Field fortification solutions

The preparation, maintenance, and integrity of field fortification solutions during a worker exposure/re-entry field study are of the utmost importance in maintaining the integrity of such a study. 

One issue that is of some importance when considering the makeup of field fortification solutions is whether to use the technical form of the active ingredient in solvent or the formulated test product in a carrier such as water. This issue has been a point of contention for many years among scientists who perform and evaluate such studies. There are some advantages and disadvantages to either choice. 

One alternative method for preparing field fortifications solutions/suspensions is to prepare each fortification sample of each matrix in a separate mini-vial in the analytical laboratory and ship the vials to the field for use. This procedure precludes the use of pipets in the field and may be useful when Field Scientists not experienced in the use of pipets are involved in the field fortification process. One disadvantage of this procedure is that the mini-vials, if not designed correctly, will be hard to handle in the field, and surface tension of the suspension or fortification solution will tend to leave unacceptable amounts of the solution/suspension in the vial or at the lip of the vial and not on the matrix in question. This procedure may lead to cross-contamination of samples as the field fortification liquid is forced from the top... 

Field fortifications were prepared to check the field/storage stability of the dermal dosimeters, handwashes, and air filters. The field fortifications were prepared using the formulated product undiluted for "high" level spikes and diluted with water (-1 pg/mL chlorpyrifos) for the "low" level field spikes. Field fortification solutions for urine were prepared from a 3,5,6-TCP standard in acetonitrile utilizing an 1.2-pg/mL solution for the "high" field fortifications and an -0.01-ug/mL solution for the "low" level fortifications. 

Control urine should be collected from individuals who have no apparent past history of exposure to the active ingredient. This control urine must be stored frozen until used for field fortification purposes. The urine is then thawed, shaken well, and a certain amount should be aliquoted into a small jar/bottle to use for field fortification. The active ingredient is then added to the urine using a 1-mL volumetric pipet, the solution is shaken well, and the sample is immediately frozen. Occasionally, the fortified sample can be left at room temperature or at some lower temperature in a liquid state to simulate field storage during collection of the urine sample. After leaving the sample at such temperatures for the prescribed length of time, the sample is immediately stored frozen. 

When fortifying air tubes or air filters, the use of the formulated active ingredient in water is not recommended since the material on the air tube or filter must dry before air is drawn over the matrix. If the field fortification is nol dry on tiie sorbenf or air filter, breakthrough of the fortification solution may occur through the air filter or air tube into the back portion of the air tube and invalidate the procedure. 

Field forms can be used to document the fortification of the matrices during the field-fortifying phase of the study. The matrix fortified, the sample number, the identification and the amount of fortification solution used, the time fortified, and the time that the matrices were removed from the field and stored should be... 

Fresh oxamyl standards were prepared for each fortification event. Concentrations of 50 and 400 qg mL analytical-grade oxamyl were prepared in a 20% acetonitrile-80% FIPLC-grade water solution. The solutions were tranferred in 1-mL aliquots into uniquely identified vials so that each vial contained the correct volume of oxamyl standard to fortify one quality control sample. The vials were shipped as needed during the course of the study to each field site. 

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