Keywords: Sample Preparation, Lab Automation, LC/MS/MS, SBSE
One of the most important aspects of reducing pesticide exposure is monitoring of pesticide residues in foods. A number of analytical methods have been developed, many of them based on traditional liquid-liquid extraction in combination with GC-MS or LC-MS. The QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation methods have been developed to help monitor pesticides in a range of food samples . The dispersive Solid Phase Extraction (SPE) used to clean up these extracts can leave co-extractants, which can result in interferences such as ion suppression with the analytical results.
Stir bar sorptive extraction (SBSE) is a sorptive extraction technique based on polydimethylsiloxane (PDMS) coated stir bars. SBSE was developed to concentrate nonpolar analytes from aqueous solutions, and has recently been shown to effectively extract and concentrate PAHs from QuEChERS extracts while eliminating matrix interference for GC/MS analysis .
In this study we describe the potential benefits of using SBSE to concentrate pesticides from QuEChERS extracts and provide additional clean-up resulting in less matrix interference during LC-MS/MS.
Keywords: Stir Bar Sorptive Extraction, SBSE, Multi-residue Method, Pesticides, Vegetables, Fruits, Green Tea, GC/MS
A multi-residue method for determination of five groups of 85 pesticides - organochlorine, carbamate, organophosphorous, pyrethroid and others - in non-fatty food, e.g. vegetables, fruits and green tea is described. The method is based on stir bar sorptive extraction (SBSE) coupled to thermal desorption (TD) and retention time locked (RTL) GC/MS in scan mode. The method was applied to the determination of pesticides at low μg/kg levels in tomato, cucumber, green soybeans, spinach, grapes and green tea.
Keywords: Microvial, QuEChERS, Pesticide Residue, Motor Oil, Thermal Desorption, GRO, GC/MS
In this study we describe direct liquid injection techniques compatible with “dirty” samples containing non-volatile components. Using a glass liner that can be removed and replaced after the injection can eliminate interference from accumulated sample matrix components. Liners are designed to accommodate larger than normal liquid injection volumes to provide improved detection limits. Furthermore, the entire process including the liner exchange can be automated. To illustrate the utility of the technique, challenging liquid sample types such as samples prepared by the QuEChERS method for pesticide analysis and contaminated motor oils were repeatedly introduced into the GC. Chromatographic performance using the new sample introduction technique is compared to conventional injections into a hot inlet.
Keywords: Dual Stir Bar Sorptive Extraction (Dual SBSE), Thermal Desorption, Fast GC/MS, Low Thermal Mass Column Heater, LTM, Pesticide Multiresidues, Aqueous Samples
A method for fast screening of pesticide multi-residues in aqueous samples using dual stir bar sorptive extraction (dual SBSE) - thermal desorption (TD) - fast GC/MS has been developed. Recovery of 82 pesticides – organochlorine, carbamate, organophosphorous, pyrethroid and others – for the SBSE. The method showed good linearity (r2 > 0.9900) and high sensitivity (limit of detection:< 10 ng/L) for most of the target pesticides. The method was applied to the determination of pesticides at ng/L levels in river water and brewed green tea.
Keywords: DPX, SPE, Pesticides, Fruits, Vegetables
Disposable Pipette Extraction (DPX) has been shown to be a rapid, efficient and reproducible method for performing solid-phase extraction (SPE) of pesticides from fruits and vegetables. DPX is a unique SPE method because the solid phase sorbent is contained inside a disposable pipette tip and is mixed with sample solutions. This mixing allows for the use of less solid phase sorbent material and results in faster extractions. Elution can be performed using small amounts of solvent, effectively providing a concentration step. Hence, solvent evaporation is not required for many applications such as pesticide analyses. Without the need for centrifugation or solvent evaporation, DPX methods can be readily automated and the resultant eluents directly injected into a gas or liquid chromatograph. The analyst is only required to initially process the samples to be analyzed and place the sample solutions into corresponding vials. The rest of the sample preparation can be automated, including the injection of the eluent into the analytical instrument. In this study, samples of fruits and vegetables (spiked with various pesticides) are blended with organic solvent, and the samples are then filtered and placed into sample vials. A GERSTEL MultiPurpose autosampler (MPS) is used to perform the DPX extractions and inject into the chromatographic instrument. Various types of fruits and vegetables are included in this study, and numerous pesticides are analyzed by this method including organophosphates, organochlorines, pyrethroids, and fungicides.
Keywords: Sequential Stir Bar Sorptive Extraction, Sequential SBSE, Thermal Desorption, GC/MS, Organic Pollutants, Water Analysis
A novel stir bar sorptive extraction (SBSE) procedure - "Sequential SBSE" was developed. Compared to conventional SBSE, sequential SBSE provides more uniform enrichment over the entire polarity/volatility range for organic pollutants at ultra-trace levels in water. Sequential SBSE consists of a SBSE performed sequentially on a 5-mL sample first without modifier using one stir bar, then on the same sample after addition of 30 % NaCl using a second stir bar. The method showed good linearity (r2 > 0.9900) and high sensitivity (limit of detection: < 10 ng/L) for most of the model compounds even with the scan mode in the MS. The method was successfully applied to screening of pesticides at ng/L level in river water samples.
Keywords: Solid Phase Extraction, SPE, Liquid Chromatography, Sample Analysis, Lab Automation
Solid phase extraction (SPE) is one of the sample preparation methods most widely used by chromatographers, as demonstrated by the numerous published SPE methods found in the literature. Manual SPE cartridge formats can vary from disks through individual cartridges with a range of different volumes to 96-well plates. However, solid phase extraction methods can be tedious and time consuming when performed manually. There is therefore an increasing need for the automation of solid phase extraction methods. A robotic X-Y-Z coordinate autosampler commonly used for sample introduction in GC or HPLC can be used to perform a wide variety of sample preparation techniques using a single instrument and controlling software. The MAESTRO software allows the user to control the automation of solid phase extraction methods. In addition to ease of use and intuitive windows-based programming, the tools to optimize method parameters ensuring efficient sequence creation and maximum sample throughput. The sampler can be configured as part of a GC or LC system or as a benchtop workstation. In this study, we show that existing manual SPE methods can be transferred to standard format automation cartridges and automated using the robotic autosampler in conjunction with the software. Examples of solid phase extraction methods illustrating the conversion from manual to automated methods are shown.
Keywords: QuEChERS, LC/MS/MS, Sample Preparation, Lab Automation
QuEChERS (quick, easy, cheap, effective, rugged, and safe) sample preparation methods were developed to help monitor pesticides in a range of food samples . These methods are quite labor intensive, however, since they include several manual steps, such as shaking, centrifugation, and dispersive SPE. If dispersive SPE clean up of QuEChERS type extracts could be automated, laboratory productivity for monitoring pesticide residues in food could be improved significantly. In the work presented here, an automated dispersive SPE clean-up method for QuEChERS extracts was developed and combined with LC/MS/MS analysis of the cleaned extracts. Extracts were prepared with commercially available kits from Agilent Technologies. Automation was achieved using a GERSTEL MPS XL PrepStation configured with an Anatune CF-100 centrifuge. Analytical methodology for confirming the presence of a variety of pesticides in a range food samples was developed using an Agilent G6460A Triple Quadrupole Mass Spectrometer. The sensitivity and selectivity of LC/MS/MS enable sufficiently low limits of determination to meet acceptance criteria for reporting the maximum residue levels (MRLs) that are established by regulatory agencies. The ability to automate the dispersive SPE clean-up of QuEChERS extracts combined with introduction of the cleaned extract directly to the LC/MS/MS system results in improved laboratory productivity by streamlining the complete analytical process.
Keywords: Pesticide Analysis, Matrix Effects, QuEChERS, Automated Liner Exchange, ALEX, Cooled Injection System, CIS, PTV
Fruit and vegetable extracts that are produced following the well established QuEChERS method typically contain a significant amount of nonvolatile matrix material. After several injections of such extracts into the GC, sufficient matrix residue will be present in the GC inlet liner to lower or sometimes even increase the response of certain pesticide compounds affecting the accuracy of the analysis. The performance can be restored by exchanging the GC inlet liner. Normally this has to be done manually which means stopping the analysis sequence. The GERSTEL Automated Liner Exchange system (ALEX) provides an automated solution. As this study shows, automated liner exchange restores the original performance of the GC system and is therefore generally useful for the analysis of extracts that contain nonvolatile matrix residue.
Keywords: Dispersive Solid Phase Extraction, Automation, QuEChERS, Pesticides
This paper describes an automated dispersive SPE (dSPE) cleanup method for QuEChERS extracts that is performed with commercially available kits from Agilent® Technologies. Extraction and clean-up is performed using a micro-scale version of this method and automation is achieved using a GERSTEL MPS autosampler equipped with an Anatune CF-100 centrifuge. The clean-up process is followed by automated injection of the cleaned extract to a GC/MS system using the GERSTEL Automated TDU-liner EXchange (ATEX) technique. The sensitivity and selectivity of GC/MS combined with the described injection technique, results in method detection limits that meet acceptance criteria for reporting maximum residue levels (MRLs) as established by regulatory agencies. The ability to automate the dSPE clean-up of QuEChERS extracts and to couple extraction and clean-up directly to GC/MS analysis, results in the improved laboratory productivity by streamlining the complete analytical process.
Keywords: Pesticide Residue Monitoring, QuEChERS, LC/MS/MS, Sample Preparation, DPX, Lab Automation
In this report, we describe an automated sample preparation and analysis workflow for the screening of pesticides residues in different food matrices (fruits, vegetables and spices) by LC/MS/MS. The automated cleanup of the QuEChERS extracts methodology was performed using disposable pipette extraction (DPX). Analytical methodology for confirming the presence of a variety of pesticides in various food samples was developed using a GERSTEL MultiPurpose Sampler (MPS), a combined autosampler and liquid handling robot, interfaced to an AB SCIEX QTRAP® 4500 LC/MS/MS System.