Her first step should be to send him back to recollect the samples. The first rule of analytical chemistry is the same as for computer programming: "garbage in, garbage out." Sampling cannot be separated from analysis. Household glass containers are most likely soda glass, which contains percent amounts of sodium, calcium, magnesium, aluminum, and potassium as well as numerous trace elements. The blue coloration is likely due to large amounts of cobalt. Even borosilicate glass, which is used in laboratory apparatus, contains percent amounts of sodium, potassium, aluminum and boron. All of these elements can leach from the glass surface into the water once it has been acidified to facilitate long-term storage. This will contaminate the sample and cause false analytical results. Therefore, she looks around her laboratory for plastic containers and locates 100-mL bottles made of low density polyethylene (LDPE), high density polyethylene(HDPE), and polypropylene(PP). Which should she give him to collect the samples and how should she tell him to collect them?

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