A novel active sampler coupling osmotic pump and solid phase

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Environmental Measurements Methods

A novel active sampler coupling osmotic pump and solid phase extraction for in situ sampling of organic pollutants in surface water Kunde Lin, Ling Zhang, Quanlong Li, Bingyan Lu, Yue Yu, Junxian Pei, Dongxing Yuan, and Jay J. Gan Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b03760 • Publication Date (Web): 04 Feb 2019 Downloaded from http://pubs.acs.org on February 5, 2019

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Environmental Science & Technology

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A novel active sampler coupling osmotic pump and solid phase extraction for in situ

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sampling of organic pollutants in surface water

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Kunde Lin,† Ling Zhang,† Quanlong Li,†,* Bingyan Lu,† Yue Yu,† Junxian Pei,† Dongxing

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Yuan,† and Jay Gan‡

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† State

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for Coastal Ecology and Environmental Studies, Center for Marine Environmental Chemistry

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and Toxicology, College of the Environment & Ecology, Xiamen University, 361102,

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Xiamen

Key Laboratory of Marine Environmental Science, Fujian Provincial Key Laboratory

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‡ Department

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92521

of Environmental Sciences, University of California, Riverside, California

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* Corresponding author:

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Quanlong Li

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College of the Environment & Ecology

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Xiamen University, 361102, Xiamen

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Tel: +86-592-2183137

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E-mail: [email protected]

1 ACS Paragon Plus Environment


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ABSTRACT

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Active samplers for ambient monitoring of trace contaminants in surface water are highly

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desirable, but their use is often constrained by power supply. Here we proposed a novel

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solution by coupling an improved osmotic pump (OP) with a solid-phase extraction (SPE)

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cartridge to construct a power-free active sampler for organic contaminants. The OP simply

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consisted of two cylindrical chambers separated by a reverse osmosis membrane. We for the

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first time added ion-exchange resins into the OP inlet chamber and successfully constructed

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OPs with a smooth and constant flow. In the OP-SPE sampler, water was continuously drawn

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through the SPE cartridge at a constant flow, and time-weighted average concentration over

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the sampling course may be easily calculated from the amount of target analytes retained on

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the SPE cartridge and water collected in the sampler. The OP-SPE samplers were deployed in

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a river to detect herbicides, and the measured concentrations were largely in agreement with

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the average of 11 daily spot samples. Given that a wide range of SPE cartridges are available

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for different classes of organic contaminants, this approach is versatile and may find

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widespread applications for in situ sampling of surface water under different conditions,

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including poorly accessible locations.


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TOC/Abstract Art

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Note: The photo was taken by one of the authors.



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INTRODUCTION

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Sampling is the first step in the monitoring of trace organic contaminants in surface aquatic

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environments, but it also contributes the most to the overall uncertainty in reported

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measurements.1 Currently, spot (bottle/grab) sampling is the most commonly used method for

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collecting surface water samples. However, spot samples only provide a snapshot of the target

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contaminants in the water at a singular point in time and space. As a result, spot sampling

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often fails to accurately present the whole picture of a contamination episode. Although

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increasing the sampling frequency may decrease the bias, doing so is time- and

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resource-consuming, and the need to process a large number of samples involving extraction,

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purification, concentration, and instrumental analysis makes this option often impractical.2

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Therefore, it is highly valuable to streamline sample collection, extraction, and concentration

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into a single step, with the analysis reflecting a time weighted measurement. A strategy to

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achieve this goal is the application of in situ passive and active samplers.

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Passive sampling is based on the diffusion of analyte molecules from the sampled

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medium to a receiving phase, driven by the difference in chemical potential of the analyte

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between the two media.3 This sampling technique does not require power supply and may be

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deployed in a wide range of environments. For example, semi-permeable membrane device,

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polar organic chemical integrative sampler, polyethylene devices, and solid phase

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microextraction have found use for monitoring various organic contaminants in surface

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aquatic systems.4-11 Most passive samplers operate on the principle of phase partition, and

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rely on the use of a partition coefficient (Ksampler) at equilibrium to derive the aqueous phase

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concentration (Cw). Therefore, the most successful use of passive samplers has been limited to

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hydrophobic organic compounds, as they have a strong affinity (i.e., large Ksampler) for

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polymers such as polyethylene. However, for strongly hydrophobic compounds, it may take

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weeks or even months to reach equilibrium, and Ksampler is also known to be sensitive to the


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sorbent material (e.g., density, thickness) as well as environmental conditions (e.g., salinity,

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temperature).12 The need to determine Ksampler for target analytes through preliminary

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experiments, and the stringent requirements for sampling conditions, are hurdles limiting a

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broader use of passive samplers for in situ sampling.

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Unlike passive samplers, active samplers are less selective to the target analytes and

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sampling conditions. Active samplers generally use a pump to collect samples at preset

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sampling frequency and sample volumes. When integrated with solid-phase extraction (SPE),

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active samplers may be employed to streamline sample collection with analyte concentration.

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For example, Coes et al. used a continuous low-level aquatic monitoring (CLAM) sampler to

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measure 69 trace organic compounds in a river in southeastern Arizona, USA.16 The CLAM

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sampler uses a battery to power a diaphragm pump to continuously pull water through SPE

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cartridges. Supowit et al. developed a similar active sampler, but with a multi-channel pump

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coupled with an array of SPE cartridges to increase the sampling capacity.17 However, these

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active samplers require line power or large batteries, and are only suitable for short-term

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deployment.

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A novel development in active samplers is the use of osmotic pumps (OPs) in lieu of a

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powered pump.18-20 Osmotic samplers do not need electrical power or mechanical moving

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parts, and the sampling volume may be accurately measured in the recovered sampler.19

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Osmotic samplers have been successfully deployed in riverine and marine environments for in

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situ sampling of inorganic ions (e,g., Cl-, SO42-, NO3-, Na+, Mg2+, Ca2+, and K+) for up to

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months and years.19,20 To date, osmotic samplers are mostly constructed by modifying the

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commercially available Alzet® OPs, with flow rates commonly ranging from 0.1 μL/h to 10

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μL/h. In order to sample 2.0 mL/d of water, up to 12 Alzet OPs were combined in parallel in

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one sampler, and a specially designed pump assembly was needed.20 This practice greatly

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increased the complexity and cost of osmotic sampler. Jannasch et al. attempted to construct



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OPs from commercial reversed osmosis (RO) membrane, but found that the flow rates of such

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OPs declined slowly because of the leakage of salt across the membrane.19 The lack of OPs

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with higher and stable flow rates limits a wider application of osmotic samplers.

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The objectives of this study were to construct OPs with higher and stable flow rates

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using RO membrane, and to develop a power-free active sampler by integrating OPs with

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commercial SPE cartridges.

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EXPERIMENTAL SECTION Chemicals and RO Membranes. Individual standard solutions (100 mg/L in acetone

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or hexane) of herbicides (alachlor, acetochlor, metolachlor, butachlor, and atrazine) were

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purchased from TMstandard (Beijing, China). Cyflufenamid standard solution (10 mg/L in

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acetone) was purchased from China Agro-Environmental Protection Institute (Tianjin, China).

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Analytical grade of NaCl were purchased from Xilong Scientific (Shantou, Guangdong,

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China). Deionized water (18.2 MΩ·cm resistivity) was prepared using a Milli-Q water

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purification system (Millipore, Bedford, MA). Solvents (acetone, hexane, and methanol) were

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of high performance liquid chromatography grade. Filmtec membranes of TW30-1812-50,

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TW30-1812-100, TW30-1812-100HR, and SW30-2524 were purchased from DOW Chemical

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Company (Edina, MN). Osmotics Desal membranes of SE4040 and SG2540 were purchased

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from GE Water & Process Technologies (Boston, MA). Sep-pak® C18 (820 mg) and Oasis

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HLB (225 mg) SPE plus short cartridges were purchased from Waters (Milford, MA).

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Design and Optimization of OP. The principles of design and operation of OPs were

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modified from Theeuwes and Yum.21 A schematic diagram of the OP is shown in Figure 1. A

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typical OP simply consists of two cylindrical chambers (e.g., 50 mm inner diameter, i.d.)

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separated by one piece of semipermeable RO membrane. The pump’s housing was made from

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polymethyl methacrylate. The pump was assembled by stainless steel screws and two silicone


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O-rings to seal the two chambers and membrane. Flow within the pump is created when the

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inlet and outlet chambers are filled with deionized water and saturated brine solution,

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respectively. Driven by osmotic pressure, water in the inlet chamber will continuously

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transport across the membrane into the outlet chamber, resulting in a net flow. The flow rate

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of an OP is dependent on the membrane (total effective area, thickness, and porosity), the

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osmotic gradient (difference in salt concentration between two solutions on either side of the

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membrane), and the diffusion coefficient of water, which depends primarily on

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temperature.18,19 To generate a smooth pumping rate, it is necessary to keep the osmotic

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gradient constant. In practice, the osmotic gradient is generally maintained by filling the inlet

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and outlet chambers with deionized water and supersaturated brine with excess amount of salt

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(NaCl), respectively.

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Using different pump chambers and RO membranes, we have built OPs with flow rates

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ranging from 0.1 mL/d to 150 mL/d. For example, an OP with chambers (50 mm i.d.)

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separated by TW30-1812-50 membrane (DOW) was able to generate an approximate flow of

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55 mL/d at 25°C. Using the typical OP structure, pump’s performances were evaluated. First,

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six commercially available RO membranes were used to construct OPs and their pumping

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rates were evaluated. The pumping rate was measured by collecting the outflow from OPs

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every 24 h. Second, we investigated the role of ion-exchange resins on the stabilization of

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pumping rates. The adding amount of resins depends on their ion-exchange capacity, the

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expected pumping volume, and the property of RO membrane used for OP construction. In

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this study, 40 mL of MN6150 ion-exchange resins with an average particle size of 0.50 mm

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(Jiangying Environmental Protection Equipment, Shanghai, China) were added to the inlet

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chambers of OPs. The resins was a mixture of strong acid cation and strong base anion

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exchange resins and had a volume exchange capacity > 1.9 mmol/mL for cations and > 1.0

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mmol/mL for anions. Before adding to the pumps, resins were soaked in deionized water



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overnight. The pumps were run at room temperature for 7 d and the pumping rates and

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conductivities in the inlet chambers were observed every 24 h. Last, the effect of temperature

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on OPs was evaluated by sequentially running an OP at 10°C, 20°C, and 30°C every three

150

days.

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OPs may be easily modified to achieve different pumping rates by using chambers with

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different inner diameters or different types of RO membrane. Prior to sampler construction,

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OPs were tested with positive pressure head of 100 cm and the pumping rates were measured.

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Construction of OP-SPE Sampler. The principle underlying the OP-SPE sampler is

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illustrated in Figure 2. A typical OP-SPE sampler consists of an inline glass fiber filtration

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disc (0.45 μm pores, 47 mm i.d., Xinya Purification Equipment, Shanghai, China) to remove

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large particles, a SPE cartridge to extract organic pollutants, an OP with 50 mm i.d. chambers

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and deionized water coil, and an outflow container to collect the effluent from OP. The

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selection of SPE cartridges depends on the target compounds to monitor. In this study, two

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popular SPE cartridges (i.e., C18 and HLB) were selected for sampler construction. The other

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materials used for the sampler construction were carefully chosen to avoid any potential

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interactions with target organic pollutants in water. Silicone rubber tubing (4 mm or 6 mm i.d.)

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was carefully coiled on a spool and directly connected to the OP inlet to supply deionized

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water and store eluent from the SPE cartridge during deployment. The length of silicone

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rubber tubing depends on the expected sampling volume. By using an appropriate length of

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silicone rubber tubing, samplers could be designed and constructed to prevent the SPE

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effluent from entering the inlet chamber of the OP. For example, 80 m of tubing (4 mm i.d.)

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can accommodate about 1.0 L of deionized water and support to sample about equal volume

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of water. The inlet of SPE cartridge was directly plugged into the filter outlet to reduce dead

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volume. All the parts were mounted on stainless steel plates and assembled with stainless

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steel screws. To prevent any possible direct collision damage, the sampler assembly was fitted


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into a PVC casing (20 cm i.d., 50 cm height). When an OP-SPE sampler was deployed, the OP continuously drew a constant flow

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through the filter and SPE cartridge, in which organic pollutants in the sample were retained.

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The sampling volume (Vsample) was closely equal to the water collected in the outflow

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container. And the TWA concentration of target compounds in water during the sampler

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deployment can be simply calculated by

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TWA concentration = mSPE/Vsample

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where mSPE is the mass of target compounds extracted on the SPE cartridge and can be

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determined by the chemical analysis described below.

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(eq. 1)

Field Deployment and Retrieval. To validate OP-SPE samplers for in situ sampling of

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pesticides in surface water, samplers were deployed in Jiulong River, the second largest river

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in Fujian, China (Figure S1 in Supporting Information). The catchment has an area of 14,700

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km2. Previous studies showed that the river was contaminated with nanograms-per-liter of

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pesticides, due to heavy agricultural activities in the Jiulong River basin.22,23 On October 16,

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2015, duplicate OP-C18 SPE samplers (~50 mL/d) were deployed at Jiangdong station

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(24°31′19.71″N, 117°47′09.94″E) in the Jiulong River for 10 d to detect acetanilide herbicides

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(alachlor, acetochlor, metolachlor, and butachlor). The water temperature during the

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deployment period was in the range of 24.5°C - 28.8°C. On May 8, 2018, duplicate OP-HLB

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SPE samplers (~90 mL/d) were deployed at the same station for 10 d to monitor commonly

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used herbicides (i.e., alachlor, acetochlor, metolachlor, butachlor, and atrazine). The water

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temperature fluctuated between 25.8°C and 30.2°C during the second deployment.

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For field deployment, the samplers were suspended and submerged ~20 cm below the

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water surface by nylon ropes fixed on a bridge. After deployment for designated time, all

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samplers were retrieved in good working condition (Figure S2). The samplers were

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immediately returned to the laboratory. The outflow containers were detached to measure the



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sampling volume. The samplers were then taken to do leaking and clogging check. Briefly,

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the samplers were used to sample deionized water for several hours and examined if their

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intake and outflow volumes were equal. At last, the SPE cartridges were detached and

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immediately taken to analyze target compounds.

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In order to compare with traditional spot sampling, 500 mL or 1000 mL of water

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samples were manually collected every 24 hours during the sampler deployment. The

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collected samples were immediately stored at 4°C until analysis.

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Chemical Analysis. For the first deployment, the recovered C18 cartridges were first

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rinsed with 5 mL of deionized water and dried with a nitrogen stream for 15 min.

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Subsequently, the cartridges were eluted with 15 mL of 50/50 (v/v) acetone/hexane mixture.

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The eluent was collected and condensed to near dryness (0.2~0.5 mL) under a gentle nitrogen

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stream at 30°C. The extract was finally reconstituted in 400 µL of acetone/hexane mixture.

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The manually collected water samples (500 mL) were firstly filtered through glass fiber

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membrane filters (0.45 μm pores, 47 mm in diameter, Xinya Purification Equipment). Then

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the samples were passed through C18 SPE cartridges at a flow rate of 6 mL/min using a

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Visiprep SPE vacuum manifold (Supelco, Bellefonte, PA) to extract target compounds.

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Thereafter the cartridges were subjected to the aforementioned procedures to obtain final

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extracts in 400 µL of acetone/hexane mixture. For the second deployment, the recovered HLB

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cartridges from the samplers were subjected to similar procedures and the final extracts were

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brought to 200 µL of acetone/hexane mixture. The manually collected water samples (1000

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mL) were filtered and extracted with HLB cartridges. The final extracts were finally

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reconstituted in 200 µL of acetone/hexane mixture. One portion (2 µL) of the final samples

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was used for instrumental analysis to quantify pesticide residues. The extracts from the first

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deployment were analyzed on an Agilent 7890A gas chromatography (GC) coupled with an

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Agilent 5975C mass spectrometer (MS) (Agilent Technologies, Wilmington, DE). The


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analytes were separated on a DB-5MS column (50 m × 0.25 mm, 0.25 µm thickness; Agilent).

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The extracts from the second deployment were analyzed on a Trace 1300 GC coupled with an

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ISQ QD300 MS (Thermo Fisher Scientific, Rodano, Milan, Italy). A HP-5MS ultra inert

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column (30 m × 0.25 mm, 0.25 µm thickness; Agilent) was employed for the herbicide

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separation. The MS detectors were operated in selective ion monitoring mode. The other

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parameters for the GC-MS analysis are given in Text S1 (Supporting Information).

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Quality Assurance and Quality Control. The performance of OP-SPE samplers

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depends greatly on the working status of SPE cartridges and OPs. Prior to field deployment,

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samplers were tested to sample 500 mL or 1000 mL of deionized water spiked with target

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compounds and the recoveries of each target compound were evaluated. Prior to field

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deployment, 100 ng of acetanilide structural analog cyflufenamid (not registered for use in

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China) was preloaded on the cartridge to evaluate the stability of extracted compounds on the

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cartridges over the deployment course. The recoveries of cyflufenamid in samplers ranged

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between 85.0% and 108%, suggesting that the extracted compounds on the SPE cartridges

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were stable during the sampling period. One of the samplers in the first deployment was

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installed with two C18 cartridges in series and no breakthrough was observed. In addition, the

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average flow rate of each sampler during deployment was in close agreement with those

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measured before and after deployment. No leaking or clogging was observed for all samplers.

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Laboratory and field blanks were included during each trip to deploy or retrieve the samplers.

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No analytes were detected in any of the blanks.

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RESULTS AND DISCUSSION OP Performance. The semipermeable RO membrane is the core part of an OP. Six

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commonly commercial membranes were used to construct OPs and their pumping capacity

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was evaluated. The pumping rates of these OPs in the first day ranged from 10 mL/d



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(TW30-1812-100 membrane) to 94 mL/d (TW30-1812-100HR membrane), clearly

248

demonstrating that the membranes markedly influenced pumping capacity (Figure S3 in

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Supporting Information). This result could be easily explained by the fact that different

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membranes had different properties (e.g., hydrophilicity, structure, porosity, and thickness),

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which influenced the osmotic capacity.18 OPs with different pumping capacities may be

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further developed for various applications. The selection of RO membrane was based on the

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flow of OP-SPE sampler to be constructed. In this study, TW30-1812-50 membrane and

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TW30-1812-100HR membrane were selected to construct OP-SPE samplers with flow rates

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of about 50 mL/d and 90 mL/d, respectively.

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Besides pumping rate, the stability of pumping flow is very important for practical

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applications. However, the pumping rates for OPs constructed from all the membranes

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gradually decreased over time, especially for OPs with higher flow rates (Figure S3). For

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example, the pumping rate of the OP with TW30-1812-50 membrane steadily decreased from

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55 mL/d to 46 mL/d, showing about 16% of reduction in three days. And this situation

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became more prominent as the OPs were run for 7 d (Figure 3A). For the two OPs with

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TW30-1812-50 membrane, one OP’s pumping rate decreased from 51 mL/d to 29 mL/d,

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while the other one deceased from 44 mL/d to 30 mL/d, both showing more than 32% of

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reduction over the test course. Meanwhile, the solution conductivities in the inlet chambers of

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the two OPs steadily increased from 1.4 × 10-3 mS/cm to more than 6.3 mS/cm (Figure 3B).

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The estimated NaCl concentrations in the inlet chamber were increased from none to more

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than 3500 mg/L after 7 d of operation, clearly suggesting that Na+ and Cl- ions in the outlet

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chamber slowly transported across the membrane and accumulated in the inlet chamber. In

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fact, salt passage through RO membranes is a common phenomenon in the membrane

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industry. The passage amount is dependent on membrane age, chemistry, thickness, pore size,

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and charge density as well as osmotic gradient.24 The salt passage inevitably caused a steady


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decrease of osmotic gradient and thus the decline of pumping rate. Due likely to the same

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reason, Jannasch et al. also found that OPs constructed from commercial RO membrane

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suffered from severe effect of salt passage and failed to provide a reliable and smooth

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pumping rate.19

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Apparently, OPs with decreasing flow rates were not suitable for osmotic sampler

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construction. To solve this problem, we introduced ion-exchange resins into the inlet chamber

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of OPs to remove Na+ and Cl- ions. The resins used in this study were a mixture of strong acid

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cation and strong base anion exchange resins. Upon the addition of resins, the Na+ and Cl-

280

ions in the inlet chamber were trapped by the resins with the accompanying release of

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exchangeable ions H+ and OH-, which react to form H2O. Results apparently showed that

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solution conductivities in the inlet chamber were consistently kept below 1.4 × 10-3 mS/cm

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when resins were added into the OPs. More importantly, pumping rates became stable and

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only varied within a small range over the test course. For example, one of the OPs’ flow rates

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fluctuated between 50 mL/d and 56 mL/d (mean 53 ± 2 mL/d), and the other one fluctuated

286

between 47 mL/d and 58 mL/d (mean 52 ± 4 mL/d), both showing less than ± 8% uncertainty

287

(Figure 3). The total flows of the OPs in seven days were 361 mL and 369 mL, respectively.

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Like other OPs, the flow rates of OPs fortified with ion-exchange resins increased with

289

rising temperature (Figure S4). For example, the flow rates of an OP (50 mm i.d. chambers,

290

TW30-1812-50 membrane) were 36 mL/d at 10°C, 42 mL/d at 20°C, and 49 mL/d at 30°C,

291

showing about 16.7% of flow increase for every 10°C of incensement. The flow rates of

292

commercial Alzet OPs were also temperature dependent.19,20 The rise of temperature results in

293

the increase of water diffusion coefficient and may also modify the surface properties of RO

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membrane.19 Therefore, the flow rate of OPs needs to be measured at similar temperatures

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before use.

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OP-SPE Sampler Performance. Laboratory experiments demonstrated that the



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samplers were able to continuously draw a constant flow at the designed pumping rate. In

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addition, all the samplers demonstrated efficient extraction capacities for the target

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compounds spiked in water (Table 1). For example, the recoveries of alachlor, acetochlor,

300

metolachlor, and butachlor in the OP-C18 SPE samplers were between 85.5% and 103.7%,

301

with relative standard deviations (RSDs) being < 9.5%. In contrast, the recoveries of alachlor,

302

acetochlor, metolachlor, butachlor, and atrazine in the OP-HLB SPE samplers ranged from

303

84.3% to 114.6%, with RSDs less than 14.4%. The limits of detection (LODs) and limits of

304

quantification (LOQs) of the samplers were dependent on the sampling volume, concentration

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factor, and instrumental sensitivity. In this study, the designed sampling volumes were about

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500 mL for OP-C18 SPE samplers and 1000 mL for OP-HLB SPE samplers.The

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corresponding LODs and LOQs for each ananlyte are given in Table 1.

308

Both OP-C18 SPE and OP-HLB SPE samplers successfully measured some commonly

309

used herbicides in the Jiulong River. In the first deployment, the total sample volumes in the

310

two samplers were 552 mL and 505 mL, respectively. Except that metolachlor was not

311

detected, alachlor, acetochlor and butachlor were successfully measured by OP-C18 SPE

312

samplers (Figure 4). For example, TWA concentrations of alachlor, acetochlor, and butachlor

313

were 12.9 ng/L, 50.2 ng/L, and 34.9 ng/L in one OP-C18 SPE sampler, respectively, while the

314

corresponding concentrations in the other sampler were 19.3 ng/L, 34.3 ng/L, and 29.2 ng/L.

315

The relative percent difference (RPD) values between the two samplers were 40% for alachlor,

316

38% for acetochlor, and 18% for butachlor. In the second deployment, the total sample

317

volumes in the two samplers were 852 mL and 905 mL, respectively. Results showed that

318

atrazine, acetochlor, and metolachlor were measured by the OP-HLB SPE samplers (Figure

319

5). The measured concentrations for atrazine, acetochlor, and metolachlor in one OP-HLB

320

SPE sampler were 10.3 ng/L, 25.3 ng/L, and 12.0 ng/L, respectively, and were 22.6 ng/L,

321

38.6 ng/L and 26.2 ng/L in the other OP-HLB SPE sampler. The RPDs between the two


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OP-HLB SPE samplers were 75% for atrazine, 42% for acetochlor, and 74% for metolachlor.

323

Most of the RPDs for the measured herbicides from the samplers failed to meet the traditional

324

acceptance criteria (≤30%) in water analysis.25 However, it should be noted that the RPDs

325

(18%-75%) in this study displayed the overall uncertainties including sampling, sample

326

preparation, and the final instrumental analysis. At this stage, we still could not figure out the

327

reason that caused the high RPDs observed, especially for atrazine and metolachlor in

328

OH-HLB samplers. Therefore, a further investigation is needed to improve the reliability of

329

OP-SPE samplers in the future.

330

Field validation of the OP-SPE samplers was based on the comparison against daily

331

samples collected manually. For spot samples, it is obvious that the concentrations of detected

332

compounds varied considerably with sampling time (Figures 4 and 5). For example, the

333

measured concentrations in the first deployment ranged from < 10 ng/L to 40.8 ng/L for

334

alachlor, from < 5.4 ng/L to 72.5 ng/L for acetochlor, from < 2.2 ng/L to 31.7 ng/L for

335

butachlor (Figure 4). The detection frequencies of the acetanilide herbicides followed the

336

order butachlor (73%) > acetochlor (45%) > alachlor (36%) > metolachlor (0%). Apparently,

337

spot sampling may miss the detection of target analytes, especially for the compounds with

338

lower detection frequencies (e.g., alachlor and acetochlor in the first deployment). Therefore,

339

the measurements of these compounds from single or multiple spot samples at low-frequency

340

(e.g., daily, weekly, or monthly) could not provide accurate information on their occurrence in

341

the dynamic aquatic environment. To make a rough comparison between spot sampling and

342

OP-SPE sampler, the total daily spot samples were used to estimate the average

343

concentrations over the sampling period. The RPDs between the average sampler

344

concentrations and the average spot concentrations were 24% for alachlor, 47% for acetochlor,

345

59% for butachlor in the OP-C18 samplers, and 60% for atrazine, 116% for acetochlor, 62%

346

for metolachlor in the OP-HLB samplers (Figures 4 and 5). The observed high RPDs might be



Page 16 of 26

347

attributed to the inherent differences between spot sampling and OP-SPE sampler. The spot

348

samples provided instantaneous concentrations at a specific moment, while OP-SPE samplers

349

offered TWA concentrations over the sampling course.

350

Environmental Implication. Osmotic pumps with higher and stable flow rates were

351

successfully built using commercial RO membrane and by adding ion-exchange resins into

352

the inlet chamber of OPs. The OPs may be easily modified to achieve different pumping rates

353

(up to hundreds of mL/d) by using chambers with different inner diameters or different types

354

of RO membrane. The excellent performance of OPs built in this study suggests their

355

applicability for the construction of osmotic samplers.

356

This work also clearly demonstrated the potential of OP-SPE samplers for in situ

357

sampling of pesticides in surface water. The samplers used filters (0.45 μm) and SPE

358

cartridges, which are both recommended by United States Environmental Protection Agency

359

for the analysis of organic contaminants in surface water. Therefore, OP-SPE samplers

360

provide TWA concentrations of target contaminants in the aqueous phase over the sampling

361

period. The measured concentrations using OP-SPE samplers may be lower than those

362

determined by whole-water sample analysis (e.g., liquid-liquid extraction), especially for

363

water with high suspended particles and for hydrophobic compounds that have high affinity

364

for particles. However, the dissolved concentration measured by OP-SPE samplers may be

365

directly related to the bioavailable fraction and therefore is more useful for the ecological risk

366

assessment of target compounds.

367

Overall, the OP-SPE sampler is power-free, relatively simple to fabricate, cost-effective,

368

and easy to deploy. Except the filter membrane and SPE cartridge, most of the other parts can

369

be reused. When integrated with appropriate SPE cartridges, this approach is versatile and

370

may find widespread applications for in situ sampling of surface water under different

371

conditions, including poorly accessible locations. It is recommended to preload isotopically


Page 17 of 26


372

labeled target compounds on the SPE cartridges as field surrogates to monitor the

373

performance of the sampler.

374 375

ASSOCIATED CONTENT

376

Supporting Information

377

The detail parameters for GC-MS analysis, the map of the sampling station, photos showing

378

sampler deployment and retrieval, and figures illustrating the performances of OP.

379 380

AUTHOR INFORMATION

381

Corresponding Author

382

*E-mail: [email protected].

383

Notes

384

The authors declare no competing financial interest.

385 386

ACKNOELEDGMENTS

387

This work is financially supported by National Natural Science Foundation of China

388

(21577112), Xiamen Southern Oceanographic Center (14GQT58HJ28), and Science and

389

Technology Planning Project of Fujian Province (2015Y0041). The authors thank Kun Wang

390

and Lu Peng for their assistance in field sampling.

391 392

REFERENCES

393

(1) Zhang, J.; Zhang, C. Sampling and sampling strategies for environmental analysis. Int. J.

394

Environ. Anal. Chem. 2012, 92 (4), 466–478.

395

(2) Madrid, Y.; Zayas, Z. P. Water sampling: Traditional methods and new approaches in

396

water sampling strategy. Trac-Trends Anal. Chem. 2007, 26 (4), 293–299.



Page 18 of 26

397

(3) Vrana, B.; Allan, I. J.; Greenwood, R.; Mills, G. A.; Dominiak, E.; Svensson, K.;

398

Knutsson, J.; Morrison, G. Passive sampling techniques for monitoring pollutants in water.

399

Trac-Trends Anal. Chem. 2005, 24 (10), 845–868.

400

(4) Huckins, J. N.; Manuweera, G. K.; Petty, J. D.; Mackay, D.; Lebo, J. A. Lipid-containing

401

semipermeable-membrane devices for monitoring organic contaminants in water. Environ.

402

Sci. Technol. 1993, 27, 2489–2496.

403

(5) Balmer, M. E.; Buser, H. R.; Muller, M. D.; Poiger, T. Occurrence of some organic UV

404

filters in wastewater, in surface waters, and in fish from Swiss lakes. Environ. Sci. Technol.

405

2005, 39 (4), 953–962.

406

(6) Alvarez, D. A.; Petty, J. D.; Huckins, J. N.; Jones-Lepp, T. L.; Getting, D. T.; Goddard, J.

407

P.; Manahan, S. E. Development of a passive, in situ, integrative sampler for hydrophilic

408

organic contaminants in aquatic environments. Environ. Toxicol. Chem. 2004, 23 (7),

409

1640–1648.

410

(7) Petty, J. D.; Huckins, J. N.; Alvarez, D. A.; Brumbaugh, W. G.; Cranor, W. L.; Gale, R.

411

W.; Rastall, A. C.; Jones-Lepp, T. L.; Leiker, T. J.; Rostad, C. E. A holistic passive

412

integrative sampling approach for assessing the presence and potential impacts of waterborne

413

environmental contaminants. Chemosphere 2004, 54 (6), 695–705.

414

(8) Adams, R. G.; Lohmann, R.; Fernandez, L. A.; Macfarlane, J. K.; Gschwend, P. M.

415

Polyethylene devices: Passive samplers for measuring dissolved hydrophobic organic

416

compounds in aquatic environments. Environ. Sci. Technol. 2007, 41 (4), 1317–1323.

417

(9) Tomaszewski, J. E.; Luthy, R. G. Field deployment of polyethylene devices to measure

418

PCB concentrations in pore water of contaminated sediment. Environ. Sci. Technol. 2008, 42,

419

6086–6091.

420

(10) Fernandez, L. A.; Lao, W.; Maruya, K. A.; White, C.; Burgess, R. M. Passive sampling

421

to measure baseline dissolved persistent organic pollutant concentrations in the water column


Page 19 of 26


422

of the Palos Verdes Shelf superfund site. Environ. Sci. Technol. 2012, 46, 11937–11947.

423

(11) Lin, K. D.; Lao, W. J.; Lu, Z. J.; Jia, F.; Maruya, K.; Gan, J. Measuring freely dissolved

424

DDT and metabolites in seawater using solid-phase microextraction with performance

425

reference compounds. Sci. Total Environ. 2017, 599-600, 364–371.

426

(12) Meczykowska, H.; Kobylis, P.; Stepnowski, P.; Caban, M. Calibration of passive

427

samplers for the monitoring of pharmaceuticals in water-sampling rate variation. Crit. Rev.

428

Anal. Chem. 2017, 47(3), 204–222.

429

(13) Booij, K.; Robinson, C. D.; Burgess, R. M.; Mayer, P.; Roberts, C. A.; Ahrens, L.; Allan,

430

I. J; Brant, J.; Jones, L.; Kraus, U. R. Passive sampling in regulatory chemical monitoring of

431

nonpolar organic compounds in the aquatic environment. Environ. Sci. Technol. 2016, 50,

432

3–17.

433

(14) Booij, K.; Smedes, F. An improved method for estimating in situ sampling rates of

434

nonpolar passive samplers. Environ. Sci. Technol. 2010. 44 (17), 6789–6794.

435

(15) Huckins, J. N.; Petty, J. D.; Lebo, J. A.; Almeida, F. V.; Booij, K.; Alvarez, D. A.; Clark,

436

R. C.; Mogensen, B. B. Development of the permeability/performance reference compound

437

approach for in situ calibration of semipermeable membrane devices. Environ. Sci. Technol.

438

2002, 36 (1), 85–91.

439

(16) Coes, A. L.; Paretti, N. V.; Foreman, W. T.; Iverson, J. L.; Alvarez, D. A. Sampling trace

440

organic compounds in water: A comparison of a continuous active sampler to continuous

441

passive and discrete. Sci. Total Environ. 2014, 473-474, 731–741.

442

(17) Supowit, S. D.; Roll, I. B.; Dang, V. D.; Kroll, K. J.; Denslow, N. D.; Halden, R. U.

443

Active sampling device for determining pollutants in surface and pore water-the in situ

444

sampler for biphasic water monitoring. Sci Rep. 2016, 6, 21886.

445

(18) Jannasch, H. W.; Johnson, K. S.; Sakamoto, C. M. Submersible, osmotically pumped

446

analyzers for continuous determination of nitrate in situ. Anal. Chem. 1994, 66, 3352–3361.



Page 20 of 26

447

(19) Jannasch, H. W.; Wheat, C. G.; Plant, J. N.; Kastner, M.; Stakes, D. S. Continuous

448

chemical monitoring with osmotically pumped water samplers: OsmoSampler design and

449

applications. Limnol. Oceanogr. Meth. 2004, 2, 102–113.

450

(20) Gkritzalis-Papadopoulos, A.; Palmer, M. R.; Mowlem, M. C. Adaptation of an

451

osmotically pumped continuous in situ water sampler for application in riverine

452

environments. Environ. Sci. Technol. 2012, 46, 7293−7300

453

(21) Theeuwes, F.; Yum, S. I. Principles of the design and operation of generic osmotic

454

pumps for the delivery of semisoild or liquid drug formulations. Ann. Biomed. Eng. 1976, 4,

455

343–353.

456

(22) Song, W.; Lin, S. S.; Sun, G. D.; Chen, M.; Yuan, D. X. Simultaneous determination of

457

87 pesticides in river water and seawater using solid phase extraction-gas

458

chromatography-mass spectrometry. Chinese J. Chromatogr. 2012, 30 (3), 318–328.

459

(23) Zheng, S. L.; Chen, B.; Qiu, X. Y.; Chen, M.; Ma, Z. Y.; Yu, X. G. Distribution and risk

460

assessment of 82 pesticides in Jiulong River and estuary in South China. Chemosphere 2016,

461

144, 1177–1192.

462

(24) Bartels, C.; Franks, R.; Rybar, S.; Schieracn, M.; Wilf, M. The effect of feed ionic

463

strength on salt passage through reverse osmosis membranes. Desalination 2005, 184,

464

185–195.

465

(25) United States Environmental Protection Agency. Method 523: Determination of triazine

466

pesticides and their degradates in drinking water by gas chromatography/mass spectrometry

467

(GC/MS). EPA Document No. 815-R-11-002. February 2011.


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Table 1. Recoveries, limits of detection (LODs), and limits of quantification (LOQs) of the

470

analytes using OP-SPE samplers. Recovery, % a

LOD, ng/L

LOQ, ng/L

alachlor

85.5 ± 6.7

3.0

10.0

acetachlor

90.4 ± 8.5

5.4

15.0

metolachlor

103.7 ± 9.8

2.0

4.6

butachlor

96.3 ± 8.6

2.2

13.0

alachlor

84.3 ± 12.2

0.20

0.6

acetachlor

114.6 ± 10.0

0.20

0.6

metolachlor

107.3 ± 10.3

0.15

0.5

86.6 ± 9.1

0.20

0.6

105.9 ± 12.1

0.10

0.3

Sampler

Compound

OP-C18 SPE

OP-HLB SPE

butachlor atrazine 471

a

472

spiked with 40 ng/L of analytes, while the recoveries for OP-HLB SPE samplers were

473

assessed by sampling 1000 mL of water spiked with 1.0 ng/L of analytes. Results are given as

474

means ± standard deviations from triplaicate measurements.

The recoveries for OP-C18 SPE samplers were evaluated by sampling 500 mL of water



Page 22 of 26

476 477 478

Figure 1. Schematic diagram of the osmotic pump (OP) (A) and a typical OP assembly (B).

479

The numbers denote (1) pump housing, (2) inlet chamber, (3) reversed osmosis membrane, (4)

480

outlet chamber, (5) ion-exchange resins, (6) O-ring sealing, and (7) NaCl.


Page 23 of 26


Osmotic pump

Deionized water coil

SPE cartridge

Filter 482 483

Figure 2. Schematic diagram of the osmotic pump-solid phase extraction (OP-SPE) sampler.

484



Page 24 of 26

486 487

Figure 3. The changes of pumping rate (A) and conductivity (B) for osmotic pumps (OPs)

488

fortified with/without ion-exchange resins. Hollow symbols represent data from OPs without

489

ion exchange resins, while filled symbols from OPs with ion-exchange resins. The OPs had

490

50 mm i.d. chambers separated by TW30-1812-50 membrane (DOW).



494

Figure 4. The measured concentratons of alachlor, acetachlor, and butachlor in the Jiulong

495

River by spot samples and OP-C18 SPE samplers during October 16-26, 2015. ND denotes

496

that the concentrations were below dectection limits, with alachlor < 3.0 ng/L, acetachlor

A novel active sampler coupling osmotic pump and solid phase

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