Frequent Questions

Is SW-846 Method 9045D (pH of solids) applicable to organic liquid waste matrices?

Is Method 9045D (pH of solids) applicable to organic liquid waste matrices? 


Section 1.1 of Method 9045D states that the pH of non-aqueous liquids can be determined by the procedure.  Water should be added to the non-aqueous liquid and mixed, because pH cannot be determined without the presence of water.  The non-aqueous liquid should be separated from the water [aqueous phase] and the water analyzed.  The pH of the water is representative of the pH of the waste thereby, the waste is not directly measured.  Liquid organic wastes, such as oily wastes, may damage the pH electrode if the electrode is exposed directly to the oil. 

Note: This does not mean that you must use Method 9045D to evaluate non-aqueous liquids to see if they exhibit the RCRA characteristic of corrosivity (40 CFR §261.22).

First, the characteristic of corrosivity is limited to wastes that are aqueous with pH less than or equal to 2 or greater than or equal to 12.5 using Method 9040C; OR any liquid that corrodes steel at a rate greater than 6.35 mm per year using Method 1110A.

A clarification was written to explain “aqueous” as a waste that is amenable to pH measurement.  It is accepted that this can include liquids, gels, and sols.  The inclusion of Method 1110(A) in the regulation was discussed in the original background document.  The intention was to regulate liquids that have pH between 2 and 4, but can corrode steal at a rate that can cause harm to humans and/or the environment in a relatively short period of time.

When a sample is so corrosive that it exceeds the capacity of the electrode and/or the meter (for both high and low pH), the analyst may want to include additional testing to support Method 9040C.  Diluting the waste in water (similar to Method 9045D) and measuring the pH again can demonstrate that the original pH is much less than 2 or much greater than 12.5.  Additionally, millivolt readings can be used to calculate pH values in support of Method 9040C.

Method 9045D may be used to evaluate pH properties of non-aqueous liquids, solids, and sludges, but not for the RCRA characteristic of corrosivity.  Organic liquids may be diluted/extracted in water according to Method 9045D, and the pH of the aqueous phase can be measured.  If the organic liquid (such as organic acids) contributes hydronium ions to the solution, the measured pH is reflective of the pH of the organic liquid.  However, if the organic liquid (such as hexane) does not contribute hydronium ions, the pH being measured is that of the water that was used for the dilution/extraction.  It should be noted that many organic liquids (even those miscible with water) may interfere with and/or damage pH electrodes.

Other Category: 9000 Series

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