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Keywords: Headspace, Solid Phase Microextraction, SPME, Thermal Desorption, Herbs, Coffee, Tea, Polyethylene ABSTRACT
The analysis of volatiles in solids is a common analytical problem. Examples include volatile aroma compounds in foods and plant materials (coffee, tea, and herbs), residual fragrances from soaps and fabric softeners on textiles, and volatiles in polymer resins, films and plastic products. Several techniques are available that allow direct analysis of the volatiles in a variety of solid matrices with little or no sample preparation. Static headspace GC (HS-GC) is probably the most commonly applied technique for analysis of volatiles in solids. Direct thermal desorption (TDS), sometimes referred to as dynamic headspace analysis, and Solid Phase Microextraction (SPME) are alternative techniques that can now be automated. The relative sensitivity of these techniques, and the strengths and limitations of each when applied to a variety of solid matrices should be considered when choosing the most appropriate approach for a new analysis. Until now a direct comparison of these techniques for a variety of samples on equivalent instrumentation has been difficult to find. Samples from the classes mentioned above were analyzed using HS-GC, SPME and TDS sample introduction into the same HP 6890 GC instrument. Column and detector conditions were maintained the same for all sample introduction methods. Generally, sensitivity of static headspace sampling was 10-50x lower than SPME sampling. Direct Thermal Extraction was found to be 50-100x higher sensitivity than SPME sampling. Besides sensitivity, advantages and limitations of the three sample introduction techniques for dealing with various sample types (low vs. high boilers, wet samples) should be considered before choosing an analytical approach.
Keywords: PAH, SPME, Stir Bar Sorptive Extraction, SBSE, GERSTEL Twister, Thermal desorption, GC-MS, PCB
Two extraction techniques that avoid solvent consumption and cut down the sample preparation to a minimum - Solid Phase MicroExtraction (SPME) and Stir Bar Sorptive Extraction (SBSE) – were compared on the basis of their reproducibility and sensitivity for 16 US EPA PAH compounds.
Keywords: Flavors, GC/MS, Retention Time Locking, SPME, SBSE
Analysis of foods, flavors and fragrances is commonly done by capillary gas chromatography coupled to a range of detectors depending on the particular needs of the analysis. Using Retention Time Locked (RTL) methods can facilitate the transfer from one instrument to another, particularly if different detectors (eg. MSD and FID) are used. Although liquid or headspace injection methods are often used for these analyses, difficult and time-consuming sample preparation steps, or lack of sensitivity are commonly encountered. Automated Solid Phase Microextraction (SPME) or Stir Bar Sorptive Extraction (SBSE) can often provide substantial improvements to existing methods. In this contribution, we illustrate the use of RTL methods and the Agilent RTL Flavor Library when the GERSTEL MPS 2 autosampler is used to automate either SPME or SBSE as sample extraction and introduction technique. Procedures are given for calibrating the GC method using either technique. RTL methods created for both sample introduction techniques could be moved from a GC/FID to a GC-MSD system with different column head pressure requirements. Calibrated RTL SPME or SBSE methods were then used to analyze several sample types that otherwise would pose significant matrix interference or detection limit issues. Example chromatograms with identifications based on the RTL flavor library are given.
Keywords: Gas Chromatography, GC, MS, Fast GC Analysis, Low Thermal Mass Heater, LTM, Headspace, Solid Phase Microextraction, SPME
A fast HS-SPME-GC/MSD method for the analysis of flavor compounds of apples was developed. A complete profile was obtained after solid phase micro-extraction within 3 minutes GC run-time using a low thermal mass heater (LTM). Detection with a state-of-the-art quadrupole MSD allowed a data acquisition rate of 20 Hz, while the mass spectral data quality was maintained. The gain in analysis speed was approximately a factor 10 in comparison to the standard method used in the customers laboratory.
Keywords: Selectable 1D/2D GC/MS, SPME, Food, Flavor, Fragrance
Identification of important trace components in complex samples like fragrances, natural products, polymers or food products can be challenging. Achieving the mass on column and resolution necessary to locate peaks and identify trace components using a single column chromatographic separation can be difficult, if not impossible. A selectable 1D/2D GC/MS configuration based on Agilent® Technologies capillary flow technology (CFT) and low thermal mass (LTM) GC column modules with dissimilar column phases was used to perform two-dimensional GC analysis of different foodstuffs. Heartcutting was used to transfer analytes from the first to the second column. Mass spectrometry and olfactory detection were performed in parallel. Solid Phase Microextraction was used as a solventless means to introduce sufficient mass of sample onto the pre-column of the multidimensional system. SPME offers the added benefit of enabling "tuning" of the selectivity of the extraction through the choice of coating on the fiber. Separation and identification of selected flavor compounds from food products were used to demonstrate the effectiveness of the system. The main advantages of this configuration were the simple selection of one or two dimensional operation in combination with the ability to use mass spectrometry and olfactory detection in both dimensions for the analysis of odor active compounds.
Keywords: Automation, Solid Phase Microextraction, MAESTRO Software, GC/MS, Automated Sample Preparation
Solid phase microextraction (SPME) is a powerful technique for the analysis of trace components in a wide variety of matrices. The types of compounds which can be analyzed by this technique ranges from non-polar to semi-polar materials due to the different fi ber materials available. Most applications favor headspace over immersion sampling, therefore the analytes must be volatile enough to partition into the headspace of the vial being sampled. Often, heating and agitation of the sample are required. Quantifi cation can be a challenge due to matrix effects. Automation of these and other steps can help with sample throughput, precision and accuracy.
The MPS PrepStation is a dual-rail/dual robot configuration of the GERSTEL MPS 2 MultiPurpose Sampler. The PrepStation is fully programmable, combining automated sample preparation and sample introduction. One MPS 2 rail of the MPS PrepStation is an automated liquid sample handler that performs a wide range of sample preparation functions. The second MPS 2 rail can provide several automated sample introduction options, depending upon the selected MPS 2 hardware configuration.
The new GERSTEL MAESTRO software provides users control software with a simplified user interface combined with significantly expanded capabilities. The sample preparation functions have been expanded, are easy to set up and have been extended to provide more operational flexibility.
This paper illustrates the use of automation to simplify sample preparation steps, such as derivatization, heating, agitation, and standard addition.