A conversation with sample extraction experts Dr. Kang Xia and William Ickes
In March 2013, Lab Manager, along with BUCHI Corporation, hosted a Product Spotlight webinar, “Cutting-Edge Developments in the Evaluation of Contaminants.” Kang Xia, PhD, an associate professor in the Department of Crop and Soil Environmental Sciences at Virginia Tech, discussed some methods that she has developed in her lab to extract emerging contaminants from complicated environmental samples. Following Dr. Xia’s presentation, William Ickes, product specialist for extraction and Kjeldahl at BUCHI Corporation, discussed ways to increase sample extraction efficiency and throughput, particularly using the pressurized solvent extraction technique. Their presentations were followed by a question-and-answer session in which attendees asked questions and received feedback from the two experts. The live webinar was attended by a global audience, representing diverse industries and varying levels of expertise. This event provided them with a unique opportunity to interact with the experts in real time and to seek their guidance and advice on various issues related to evaluation of emerging contaminants. The event was moderated by Tanuja Koppal, PhD, contributing editor for Lab Manager. Here are some key questions and topics that were addressed.
Koppal: What are the analytical challenges that need to be overcome when looking at emerging contaminants in complicated environmental matrices?
Xia: There are three major challenges that need to be overcome when analyzing emerging contaminants in complicated environmental matrices. The first challenge is how to consistently achieve 100 percent extraction efficiency of trace levels of target analytes from environmental samples. The second is how to completely separate the target analytes from the co-extracted interferences. The third challenge is to be able to detect the target analytes at trace levels on analytical instruments.
Koppal: What are the pros and cons of some of the existing methodologies for extraction?
Ickes: There are many existing methodologies for extraction on the market today, including but not limited to pressurized solvent extraction, automated and traditional Soxhlet, microwave-assisted extraction, and sonication extraction. When evaluating an extraction methodology, it is important to consider recovery of targeted analyte, extraction time, solvent consumption, and level of automation. The accompanying chart offers some comparison of key parameters to be considered.
Koppal: How do you go about testing and evaluating methods that provide the speed and extraction efficiency that you are looking for?
Ickes: It is common to evaluate different extraction methods with a known standard that matches your target analyte/analytes. This standard is then spiked into your sample matrix, along with an internal standard, and then run through the extraction process. The method should be evaluated until you determine the minimum extraction time and other process parameters that will result in sufficient recovery of the analyte/analytes. From this evaluation, you can then compare analyte recovery, extraction time, and solvent consumption.
Koppal: What factors need to be considered when optimizing an extraction method?
Ickes: Method optimizations are typically performed to increase analyte recovery, reduce extraction time, and reduce solvent consumption. They are also performed to eliminate the possibility of problems with difficult matrices or heavily contaminated samples. Some of the problems associated with difficult matrices or heavily contaminated samples are the co-extraction of undesirable analytes, interference with water, temperature sensitivity of the analyte, or clogging associated with the presence of a heavily contaminated sample.
Koppal: What are some of the parameters that impact the speed and recovery of extraction?
Ickes: The most important parameters that impact speed and recovery are temperature, pressure, extraction hold time, surface area of analyte, solvent type, and elimination of interfering components of the matrix.
Koppal: What are the advantages and limitations of using pressurized solvent extraction?
Ickes: The advantages of pressurized solvent extraction are that the technique is fully automated, yields high analyte recovery, has a fast extraction time, and requires little solvent consumption. The disadvantage of pressurized solvent extraction is that exit pathways leading away from the sample cells are narrow, so they are susceptible to slightly soluble analytes that precipitate in the lines.
Koppal: What are some of the trends and improvisations taking place in extraction techniques?
Ickes: One of the upcoming trends in extraction is to combine cleanup with the extraction process. It is advantageous to perform in-cell cleanup so you do not have to perform these steps prior to or following the extraction.
For more information, check out www.mybuchi.com.
Archive of the webinar is at www.labmanager.com/contaminantevalspotlight.
William H. Ickes is a product specialist for extraction and Kjeldahl at BUCHI Corporation. He specializes in application support for the BUCHI Speed Extractor Pressurized Solvent Extraction Unit.
Dr. Kang Xia is an associate professor in the Department of Crop and Soil Environmental Sciences at Virginia Tech. She received her PhD in soil chemistry from the University of Wisconsin-Madison, her MS in soil chemistry from Louisiana State University, and her BS in soil chemistry from Beijing Agricultural University.