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Choose the right sample prep technique to maximize analyte recovery in food analysis

By Derick Lucas, Limian Zhao, and Daniela Daniel
Agilent Sample Prep Applications

Analysis of food samples is very challenging because of huge variations in matrix complexity, the diversity of analytes, and the low tolerance levels testing laboratories need to meet. Every food analysis begins with some form of sample prep, which has a major influence on the integrity of the downstream investigation. Because the effective preparation of testable food samples varies greatly depending on the matrix and nature of the analytes examined, maintaining the efficiency and precision of all analysis processes becomes very difficult. A good test of the effectiveness of your sample prep procedure is to assess recovery. In this article we highlight three methods of contrasting sample prep, all with good recovery.

Method 1: use QuEChERS to extract antiparasitic drugs from milk

Regina Fulani and her colleagues, from the Food Technology Institute in Brazil, developed a fast and easy method to analyze antiparasitic drug residues in milk using an Agilent QuEChERS Kit for sample prep, followed by LC/MS/MS (see Agilent Application Note 5991-3948EN). They developed and validated this method for simultaneous assessment of ivermectin, abamectin, doramectin, eprinomectin, moxidectin, and diflubenzuron residues. The limits of quantification were less than 2.5 µg/L for all compounds, and recovery ranged from 75 to 122%, with RSD under 8.0% (shown in Table 1). This method takes less than five minutes using an Agilent ZORBAX Eclipse Plus C18 column, in an Agilent 1290 Infinity LC with 6460 Series Triple Quadrupole LC/MS.

Table 1. Percentage of recoveries for three fortification levels of antiparasitic drugs in milk.

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Figure 1. Recovery ranges of 176 pesticides using Agilent QuEChERS, ZORBAX RRHD Eclipse Plus C18, and 1290 Infinity LC with 6410 Series Triple Quadrupole LC/MS.

Method 2: QuEChERS kits for extracting pesticides from herbal tea

In an Agilent sample prep test laboratory in the USA, Derick Lucas investigated pesticide residues in herbal teas by using a QuEChERS kit with an LC column and instrument in a similar setup. This time however, a graphitized carbon black (GCB) sorbent was used, as well as a primary secondary amine, in the QuEChERS step. The use of GCB is becoming increasingly valuable when extracting from highly pigmented samples such as tea, though it must be used with care to avoid removing analytes of interest, such as those with planar geometry. This optimized method delivered excellent recovery and reproducibility for the vast majority of the 176 pesticides in green and black teas. For green tea samples, 82% of the pesticide recoveries at 10 ppb and 92% of recoveries at 100 ppb were between 70 and 120%. For black tea samples, 76% of the pesticide recoveries were at 10 ppb and 88% of recoveries at 100 ppb were between 70 and 120%. This was accompanied with a relatively low number of pesticide recoveries below 50% and some non-detected pesticides (Figure 1).

Method 3: use syringe filtration to extract food additives from beverages

Limian Zhao, also with Agilent Sample Prep Applications in the USA, investigated the use of syringe filters for sample prep with an Agilent Poroshell 120 EC-C18 LC column on a regular 400 bar system. Major concerns were sample loss caused by filters, which can result from unwanted interaction between the filter membrane and analytes – and the poor solubility of analytes in the sample media that can block the filter. As a result, the selection of filter membrane depends on the sample medium, and interaction between the membrane and the sample. Regenerated cellulose Agilent Captiva Premium Syringe filters provided the highest recoveries overall in both aqueous and aqueous/organic sample media (Table 2).

Table 2. Recoveries of food additives from beverages using Agilent Captiva Premium Syringe filters.

Count on Agilent for outstanding food analysis solutions

Recovery, consistency, and reproducibility are essential for successful food analysis. That’s where Agilent leads the industry, with products, services, and tools to help you deliver the results your customers demand. Agilent instruments, systems, and supplies are used throughout the food production chain, including incoming inspection, new product development, quality control and assurance, and packaging. Discover more about Agilent solutions for food and agriculture in our applications compendia.

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