In the rivers, samples are taken in the central area at a depth of 0.25–1 m [8, 24,
44, 53, 57, 64, 70]. It is recommended to account for the flow rate on the date the
sample is taken [28, 75, 118]. Samples of lakes are taken at the deepest point
[32]. The sample volume depends on the type of analysis to be performed. It usually
ranges between 0.5 and 4 L [8, 16, 24, 28, 32, 47, 51, 53, 54, 56, 57, 60–62, 64, 70,
73–76, 80, 83–85, 113, 117] although it can be greater [47, 48, 107, 112] or less
[45, 69, 72, 113]. To take samples of tap water, the water source is first allowed to
run for 1–30 min and then the desired amount is collected [17, 61]. In treatment
plants, the samples are taken at specific points according to the installed technology
[30, 56, 68, 72, 79, 83] and the objective of the analysis. Water from the entry and
exit points is essential [28, 47–49, 62, 66, 71, 74–77, 81, 86, 103, 106, 108, 110,
117].
The container into which the sample is collected is very important. There are
various types of containers for collecting water samples. The most widely used is
amber glass [7, 16, 50, 62, 63, 67, 69, 72–74, 76, 83, 87, 110, 112, 113] that is
recommended for the analysis of organic compounds [118]. Clear plastic ones
[45, 47, 53, 60, 106] are also used and are indicated for trace analysis [118]. Some
authors collect samples in stainless steel containers [32, 48, 66, 82] and then transfer
them to glass containers. Use of new containers is suggested, and reuse of those that
have contained contaminated samples, concentrated solutions, or fuels should be
avoided [118]. Glass containers are usually rinsed previously with acid [16, 117],
organic solvents [16, 48, 52, 66, 69, 73, 85, 112, 113], or only ultrapure water [5, 7,
16, 17, 48, 52, 57, 83, 105, 112]. It is suggested to coat the container prior to sample
collected, two to three times, with the water to be sampled [61, 118] and dry the
vessels in an oven after washing in order to reduce subsequent biological degradation [16, 112].
In the case of natural water, it is useful to describe the location of the sampling
points [8, 16, 28, 32, 33, 47, 57, 73, 81, 87, 88, 106, 107, 110, 113] and the dates or
periods of sample collection [8, 17, 28, 33, 60, 75, 87, 88, 105, 107, 108, 110, 113]
since changes in the meteorological conditions of the sampling site can induce
marked variations in the results.
Care must be taken to prevent sample deterioration or contamination before
running the analysis. Water samples are susceptible to changes due to physical,
chemical, or biological reactions that may occur during the time between sampling
and analysis [118]. The magnitude of these reactions depends on the chemical and
biological nature of the sample, the temperature, light exposure, the nature of the
container into which the sample is placed, the time between sampling and analysis,
and the conditions to which the sample is subjected (agitation or rest during
transport). Therefore, it is necessary to take precautions to minimize these reactions.
Ideally, the analysis should be conducted in the first 72 h after the sample is collected
[118]. The most common methods for preserving the sample are removal of
suspended material, control of temperature and pH, and the addition of reagents
that do not interfere with the subsequent analysis.
Removal of the suspended material allows exclusion of the particles that may
interfere with the extraction stage, in particular if this stage is executed in the solid
90
K. Isaac-Olivé et al.
44, 53, 57, 64, 70]. It is recommended to account for the flow rate on the date the
sample is taken [28, 75, 118]. Samples of lakes are taken at the deepest point
[32]. The sample volume depends on the type of analysis to be performed. It usually
ranges between 0.5 and 4 L [8, 16, 24, 28, 32, 47, 51, 53, 54, 56, 57, 60–62, 64, 70,
73–76, 80, 83–85, 113, 117] although it can be greater [47, 48, 107, 112] or less
[45, 69, 72, 113]. To take samples of tap water, the water source is first allowed to
run for 1–30 min and then the desired amount is collected [17, 61]. In treatment
plants, the samples are taken at specific points according to the installed technology
[30, 56, 68, 72, 79, 83] and the objective of the analysis. Water from the entry and
exit points is essential [28, 47–49, 62, 66, 71, 74–77, 81, 86, 103, 106, 108, 110,
117].
The container into which the sample is collected is very important. There are
various types of containers for collecting water samples. The most widely used is
amber glass [7, 16, 50, 62, 63, 67, 69, 72–74, 76, 83, 87, 110, 112, 113] that is
recommended for the analysis of organic compounds [118]. Clear plastic ones
[45, 47, 53, 60, 106] are also used and are indicated for trace analysis [118]. Some
authors collect samples in stainless steel containers [32, 48, 66, 82] and then transfer
them to glass containers. Use of new containers is suggested, and reuse of those that
have contained contaminated samples, concentrated solutions, or fuels should be
avoided [118]. Glass containers are usually rinsed previously with acid [16, 117],
organic solvents [16, 48, 52, 66, 69, 73, 85, 112, 113], or only ultrapure water [5, 7,
16, 17, 48, 52, 57, 83, 105, 112]. It is suggested to coat the container prior to sample
collected, two to three times, with the water to be sampled [61, 118] and dry the
vessels in an oven after washing in order to reduce subsequent biological degradation [16, 112].
In the case of natural water, it is useful to describe the location of the sampling
points [8, 16, 28, 32, 33, 47, 57, 73, 81, 87, 88, 106, 107, 110, 113] and the dates or
periods of sample collection [8, 17, 28, 33, 60, 75, 87, 88, 105, 107, 108, 110, 113]
since changes in the meteorological conditions of the sampling site can induce
marked variations in the results.
Care must be taken to prevent sample deterioration or contamination before
running the analysis. Water samples are susceptible to changes due to physical,
chemical, or biological reactions that may occur during the time between sampling
and analysis [118]. The magnitude of these reactions depends on the chemical and
biological nature of the sample, the temperature, light exposure, the nature of the
container into which the sample is placed, the time between sampling and analysis,
and the conditions to which the sample is subjected (agitation or rest during
transport). Therefore, it is necessary to take precautions to minimize these reactions.
Ideally, the analysis should be conducted in the first 72 h after the sample is collected
[118]. The most common methods for preserving the sample are removal of
suspended material, control of temperature and pH, and the addition of reagents
that do not interfere with the subsequent analysis.
Removal of the suspended material allows exclusion of the particles that may
interfere with the extraction stage, in particular if this stage is executed in the solid
90
K. Isaac-Olivé et al.