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The 7000 triple quadrupole GC/MS is the first quadrupole MS/MS system

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designed specifically for the unique requirements of gas chromatography applications. 

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These requirements include: enhanced selectivity, consistent low detection limits, and robust day-to-day operation.

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The typical MS/MS description focuses on the extraction of ions from the source  

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isolation of the precursor ion in the first quadrupole

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dissociation of precursor ion in collision cell

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and mass filtering of the product ions in the second quadrupole before detection.

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But let’s return to the ion source to discuss processes that are often overlooked. 

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Even for a high performance source, ionization efficiency - as a percentage of molecules entering the source - is very low. 

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This means there are many more neutrals than ions exiting the source, so a thorough description must include:

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Analytes neutrals . . . and ions

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Helium neutrals . . . and ions

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Column bleed neutrals and ions 

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And many more neutrals and ions from the matrix – at concentrations typically higher than the analyte.

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To simplify the description, let’s start with the analyte molecules and ions

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Analyte molecules enter the vacuum source from the GC capillary column and begin bouncing off the hot surfaces of the source

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Analyte ions are immediately extracted from the source and focused into the quadrupole mass filter.

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But what about the non-ionized molecules? 

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The electrical fields within the MS have no influence on these molecules.

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They follow rapid, random motion until removed by the vacuum pump.

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Parallel processes are occurring simultaneously for the molecules from the sample matrix

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 and instrument background like column bleed.

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The quadrupole analyzer performs the critical task of mass filtering 

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to isolate the analytes ions from the majority of these ions.

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Chemical noise often remains after the first quadruple, but the selectivity of MS/MS removes this final source of interference.

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Again we ask, what about the large population of non-ionized molecules. 

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Although the turbo pump removes many neutrals quickly, some will randomly diffuse into the quadrupole. 

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At the end of the GC separation, the EI source will be flooded with the highest boiling molecules from the sample matrix

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Even in a vacuum, these high boiling molecules can contaminate surfaces in the mass spectrometer. 

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A cool surface will accelerate this contamination process.

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As we think about the potential for contamination, we must not forget helium.

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The intense flux - high flow - of helium ions helps to ‘burn’ the high boiling molecules

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onto the surfaces of the source and the analyzer.

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The cooler the surfaces the faster the rate of contamination and the faster performance is lost. 

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For a LC atmospheric pressure source like ESI, 

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metal quadrupoles at a temperature of 100 C are perfectly adequate and commonly used.

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But for GC/MS/MS analyses, metal surfaces at this temperature will quickly become contaminated.

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The Agilent 7000 uses a combination of proprietary and patented technologies 

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to avoid contamination problems and ensure robust,high performance operation.

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These include: an inert source operating at up to 350 C and quartz quadrupole operating at up to 200 C. 

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With 35 years of MS experience, Agilent built the 7000 around the unique, hot quartz analyzer of the MSD, 

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not the cooler metal quadrupole rods used for LC/MS/MS.

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Before continuing to the collision cell, one more process must be mentioned. 

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An EI source produces a large number of highly energetic, metastable helium atoms.

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These highly energetic atoms follows a random path like any other neutral until removed by the pump. 

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Some will follow a path parallel to the analyzer and have a high probability

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 of traversing the entire analyzer assembly to the HED-EM detector. 

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During the development of the 7000, Agilent engineers realized a small flow of helium added to the nitrogen collision gas

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was very effective way to reduce the transmission of metastable helium through the collision cell.

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We call this patent-pending solution: “Helium Quenching”.

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A comparison of signal to noise ratio with and without Helium Quenching shows to benefit of this technology. 

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Helium Quenching has no affect on Product Ion signal, but the neutral noise component is reduced by a factor of four. 

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This technical breakthrough means lower limits of detection and quantitation.

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The 7000 MS/MS, an MS/MS system optimized for gas chromatography

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from the classical distribution of ions produced in the inert, high performance source

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to the precise isolation of the precursor ion through the path of the hot, quartz, hyperbolic quadrupole

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into the high pressure,  hexapole collision cell for efficient precursor dissociation, 

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product ion transmission and simultaneous reduction of metastables with “Helium Quenching”

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To the final, accurate mass analysis in a second, hyperbolic quadrupole field before ion collection at the Triple-Axis detector 

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The 7000 system has been carefully designed to deliver robust sensitivity and reliable quantitative results

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The Agilent 7000 quadrupole GC/MS/MS system

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an MS/MS optimized for trace analysis of your most complex GC samples

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the new standard for GC/MS/MS performance