Sample storage stability

Pyriminobac-methyl (E- and Z-isomer, separately) in rice grain (0.1 mg kg ), rice straw (0.1 mg kg ) and soil (0.02 mg kg ) are stable for up to 60 days when stored at -20 °C. 

Shinba, A. Yagi, and Y. Yusa, Degradation of a new herbicide, pyriminobac-methyl, in soils, in Abstracts of the 21st Annual Meeting of the Pesticide Science Society of Japan, p. 35 (1996). 

Matsushita, Y. Nagai, Y. Asano, and Y. Yusa, Residue analysis of pyriminobac-methyl 

Akira Yagi, Mitsumasa Ikeda and Yoshihiro Saito Kumiai Chemical Industry Co. Ltd, Japan 

Empirical formula Molar mass Melting point Vapor pressure Solubility Use pattern 

---

Sample storage stability Prohexadione-calcium in strawberry, rice grain, rice straw, wheat grain and barley grain is stable at -20 °C for 40, 140, 60, 80 and 100 days, respectively. Approximately 88% of the applied prohexadione-calcium remained in soil when stored at —20 °C after 80 days. 

Sample storage stability. The level of fenothiocarb (0.4 mg kg ) in soils stored in the dark at 3 °C decreased to 94-97% after 40 days and to 68-82% after 120 days. 

In order to avoid problems related to slow reaction kinetics and sample storage stability, precautions are often taken in the field to minimize such effects. Furthermore, sample preparation is often required to transfer the collected isocyanate derivatives to solvents, which are compatible with the analysis method of choice, or to preconcentrate the sample to improve the sensitivity of the method. 

Storage stability studies for carfentrazone-ethyl compounds on crop matrices have shown a pattern of stability for at least 7-24 months, depending on the study program or the maximum sample storage interval for the study. Carfentrazone-ethyl was not stable in field corn starch, potato tuber and bovine kidney. The residue results indicated that a significant portion of carfentrazone-ethyl was converted to C-Cl-PAc in these matrices however, the total amount of carfentrazone-ethyl and C-Cl-PAc accounted for the original spiking level. Since both carfentrazone-ethyl and C-Cl-PAc were determined in these stability studies, the instability of carfentrazone-ethyl was not of any concern. 

Storage stability studies for sulfentrazone compounds on crop matrices showed a pattern of stability for at least 3-38 months, depending on the study program or the maximum sample storage interval for the study. 

In many cases, there is difficulty in preserving residues in samples after collection and prior to pesticide analysis which coincides with a rapid further degradation and mineralization of the pesticide residues under most environmental conditions. Storage stability studies and studies on the reactivity of sample collection equipment in addition to field quality assurance procedures can help address some of these questions. Concerns are accentuated for compounds that have short half-lives in the environment but still have high acute toxicity. 

A solution to this dilemma is to place soil samples immediately in a freezer located in the field, the temperature of which is continuously monitored, as described previously. Laboratory-prepared storage study samples can then be used to determine test substance stability under freezer storage conditions that match those used in the field and during transportation and final storage. If a valid laboratory storage stability... 

A second approach to determining freezer storage stability involves the reanalysis of incurred residues found in actual samples that are stored over time. Using this approach, soil from an actual field sample containing residues is periodically analyzed... 

A reference substance can be either the formulated test substance suspended in water or the technical or analytical grade active ingredient of the test substance dissolved in a solvent. The reference substance is normally used to fortify field matrices to develop information on the field storage stability of the active ingredient. Reference substances should be prepared at the analytical facility where the matrix samples are to be analyzed. Methods to prepare reference substances for field use will be discussed later. 

Field fortification (commonly referred to as field spiking) is the procedure used to prepare study sample matrices to which have been added a known amount of the active ingredient of the test product. The purpose for having field fortification samples available in a worker exposure study is to provide some idea of what happens to the test chemical under the exact environmental field conditions which the worker experiences and to determine the field storage stability of the test substance on or in the field matrix materials. Field fortifications do not serve the purpose of making precise decisions about the chemical, which can better be tested in a controlled laboratory environment. The researcher should not assume that a field fortification sample by its nature provides 100% recovery of the active ingredient at all times. For example, a field fortification sample by its very nature may be prone to cross-contamination of the sample from environmental contaminants expected or not expected to be present at the field site. 

Field fortifications have also been used to measure the storage stability of the analyte in/on exposure matrices during freezer storage prior to analysis. Although use of field fortification samples for freezer storage stability is not the original purpose intended for field fortification samples, this has become an acceptable practice among scientists who work in this scientific discipline. 

Activities encompassed by the stability program include sample storage of either development or production batches (or both), data collection and storage/retrieval, physical, chemical, and microbiological testing, document preparation of regulatory... 

The experimental evaluation [4] of the stability of non-ionic surfactants (nonylphenol ethoxylates, NPEOs, and alcohol ethoxylates, AEOs) during sample storage showed that aqueous samples can be stored at 4°C without addition of any preservative only for a short time (a maximum of 5 days). The most often used preservative is formaline (1-8% (v/v) of 37% solution of formaldehyde in water). 

The sample storage conditions to be used. Are stability checks for specific analytes undertaken ... 

Storage Stability. It must be shown that no greater than 10% loss occurs in samples stored for seven days under ambient conditions. This will ensure ample time to ship the samples from the field to the laboratory. Preliminary tests may be performed on spiked samples, but the final testing must be done with samples collected from test air, since distribution of the analyte on the sorbent is different for spiked samples. 

Storage stability was demonstrated by collecting a set of samples of a test atmosphere at a known concentration and analyzing... 

---