Chemical Analysis of Wastewater from Unconventional Drilling Operations

Trillions of liters of wastewater from oil and gas extraction are generated annually in the US. The contribution from unconventional drilling operations (UDO), such as hydraulic fracturing, to this volume will likely continue to increase in the foreseeable future. The chemical content of wastewater from UDO varies with region, operator, and elapsed time after production begins. Detailed chemical analyses may be used to determine its content, select appropriate treatment options, and identify its source in cases of environmental contamination. In this study, one wastewater sample each from direct effluent, a disposal well, and a waste pit, all in West Texas, were analyzed by gas chromatography-mass spectrometry, inductively coupled plasma-optical emission spectroscopy, high performance liquid chromatography-high resolution mass spectrometry, high performance ion chromatography, total organic carbon/total nitrogen analysis, and pH and conductivity analysis. Several compounds known to compose hydraulic fracturing fluid were detected among two of the wastewater samples including 2-butoxyethanol, alkyl amines, and cocamide diethanolamines, toluene, and o-xylene. Due both to its quantity and quality, proper management of wastewater from UDO will be essential

Transient Ion-Pair Separations for Electrospray Mass Spectrometry

We report a novel ion-pair chromatography (IPC) approach for liquid chromatography electrospray ionization mass spectrometry (LC-ESI-MS), where the eluent does not contain any ion-pairing reagent (IPR). The IPR is injected on the column, much like the sample, and moves down the column. Significant amounts of a high retention factor IPR is injected, resulting in a transient but reproducible regional coating that progresses along the column. The sample is injected after a brief interval. The sample components interact with the IPR coated region during their passage; the chosen eluent gradient elutes the analytes of interest into the mass spectrometer before the IPR. Following analyte elution, the gradient is steeply raised, the IPR is washed out, and the effluent is sent to waste via a diverter valve until it is fully removed. As the nature of the analyte retention continuously changes along the column and with time, we call this transient ion-pair separation (TIPS). As the IPR never enters the MS, TIPS addresses two major drawbacks of IPC for ESI-MS: it avoids both ion suppression and ion source contamination. The potential of the generic approach for other modes of separation is discussed. An illustrative separation of two small inorganic ions, iodate and nitrate, is demonstrated on a reverse phase column by a transient prior injection of hexadecyltrimethylammonium chloride as IPR

Width Based Quantitation of Chromatographic Peaks: Principles and Principal Characteristics

Height- and area-based quantitation reduce two-dimensional data to a single value. For a calibration set, there is a single height- or area-based quantitation equation. High-speed high-resolution data acquisition now permits rapid measurement of the width of a peak (<i>W</i>_<i>h</i>), at any height <i>h</i> (a fixed height, not a fixed fraction of the peak maximum) leading to any number of calibration curves. We propose a width-based quantitation (WBQ) paradigm complementing height or area based approaches. When the analyte response across the measurement range is not strictly linear, WBQ can offer superior overall performance (lower root-mean-square relative error over the entire range) compared to area- or height-based linear regression methods, rivaling weighted linear regression, provided that response is uniform near the height used for width measurement. To express concentration as an explicit function of width, chromatographic peaks are modeled as two different independent generalized Gaussian distribution functions, representing, respectively, the leading/trailing halves of the peak. The simple generalized equation can be expressed as <i>W</i>_<i>h</i> = <i>p</i>(ln <i>h̅</i>)^<i>q</i>, where <i>h̅</i> is <i>h</i>_max/<i>h</i>, <i>h</i>_max being the peak amplitude, and <i>p</i> and <i>q</i> being constants. This fits actual chromatographic peaks well, allowing explicit expressions for <i>W</i>_<i>h</i>. We consider the optimum height for quantitation. The width-concentration relationship is given as ln <i>C</i> = <i>aW</i>_<i>h</i>^<i>n</i> + <i>b</i>, where <i>a</i>, <i>b</i>, and <i>n</i> are constants. WBQ ultimately performs quantitation by projecting <i>h</i>_max from the width, provided that width is measured at a fixed height in the linear response domain. A companion paper discusses several other utilitarian attributes of width measurement

Evaluation of Amount of Blood in Dry Blood Spots: Ring-Disk Electrode Conductometry

A fixed area punch in dried blood spot (DBS) analysis is assumed to contain a fixed amount of blood, but the amount actually depends on a number of factors. The presently preferred approach is to normalize the measurement with respect to the sodium level, measured by atomic spectrometry. Instead of sodium levels, we propose electrical conductivity of the extract as an equivalent nondestructive measure. A dip-type small diameter ring-disk electrode (RDE) is ideal for very small volumes. However, the conductance (<i>G</i>) measured by an RDE depends on the depth (<i>D</i>) of the liquid below the probe. There is no established way of computing the specific conductance (σ) of the solution from <i>G</i>. Using a COMSOL Multiphysics model, we were able to obtain excellent agreement between the measured and the model predicted conductance as a function of <i>D</i>. Using simulations over a large range of dimensions, we provide a spreadsheet-based calculator where the RDE dimensions are the input parameters and the procedure determines the 99% of the infinite depth conductance (<i>G</i>₉₉) and the depth <i>D</i>₉₉ at which this is reached. For typical small diameter probes (outer electrode diameter ∼ <2 mm), <i>D</i>₉₉ is small enough for dip-type measurements in extract volumes of ∼100 μL. We demonstrate the use of such probes with DBS extracts. In a small group of 12 volunteers (age 20–66), the specific conductance of 100 μL aqueous extracts of 2 μL of spotted blood showed a variance of 17.9%. For a given subject, methanol extracts of DBS spots nominally containing 8 and 4 μL of blood differed by a factor of 1.8–1.9 in the chromatographically determined values of sulfate and chloride (a minor and major constituent, respectively). The values normalized with respect to the conductance of the extracts differed by ∼1%. For serum associated analytes, normalization of the analyte value by the extract conductance can thus greatly reduce errors from variations in the spotted blood volume/unit area

A Comprehensive Analysis of Groundwater Quality in The Barnett Shale Region

The exploration of unconventional shale energy reserves and the extensive use of hydraulic fracturing during well stimulation have raised concerns about the potential effects of unconventional oil and gas extraction (UOG) on the environment. Most accounts of groundwater contamination have focused primarily on the compositional analysis of dissolved gases to address whether UOG activities have had deleterious effects on overlying aquifers. Here, we present an analysis of 550 groundwater samples collected from private and public supply water wells drawing from aquifers overlying the Barnett shale formation of Texas. We detected multiple volatile organic carbon compounds throughout the region, including various alcohols, the BTEX family of compounds, and several chlorinated compounds. These data do not necessarily identify UOG activities as the source of contamination; however, they do provide a strong impetus for further monitoring and analysis of groundwater quality in this region as many of the compounds we detected are known to be associated with UOG techniques