Adjust all reagent water used for standards to a pH of 2 before adding the 1664 standard. The samples and matrix spikes also need to have a pH of 2.
Use fresh, accurate 1664 standard that is homogeneous.
If standard precipitates out, allow reagent water to warm to room temperature prior to adding standard.
If standard continues to precipitate, dilute 5 mls of standard in 10 mls of acetone before adding to reagent water. Be sure to rinse the glassware used for the dilution with a little more acetone and add it to the sample bottle.
Be sure to have a good vacuum that can pull 25” of mercury.
Do not let the filter bed go dry of methanol in the condition step prior to sample addition.
Soak the filter bed with methanol for a full 3 minutes prior to adding sample.
Open vacuum knob to full as soon as sample is added.
After sample is through the disk completely, allow the disk to dry under full vacuum for at least 15-20 minutes to remove water.
During the elution step, rinse the sample bottle, adapter, reservoir, and sides of disk with hexane using a Pasteur pipette or syringe and add all rinsings to the disk. Allow the hexane to soak on the disk for at least 2 minutes before pulling it through the disk and into the collection vial.
After using sodium sulfate or phase separation paper to remove water, be sure to rinse them with hexane and add to eluant.
Use a smooth edged (vs. fluted), 70 mm, pre-weighed, aluminum weighing dish for the evaporation step.
Do not heat eluant above 40 degrees C in the evaporation step as hexadecane may volatilize. Hexadecane boils off completely at 53 degrees C.
