Drugs of abuse that are tested using a modern GC/MS system may get adsorbed onto any of the flow path surfaces as they are chemically active substances.
For example, in the gas phase the chemicals need to be intact throughout the passage between injection and detection to allow for accurate analysis.
This may be difficult to achieve with low concentrations and in particularly surface active agents.
Analytes may be missed or may show lower levels than actual when the quantity further declines. The peak shapes may be poor and quantitation may be inaccurate in these cases.
Agilent Inert Flow Path Solution
To reduce such errors, earlier methods have used column and linear deactivation strategies. To make the flow path inert, methods such as inlet weldments, gold seals and ferrules have been used.
Agilent J & W Ultra Inert columns and liners and inert MS source component designs take this further with split top and shell weldments.
They also include Ultra Inert Gold seals and UltiMetal Plus Flexible Metal ferrules.
A GC/FID system, containing an Agilent 7980 GC and an Agilent 7693 Automatic liquid sampler, was used to assess the influence of UltiMetal Plus Flexible Metal Ferrules in the flow path of drugs of abuse analysis.
The GC/MS system included the 7980 GC along with an Agilent 5975C MSD and a triple axis detector. The Agilent 7693 Automatic liquid sampler tower alternated between the front and back split and split-less inlets. While the front inlet was inert, the rear was standard.
Capillary flow technology was used along with Siltite or UltiMetal Plus Flexible Metal Ferrules. The conditions for both SCAN and SIM mode were kept similar.
For the assessment a 28 component mixture of GC/MS forensic toxicology analyzer was obtained from Agilent Technologies, Inc. (Santa Clara, CA) (p/n 5190-0471). This was serially diluted using volumetric glassware (Class A) and positive displacement syringes.
The diluents and syringe wash was a mixture of toluene:methanol:acetonitrile (90:5:5). Triphenyl phosphate was used as an internal standard and added at concentrations of 0.25ng/µl.
The results showed excellent peak separation of the components both when UltiMetal Plus Flexible Metal Ferrules were used for the analysis as well as with Siltite ferrules.
The figure below (Figure 2) shows an overlay of the peak signals when UltiMetal Plus Flexible Metal Ferrules were used (in blue) and when Siltite ferrules were used (in red).
The peaks showed that Siltite ferrules gave poorer peaks with nitrazepam, clonazepam, alprazolam and tremazepam. Thus UltiMetal Plus Flexible Metal Ferrules were considered a better choice especially when working with benzodiazepines in drugs of abuse tests.
Figure 3 above shows the total ion chromatogram of the check mix at 1ng/component level on the inert flow path of the 7890/5975C GC/MS. All peaks for all the components were robust. There was a switching between inert and standard flow paths in order to use the inlet connector, columnand the MSD system as control variables and balance the comparison as much as possible.
Further the IFP inlet on the Agilent 7890/5975C GC/MS system is also better in terms of performance for the benzodiazepines compared to standard component inlet. This was especially true for temazepam, clonazepam and nitrazepam. This was true for both SCAN and SIM experiments as demonstrated by Figures 4 and 5 below.
The experiment showed that Agilent Ultimetal Plus Flexible Metal ferrules show an improvement in the peak shape and response analyzing a forensic/toxicology check mix when compared to the Siltite ferrules. Benzodiazepines in the mix showed best improvements.
For example, Temazepam at 1ng was nearly missed by the Siltite ferrules but showed a sharp and well defined peak with Ultimetal Plus Flexible Metal ferrules. Thus the Agilent Ultimetal Plus Flexible Metal ferrules are a better choice over Siltite ferrules especially when working with benzodiazepines.
Further the Inert Flow Path inlet on the Agilent’s system showed more enhanced results, better detection and quantitation of benzodiazepines like Temazepam, Nitrazepam and Clonazepam compared to standard component inlet as seen in both SCAN and SIM experiments.
K. Lynam. Semivolatile Analysis Using an Inertness Performance Tested Agilent J&W DB-5ms Ultra Inert Column. Application Note, Agilent Technologies, Inc. Publiction number 5989-8616EN (2008).
L. Zhao, A. Broske, D. Mao, A. Vickers. Evaluation of the Ultra Inert Liner Deactivation for Active Compounds by GC. Technical Overview, Agilent Technologies, Inc. Publication number 5990-7380EN (2011)
Anon. Optimize your GC flow path for inertness. Poster, Agilent Technologies, Inc. Publication number 5990-8902EN (2013).
About Agilent Technologies
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