News from LabRulezGCMS Library - Week 29, 2026

In gas chromatography, the presence of column bleed impacts peak data quality. As siloxanebased stationary phase components fragment, they release bleed artifacts into the mass spectrometer (MS), producing interference and decreasing signal-to-noise ratios (S/N) of analytes. ¹ When using comprehensive twodimensional gas chromatography (GC×GC), a secondary column with an orthogonal stationary phase is used in providing improved separation between column bleed and analytes. However, it also introduces more stationary phase that can be degraded to produce more bleed artifacts.

The goal of this research was to define how replacing the primary column in a GC×GC-MS system impacts the resulting S/N and analyte identification quality, in order to clarify how column bleed impacts analytes that appear to be chromatographically resolved from column artifacts in GC×GC output. This will demonstrate the advantage that low-bleed columns can provide for future analyses.

Methods

Samples analyzed were the Century Mix2 , containing approximately 100 different analytes within different classes (i.e. Century Mix2) and a 52- component Indoor Air Standard. Both were assessed using a 5% phenyl/95% dimethylsiloxane standard column in the first dimension and a (50%-phenyl)-methylpolysiloxane standard column in the second dimension. Samples were then reanalyzed with a low-bleed column replacement in the first dimension.

Analysis of the samples was performed using the Pegasus BT4D GC×GCTOFMS with a quad-jet dual-stage cryogenic modulator (LECO Corporation). ChromaTOF software (LECO Corporation) was used to analyze the chromatographic data.

Conclusions

This work demonstrated that samples run with the low-bleed first dimension column showed a reduction in the presence of column bleed components identified and maintained or improved the quantitative signal-to-noise ratios of components compared to the samples run on standard first dimension columns. This showed that that low concentration analytes were more reliably detected in the absence of column bleed, even when contour plots showed physically resolved components. In the future, this can be applied to improve the resolution of complex samples and increase analyte signal.

3. Shimadzu: Dimethyl carbonate as a green organic modifier in supercritical fluid extraction of pesticide residue analysis in apple samples

• Technical note
• Full PDF for download

According to the Green Analytical Chemistry (GAC) principles[1], a highly promising strategy to minimize the side effects of analytical methods involves replacing potentially toxic solvents and/or obtained by non-renewable sources with more environmentally friendly alternatives. In this frame, dimethyl carbonate (DMC) is an environmentally friendly, non-corrosive, safe handling, and biodegradable chemical, extensively used in several application fields, such as pharmaceuticals, coatings, and lithium-ion battery electrolytes [2]. Additionally, instead of the historical use of toxic and corrosive phosgene as a carbonate source, simple and direct synthesis routes from carbon dioxide (CO2) have been proposed [3]. Thus, also falling within the “carbon capture and utilization” processes, ensuring the reduction of atmospheric CO2 concentration and its conversion into useful chemical products. 

Firstly introduced in the second edition of the GlaxoSmithKline’s solvent selection guide, DMC has been included among the “few issues” solvents, along with water [4]. Thereafter, it has attracted widespread attention as a valuable chemical and/or solvent, and substantial research efforts have been made in the scientific community. Its potential as a green alternative to conventional solvents in both reversed-phase liquid chromatography [5–7] and supercritical fluid chromatography [8] has been explored. The extraction capabilities of DMC toward different target molecules have been also investigated. In 2022, Alfieri et al. optimized an ultrasoundassisted extraction of two lignans from Linum species [9]. The extraction performances of a panel of green solvents and two natural deep eutectic solvents (in combination with water in a solvent/water ratio of 80:20) were tested versus methanol and chloroform (used for comparison with published studies). The results showed that, in terms of purity and recovery, DMC was the optimal media for the 6-methoxypodophyllotoxin extraction. DMC has been also employed in an in-syringe extraction coupled to solid phase extraction to assess nicotine in environmental water and sportspersons’ urine samples [10]. Extracts enriched in oleanolic acid were obtained by solid-liquid extraction of grape pomace using DMC compared to other tested solvents (ethyl acetate, acetone, n-butanol) [11]. In addition to the highest obtained recovery value, the lowest co-extraction of other matrix components was also achieved. 

Supercritical fluid extraction (SFE) represents a reliable alternative to conventional solvent-based extraction methods. Several advantages are provided when CO2 is employed as supercritical fluid due to its non-toxicity, non-flammability, abundancy, renewability (as a by-product of industrial processes, as fermentation or combustion), recyclability, and cost-effectiveness. Supercritical CO2 has a polarity similar to that of n-hexane; thus, the addition of a co-solvent is necessary for the extraction of polar molecules [12, 13]. 

This work aims to expand the use of DMC that, to the best of the author’s knowledge, is here firstly proposed as an organic modifier in SFE. The extraction efficiency and selectivity of DMC toward conventional solvents, such as acetonitrile (ACN) and bio-ethanol (EtOH) obtained from edible renewable feedstocks, has been evaluated for multi-residue analysis of pesticides (64 pesticides, representing diverse chemical classes, polarities, and molecular weights) in apple samples. Considering the sustainable and nontoxic nature of CO2 and DMC, the use of DMC in SFE represents a win-win combination. Thus, improving the overall sustainability and automation of the extraction process closely align with the GAC principles. Furthermore, in this research, always following the GAC principles, a low-pressure gas chromatography-tandem mass spectrometry (LP-GC-QqQMS) method was employed, allowing a greater sample loadability and a higher optimal linear velocity allowed by the vacuum conditions of the system, effectively reducing the analysis time at about 10 minutes [14, 15].

2. Materials and methods

2-3. Instrumentation

Low‑pressure gas chromatography triple quadrupole mass spectrometry 

The LP-GC-QqQMS analyses were performed using a GC-2010 Plus system (Shimadzu Corporation, Kyoto, Japan) coupled with a triple quadrupole mass spectrometer (TQ8040, Shimadzu). Injection was performed using an AOC-20i autosampler and a split/splitless injector (injection temperature 280 °C) equipped with a focus liner (volume: 810 μL). The injection was performed in splitless mode (3 μL) using the high-pressure injection mode function (290 kPa for 0.5 min). 

To avoid that sub-ambient pressure conditions reach the injector, an uncoated column (0.48 m × 0.1 mm ID) was installed before the separation column, a non-polar Equity-5 [poly(5% diphenyl/95% dimethyl siloxane)] of the following dimension: 5 m × 0.53 mm ID × 0.53 μm df. Both the columns were provided by Merck KGaA. The oven was temperature programmed as follows: 40 °C (2 min) to 320 °C raised at 30 °C min−1. Helium was used as carrier gas with an average constant linear velocity of 100 cm s−1 (into the separation column). 

Electron ionization was performed at 70 eV. The interface and ion source temperatures were 320 and 280 ˚C, respectively. The collision gas was argon at a pressure of 200 kPa. The targeted analyses were carried out in the multiple reaction monitoring (MRM) acquisition mode (acquisition frequency: 3.3 Hz). To ensure univocal identification, two different MRM transitions (quantifier and qualifier) were monitored for each compound (Table S1). The SCAN analysis was performed with an acquisition frequency of 3.3 Hz and a mass range of 50–600 m/z. The GCMS Solution v.4.45 software (Shimadzu) was used for data collection and processing.

4. Conclusions 

Under the optimized extraction conditions, the use of DMC as a co-solvent in SFE demonstrated promising performance in the analysis of pesticide residues in apple samples. The method achieved an average extraction yield of 85% across the 64 analyzed pesticides, spanning a broad range of chemical classes, polarities, and molecular weights. Notably, DMC provided cleaner extracts with significantly lower amounts of co-extracted matrix components compared to conventional solvents like ACN and EtOH. Despite the recovery for certain analytes being below 70%, the results remained within acceptable precision limits according to SANTE guidelines. Overall, DMC not only fulfills the analytical requirements for pesticide residue determination but also offers a greener, more sustainable alternative that supports enhanced instrument maintenance and aligns with the principles of GAC.

4. Thermo Fisher Scientific / ASMS: Improved detection capabilities for polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) using GC Orbitrap MS

• Poster
• Full PDF for download

Polychlorinated dibenzo-p-dioxins/furans (PCDD/F) analysis requires ultra-high sensitivity and selectivity due to their toxicity at trace levels. Regulatory compliance requires laboratories to adhere to strict analytical criteria (Figure 1). Through the integration of NVAEI source (NVAEI) with HRAM Thermo Scientific Orbitrap mass spectrometer, the Orbitrap Exploris GC S delivers mass resolution and accuracy that far exceed those required while delivering enhanced sensitivity required for pg/g (part per trillion (ppt)) detection within food and feed matrices.

Conclusions 

Enhanced sensitivity of the NeverVent AEI ion source coupled to the Orbitrap Exploris GC S delivers accurate quantitation down to 2 fg/μL (10 fg on column) of TCDD while meeting analytical criteria required for Dioxin analysis compliance. 

Response of 2 fg/μL (10 fg on column) of TCDD standard remained stable over a 185-injection sequence of food/feed extract, demonstrating robust performance of the NeverVent AEI at maintaining trace level sensitivity. 

Good agreement in the analysis of food and feed extracts preformed by GC-HRMS magnetic sector demonstrates the Orbitrap Exploris GC S can deliver accurate quantitation at and below regulatory limits.