Solid Phase Microextraction (SPME) Method for 4-methyl-1-cyclohexanemethanol (MCHM) and propylene glycol phenyl ether (PPH) in Water

Background
4-Methyl cyclohexane methanol (MCHM) and propylene glycol phenyl ether (PPH) are chemicals used in the coal cleaning process. On January 9, 2014, there was an accidental release into the Elk River in West Virginia of an estimated 10,000 gallons of a mixture of these chemicals[1]. According to the owners of the tank, the mix contained 88.5% 4-methylcyclohexane methanol (MCHM), 7.3% PPH Stripped basic, and 4.2% water[2]. PPH Stripped basic consists of a mixture of propylene glycol phenyl ether (PPH) and dipropylene glycol phenyl ether (DiPPH). Consequently, drinking water for the local community became contaminated, with the MCHM imparting a "black licorice-like" odor. The Centre for Disease Control (CDC) has set advisory limits in drinking water of 1 ppm maximum for MCHM and 1.2 ppm for PPH[3,4]. However, detection limits in the ppb range are beneficial to ensure that the compounds are at the "non-detect" level in the drinking water supply.

In this application, an SPME method was developed to provide a quick and quantitative determination of both MCHM and PPH. The method was able to detect both compounds at a spiking level of 1 ug/L in surface water. In addition, to test the method in the presence of heavy matrix background, a sample of diet cola was spiked and evaluated for recovery.

Experimental
Samples

  1. Local municipal tap water
  2. Private well water
  3. Local creek water
  4. Diet cola drink

All samples were tested unspiked and spiked at 1 ug/L with MCHM (total of two isomers) and PPH. The diet cola sample was spiked at 10 ug/L. Four replicates of each spiked sample were analyzed.

SPME conditions
Fiber: polydimethylsiloxane (PDMS), 100 µm film (Cat. No. 57301)
Extraction: 5 min equilibration, followed by 5 min extraction - headspace, 55 °C with agitation, 250 rpm
Desorption: 270 °C, 2 min (splitter open at 0.75 min)
Fiber postbake: 5 min, 270 °C
Sample: 6 mL with 1.5 g NaCl (25%) in 10 mL headspace vial

GC conditions
Column: VOCOL®, 20 m x 0.18 mm I.D., 1.0 µm (Cat. No. 28463-U)
Oven: 50 °C (1 min), 15°C/min to 220 °C (5 min)
Carrier: helium, 1 mL/min
MS conditions: aux at 220 °C, source at 230 °C, quads at 150 °C, autotune
SIM: m/z= 110 (quant), 97 for MCHM m/z=94 (quant), 152 for PPH
Liner: 0.75 mm I.D SPME liner

Quantitation

  • Water samples: external standards, using a 6-point calibration curve from 0.1 ug/L to 10 ug/L extracted from DI water. r2 for each analyte was >0.995
  • Diet cola samples: external standards, using a 5-point calibration curve from 5 ug/L to 100 ug/L, extracted from DI water. r2 for each analyte was >0.995

Results
A summary of recoveries is presented in Table 1. No MCHM or PPH were detected in the unspiked water samples. Recoveries and reproducibility were very good, with the exception of PPH in the tap water sample. Since this compound was recovered easily from the private well and creek water samples, it is believed that the presence of chlorine in the tap water may have degraded PPH.

The diet cola contained more matrix interference than the water samples. In anticipation of this, the cola samples were spiked at a higher level of 10 ug/L. Matrix interference peaks were detected which coeluted with the second MCHM isomer and PPH. These were quantitated and subtracted out when calculating recovery values. Recovery of the MCHM was quite good; however, PPH appears to have been affected by matrix constituents in the cola.

Representative chromatograms obtained from the GC-MS/SIM analysis of the creek water and cola samples are presented in Figures 1 and 2. The MCHM and PPH peaks were easily detectable above the sample background. The addition of salt to the samples prior to extraction was found to increase response of the analytes by 10X and thus is critical to achieving the 1 µg/L detection level.

Table 1. Recovery and Reproducibility (%RSD) Results Using SPME Method, n=4
  Private
Well Water
Creek Water Municipal
Tap Water
Diet Cola
Spiking level 1 µg/L 1 µg/L 1 µg/L 10 µg/L
MCHM isomer #1 97 (±5) 114 (±9) 122 (±6) 102 (±5)
MCHM isomer #2 97 (±7) 106 (±13) 115 (±5) 73 (±5)
PPH 83 (±2) 93 (±6) 0 59 (±3)

Figure 1. TIC of Creek Water, Spiked at 1 µg/L; Extracted using SPME

 

Figure 2. TIC of Diet Cola, Spiked at 10 µg/L; Extracted using SPME (Note - scale is different from Figure 1)

 

Conclusion
Solid phase microextraction can be used to achieve a detection level of 1 ug/L for MCHM and PPH from various water sources. A lower detection level may be possible with further instrument optimization. In the case of PPH, degradation may occur in water sources containing chlorine; however, this needs to be confirmed with further testing.

References

  1. Centers for Disease Control and Prevention.
  2. Summary Report of Short-term Screening Level Calculation and Analysis of Available Animal Studies for Dipropylene Glycol Phenyl Ether (DiPPH) and Propylene Glycol Phenyl Ether (PPH).
  3. Centers for Disease Control and Prevention.
  4. Centers for Disease Control and Prevention.
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