US EPA Method 625 is a GC-MS method applicable to analysis of organic compounds in water and soil. The sample is serially extracted with methylene chloride at pH >11, then at pH <2; the extract is dried, concentrated, and analyzed. We have offered numerous mixes for this method: phenols, benzidines, phthalate esters, polyaromatic hydrocarbons, chlorinated pesticides, isophorone, toxaphene, Aroclor PCBs. Our Semivolatiles MegaMix EPA Method 625 combines many of these analytes, including all the phenols, for faster and more convenient preparation. The mixture has been formulated carefully, to ensure maximum stability. For completeness, we also include target compounds listed as additional in Method 625.
Some of the target compounds in Method 625 are subject to thermal or chemical degradation and consequent unpredictable chromatographic performance. Hexachlorocyclopentadiene can decompose at the GC inlet. N-nitrosodimethylamine is difficult to separate from the Method 625 solvent; Method 625 suggests that the analyst follow Method 607 to identify this analyte. Some phenolic compounds in the target list, including chlorinated, methylated, and nitro-substituted phenols, are susceptible to adsorption and/or thermal degradation at the GC inlet. In addition, peak tailing can be a problem with phenols.
We implemented several steps to deal with these problems. We include diphenylamine, rather than N-nitrosodiphenylamine, in the MegaMix formulation because N-nitrosodiphenylamine decomposes to diphenylamine at the GC inlet.
Acenaphthene (83-32-9)
Acenaphthylene (208-96-8)
Anthracene (120-12-7)
Benz[a]anthracene (56-55-3)
Benzo[a]pyrene (50-32-8)
Benzo[b]fluoranthene (205-99-2)
Benzo[g,h,i]perylene (191-24-2)
Benzo[k]fluoranthene (207-08-9)
Benzyl butyl phthalate (85-68-7)
Bis(2-chloroethoxy)methane (111-91-1)
Bis(2-chloroethyl)ether (111-44-4)
Bis(2-ethylhexyl)phthalate (117-81-7)
4-Bromophenyl phenyl ether (101-55-3)
4-Chloro-3-methylphenol (59-50-7)
2-Chloronaphthalene (91-58-7)
2-Chlorophenol (95-57-8)
4-Chlorophenyl phenyl ether (7005-72-3)
Chrysene (218-01-9)
Dibenz[a,h]anthracene (53-70-3)
1,2-Dichlorobenzene (95-50-1)
1,3-Dichlorobenzene (541-73-1)
1,4-Dichlorobenzene (106-46-7)
2,4-Dichlorophenol (120-83-2)
Diethylphthalate (84-66-2)
2,4-Dimethylphenol (105-67-9)
Dimethylphthalate (131-11-3)
Di-n-butylphthalate (84-74-2)
4,6-Dinitro-2-methylphenol (Dinitro-o-cresol) (534-52-1)
2,4-Dinitrophenol (51-28-5)
2,4-Dinitrotoluene (121-14-2)
2,6-Dinitrotoluene (606-20-2)
Di-n-octyl phthalate (117-84-0)
Diphenylamine (122-39-4)*
Fluoranthene (206-44-0)
Fluorene (86-73-7)
Hexachlorobenzene (118-74-1)
Hexachloro-1,3-butadiene (87-68-3)
Hexachlorocyclopentadiene (77-47-4)*
Hexachloroethane (67-72-1)
Indeno[1,2,3-cd]pyrene (193-39-5)
Isophorone (78-59-1)
Naphthalene (91-20-3)
Nitrobenzene (98-95-3)
2-Nitrophenol (88-75-5)
4-Nitrophenol (100-02-7)
N-Nitrosodimethylamine (62-75-9)*
N-Nitroso-di-n-propylamine (621-64-7)
2,2-Oxybis(1-chloropropane) (108-60-1)
Pentachlorophenol (87-86-5)
Phenanthrene (85-01-8)
Phenol (108-95-2)
Pyrene (129-00-0)
1,2,4-Trichlorobenzene (120-82-1)
2,4,6-Trichlorophenol (88-06-2)
*N-Nitrosodiphenylamine is a reactive species that can initiate premature decomposition of other compounds in the mix. For these reasons, diphenylamine is used in the preparation of this mixture. The six other "additional compounds" are components in other Restek reference mixes used for Method 625: benzidine is included in cat.# 31030; β-BHC, δ-BHC, endosulfan I, endosulfan II, endrin are in cat.# 32291 and cat.# 32415.
