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Biological Systems Engineering: Papers and
Publications
Biological Systems Engineering
2012
Evaluation of a rhodamine-WT dye/glycerin
mixture as a tracer for testing direct injection
systems for agricultural sprayers
Joe D. Luck
University of Nebraska-Lincoln, [email protected]
Scott A. Shearer
Ohio State University, Columbus, Ohio
Brian D. Luck
Mississippi State University, Starkville, Mississippi
Fred A. Payne
University of Kentucky, Lexington, Kentucky
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Luck, Joe D.; Shearer, Scott A.; Luck, Brian D.; and Payne, Fred A., "Evaluation of a rhodamine-WT dye/glycerin mixture as a tracer
for testing direct injection systems for agricultural sprayers" (2012). Biological Systems Engineering: Papers and Publications. Paper 405.
http://digitalcommons.unl.edu/biosysengfacpub/405
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TECHNICAL NOTE:
EVALUATION OF A RHODAMINE-WT DYE/GLYCERIN
MIXTURE AS A TRACER FOR TESTING DIRECT INJECTION
SYSTEMS FOR AGRICULTURAL SPRAYERS
J. D. Luck, S. A. Shearer, B. D. Luck, F. A. Payne
ABSTRACT. The purpose of this study was to provide valuable insight regarding the use of Rhodamine WT (red) dye as a
tracer for evaluating injected concentrations. More specifically, the effects of mixing the dye with glycerin to simulate the
viscosity of a pesticide (e.g., glyphosate) or injecting the dye/glycerin mixture into deionized (DI) versus tap water on
developing appropriate calibration equations were evaluated. Test results indicated that mixing the dye in a solution of
glycerin and DI water significantly affected absorbance measurements compared to the dye mixed solely in DI water. The
error in estimating absorbance was 7.4% between the two calibration equations. Therefore, any calibration curves must
include a solution containing glycerin to compensate for this. Absorbance results also indicated that potable tap water
could be used to simulate the spray carrier as opposed to the DI water. A calibration curve was developed for the
simulated pesticide (dye/glycerin/DI water solution) injected into the carrier (tap water) for solutions ranging from
2,000:1 (carrier:pesticide) to 500,000:1; an overall dilution range of 250:1. This dilution range exceeded typical pesticide
tank-mixed dilutions which were on the order of 11:1 for the application of glyphosate for corn or soybeans. The
regression model standard error for predicting the dye concentration based on absorbance measurements was 5.3x10-6.
Keywords. Pesticide application, Precision agriculture, Spraying equipment, Pesticides.
T
he development of variable-rate pesticide
application technologies has received significant
attention in recent years and could provide
solutions to various spray application errors.
Direct chemical injection, an alternative to tank mixing, is
one type of variable-rate technology that has been
extensively tested over the years. The chemical concentrate
and carrier are typically pressurized separately and
Submitted for review in January 2012 as manuscript number PM 9583;
approved for publication by the Power & Machinery Division of ASABE
in June 2012. Presented at the 2011 ASABE Annual Meeting as Paper No.
1111758.
The information reported in this paper (No. 12-05-003) is part of a
project of the Kentucky Agricultural Experiment Station and is published
with the approval of the Director. Mention of trade names is for
informational purposes only and does not necessarily imply endorsement
by the Kentucky Agricultural Experiment Station.
The authors are Joe D. Luck, ASABE Member, Assistant Professor,
Department of Biological Systems Engineering, University of NebraskaLincoln, Lincoln, Nebraska; Scott A. Shearer, ASABE Member,
Professor and Chair, Department of Food, Agricultural and Biological
Engineering, The Ohio State University, Columbus, Ohio; Brian D. Luck,
ASABE Member, Graduate Research Assistant, Department of
Agricultural and Biological Engineering, Mississippi State University,
Starkville, Mississippi; and Fred A. Payne, ASABE Fellow, Professor,
Department of Biosystems and Agricultural Engineering, University of
Kentucky, Lexington, Kentucky. Corresponding author: Joe D. Luck,
Department of Biological Systems Engineering, 206 L.W. Chase Hall,
University of Nebraska-Lincoln, Lincoln, NE 68583-0726; phone: 402472-1488; e-mail: [email protected].
combined in a mixing chamber ahead of the spray nozzle.
The two most common performance factors related to
direct injection systems are lag time (time delay between
injection and discharge) and mixing uniformity of the
chemical and carrier prior to discharge. Accurate methods
for evaluating direct injection system performance are
essential for the continuing development of these systems.
One method for performance evaluation utilizes
fluorescent tracer dyes which are injected into the carrier
stream. The resulting effluent concentrations are then
estimated based on absorbance measurement determined
by spectrophotometry. Preliminary calibration is typically
required to estimate effluent concentrations based on
absorbance measurements using mixtures of carrier and
dye concentrate at known concentrations. Smart and
Laidlaw (1976) conducted an evaluation of several
fluorescent dyes for use in environmental water tracing.
The study recommended either using either Rhodamine
WT (orange), lissamine FF (green), or amino G acid (blue)
dye for water tracing studies based on sensitivity, minimum
detectability, photochemical decay rates, and adsorption
losses.
More recently, researchers have chosen a variety of
fluorescent dyes to evaluate direct injection systems for
spray application. Xu (1993) utilized a red dye (Rhodamine
B) to assess the performance of a single nozzle direct
injection system for pesticide application (which
Applied Engineering in Agriculture
Vol. 28(5): 643-646
© 2012 American Society of Agricultural and Biological Engineers ISSN 0883-8542
643
determined an optimal detection wavelength of 522.5 nm
for the dye). Zhu et al. (1998a) used an oil-soluble tracer,
UVITEX OB, to evaluate lag time and mixture uniformity
for direct in-line injection sprayers. Mixture uniformity in
the supply lines and spray pattern from an injection sprayer
were evaluated by Zhu et al. (1998b) using a water-soluble
Acid Yellow 7 dye along with the UVITEX OB dye. In a
related study, Zhu et al. (1998c) studied factors contributing
to lag time on injection sprayers including: number of
active nozzles, boom size, travel speed changes, and
pesticide viscosity, where the UVITEX OB dye was also
used.
Sumner et al. (2000) developed a system using string
collectors to evaluate lag time on injection sprayers. Cotton
string collectors (typically used in aerial applications) were
used to collect a solution of Rhodamine-B dye which had
been injected into the carrier. Luck (2010) also used
Rhodamine B dye to evaluate the response characteristics
of a high pressure direct nozzle injection system.
Evaluating the effects of temperature and viscosity on
accurate metering of pesticides has also been identified as
an important component for evaluating direct injection
systems (Gebhardt et al., 1984). To compensate, some
researchers have utilized glycerin as a viscosity modifier
(Xu, 1993; Luck, 2010), however the effects of glycerin on
absorbance measurements to estimate these injected tracer
concentrations has not been well documented.
The goal of this study was to provide information
regarding absorbance measurements for tracers containing
glycerin solutions. Specific objectives were to 1) develop
calibration equations for predicting tracer concentrations
based on absorbance measurements, 2) determine the
effects of glycerin on absorbance readings, and
3) determine the effects of carrier type [deionized (DI)
versus tap water] on absorbance measurements.
MATERIALS AND METHODS
For the purposes of this project, glyphosate was used as
the reference pesticide because of its extensive use in U.S.
grain crop production. Glyphosate is a very popular
pesticide for no-till producers and others who grow
glyphosate-resistant crops. Because of EPA regulations,
producers must follow label rates when applying chemicals
which provide minimum and maximum tank-mix
concentrations. For instance, pre-emergence treatments for
corn and soybeans are allowed within a range of 710 to
1420 mL per acre of glyphosate mixed with 37.9 to 75.7 L
of water (Monsanto, 2002). The resulting minimum and
maximum allowable ratios of carrier to glyphosate would
be 107:1 and 27:1, respectively. By observing allowable
rates for treatments to glyphosate-resistant corn and
soybeans, the maximum allowable ratio of water to
glyphosate would be 10:1 (post-emergence soybeans) while
the minimum allowable ratio was 107:1 (pre-emergence
corn and soybeans).
Applications at concentrations above the maximum ratio
could result in crop damage (post-emergence treatments),
while applying at concentrations below the minimum ratio
644
would not be effective at controlling weed competition.
Therefore, the desired operating range for the proposed
direct injection nozzle was between 10:1 and 107:1, and as
such, it was necessary to measure concentrations over an
11:1 range to characterize the maximum and minimum
allowable carrier to glyphosate ratios.
A spectrophotometer (SPm) (Evolution 60, Thermo
Electron Scientific Instruments, LLC, Madison, Wis.) was
used to conduct the Rhodamine WT (RhoWT) dye
absorbance tests. The SPm essentially determines
absorbance readings of a given media by passing light
through a sample at a predetermined wavelength and
comparing the light intensity entering and exiting the
sample (Thermo Scientific, 2007). RhoWT dye was chosen
as the tracer because of its extensive use as a simulant for
direct injection systems.
All tests were conducted in a laboratory with a
controlled temperature ranging from 18°C to 21°C. RhoWT
dye was mixed (by volume) with DI water at
concentrations ranging from 1:1 to 1 ppm in 15-mL
centrifuge tubes. The tubes were sealed and mixed for 30 s
on setting 10 using a vortex mixer (Mini Vortexer, Thermo
Fisher Scientific Inc., Pittsburgh, Pa.). The tubes (sealed)
were allowed to set for 30 min to allow any air bubbles to
surface. A 1-mL cuvette was filled from each mixture and
placed in the SPm where three measurements were taken
per sample using DI water as the blank cuvette at a
wavelength setting of 522.5 nm (Xu, 1993).
Glycerin and DI water were mixed (73% glycerin, 27%
DI water by mass) to simulate the viscosity of glyphosate
(Luck, 2010). RhoWT dye was mixed into the glycerin/DI
water solution at concentrations ranging from 1:1 to 1 ppm.
Absorbance readings were then taken (three per sample)
with the SPm for the RhoWT/glycerin/DI water mixtures.
The RhoWT/glycerin/DI water solution at a concentration of 2000:1 was mixed with DI water and ordinary tap
(potable) water (KAWC, 2010) to produce dilutions from
2000:1 to 500,000:1. SPm measurements (three per sample)
were recorded and regression lines were fit to the data. A
linear regression analysis was performed using MS Excel to
develop calibration equations for predicting absorbance
based on the RhoWT concentrations. The standard errors of
the regression were calculated according to procedures
outlined by Haan (2002). SAS software was used to
determine if the trendline slopes were significantly
different using the proc glm procedure.
RESULTS AND DISCUSSION
A plot of the absorbance measurements versus RhoWT
concentrations is shown in figure 1. As expected, the SPm
was not able to record absorbance measurements for high
dye concentrations (above 50:1). Therefore, further
absorbance tests were limited to the linear range of the
response. The linear regression models were based on
Beer’s Law which has been discussed by others (Xu, 1993)
as a model for comparing tracer concentrations to light
absorbance. Beer’s Law essentially states that the
absorbance of a solution shares a linear relationship with its
APPLIED ENGINEERING IN AGRICULTURE
Figure 1. Raw absorbance data for concentrations of Rhodamine WT
dye in DI Water.
Figure 3. Results of linear regression on absorbance readings for
glycerin added to the RhoWT dye/DI Water mixture.
concentration, with zero absorbance at concentrations equal
to zero. Therefore, a regression model with a zero intercept
was developed from the absorbance data and is shown in
figure 2 with a model SE of 4.12 × 10-6 for RhoWT dye
concentrations ranging from 2000:1 to 500,000:1.
The absorbance test results for the RhoWT dye mixed
with DI water and glycerin/DI water are shown in figure 3.
Regression models for both solutions resulted in a good fit
(R2 of 0.999) with low SE values (0.009 for the RhoWT/DI
water and 0.01 for the RhoWT/glycerin/DI water). Results
of the SAS analyses indicated that the trendline slopes were
significantly different (p<0.0001), meaning that the use of
glycerin as a viscosity modifier affected the absorbance.
Comparing predicted absorbance values from the two
calibration equations in figure 3 produced a 7.4% error
when calculating absorbance based on these data.
Therefore, calibration equations should be developed from
a solution containing the appropriate amount of glycerin.
Absorbance tests results for the carrier type (DI water
vs. tap water) are shown in figure 4 with results of the
linear regression analyses. Results of the statistical analysis
in SAS indicated that the trendline slopes were not
significantly (p=0.37) different. Therefore, DI water was
not necessary as a carrier, and potable tap water (KAWC,
2010) could be used as a substitute.
A final calibration curve was generated for the simulated
pesticide (RhoWT/glycerin/DI water) that was injected into
tap water as the carrier (fig. 5). The resulting model had a
low SE value (5.3 × 10-6) for the range of concentrations
from 2000:1 to 500,000:1. This also provided an overall
dilution range of about 250:1, which exceeded the required
range of 11:1 for typical tank-mixed pesticide
concentrations.
Figure 2. Calibration curve for determining Rhodamine WT
concentration in DI Water based on absorbance.
Figure 4. Plot of data illustrating the effects of DI water vs. tap water
on absorbance readings.
28(5): 643-646
CONCLUSIONS
Test results showed that using glycerin as a viscosity
modifier to simulate pesticides significantly affected
absorbance measurements with a 7.4% error in absorbance
predictions using a calibration equation developed without
the addition of glycerin to the dye/water mixture.
Therefore, any calibration curve must include a solution
containing the desired concentration of glycerin to
645
Figure 5. Calibration curve for determining Rhodamine WT
concentration based on absorbance.
compensate for this. Absorbance results also indicated that
potable tap water could be used to simulate the sprayer
carrier as opposed to DI water. A calibration curve was
developed for the simulated pesticide (Rhodamine
WT/glycerin/DI water) injected into the carrier (tap water)
for solutions ranging from 2000:1 to 500,000:1, an overall
dilution of 250:1. This range far exceeded the desired range
of typical pesticide tank-mixed solutions which were
estimated to be approximately 11:1. The regression model
had a low standard error (5.3 × 10-6) in predicting the
Rhodamine WT/glycerin/DI water mixture concentration.
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APPLIED ENGINEERING IN AGRICULTURE