Dan Li, Rebecca Stevens, Jason Thomas and Chris English
If you don’t have a GC-MS for identification of the EPA regulated phthalates, don’t worry! Here we introduce a parallel dual column set for the analysis of regulated phthalates using µECD. As shown in my previous blog , the Rtx-440 column (cat. # 12923) is a perfect choice for fast phthalate separation and quantification. The Rxi-35sil (cat. # 13823) is a good choice for a confirmation column. The dual column set can separate the 16 target phthalates listed in method EPA 8061A, including the internal standard benzyl benzoate (cat. # 31847), in less than 8 minutes
As seen in the chromatogram below, 4 pairs of phthalate peaks (in red) switched elution orders on the Rxi-35sil column, which provides confirmative information for identification. (Note: the peaks were numbered according to the EPA 8061A method.) Concentrations of the phthalates have been adjusted to get adequate and relatively equivalent response to the µECD.
Columns: Rtx-440 30 m, 0.25 mm ID, 0.25 μm (cat. # 12923) and Rxi-35sil 30 m, 0.25 mm ID, 0.25 μm (cat. # 13823) using Rxi guard column 5 m, 0.25 mm ID (cat.# 10029) with deactivated universal “Y” Press-Tight® connector (cat.# 20405-261); Sample: EPA Method 8061A Phthalate Esters Mixture (15 components) (cat.# 33227), hexyl 2-ethylhexyl phthalate, benzyl benzoate (internal standard) (cat. # 31847); Injection: Inj. Vol.: 2 μL split ratio :50:1, Inj. Temp.: 280 °C; Liner: Restek Premium 4.0 mm ID Cyclo Double Taper Inlet Liner (cat.# 23310) Oven: Oven Temp: 150 °C (hold 1 min) to 330 °C at 30 °C/min (hold 2 min); Carrier Gas: He; Detector: μ-ECD @ 330 °C; Notes: Instrument was operated in constant flow mode (3.4 mL/min). This chromatogram was obtained using an Agilent μ-ECD. To obtain comparable results, you will need to employ a μ-ECD in addition to dual columns connected to a 5-meter guard column using a “Y” Press-Tight® connector. Concentrations are as listed.
Compared to the method recommended by EPA 8061A using a 5-type/1701-type column set, the run time using the Rtx-440 / Rxi-35Sil MS columns has been greatly reduced from 40 minutes to 8 minutes. Additionally, the resolution has been greatly improved, especially for bis(4-methyl-2-pentyl) phthalate / bis(2-methoxyethyl) phthalate (peaks 5 and 6) and diamyl phthalate / bis(2-ethoxyehtyl) phthalate (peaks 7 and 8). The Rtx-440 column showed superior selectivity over 5-type columns resulting in a faster runtime.
Overall, we recommend the Rtx-440 / Rxi-35sil dual column set as an ideal solution for fast phthalate separation and identification. Due to flow rate limitations on some mass spectrometers, the short run time on GC-µECD may not be able to be reproduced on the GC-MS.
Figure 1 and Table 1 are from EPA Method 8061A . Column 1 is a 30 m x 0.53 mm ID x 1.5 µm 5-type column. Column 2 is a 30 m x 0.53 mm x 1.0 µm 1701-type column. Temperature program is 150 ºC (0.5 min hold) to 220 C at 5 ºC/min, then to 275 ºC(13 min hold) at 3 ºC/min.