Instrument Performance Standards: How to Test GC–MS Sensitivity and Performance Quickly and Efficiently for the Analysis of Dioxins and Furans

A concept for testing GC–MS analytical instrument performance is described, which is based on a specifically designed set of dioxin standards.

Dioxins and furans need to be monitored at lowest levels in food, feed, and other matrices. To achieve this, GC–MS instruments must be able to detect and quantify absolute amounts of dioxins and furans down to the low femtogram range in routine. Efficient tools to develop and optimize instrument methods which meet these requirements and fast tests on the instrument performance are needed.

Material and Methods

All measurements were carried out on a Thermo Scientific™ DFS™ magnetic sector high resolution mass spectrometer coupled to two Thermo Scientific™ Trace™ 1310 GC supported by an extra-wide Thermo Scientific™ Triplus RSH™autosampler.

The concept for the instrument performance standards was developed and defined at the Thermo Scientific POPs application laboratory in Bremen (Germany).

Figure 1: Sensitivity standard on Thermo Scientific DFS GC-HRMS. Quantification and ratio mass trace of tetra Dioxins: TCDD congeners from left to right: 1368-2 fg/µL, 1379-5 fg/µL, 1378-10 fg/µL, 1478-25 fg/ µL, 1234-50 fg/µL, and 2378-100 fg/µL (in nonane); 1 µL injected.

Results and Discussion

Typically the sensitivity of a GC–MS for dioxin analysis is checked by measuring a low concentrated standard. Often the limits of detection and quantitation are then extrapolated from the concentration levels in these standards down to far lower values. Real measurements of these very low levels seldom take place and would require repeated injections of decreasing concentrations until the point of minimum signal-to-noise values are met. Most laboratories do not have time for this. This leaves significant uncertainty concerning the real instrument performance for very low levels. The special Instrument Performance standard 1 (1: "sensitivity/linearity standard") contains six different native tetra dioxin congeners which can easily be separated via GC on 30 or 60 m 5-Phenyl type apolar columns. The concentrations of the different congeners rise from 2 fg/µL for the first to 100 fg/µL for the last eluting analyte. One internal standard is included at 5 pg/µL (2378 ¹³C TCDD).

A single injection allows checks on the following parameters at six different concentration levels:

• Lowest level detected

• RRFs at different levels

• Signal-to-noise at different levels

• Correct ratios of peak areas (isotope ratios)

• Single injection calibration curve

Based on the results of such measurements it can be decided if further method optimization is needed to meet the sensitivity requirements in a given situation, how much sample should be processed to reach overall low level analysis goals of the complete method, if maintenance is needed to re-establish the former instrument performance, and so forth.

A second standard (2: "repeatability/stability") is available. It contains the same congeners, but all at the same concentration. Here all congeners are equally concentrated (5 pg/µL).

Also the comparison of different analytical methods, instruments, or technologies are possible.

The Thermo Scientific DFS Magnetic Sector GC-HRMS has been tested with these standards over years for its superior performance in dioxins and POPs analysis.

Remark

The standards are commercially available from Wellington Laboratories Inc. (Ontario, Canada): TF-TCDD-MXB.

Thermo Fisher Scientific
81 Wyman Street, Waltham, MA 02451
tel. (781) 622-1000, (800) 678-5599
Website: www.thermofisher.com