Automated Tuning (EPA Tune) of Q-Tek quadrupole mass selective detector «Maestro-αMS» to meet requirements of USEPA volatiles methods.

USEPA volatiles methods evaluate the mass selective detector ion source tune using BFP (1-Bromo-4-fluorobenzene ) to make sure the ion responses of BFB meet the specified criteria:

  • The EPA tune procedure must adjust PFTBA ion responses in order to get desired BFB response ratios later on;
  • Verify the ion source tune parameters by BFB injection to make sure ion abundances of BFB spectrum meet predefined

Most BFB tuning criteria are very similar for various USEPA volatiles methods, however, there are small differences one must pay special attention to. The criteria are listed in the table below for each of the methods.

Table 1. Comparison of ion abundance ratios in BFB spectrum for several USEPA volatiles methods.

BFB, (m/z) method 542.2 method 542.3 method 624 method 8260C CLP-SOW
50 15 – 40% N/A 15 – 40% 15 – 40% 8 – 40%
75 30 – 80% N/A 30 – 60% 30 – 60% 30 – 66%
95 100% 100% 100% 100% 100%
96 5 – 9% 5 – 9% 5 – 9% 5 – 9% 5 – 9%
173 < 2% < 2% < 2% < 2% < 2%
174 > 50% > 50% > 50% > 50% 50 – 120%
175 5 – 9% 5 – 9% 5 – 9% 5 – 9% 4 – 9%
176 > 95 – < 101% > 95 – < 105% > 95 – < 101% > 95 – < 101% 93 – 101%
177 5 – 9% 5 – 10% 5 – 9% 5 – 9% 5 – 9%

Q-Tek developed the Automated Tuning Feature to enable Q-Tek quadrupole mass selective detector «Maestro-αMS» for meeting USEPA specific tuning criteria prior to VOC /SVOC analysis in water samples as well as in a variety of solid waste matrices.  The user needs to select EPA Tune option in MAESTRO-Operator Software to tune the ion source of the MSD, as required.

This work was done to verify how well the EPA Tune feature works for a user.

We ran EPA Tune on Q-Tek «Maestro-αMS», then injected BFB to verify the Detector response. Method parameters are described below:
GC method parameters:  Column: RTX-5MS (30m x 0.25, 250); T° Oven: 60°C (0.5 min), 30°C/min – 150°C (0.0 min);  T° Inlet: 250°C; Constant Flow mode, 1 ml/min flow; Split mode: 70:1; T° Interface: 250 ° C    MSD data acquisition parameters: Mass Range: 35– 300 amu;  Average = 2; Solvent Delay = 150 sec

Thus, having BFB eluting at RT=2.85min (fig 1)

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Fig. 1 Chomatographic peak of BFB eluting at RT=2.85 min

USEPA methods base their tuning criteria on  the ion responses of BFB. All ions are reported relative to m/z=95 which is the base peak. Even though there are differences in tuning criterial for these methods, in practice analyst is allowed to use tuning criteria of other USEPA methods – as an example one can use 524.2 criteria for 8260C or even manufacturer’s tune criteria provided method performance is not compromised.

Fig. 2 shows BFB spectrum,  calculated ion abundance ratios for all target ions.

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Fig. 2 Calculated ion abundance ratios for all target ions in BFB spectrum.

Actual ion abundance ratios for all target BFB ions measured on Maestro-αMS following the BFB standard injection and comparison of those vs EPA criteria are listed in Table 2.

Table 2. Actual ion abundance ratios for all target BFB ions measured on Maestro-αMS following the BFB standard injection and comparison of those vs EPA criteria

BFB, (m/z) Actual BFB ratios, %

On Maestro-αMS

result method 542.2 [1] method 8260C [4] CLP-SOW [5]
50 20.3 ОK 15 – 40% 15 – 40% 8 – 40%
75 47.5 OK 30 – 80% 30 – 60% 30 – 66%
95 100.0 OK 100% 100% 100%
96 7.1 OK 5 – 9% 5 – 9% 5 – 9%
173 0.6 OK < 2% < 2% < 2%
174 93.3 OK > 50% > 50% 50 – 120%
175 7.5 OK 5 – 9% 5 – 9% 4 – 9%
176 95.6 OK > 95 – < 101% > 95 – < 101% 93 – 101%
177 6.7 OK 5 – 9% 5 – 9% 5 – 9%

Conclusion. Q-Tek special EPA tune algorithm developed for GC-MS system Maestro-αMS provides automated ion source tuning to obtain spectra fully compliant with USEPA requirements for the above volatiles methods. The actual Maestro-αMS MSD performance was verified by injection of BFB standard to prove compliance with the above described criteria.