###### Abstract  
A new method is presented for the simultaneous determination of 13 multiclass pesticides along with glyphosate. The multiclass pesticides were extracted by creating a soil slurry with 2% ethanol in water (\(v/v\)), and then, applying direct-immersion solid-phase microextraction (DI-SPME) with a new type of semi-disposable SPME fiber configuration called LC-Tips. The fibers were then retroextracted to ethanol, and aqueous ammonia was added to the slurry to extract glyphosate. Derivatization of the glyphosate extract was accomplished with a mixture of trifluoroacetic anhydride and trifluoroethanol, after which the reaction mixture was dried and resuspended with the SPME ethanol extract. To this, a mixture of analyte protectants was added, and it was analyzed by GC-MS/MS in multiple-reaction-monitoring mode. All analytes showed a coefficient of determination greater than 0.95 in the 0.1-100 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{kg}\) calibrated range, and the limits of detection were between 0.1 and 1 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{kg}\), except for glyphosate, which was 0.01 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{kg}\). The method shows relatively high replicate relative standard deviation (as much as 37% for five extractions at 20 \(\mathrm{\SIUnitSymbolMicro g}/\mathrm{kg}\)), but the isotopically labeled internal standard was effective at mitigating this effect for some analytes. m +
Footnote †: journal: _Sci_  
In terms of GC-MS analysis, it is important to obtain an extract which is relatively free from matrix interfere, most notably those which are not detected by the technique, e.g., non-volatile compounds such as inorganic salts, which can compromise the instrument over many runs, causing among other things adsorption of the pesticides and eventual poor peak shape. Also, moderately volatile and/or polar matrix components can cause matrix-induced response enhancement, which results in the sample peaks being significantly larger and more symmetrical than those injected in pure solvent. Generally, matrix-matching calibration has been used to mitigate this problem, but the use of analyte protectants has also been proposed, in which moderately volatile compounds such as some sugars are added to the sample in order to \"protect\" the analytes from chemical adsorption, resulting in the same effect as matrix-induced response enhancement [7], both in the samples and calibration solutions. When designing a method which could quantify glyphosate along with other commonly used pesticides, several avenues were considered. Since the extraction of glyphosate from soil is always performed with an aqueous solution [8], two serial extractions would always be needed, since low-polarity analytes will not readily extract onto aqueous phases. Furthermore, since glyphosate extraction is commonly performed with very basic solutions (either with KOH or aqueous NH\({}_{3}\)), and some pesticides are known to degrade under basic pH [9], it was thought that the aqueous extraction would have to occur last. Thus, the idea was to modify a previously existent multiresidue method which can extract organochlorines, organophosphates, triazoles, among others, and then, perform the glyphosate extraction. The most important condition would be that the first extraction did not degrade or modify the sample to an extent that the glyphosate extraction would be impaired. Thus, QuEChERS was ruled out, since it requires the addition of salts, which would have made the aqueous extraction impossible. The original conception was to perform ultrasound-assisted extraction (UAE) with an organic solvent, remove the entirety of the extract volume, and then, add the aqueous solution for glyphosate extraction. However, UAE has several drawbacks and does not inherently provide significant concentration factors [6]. Also, the removal of the entire extract solvent volume is operationally challenging, even after centrifugation, and could induce repeatability problems.