Scribd
Upload
87 views1 page

Soil Phosphorus Testing: ICP vs. Colorimetric

The document compares colorimetric and ICP methods for determining phosphorus concentration in soil extracts. It finds that ICP methods consistently yielded significantly higher phosphorus concentrations than colorimetric methods for most extractants, likely due to ICP detecting organic phosphorus. However, for Olsen P extractant, the colorimetric and ICP methods did not differ significantly, possibly because the alkaline nature of the extractant helped hydrolyze organic phosphorus. Studies with various soil types also found ICP methods yielded higher phosphorus values than colorimetric, with greater differences at lower phosphorus concentrations.

Uploaded by

parag parag
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
87 views1 page

Soil Phosphorus Testing: ICP vs. Colorimetric

The document compares colorimetric and ICP methods for determining phosphorus concentration in soil extracts. It finds that ICP methods consistently yielded significantly higher phosphorus concentrations than colorimetric methods for most extractants, likely due to ICP detecting organic phosphorus. However, for Olsen P extractant, the colorimetric and ICP methods did not differ significantly, possibly because the alkaline nature of the extractant helped hydrolyze organic phosphorus. Studies with various soil types also found ICP methods yielded higher phosphorus values than colorimetric, with greater differences at lower phosphorus concentrations.

Uploaded by

parag parag
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as DOCX, PDF, TXT or read online on Scribd
You are on page 1/ 1

Comparison of Colorimetric and ICP Methods of Phosphorus Determination in

Soil Extracts

The concentrations of P measured by the two methods were statistically analyzed. Mean
comparison showed that P amounts determined by ICP in Mehlich 3, water, and CaCl 2
solutions were significantly greater than those determined by colorimetric method (P <
0.05) in the study. The differences between P determinations by the two analytical
methods in the extractants were probably due to the presence of organic P, which was
included in ICP determination but not in colorimetric determination. The influence of other
factors such as the presence of colloidal particles on the P that was determined by the two
methods could not be ruled out. However, Olsen P determined by the colorimetric method was
not significantly different from the values determined by ICP (P > 0.05) probably because the
alkaline nature of this extractant enhanced the hydrolysis of organic P in the extract, thus
including organic P in the colorimetric determination of P.

It was established that ICP-MS consistently yielded significantly higher P concentrations


than the colorimetric method in both extraction tests (Ca and NahCO3), and the relative
differences were greatest in soils with lower P concentrations.

During the last years soil and plant laboratories have moved from colorimetry to
inductively coupled plasma (ICP) spectrometry to quantify phosphorous in soil and
plants (Sicoria et al. 2005). The main reason is the increasing critical attitude to the
colorimetric measurement due to the significant interference problems upon Р
determination in soils and plants, as well as the advantages of ICP–method related to the
fast measurement and the opportunity to simultaneously determine the main part of the
macro-and microelements, contained in soils and plants. Its adaptation and priority for soil
status evaluation is not trouble-free due to controversial results when compared to the
colorimetric method. We have expanded the studies in this sphere to obtain more
experimental results related to sample preparation methods and soil diversity. Several
profound studies comparing both methods for determination of total and mobile phosphorus
in various soils are known. Upon the test falling within the scope of North American
Proficiency Testing (NAPT) program conducted in 2001 and 2002, 18 laboratories used
the spectrophotometric method and 34 laboratories used the ICP–method (Sicoria et
al. 2005). In 40 samples ICP values for phosphorus, extracted by Mehlih 3 (Mehlih 1984)
exceeded the values determined by means of spectrophotometric method by 7.4 mg/kg on
average. Thus the ICP–method is not recommended for determination of standards for
phosphorus fertilizers. Pitman et al. (2005) compared phosphorus determined by ICP and
spectrophotometric methods in Mehlich 3 extract of 6400 soil samples and established a
significant correlation between both methods at Р concentrations exceeding 60 mg/kg, the P
determined by the spectrophotometric method was 80–90% of the phosphorus determined
by ICP–method. Sicoria et al. (2005) studied 1536 soils having various origins and found
significant differences between both methods. Values obtained by ICP are higher in most
cases, but a few samples showed the opposite result. According to Piersynski et al. (2005)
the ICP results for phosphorus contained in aqueous extracts of fertilizers were up to
15 % lower than those determined by the spectrophotometric method. The reasons for
these results are not clarified yet.

You might also like