LABORATORY INFORMATION BULLETIN
Detection, Quantification and Confirmation of Myclobutanil (Systhane)
in Strawberries by Ion Trap Technology
Walden Lee, Kin S. Chiu and Thomas Cairns
Mass Spectrometry Center
Los Angeles District Laboratory
U.S. Food and Drug Administration
Recently, the approval to employ the new fungicide, myclobutanil (Systhane, Rally, Nova, Eagle) to control powdery mildew on pome fruit has prompted its illegal application on strawberries. In the fiscal years 1993 and 1994, residue surveillance of strawberries from Mexico indicated widespread use of Systhane in spite of the lack of a tolerance level. Therefore such samples were determined to be violative. Such residue findings were required to be confirmed and the application of the ion trap technology was a convenient and simple method for development. The purpose of this paper is to describe this method of analysis for myclobutanil in strawberries by gas chromatography with ion trap detection.
Acetone, methylene chloride and petroleum ether (B & J brand, pesticide grade and distilled in glass).
Malinkrodt no. 8024, anhydrous and granular.
Solid-phase extraction (SPE) cartridges
Waters brand, Sep-pak plus: C-18 part no. 20515; Varian brand, Bond-elut: Strong Anion Exchange (SAX) cat no. 1210-2044; Primary/Secondary Amine (PSA) cat no. 1210-2042
Pesticide analytical standards, the ion trap, the analytical protocol, and method of quantification havebeen described previously (1-3).
The samples were analyzed by the Luke modified procedure described previously (4) with the following modifications. The QMA and NH2 Solid Phase Extraction (SPE) cartridges were replaced with SAX and PSA cartridges described in the equipment section. Preparation of the samples for injection into the GC of the ion trap involved removal of 1.0 mL of sample from a final sample volume of 4 mL. This aliquot was placed into a vial for auto-injection and 1 ug of the mixed internal standards [various deuterated polyaromatic compounds] was added.
Two three point calibration curves were constructed using the ions at m/z 70 [representing Systhane] and m/z 189 [representing the internal standard phenanthrene-d10] to cover approximately two orders of magnitude in concentration ranging from 0.02 to 0.7 ppm. As illustrated in Figure 1, one of the concentration ranges was constructed from 0.02 ppm through 0.05 ppm and terminating at 0.07 ppm. A second calibration range was constructed from 0.2 ppm, through 0.5 ppm with termination at 0.7 ppm.
Samples were fortified at the 0.1 and 0.5 ppm levels with Systhane. Each concentration level was analyzed in triplicate to provide a relative standard deviation measurement.
Figure 1. Calibration curve for Systhane (m/z 70) versus the internal standard, Phenanthrene (m/z 189).
RESULTS AND DISCUSSION
The recovery data is illustrated in Table 1.
Table 1. Recovery Data obtained for Systhane in Strawberries.
|Spiking Level(ppm)||Amount found(ppm)||%Recovery||Mean Recovery(ppm)||RSD(%)|
The recovery data at 0.5 ppm Systhane exhibited reasonable precision and accuracy with an average recovery of 112% with a relative standard deviation of 6%. In the case of recoveries at the lower level of 0.1 ppm, the data illustrated a slightly higher average recovery of 116% and a higher relative standard deviation of 11%.
While the recovery data is acceptable, it is worthwhile to discuss the ion selection for Systhane. As can be observed the base peak for Systhane is the ion at m/z 70 (Fig. 2) statistical prevalence of m/z 70 in the extract must therefore be considered to be high and might be the cause of poor quantification at the low levels of 0.1 ppm. A higher ion, such as the protonated molecular ion at m/z 289, would have provided a better choice. However, the calibration data obtained could not meet the lower QA/QC criteria of a CV of no less than0.995.
The use of the ion at m/z 70 to detect the presence of Systhane in the sample provided the desired Gaussian shaped ion elution profile within 5 scans of the experimentally observed reference standard. In the case of the spectral matching process, the spectral fit value assigned was 804, i.e. below the QA/QC lower limit of 850 units. It was concluded from this comparison that the ion at m/z 289 had a major contribution from the matrix placing it as the base peak in the incurred residue spectrum. This finding confirms the reason for the inability of the ion at ion m/.z 289 to provide acceptable Linear calibration curve. The S/N at the recovery level of 0.5 ppm was determined to be 31:1. The limit of detection (LOD) was determined to be 0.05 ppm with a S/N of 6:1. The limit of quantification (LOQ) was found to be 0.1 ppm. with S/N of 15:1.
. Typical computer printout illustrating quantification procedure using Quality Control parameters.
(1) Cairns, T., Chiu, K.S., Siegmund, E.G., Rapid Communications In Mass Spectrometry, 6, 331-338 (1992).
(2) Cairns, T., Chiu, K.S., Navarro, D., Siegmund, E.G., Rapid Communications In Mass Spectrometry, 7, 971-988 (1993).
(3) Cairns, T., Chiu, K.S., Lee, Walden, Laboratory Information Bulletin, #3916 (1995).
(3) Cairns, T., Chiu, K.S., Navarro, D., Siegmund, E.G., Rapid Communications In Mass Spectrometry, 7, 1070-1076 (1993).
The Laboratory Information Bulletin is a communication from the Division of Field Science, Office of Regulatory Affairs, U.S. Food and Drug Administration for the rapid dissemination of laboratory methods (or scientific regulatory information) which appear to solve a problem or improve an existing problem. In many cases, however, the report may not represent completed analytical work. The reader must assure, by appropriate validation procedures, that the reported methods or techniques are reliable and accurate for use as a regulatory method. Reference to any commercial materials, equipment, or process does not, in any way, constitute approval, endorsement, or recommendation by the U.S. Food and Drug Administration.