JPH07119748B2 - Determination of trace bromine ions in seawater - Google Patents

Description

TECHNICAL FIELD The present invention relates to the quantitative analysis of trace bromine ions in seawater by ion chromatography.

<Prior art> Conventionally, when quantifying tens of ppm of bromine ions in an aqueous solution containing chlorine ions of 10,000 ppm or more like seawater, an iodine titration method using hypochlorite called a sodium formate method is used. Are known. This method is the same in principle, and various improved methods (Analytical Chemistry Handbook Revised 3rd Edition 198
1. Maruzen Co., Ltd., but both methods are near the limit of sensitivity for quantifying bromine ions of several tens of ppm,
Even a skilled person has a large error. Further, the measurement time also requires 2-3 hours for each sample. In recent years, the progress of ion chromatography, which is a field of liquid chromatography, has made it possible to analyze trace amounts of ions with extremely high sensitivity and accuracy.

However, in normal ion chromatography,
Since an electric conductivity detector is used, if the separation of bromine ion and chloride ion is incomplete, the peak of bromine ion will be on the shoulder of the peak of chloride ion, making it difficult to quantify. Moreover, it is very difficult to completely separate a sample containing 200 times more chlorine ions than bromine ions, such as seawater. There is a method of separating bromide and chloride using a mixed solution of sodium (Analytical Chemistry Vol. 29 P
239 ~ P242 (1980)). However, in order to separate the peaks of bromine ion and chlorine ion by this method, it is necessary to make the column length 1 m or more, and even in this case, the measurement time is about 1 hour.

Therefore, a simple and rapid analysis method is desired.

<Problems to be Solved by the Invention> An object of the present invention is to provide a method for carrying out quantitative analysis of a trace amount of bromine ion in seawater accurately and simply and more quickly than the conventional method as described above.

<Means for Solving the Problem> The present invention utilizes the ion exchange action, which is the separation mechanism of ion chromatography, to separate bromine ions and chlorine ions according to their dissociation constants, and thus the difference in their isoelectric points. The peculiar thing is that bromine ion has absorption in the ultraviolet,
Focusing on the fact that chlorine ions do not have absorption, this is a method of separating by ion chromatography by using a phosphate eluent having a small ultraviolet absorption. That is, the actual sample contains substances having an ultraviolet absorption much higher than bromine ions, such as trace amounts of nitrate ions and nitrite ions, and other unknown trace amounts of organic substances, in addition to chlorine ions and bromine ions. Therefore, a bromine ion and a substance having these ultraviolet absorptions are separated, and an ultraviolet detector that selectively detects only the bromine ion is used after roughly separating even if the separation of the bromine ion and the chlorine ion is incomplete. This enables quantitative analysis of a trace amount of bromine ions.

At this time, when chlorine ion and bromine ion are not separated, and only the substance having ultraviolet absorption is separated, the eluent is diluted with chlorine ion, and the baseline is greatly overscaled to minus, making it difficult to measure. Therefore, it is not preferable.

Hereinafter, the present invention will be described in detail.

The present invention uses an ion chromatograph, the main part of which is connected in series with a liquid feed pump, an anion separation column, and a detector in that order, in an alkaline salt solution of phosphoric acid that is being passed through the apparatus as an eluent. The sample is introduced into the sample to roughly separate chlorine ions and bromine ions in the anion separation column, and then only the bromine ion component is detected by the ultraviolet detector.

The packing material for the anion separation column is not particularly limited, but an anion exchanger having an exchange capacity of 0.005 to 1 meq, particularly 0.05 to 0.5 meq per 1 g of the packing is preferable.

If the exchange capacity is less than 0.005 meq, chlorine ions and bromine ions are difficult to separate, and if it exceeds 1 meq, it is not adsorbed and does not elute.

The alkaline salts of phosphoric acid used as the eluent include sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, and phosphoric acid. Examples of the monohydrogen phosphate or dihydrogen phosphate such as ammonium monohydrogen and ammonium dihydrogen phosphate can be mentioned, but in terms of economy,
The sodium and potassium salts of the monohydrogen and dihydrogen salts of phosphoric acid are preferred. In addition, it is preferable to use a mixture of alkaline salts of phosphoric acid in order to accelerate the elution of sulfate ions.

The alkali salt concentration of phosphoric acid is 1 to 10 mmol, especially 3 to 5
The millimolar range is preferred. If the concentration is less than 1 millimole, the elution time will take more than 1 hour, and if it exceeds 10 millimole, the bromine ion and the chloride ion will not be separated, which is not preferable.

The measurement wavelength of the ultraviolet absorption detector is 250 nm or less, preferably 190
nm to 200 nm. If it exceeds 250 nm, the sensitivity is poor and the conductivity detector is inferior, which is not preferable.

Hereinafter, the present invention will be specifically described with reference to examples.

<Example> Example 1 A sample solution is a solution prepared by diluting seawater to 1/50 with pure water. Next, as a device for ion chromatography, Model 11 manufactured by Dionix Co., Ltd., a UV-visible spectrophotometer UV-8 Model II manufactured by Toyo Soda Kogyo (KK) is used as a detector, and the measurement wavelength is UV195n.
m, sensitivity full scale 0.08. Column (diameter 4.6m
m, 5 cm in length) is filled with anion exchange resin IC anion PW manufactured by Toyo Soda Kogyo (KK), and the eluent is mixed with 4 mM sodium monohydrogen phosphate and 4 mM potassium dihydrogen phosphate at a ratio of 6: 4. Using the above liquid, flow at a flow rate of 1 ml / min and a pressure of 30 kg / cm ² . 100 μm of the sample solution was injected into an ion chromatography device to perform separation detection. The resulting chromatograph is shown in FIG. Bromine ions were detected with an elution time of about 8 minutes. Similarly measured bromine ion concentration 1p
The chromatogram of the pm standardized sample is shown in FIG. From FIG. 2, the bromine ion concentration was determined to be 64 ppm.

Example 2 A sample solution was prepared by dissolving 2 g of reagent grade sodium chloride manufactured by Company A in 100 ml of pure water, and further diluting it to 1/10 with pure water. The apparatus and measurement conditions were measured as in Example 1.
The chromatogram obtained as a result is shown in FIG. Similarly, from Fig. 2, bromine in sodium chloride is 30 ppm.
Was quantified.

<Effect> As described above, the present invention uses only bromine ions as compared with the anion analysis method in seawater by ion chromatography using the electric conductivity detector described above, but the sensitivity is 20 times or more. The analysis time is high and the analysis time can be reduced to about 1/15.

[Brief description of drawings]

1 and 3 are chromatographs obtained by separating bromine ions in a sample, and FIG. 2 is a chromatograph of a standard sample of bromine ions.

Claims (1)

[Claims] 1. Sea water is introduced into an anion separation column packed with a packing material having an ion exchange capacity of 0.005 to 0.5 milliequivalent / g as an eluent of an alkaline salt solution of phosphoric acid having a concentration of 1 to 10 millimoles. A method for the determination of trace bromine ions in seawater, which comprises detecting bromine ions separated by an anion separation column with an ultraviolet detector.