Chapter 2 Rainwater Analysis (Phân tích nước mưa) - Practical Environmental Analysis, 2nd Edition - M. Radojevic, V. Bashkin

60 Chapter 2
2.4.2.2 Experimental Procedure. Take several polypropylene bottles
(150–1000 mL), label them, and weigh them on an open top balance. Record
the weights of the empty bottles. Before sampling rainwater it is necessary
to clean the sampling bottles. Take the weighed 150 mL polypropylene bottles
and repeatedly rinse them with laboratory-grade water. Then fill the
cleaned bottles with laboratory grade water to the brim and cap. Some bottles
may be filled with water and analysed as blanks. You should take these
blank bottles into the field and back to the laboratory, and store in the same
way as your samples. An analysis of these blanks may reveal just how rigorous
you are in your work; if any contamination shows up, it means that you
are being sloppy!
Although chemical-cleaning reagents such as chromic acid or DECON 90
may be used for cleaning bottles, extreme care must be taken to avoid contamination
of the bottles by the cleaning reagent itself. Due to the great
purity of many rainwater samples even minute traces of contaminants could
lead to errors.
2.4.3 Sampling
2.4.3.1 Materials.
● Polypropylene funnel 15–25 cm in diameter or a plastic bucket
● Retort stand and clamp
2.4.3.2 Experimental Procedure. The main objective is to obtain a representative
sample and to avoid any contamination. Find a suitable sampling
location, giving consideration to the following criteria. The sampler should
be placed in an open area with no obstructions above or near the sampler
which may impede the flow of falling rain, or contaminate the sample (i.e.
do not place the sampler under or near trees, near tall buildings, next to walls,
etc.). Good locations for placing samplers are flat roofs of building or in a
clearing such as a field. The sampler should be placed at a height of 1 m
above the surface if possible.
Take a 150–1000 mL sampling bottle, empty out the water, and shake it
to dislodge any droplets of water. Insert into the bottle the polypropylene
funnel and expose the sampler in the field at your chosen sampling site. You
may have to use a retort stand and clamp, or some other method, to hold the
bottle and the funnel firm and prevent the sampler from toppling over in the
wind. If you do not have a funnel you may use a bucket to collect the sample
and transfer it to a bottle after collection. Be sure to note exactly the time
and date when you expose the sampler in the field as well as the time and
date when you remove the sampler from the site or change over the sampling
bottle. Ideally, you should expose the sampler just before a shower and