced plasma-mass spectrometer (MIP-MS) were achieved by optimizing power transfer to the cavity using a tunable coaxial MIP. The MIP, operating at atmospheric pressure, was sustained with 30 mL/min He and 60 W of power. Measurement precision and sensitivity for the standard waveguide and coaxial systems were determined using 16 organochlorine pesticide solutions separated by gas chromatography (GC). The linear dynamic range obtained with the tunable MIP-MS extended over 3 orders of magnitude, a 10 time improvement with respect to the standard MIP. Detection limits were between 3 and 19 pg of Cl mol(-1) s(-1), 7 times lower than the detection limits obtained with the nontunable MIP-MS. Analysis of pesticides containing sulfur atoms was also possible, further demonstrating multielement MIP-MS detection. Excellent accuracy (10% recovery) and precision (5% RSD) were found for the detection of the pesticides in a petroleum-contaminated reference soil. By placing the GC column at the plasma expansion stage, molecular fragmentation of a mixture of volatile organic compounds was also demonstrated. With the MS operated in the selected ion monitoring mode, measurement sensitivity was approximately 500 pg/s per compound.

Plasma-based mass spectrometry for simultaneous acquisition of elemental and molecular information

“…Quantitative data were produced for both elemental and molecular ionization processes with the same MIP ionization source by reducing the flow rate (and without the need to re-tune the MIP cavity). 6 By reducing the flow rate to 2.5 mL min À1 , the tunable MIP yielded nearly the same fragmentation patterns as found by EI-MS for a mixture of volatile organics. Elemental sensitivity was sacrificed, but allowing simultaneous detection of fragment and molecular ions.…”

“…More recently, an atmospheric pressure MIP was used as the ion source for the analysis of pesticides. 6,22 The method is particularly attractive because the microwave plasma was capable of generating simultaneous quantitative information for carbon-, chlorine-, sulfur-and phosphorus-containing molecules and also could generate molecular ions to help the identification of the parent pesticide species. Quantitative data were produced for both elemental and molecular ionization processes with the same MIP ionization source by reducing the flow rate (and without the need to re-tune the MIP cavity).…”

“…Plasma-based ionization sources operated under different conditions could provide atomic and molecular detection. In particular, stationary low power (LP)/reduced pressure (RP) inductively coupled plasmas (ICPs), 5 microwave-induced plasmas (MIPs) 6 and glow discharges (GDs), 7 could act as hard (elemental) and soft (molecular) sources, depending on the conditions. Glow discharge plasmas could play a prominent role in this sense for chemical speciation, because special GD powering operation modes can produce quasi-simultaneous atomic and molecular mass spectra, as proved already in modulated and in pulsed GDs.…”

Speciation Analysis of Non-Metallic Elements Using Plasma-Based Atomic Spectrometry for Detection

“…MIP-MS is also used for the analysis of these types of compounds achieving a better signal stability as well as additional structural information. For example, Zapata et al, [50] used a tunable coaxial MIP-MS and by optimizing its power transfer to the cavity obtained better signal stability, resulting thus a detection limits in the range of 3 and 19 pg of Cl, 7 times lower than the detection limits obtained with the non-tunable MIP-MS. GC-MIP-MS arrangements were also used for determiing organochlorine pesticides in a petroleumcontaminated reference soil and also for the analysis of 15 different halogenated pesticides and PCBs homolog present in U.S. EPA method 505 mixture #1 [51]. Polluted ground water samples were also analyzed and the presence of major chlorinated pollutants was confirmed.…”

Plasma-source mass spectrometry for speciation analysis: state-of-the-art

“…Indeed, the first GC-MIP studies performed in 1965 [137] were followed by the introduction of a commercial GC-MIP-AES system [138], which has enjoyed extensive use for the analysis of a wide range of environmental samples. Analysis of pesticides by this method is particularly attractive because the microwave plasma is capable of generating simultaneous quantitative information for carbon-, chorine-, sulfur-and phosphorous-containing molecules or can provide molecular ions to help identify the parent pesticide species [139]. In addition, a vast number of studies have focused on speciation of volatile compounds by coupling the microwave plasma with gas chromatography for the determination of arsenic [140], mercury [141][142][143], tin [141,142], and selenium [144], to name a few.…”