While using matrix-matched calibration standards can mitigate matrix effects and increase reporting accuracy, this approach is time-consuming, labor intensive, and sometimes limited by the availability of suitable blank matrix. The use of analyte protectants (AP) in gas chromatography is an intriguing alternative because it is much simpler in practice and can allow good results to be achieved with solvent-based calibration standards [1]. Analyte protectants, such as the sugar derivative shikimic acid, work by binding strongly to active sites in the inlet, which effectively blocks these sites from interacting with target compounds. This prevents analyte loss, improves transfer to the column, minimizes degradation in peak shape and response, and can potentially improve accuracy and reliability for low-level analysis.<\/p>\n\n\n\n
Since using matrix-matched calibration standards is not feasible in all situations, a series of experiments was conducted to evaluate the effects of using an analyte protectant with solvent-based calibration standards on recovery and critical peak characteristics (area, symmetry, width, and tailing) for a variety of pesticides. The experiments were (1) recovery of 40 pesticides in kale samples; (2) response of captan in apple, strawberry, kale, grape, and celery samples; and (3) response of 40 pesticides in kale and strawberry samples. For all tests, the analyte protectant was shikimic acid (1 mg\/mL), and 1 \u00b5L of it was co-injected with 1 \u00b5L of sample (for samples without analyte protectant, 1 \u00b5L of acetonitrile was co-injected).<\/p>\n\n\n\n
To determine if 1.0 mg\/mL shikimic acid analyte protectant could increase pesticide recovery in matrix, kale samples were fortified at 10 and 50 ppb with a 40-compound QuEChERS performance standards kit (cat.# 31152). Quantification was done using matrix-matched calibration standards, solvent-based calibration standards with shikimic acid, and solvent-based calibration standards without shikimic acid. As shown in Figures 1 and 2, when using solvent standards, the analyte protectant did help more pesticides fall into the desired recovery range (70-120%), particularly at the higher spike level. However, matrix-matched calibration still outperformed solvent calibration with analyte protectant at both spike levels, and this was especially pronounced at the lower spike level.<\/p>\n\n\n