Mass Selective Detector MSD

Detectors Operation Principle Detection Limit D3mamic Range Selectivity 

Nitrogen Phosphorus (NPD) Alkah ions are usedt 0 enhance ionization of N- P-compounds 0.1-10 pg 10 P,N 

Flame Photometric (FPD) Flame excitation produces chemiluminescent species of S-and P-hydrocarbons 1-20 pg 103 for S lO-iforP High selective forS,P 

Hehum Ionization (fflD) He atoms excited 1 ng by radioactive source and ionize compounds with low ionization potential 10 Respond to aU gases and vapours except to Ne 

Photo- ionization (PID) Samples are ionized by excitation by photons from a UV lamp 1-10 pg 10 More sensitive to aromatics than to aUphatics 

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Chromatographic systems were finally coupled with relatively inexpensive, yet powerful, detection systems with the advent of the quadrupole mass selective detector (MSD). The operational complexity of this type of instrumentation has significantly declined over the last 15 years, thus allowing routine laboratory use. These instruments... 

Specificity is unsurpassed. Traditionally, MS was performed on very large and expensive high-resolution sector instruments operated by experienced specialists. The introduction of low-resolution (1 amu), low-cost, bench-top mass spectrometers in the early 1980s provided analysts with a robust analytical tool with a more universal range of application. Two types of bench-top mass spectrometers have predominated the quadrupole or mass-selective detector (MSD) and the ion-trap detector (ITD). These instruments do not have to be operated by specialists and can be utilized routinely by residue analysts after limited training. The MSD is normally operated in the SIM mode to increase detection sensitivity, whereas the ITD is more suited to operate in the full-scan mode, as little or no increase in sensitivity is gained by using SIM. Both MSDs and ITDs are widely used in many laboratories for pesticide residue analyses, and the preferred choice of instrument can only be made after assessment of the performance for a particular application. 

In the past decade, as systems have become simpler to operate, mass spectrometry (MS) has become increasingly popular as a detector for GC. Of all detectors for GC, mass spectrometry, often termed mass selective detector (MSD) in bench-top systems, offers the most versatile combination of sensitivity and selectivity. The fundamentals of MS are discussed elsewhere in this text. Quadrupole (and ion trap, which is a variant of quadrupole) mass analyzers, with electron impact ionization are by far (over 95%) the most commonly used with GC. They offer the benefits of simplicity, small size, rapid scanning of the entire mass range and sensitivity that make an ideal detector for GC. 

Atomic emission detectors (AEDs) and mass selective detectors (MSDs) are also being used to enhance selectivity and sensitivity for air analyses (Yamashita et al. 1992). 

The derivatized samples were analyzed on a Hewlett-Packard 5890 series IIGC (helium carrier gas) coupled to a Hewlett-Packard 5971 mass-selective detector (MSD). A 60 m, 0.32 mm i d., 0.25-im film, SE-30 fused silica capillary column (J W Scientific, Folsom, CA) was installed in the GC, and an on-column injector (SGE model OCl-3) held at ambient temperature was fitted to the colunrn inlet. Samples (0.5 p,L) were injected directly into the column held at 105°C... 

While HPLC does not always produce superior results to those with TLC it allows greater versatility and is more suitable for the analysis of complex organic matrices such as cereals. HPLC coupled to sensitive detection and sophisticated data retrieval has improved the identification of selected mycotoxins at levels much less than achieved by TLC. Additional chromatographic modes such as normal-phase, reverse phase and ion-exchange chromatography have been employed. There are no truly universal detectors available for HPLC. Detectors presently in use include Fourier transform infrared detections (FT-IRD), diode array ultraviolet detection (DAD) and mass selection detectors (MSD) (Coker, 1997). 

The confirmation of pesticides by GC/MS should be more reliable than that on the GC-ECD using an alternate column. Presence of stray interference peaks, even after sample cleanup, and the retention time shift and coelution problem, often necessitate the use of GC/MS in compounds identification If a quantitative estimation is to be performed, select the primary ion or one of the major characteristic ions of the compounds and compare the area response of this ion to that in the calibration standard. Quantitation, however, is generally done from the GC-ECD analysis, because ECD exhibits a much greater sensitivity than the mass selective detector (MSD). For example, while ECD is sensitive to 0.01 ng dieldrin, the lowest MSD detection for the same compound is in the range of 1 ng. The primary and secondary characteristic ions for qualitative identification and quantitation are presented in Table 2.20.3. The data presented are obtained under MS conditions utilizing 70 V (nominal) electron energy under electron impact ionization mode. 

Giachetti et al. [60] compared the performance of mass selective detector (MSD), electron capture detector (ECD) and nitrogen-phosphorus detector (NPD) of gas chromatography systems in the assay of six nonsteroidal antiinflammatory drugs in the plasma samples. As a practical test, six NSAIDs (mefenamic, flufenamic, meclofenamic and niflumic acids, diclofenac and clonixin) added to plasma samples were detected and quantified. The analyses were carried out after solvent extraction from an acidic medium and subsequent methylation. The linearity of response was tested for all the detection systems in the range of 1-25 ng/mL. Precision and accuracy were detected at 1, 5 and 10 ng/mL. The minimum quantifiable level for the six drugs was about 1 ng/mL with each of the three detection systems. 

TCD) detector or the flame-ionization (FID) detector, which are the two most common detectors in gas chromatography, respond to all (organic) compounds except the carrier gas. On the contrary, a selective detector responds to a range of compounds with a common physical or chemical property. Representatives of the latter group of detectors are the nitrogen-phosphorus detector (NPD), the electron capture detector (ECD), the mass selective detector (MSD) and - last, but not least - the tandem mass spectrometer (MS/MS). 

Detection Hewlett-Packard 5970B mass-selective detector (MSD) the MSD was maintained at 280 °C. 

These limitations can be overcome by reacting the polymer with boron trifluoride etherate under defined conditions in a headspace sampler. The reaction results in a mixture of gaseous fluorosilanes that is transferred directly, without further workup, into a gas chromatograph, where they components are separated and quantified by means of a flame ionization detector (FID) or mass selective detector (MSD). 

This handbook s primary aim is to provide the tools to help a bench chemist to obtain a more complete listing of additives present in a particular matrix. The techniques that we have been using successfully are described in this book to help the analyst to correctly identify the complex nature of the materials that have been added to the plastic. We provide information on analyzing polymers through thermal desorption, and the use of GC with a mass selective detector (MSD). Many compounds break apart either during extraction or analysis, so identification by key fragments, and typical moieties for the final compound is critical. The use of the GC/MS system allows the analyst to characterize a compound based on the utilization of these fragments or moieties. 

A Hewlett Packard (Little Falls, DE) 5890 Series II GC was interfaced to an HP 5972 series Mass Selective Detector (MSD) for GC-MS analysis. A DB-5 MS column (0.25nun x 30m, dr0.25 un) from J W Scientific (Folsom, CA) was used for separations. An HP 7673 GC automatic injector was used to introduce 1 pL of organic layer in the spiitless mode. The injector and detector temperatures were maintained at 300°C. The oven temperature was held initially at 40°C for 2 min and then ramped to 145°C at 4°C/min and held for 1 min, then heated at 5 °C/min to 220°C and held for 30 min, and finally heated at 7°C/min to 300°C and held for 10 min. The extractables were identified using an HP Chem Station equipped with the Wiley library of mass spectral data. The composition of the extracts is expressed in terms of weight percent of each identified analyte in the total extract. 

The chemical composition of S. desoleana oil was determined by GC and GC/MS analyses by different authors [6, 71-72, 74], Generally, GC analyses were performed using fused silica capillary columns with different polarity like 5% diphenyl 94% dimethyl 1% vinylpolysiloxane bonded phase and Carbowax 20M bonded phase columns. Moretti et al. [72, 74] reported the relative retention indices of the oil constituents, calculated as described in the literature [75], and quantitative data obtained using ethylene glycol monobutyl ether as an internal standard. These authors also reported GC/MS data obtained from a GC apparatus directly coupled to a mass selective detector (MSD, 70 eV). 

Gas Chromatagraphy-Mass. Spectrometry (flC-MS). CiC-MS system eun asietl of an HP SB90 Series II GC /HP 5972 mass selective detector (MSD, llewleil I aekaid. 

Eight different lime and lemon flavor formulations were provided by a commercial flavor company (Table I). Six replicas of each flavor were analyzed using 7.5 uL aliquots. The aliquots were placed in 10 mL vials which were crimped and equilibrated for 15 minutes at 60 °C before static headspace sampling. The headspace parameters were 15 min incubation, 65 °C syringe, 0.75 min flushing of syringe after injection, cycle time of 4 min. Two mL were filled and injected at a 250 uL/s. There is no column for a separation prior to the mass selective detector (MSD), the entire headspace of each sample is introduced into the MSD. 

The GC detector is the last major instrument component to discuss. The GC detector appears in Fig. 4.7 as the box to which the column outlet is connected. Evolution in GC detector technology has been as great as any other component of the gas chromatograph during the past 40 years. Among all GC detectors, the photoionization (PID), electrolytic conductivity (EICD), electron-capture (ECD), and mass selective detector (MSD) (or quadrupole mass filter) have been the most important to TEQA. The fact that an environmental contaminant can be measured in some cases down to concentration levels of parts per trillion (ppt) is a direct tribute to the success of these very sensitive GC detectors and to advances in electronic amplifier design. GC detectors manufactured during the packed column era were found to be compatible with WCOTs. In some cases, makeup gas must be introduced, such as for the ECD. Before we discuss these GC detectors and their importance to TEQA, let us list the most common commercially available GC detectors and then classify these detectors from several points of view. 

Because volumes have been written concerning mass spectrometry over the past 40 years, our approach here is to focus on the type of mass spec instrumentation required to perform EPA methods and those systems can be described as being of a low-resolution nature and the most affordable. The quadrupole mass filter or mass selective detector (MSD) and quadru-pole ion trap mass spectrometer (ITD) fit this criteria and will be the only mass specs discussed. Onuska and Karasek have given a good definition and description of the importance of gas chromatography-mass spectrometry (GC-MS) to TEQA (76) ... 

Fig. 1. Swinglea glutinosa essential oil chromatograms. A. Acquired on a chromatographic colunrn with polar stationary phase (DBWAX, 60 m x 0,25 mm x 0,25 pm). B. Column with non-pxrlar stationary phase (DB-1, 60 m x 0,25 mm x 0,25 pm). Flame ionization detector, split ratio 1 30, oven temperature program 40 °C (5 min) 3 °C/min to 250 °C (5 min), a -p-Cymene b - Linalool c - a-Bergamotene d -cis-Allocymene e - CitroneUal f - Neral. C. Splitless injection. D. Split (1 30) injection. Injection volume -1 pL (20% in dichloromethane). Mass selective detector (MSD, El, 70 eV). Acquisition mode full scan m/z 30 - 400).

Volatile and aromatic components Separation of volatile components is achieved on either fused silica capillary columns or packed columns. Individual volatile components are detected with a FID and identified by the use of reference standards. Methods using specific detectors, such as the NPD, sulfur-specific flame photometric detector, and mass-selective detector (MSD) have also been used. The MSD has the additional advantage of providing structural identification of the individual components. 

Mass spectrometers can be used as GC detectors. They need to have compatible characteristics and be properly coupled to the chromatograph. Some of them are referred to as mass selective detectors (MSD), which indicates that they are considered GC detectors, but the combined technique can also be called GC/MS, which indicates the coupling of two analytical instruments. Whatever the name, the use of a mass spectrometer with a gas chromatograph is a very powerful, useful, and popular combination, and it is treated in more detail in Chapter 10. 

With a few exceptions, most of the detectors used in GC were invented specifically for this technique. The major exceptions are the thermal conductivity detector (TCD, or katharometer) that was preexisting as a gas analyzer when GC began, and the mass spectrometer (or mass selective detector, MSD) that was adapted to accept the large volumes and the fast scan rates needed for GC peaks. Most recently, other spectroscopic techniques like IR and atomic plasma emission have been coupled to the effluent from gas chromatographs, serving as GC detectors. 

Hewlett-Packard Mass Selective Detector (MSD)(HP 5971A). The ion source was run in the El mode at 170 °C using an ionisation energy of 70 eV. The scan rate was 0.9 scans/sec. Data from the MSD was stored and processed using a Hewlett-Packard Vectra QS20 computer installed with Mustang software and the Wiley Mass Spectral Library. Kovats indices were calculated against extemd hydrocarbon standards. Concentrations were determined from the internal standard, butyl hexanoate, and are not corrected for detector response. 

Gas Chromatography/Mass Spectrometry. A Hewlett Packard (HP) Model 5890 gas chromatograph (GC) (Hewlett Packard, Avondale, PA) equipped with a mass selective detector (MSD) HP Model 5970 was used to identify compounds in this study. The capillary column was interfaced directly into the MSD operating at 70 eV... 

Mass spectral (MS) identification of the oxidation products was carried out on a HP Model 5971 series mass selective detector (MSD) interfaced to a HP Model 5890 gas chromatograph. Mass spectra were obtained by electron impact ionization at 70 eV and a source temperature of 250°C. The capillary colunm and GC conditions were the same as described above. 

Downstream of the thermal processor is an in-line analytical system capable of cryogenic trapping, separation, and detection of thermal decomposition products. For the replacement fluids, the thermal decomposition products were trapped using liquid nitrogen coolant at the head of a capillary GC column housed within an HP 5890 GC, The GC was then used to separate the products, and detection was accomplished using an HP 5970B mass selective detector (MSD). The MSD is a compact quadrupole mass spectrometer which permits analytes to be identified via their fragmentation patterns and quantified via peak areas. 

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