9 research outputs found
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><sub><i>h</i></sub>), 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><sub><i>h</i></sub> = <i>p</i>(ln <i>h̅</i>)<sup><i>q</i></sup>, where <i>h̅</i> is <i>h</i><sub>max</sub>/<i>h</i>, <i>h</i><sub>max</sub> 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><sub><i>h</i></sub>. We consider the optimum
height for quantitation. The width-concentration relationship is given
as ln <i>C</i> = <i>aW</i><sub><i>h</i></sub><sup><i>n</i></sup> + <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><sub>max</sub> 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><sub>99</sub>) and the depth <i>D</i><sub>99</sub> at which this is reached. For typical small
diameter probes (outer electrode diameter ∼ <2 mm), <i>D</i><sub>99</sub> 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
Environmental A Comprehensive Analysis of Groundwater Quality in The Barnett Shale Region A Comprehensive Analysis of Groundwater Quality in The
Comment on “Rapid visual detection of blood cyanide” by C. Männel-Croisé and F. Zelder, Analytical Methods, 2012, 4
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