Sains Malaysiana 45(2)(2016): 237–245
Troubleshooting and Maintenance of High-Performance Liquid Chromatography
during Herbicide Analysis: An Overview
(Merumus Masalah dan Penyelenggaraan Kromatografi Cecair Berprestasi Tinggi
semasa Analisis Herbisid: Suatu Gambaran Keseluruhan)
TAYEB, M.A.*, ISMAIL, B.S., KHAIRIATUL-MARDIANA, J. & GOH CHOO TA
ABSTRACT
Glufosinate ammonium or ammonium salt (ammonium-(2RS)-2-amino-4- (methylphosphinato) butyric acid; C5H15N2O4P)
is a commonly used polar herbicide in Malaysia and present in a variety of environmental waters at the sub-ppb level.
Thus, glufosinate ammonium is analyzed in soil and water using high-performance liquid chromatography (HPLC),
which is a complex yet the most powerful analysis tool. HPLC is tremendously sensitive and highly automated and HPLC
instrumentation and machinery have improved over the years. However, typical problems are still encountered. HPLC
users and advanced learners require help in identifying, separating and correcting typical problems. All HPLC systems
consist of similar basic components. Although it is a modular system, trouble can occur in each component and change
the overall performance. Resolving these problems may be expensive. This review describes the different aspects of HPLC,
particularly troubleshooting, common problems and easy guidelines for maintenance.
Keywords: Glufosinate ammonium; HPLC; maintenance; troubleshoot
ABSTRAK
Ammonium glufosinate atau garam ammonium (ammonium-(2RS)-2-amino-4-(methylphosphinato) asid butirik;
C5H15N2O4P) adalah herbisid berkutub yang biasa digunakan di Malaysia dan hadir di dalam persekitaran air
pada kepekatan sub-ppb. Oleh itu, ammonium glufosinate dianalisis di dalam tanah dan air dengan menggunakan
kromatografi cecair berprestasi tinggi (HPLC) yang merupakan alat yang kompleks namun sangat jitu dalam menganalisis
herbisid ini. HPLC sangat sensitif dan automatik serta prestasinya sering dipertingkatkan dari semasa ke semasa. Walau
bagaimanapun, terdapat beberapa masalah sering dihadapi pengguna. Pengguna dan pengendali HPLC pada peringkat
lebih tinggi memerlukan bantuan dalam proses pengenalpastian, pengasingan dan membetulkan permasalahan yang
sering berlaku. Kesemua sistem HPLC terdiri daripada komponen asas yang sama. Walaupun ia adalah satu sistem yang
modular, masalah boleh berlaku dalam setiap komponen dan mengubah keseluruhan prestasi. Menyelesaikan masalah ini
mungkin memerlukan kos yang tinggi. Maka, ulasan ini menerangkan pelbagai aspek HPLC, terutamanya penyelesaian
masalah HPLC, masalah yang sering berlaku dan garis panduan yang mudah untuk penyelenggaraan.
Kata kunci: Ammonium glufosinate; HPLC; merumus masalah; penyelenggaraan
INTRODUCTION
Glufosinate ammonium (ammonium-(2RS)-2-amino4-(methylphosphinato) butyric acid; C 5H 15N 2O 4P) is
a broad-spectrum herbicide. It is non-persistent in the
environment because it is rapidly degraded in water,
principally in the presence of light (Awis et al. 2013).
High-performance liquid chromatography (HPLC) is the
widely used analytical technique in herbicide separation
for more than 35 years (Xiang et al. 2006). HPLC started
in the 1960s as high-pressure liquid chromatography.
By the end of the 1970s, the column materials and
instrumentation of HPLC improved. HPLC boomed in the
beginning of the 1980s. Since 2006, new terms for HPLC,
such as ultra performance liquid chromatography (UPLC),
rapid resolution liquid chromatography (RRLC), ultra
performance liquid chromatography (UFLC) and rapid
separation liquid chromatography (RSLC) popped up. In the
early twentieth century, liquid chromatography was initially
discovered as an analytical technique and was first used
as a method of separating coloured compounds. The name
‘chromatography’ is derived from chroma, which means
colour and graphy, which means writing. In 1906, Mikhali
S. Tswett, a Russian botanist used a rudimentary form of
plant pigments into pure constituents (Bliesner 2006).
HPLC utilizes differences in the distribution of compounds
into two phases: Stationary and mobile. The mobile phase
designates the liquid that flows over the particles and
the stationary phrase designates a thin layer created on
the surface of fine particles. The solubility in the phases
and the molecular size of each component in a sample
contribute to different distribution equilibriums under a
certain dynamic condition. Consequently, the components
moved at different speeds over the stationary phases and are
thereby separated from one another. The column, which is a
238
stainless steel tube, is packed with porous and superficially
porous particles. The mobile phase is constantly fed into the
column inlet at a constant rate by a liquid pump (Ravisankar
et al. 2012). A sample injector is located near the column
inlet and injects a sample. The injected sample enters the
column with the mobile phase. The components in the
sample migrated through it and passed to the stationary
phase. The column compound migrates only when it is
in the mobile phase. Therefore, compounds that tend to
be distributed in the mobile phase migrate faster through
the column, whereas those that tend to be distributed in
the stationary phase migrate slower. In this manner, each
component is separated in the column and sequentially
elutes from the outlet. Each compound that elutes from the
column is detected by a detector connected to the outlet of
the column (Ismail et al. 2015d; Neue et al. 2001a; Tayeb
et al. 2015b). A sampling valve with a loop is used to inject
the sample in the following mobile phase just at the head of
the separation column. In order to minimize unnecessary
system peaks and to maintain good peak shapes, samples
should be dissolved in a portion of the mobile phase. An
in-line filter or guard column is utilized to prevent the
contamination of the main column by small particulates
(Tayeb et al. 2015a). A pressure gauge is inserted in front of
the separation column to measure the column inlet pressure.
The separation column contains the necessary packing to
accomplish the desired HPLC separation.
TYPES OF HPLC
The following types of HPLC are generally used in analysis
and they generally depend on the phase system used in
the process.
NP-HPLC
Normal phase chromatography ( NP-HPLC ) separates
analytes based on polarity. Retention occurs through the
interaction of the stationary phases of the polar surface
with the polar parts of the sample molecules. From Figure
1 NP-HPLC uses a non-polar mobile phase, such as heptane,
hexane, cyclohexane, dioxane, ethyl acetate and a polar
stationary phase Sio2. The polarity of a solvent depends on
electronegativity differences. The electronegativity is equal
i.e. (0) means the solvent is non-polar, if the difference >0
but <2 then it is polar. The analytes are non-ionic medium
polar compounds and derivatives (Brandit & Kuppers 2002).
RP-HPLC OR RPC
Reversed phase chromatography (RP-HPLC) retention
occurs through the partition of the analytes between the
layer of the quasi-liquid stationary and the mobile phases.
Figure 2 shows the non-polar stationary phase consists
of n-octadecyl (RP-18), n-octyl (RP-8), ethyl (RP-2) or
hydrophobic polymers and the polar mobile phase consists
of methanol or acetonitrile/water or buffer. The RP-HPLC
has polar aqueous mobile and non-polar stationary phases.
Tetrahydrofuran and certainly dioxane are rarely used as
additives in RPLC. Analytes are non-polar to medium polar
compounds, such as hydrocarbons, alcohols, phenols,
amines, carboxylic acids and derivatives with hydrophobic
molecule parts and compounds with hetero-atoms (Ismail
et al. 2013; Wiklund et al. 2005).
SEC
Size exclusion chromatography separates particles based
on size. No interaction occurred between the analyte and
1. The mechanism of retention of the solute Ph-OH is shown in a typical normal phase chromatography
separation. The charged form binds to the surface of the polar stationary phase and competes for the same positions
with solvent molecules. If the polarity of the solvent is increased the more solvent molecules bind to the surface of
the stationary phase and the solute (PhOH) elutes faster since it remains relatively untrained
FIGURE
FIGURE 2. Reversed phase chromatography mechanism. The hydrophobic solute (nonpolar solute) binds to the surface of
the hydrophobic (nonpolar) C-18 chain. A more polar mobile phase is used for solute elution to occur. The polarity of the
mobile phase is decreased by changing its composition as elution progresses (gradient elution) to speed up the process
239
the gel surface. From Figure 3 large molecules elute faster
and elution slowed down as the molecules became smaller
(Cheng et al. 2000).
FIGURE
SEPARATION COLUMNS
The column is one of the important parts of an HPLC
instrument. Figure 5 shows the columns are constructed of
heavy wall or stainless steel to withstand high pressure (up
to 6000 bar) and the chemical action of the mobile phase.
Materials used for the construction of the connection tubing
are stainless steel glass and peak polymer. The internal
diameter of the analytical column is 1.0 to 4.6 mm, with
lengths of 15 to 250 mm. Most of the columns ranged from
10 to 30 mm. For exclusion chromatography, columns are
50 to 100 mm long (Charde et al. 2013; Ismail et al. 2015a).
3. Size exclusion chromatography
separation procedure
IEC
Ion exchange chromatography retention is based on the
attraction between solute ions and charged sites bound
to the stationary phase. Figure 4 shows cation exchange
chromatography where positively charged molecules are
attracted to a negatively charged solid support. Anion
exchange chromatography negatively charged molecules
are attracted to a positively charged solid support
(Stavrianidi et al. 2005).
FIGURE
5. Liquid chromatography system
PORE SIZE
Pore size of the packing material represents the average
size of the pores within each particle. The size of the
molecules to be analyzed determines the pore size: MW <
3000 selects pore size of 60 to 100 Ȧ; 3000 < MW < 10000
selects pore size of 100 to 130 Ȧ; and 10000 < MW < 20000
selects pore size of 300 Ȧ (Kaushal & Srivastava 2010).
SELECTION OF DETECTOR
FIGURE
4. Ion exchange chromatography
INSTRUMENTATION
DELIVERY SYSTEM OF MOBILE PHASE
Mobile phases generally consist of water, aqueous buffer
or mixtures of organic solvents with or without modifiers.
The mobile phase must be delivered to the column over
a wide range of flow rate and pressure. Ultra-sonication
remove dissolved air and other gasses from the solvent
(mobile phase). The capacity to generate a solvent
gradient is another desirable feature in the solvent
delivery system. Most of the time phosphate buffer
(0.05 M) was used for glufosinate ammonium analysis,
but it crystallized in the bottle and column capillaries,
sometimes driving to an over-pressure of the pump and
loss of analyte (Ismail et al. 2015c; Kirkland et al. 1998).
Thus, phosphate buffer was replaced with phosphoric acid
0.2% because it adapted to the column and the column
did not clog (Rathore 2003).
The detector is a very important part of HPLC. Selecting
the detector depends on the chemical nature of analytes,
potential interference, limit of detection required,
availability and/or cost of a detector. A sensitive universal
detector for HPLC has not been devised yet. Thus, selecting
a detector based on the problem is necessary (Iqbal et al.
2015).
UV DETECTOR
is an absorbance detector and provides good
sensitivity for light-absorbing compounds. The UV
absorbance difference in variable wavelength ranges for
UV-VIS-190-900 and the suitable wavelength based on the
compounds (Kima et al. 2015). Diagrammatic illustration
of a UV-VIS detector optical system is shown in Figure 6.
UV
VARIABLE WAVELENGTH DETECTOR
Figure 7 shows a variable wavelength detector with a
relatively wide-band pass which offers a wide selection of
ultraviolet (UV) and visible wavelength but at an increased
cost than other detectors (Kwok et al. 2005).
240
which allows for the monitoring of many wavelengths
at once.
FIGURE
6. Diagrammatic illustration of a UV-VIS
detector optical system
FIGURE
9. Diagrammatic illustration of a DAD
detector optical system
MAINTENANCE OF HPLC
is a costly and sensitive technique. Consequently,
equipment requires regular maintenance, thus,
reducing the cost of routine maintenance is necessary.
The equipment should be inspected weekly for leaks. A
system suitability test is necessary prior to any analysis.
Suitability test closely resembles the intended assay and
should be performed to ensure that the system is operating
within the established criteria. All hazards and safe
handling practices should be familiarized before using the
mobile phase solvents. The guidelines of the manufacturer
regarding use, storage and disposal should be followed.
The guidelines are normally provided in the material safety
data sheets. Maintaining the HPLC storage condition is an
important parameter. The system should not operate in a
cold room or refrigerated area. The ambient temperature
is 10 to 35°C and ambient relative humidity is 20 to 80%
(Pieter et al. 2015). The parameters may vary depending
on the manufacturers. A few basic assumptions to maintain
the HPLC are as follows: The acetone should not be used
as a solvent at 195 nm, the water should not be used as
a gradient to hexane, methanol and water should not be
mixed without degassing them, the solvent pH should not
exceed 13 on a silica base column, but proper upper limit
is pH=7, the system should be flushed with methanol or
acetonitrile after running the buffer, the organic solvents
should be filtered through the filter that is used for aqueos
solution, the column frits should not be changed while
pressure is still present, the pure cyclohexane should not
be pumped above 2000 psi and the mobile phase container
should not be tightly sealed. Finally, the instrument should
be frequently calibrated using the appropriate procedures
(Neue et al. 2001a; Ngwa 2010).
HPLC
HPLC
FIGURE
7. Diagrammatic illustration of a VWD
detector optical system
FLUORESCENCE DETECTOR
Compared with UV-Vis detectors, fluorescence detectors
offer a higher sensitivity and selectivity that allow for
the quantification and identification of compounds
and impurities in complex matrices at extremely low
concentration levels (Cimadevillal et al. 2015). Substances
can be determined using specific excitation and emission
wavelengths. Fluorescence detection is suitable for trace
analysis. Diagrammatic illustration of a FL detector optical
system is as shown in Figure 8.
FIGURE
8. Diagrammatic illustration of a FL
detector optical system
DIODE ARRAY DETECTOR
The photodiode array detector passes a wide spectrum
of light though the sample and then the light is separated
into individual wavelengths after passing through the
sample. The spectrum of light is directed to an array of
photosensitive diodes (Martin & Guiochon 2005). Figure
9 shows each diode can measure a different wavelength,
TROUBLE SHOOTING OF HPLC
Using a systematic approach is recommended in
identifying any problems when troubleshooting the HPLC.
The problems are categorized as baseline, chromatogram,
pressure-related, leakage, and auto sampler problems.
241
Tables 1-6 and Figures 10-14; Tables 7-9 and Figure 15;
and Tables 10-12 show and describe the possible causes and
solutions of regular baseline noise, irregular baseline noise,
baseline drift, split peaks, broad peaks, loss of resolution,
TABLE
Leak
smaller than expected peaks, no peaks, negative peaks,
non-cyclic noise-fluid path problems, non-cyclic noisedetector electronics problems and cyclic noise-detector
related problems and others, respectively.
1. Regular baseline noise (Figure 10; Neng et al. 2015)
Possible cause
Solution
Air in mobile phase, detector cell or pump
Temperature effect
Check system for loose fitting, change pump seals if necessary,
check pump for leaks, salt build-up, unusual noises
Flush system to remove air from detector cell or pump, degas
mobile phase
Reduce differential or add head exchanger
Pump pulsations
Incorporate pulse dampener into system
TABLE
2. Irregular baseline noise (Figure 11; Mut et al. 2015)
Possible cause
Solution
Air bubbles in detector
Install back-pressure device after detector
Mobile phase mixture inadequate or malfunctioning
Repair or replace the mixture or mix off line if isocratic
Detector cell contaminated (even small amounts of
contaminants can produce noise)
Air trapped in system
TABLE
Solution
Column temperature fluctuation
Mobile phase recycled but detector not adjusted
Gradient solvent B absorbs more than solvent A
At high lab temperatures (28°C) more base line
instabilities compared to lower lab temperatures
(22°C) when using ACN/ water or buffer gradients
and mixtures
Sample solvent incompatible with mobile phase
Contamination on guard or analytical column inlet
Guard column voiding
Injection disrupting equilibrium
Use heat exchanger before detector, Control column and
mobile phase temperature
Use new mobile phase when dynamic range of detector is
exceeded, reset baseline
Use base line subtraction, Try a new mobile phase
Higher temperatures can enhance the polymerization of
ACN resulting in building up of polymers. Filtration of ACN
- eluent with empore SDB-XC polystyroldivinylbenzol filter
4. Split peaks (Figure 13; Malviva et al. 2010)
Possible cause
Column blockage
Flush the system with viscous solvent isopropanol
3. Baseline drift (Figure 12; Neue et al. 2001b)
Possible cause
TABLE
Clean cell by flushing with 1N HNO3
Solution
Inject sample in mobile phase or change the solvent
whenever possible, inject samples in mobile phase
Change frit or replace column, use appropriate
restoration procedure
Check the guard, in-line filter, column inlet and all
associated tubing for blockage
Remove the defective guard and replace with a new one.
Allow the system to reach equilibration and repeat the
sample injection
Dissolve the sample in mobile phase, use weaker diluent
or make a smaller injection
242
TABLE 5.
Broad peaks (Liu & Lee 2006)
Possible cause
Solution
Extra column effects: Recorder response time too high or tubing
between column and detector too long or ID too large or detector
response time or cell volume too large or column overloaded
Reduce response time or use as short a piece of 0.007-0.010
inch ID tubing as practical or use smaller cell or inject smaller
column (e.g. 10 vs. 100 μL )
Column contaminated/worn out; low plate number
Replace new column with same type, flush old column with
strong solvent if new column provides symmetrical peaks
Peak represents two or more poorly resolved compounds
TABLE
6. Loss of resolution (Figure 14; Juan & Tauler 2003)
Possible cause
Solution
Mobile phase contaminated
Obstructed guard or analytical column
FIGURE
FIGURE
Change column type to improve separation
Prepare a new mobile phase
Remove guard column and attempt
10. Regular baseline noise
FIGURE
12. Baseline drift
FIGURE
13. Split peaks
11. Irregular baseline noise
FIGURE
TABLE
14. Loss of resolution
7. Smaller than expected peaks (Kirkland & Henderson 1999)
Possible cause
Solution
Detector time constant too large
Use smaller time constant
Detector attenuation too high
Reduce attenuation
Injection size too small
Vial problem
Use large sample loop
Make sure that the vial sits correctly in the auto sampler and
the needle is not obstructed when performing an injection
243
TABLE
8. No peaks (Leister et al. 2003)
Possible cause
Solution
No mobile phase flow
Start pump or check reservoir, loose fitting, salt build up, flush the
system with methanol or isopropanol
Wrong mobile phase or wrong standard
Remove column and inject acetone solution to make a peak
TABLE
9. Negative peaks (Figure 15; Ismail et al. 2015b)
Possible cause
Solution
All peaks negative due to wrong polarity
Reverse leads or change detector polarity
Mobile phase more absorptive than sample
components to UV web length
Use mobile phase that does not absorb chosen
wavelength
Sample solvent and mobile phase differ greatly
in composition (UV-detector)
FIGURE
TABLE
Adjust or change sample solvent
15. Negative peaks
10. Non cyclic noise-fluid path problems (Gupta et al. 2015; Liu & Lee 2006)
Possible cause
Column contamination
Contaminated mobile phase
Electrochemical detectors only, air
bubbles in reference electrode
TABLE
Solution
Flush the column with mobile phase and monitor the baseline, if the baseline
contains the same level of noise, even after changing the column than it
indicates that the noise is due to another cause such as solvent miscibility,
contaminated mobile phase or contaminated guards/in-line filter
Clean all solvent inlet filters in a sonic bath with 6N HNO3 and methanol
Remove reference electrode from the instrument and gently shake it to
dislodge the air bubble
11. Non cyclic noise-detector electronics problems (Hongxia et al. 2004)
Possible cause
Detector not stable
Contaminated detector flow cell
Reference electrode leak
Solution
The baseline will be stable once the detector is stabilized. After turning
the detector on, allow it sufficient time for it to stabilized
Clean the detector flow cell cleaned with a 50/50 v/v mixture of THF/
water, than 100% THF if the system is used in normal phase
ECD only-refer to the detector maintenance for repair
244
TABLE 12.
Cyclic noise - detector related problems and others (Hassan et al. 2013; Ngwa 2010)
Possible cause
Long term detector temperature
problems
Ambient temperature fluctuations
Solution
The heater cycles on and off to maintain the detector temperature.
Change the regularity of the on/off frequency to avoid baseline noise
Stabilized the air temperature around this instrument and allow the
system to return to equilibrium. If this is not possible replace the
instrument to a laboratory position where the detector is thermally
stable, avoid placing the instrument under direct sunlight
CONCLUSION
is probably the most universal type of analytical
procedure. Its application areas include monitoring the
pesticide level in the environment, glufosinate ammonium
in soil and water level and analyzing the air and water
pollutants, process control, forensic analysis, clinical
testing and biochemistry research. HPLC also ranks as one
of the most sensitive analytical procedures and is unique
because it can easily separate multi-component mixtures.
HPLC is made by a different complex component and it
is hoped that this article helps in maintaining the HPLC
system and avoiding common problems. The guidelines
assist in reducing the maintenance cost and ameliorating
the performance of the system. The entire review showed
the common troubleshooting procedures for all the
manufacturers.
HPLC
ACKNOWLEDGEMENTS
This study was supported by research grant No. 06-0102- SF 0827 & AP-2014-009 from Universiti Kebangsaan
Malaysia and the Ministry of Education (MOE), Malaysia.
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Tayeb, M.A.*, Ismail, B.S. & Khairiatul-Mardiana, J.
School of Environmental and Natural Resource Sciences
Faculty of Science and Technology
Universiti Kebangsaan Malaysia
43600 Bangi, Selangor Darul Ehsan
Malaysia
Goh Choo Ta
Institute for Environment and Development (LESTARI)
Universiti Kebangsaan Malaysia
43600 Bangi, Selangor Darul Ehsan
Malaysia
*Corresponding author; email: atayeb91@yahoo.com
Received: 27 August 2014
Accepted: 5 August 2015