福岡県保健環境研究所年報第29号，101−105，2002

原著論文
FLOW INJECTION ANALYSIS OF ALKALINITY

Takahiko MATSUEDA and Okihiro OISHI
A flow-injection system (FIA) was described for the simple and rapid determination of alkalinity in fresh water.
The method was based on the dependence of fluorescein’s fluorescence intensity on pH, which was related to theconcentration of alkalinity in the carrier solution.
The sample solution was injected into a flow system, which was comprised of reservoir, pump, line sampler, coiland fluorescence detector and the fluorescence intensity of the fluorescein was measured. The excitation andemission wavelength was 490 nm and 517 nm, respectively. The limit of determination was 0.5 mg/1 of alkalinity
as CaCO3. A sampling rate was 80 samples per hour. The relative standard deviation was 4.5 %. The dominantconstituents in natural water did not interfere the determination of alkalinity. The results by the proposed method
agreed well with those obtained by the titration method.

〔Key Words: Alkalinity, Flow injection analysis, fluorescein, Fluorometric detection〕
1 INTRODUCTION

FIA system employing

a spectrofluorometricdetector

Alkalinity is a fundamental parameter of natural water, andconnected to a flow cell. This method was based on the pH

the determination of alkalinity is useful for the control ofdependency of fluorescein’s fluorescence intensity in aphysico-chemical and biological parameters in the treatment

carrier solution. Results using proposed method wereofcompared with those obtained by the titration method.

naturalwater

supplies.

Recent1y,naturalwater

acidification has become a serious environmental problem
throughout the world. Acidification is monitored by means

2 MATERIALS AND METHODof measuring pH and alkalinity. Therefore, a rapid and2・ 1 Reagents

simple method is important for the analysis of alkalinity in

The fluorescein disodium salt (uranine) used was of firstfresh water including drinking water, river wavter, and lake

reagent grade (Wako Chemicals). A fluorescein stockwater. Alkalinity is a measure of the contents of weak bases

solution of 2.5×10 −(mainly bicarbonate ion, carbonate ion, and hydroxideof fluorecein disodium salt in one liter of distilled water. Thecompounds) and is most commonly measured by titrationcarrier solution was prepared as follows: 1 ml of stock(l~3)5)

M was prepared by dissolving 0.94g

solution and 500 ml of 0.86 M sodium chloride solution

with strong acid . Other methods are also available, such as4)36)

ion-selective electrode , ion exchange , ion-chromatography ,were mixed, and the pH was then adjusted to 5.2 with 0.01

and gel chromatography. There is a growing demand for fast,

M hydrochloric acid solution, then7)

the final volume wasautomated measurement methods. F. Canete et al. reported

adjusted to 1000 ml. Standard alkalinity stock solution

an automated flow injection method based on the acid-basecomposed of CaCO3 at 0.01 M (1060 mg/l)

reaction and spectrophotometric detection. Other automatedby dissolving 1.06g of sodium carbonate in 1000ml of

methods have also been reported

8~10)

distilled water. The exact concentration of alkalinity was. This paper reports amethod for the determination of alkalinity by means of a
福岡県保健環境研究所（〒 818-0135

were prepared

determined by titration with 0.02 M H2SO4.

福岡県太宰府市大字向佐野 39）- 101 -2・ 2 Apparatus

3・ 1 Effect of Coil length and flow rate on theThe system was comprised of the following components: afluorescence intensity of fluorescein in carrier solution

peristaltic pump (Atto Perista mini pump model SJ-1211

Effect of coil length was studied with the injection ofJapan), a line sampler (Kyowa Japan), and a fluorescence

0.25×10 − 5 M sodium carbonate solution. The results arespectrophotometer (Simazu RF-530 Japan) equipped with ashown in Figure 2. the peak height slightly decreased as theflow cell of l0 µl. The diameter of the reaction coil (Teflon)

length of the reaction coil increased from 0.5 m to 2.5m. On

was 0.8mm. The excitation and emission wavelengths werethe other hand, as shown in Figure 3, a significant decrease

490 nm and 517 nm, respectively. The analytical manifold isin peak height and a broadening of width were observed

shown in Figure 1.

with an increasing flow rate of more than 1.5ml/min. Thus
we set the flow rate at 1ml/min and the coil length at 1.5Eml/min.

AC

B

DG120

F100

Fig.1 Manifold for the determination of alkalinity

80
Peak height (mm)

A:Reservoir B:Pump C:Line sampler D:CoilE:Fluorescence F:Detector F:Recorder G:Drain2・ 3 Procedure
The carrier solution (pH 5.2) was pumped at flow rate of604020

1.5 ml/min. Five µ1 of the sample was injected manually0with a line sampler into the carrier stream. The increase inthe emission intensity at 517 nm, owing to the dissociation

heightcanberelated

to

the0.51.0
1.5
Coil length (mm)

2.0

2.5

3.0

Fig.2 Effect of coil length
Fuluorescein concentration:0.25X10-5 M
pH:5.3, HCO3:10-3M, Injection volume:5μlof fluorescein by the alkalinity, was measured. The peakmeasured0alkalinity

concentration as CaCO3. The recommended conditions for3・ 2 Effect of pH on the fluorescence intensity ofthe determination of alkalinity are listed in Table 1.

fluorescein in carrier solution
In order to identify the effect of pH on the fluorescence

Table 1 Recommended conditions for determination of alkalinity
by flow injection method
Recommended condition
Conditions
1.5
Coil length (m)1Flow rate (ml/min)Concentration of carrier solution (M)Concentration of sodium chloride (M)

0.25×100.43

pH of carrier solution

5.2

Diameter of coil (mm)0.8

Excitation wave length (nm)490

Emission wave length (nm)517

intensity of fluorescein in the carrier solution, the following
experiment was performed. The initial pH value of thecarrier solution was maintained at 4, and that of the carrier-5solution in a reservoir was adjusted by dropping dilutedhydrochloric acid solution ranging from pH 4 to 8.5 stepwise.
The fluorescence intensity was measured at each pH byusing the FIA system described in Figure 1. The results are

3 RESULTS AND DISCUSSIONillustrated in Figure 4. The increase of pH, the cause of the- 102 -3・ 3 Effect of initial pH of the carrier solution on theAfluorescence intensity of fluorescein
The effect of initial pH of the carrier solution on thefluorescence intensity were studied by means of injecting

Ｂ

0.25×10 − 5 M sodium carbonate solution. As shown inＣFigure 5, the peak height increased with an increase of pH in
the range of 3.8 to 4.8. Maximum and constant peak heights
were obtained in the pH range from 4.8 to 5.5.
On the other hand the peak broadened and tailed with theD

increase of pH. It was presumed that the increment of pHE

causes the decrease of the reaction rate between the carrier
solution and carbonate ions. The most suitable pH of thecarrier solution was 5.2 which was chosen for all

Fig.3 Effect of flow rate on the peak widthof flow signals

experiments regarding the determination of alkalinity.

A:0.5〜1.5 B:2.0 C:2.5 D:3.0 E:3.5
Units:ml/min
120

change of fluorescence intensity due to the dissociation offluorescein (which acts as a proton donor), caused a change

100Peak height (mm)of fluorescence intensity.
We applied this phenomena to the determination foralkalinity.

806040202000Peak height (mm)15034567Fig.5 Effect of pH of carrier solution on the determinationof alkalinity
100

Fuluorescein concentration:0.25X10-5 M
HCO3:10-3M, Injection volume:5μl,coil
length:1.5m

50

3・ 4 Effect of diverse ions on the determination of0456pH

78alkalinity

9The effects of diverse ions on the determination of 50 mg/1

Fig.4 Effect of pH on the fuluoresce intensity of fuluoroscein
Fuluorescein concentration:0.125X10-5 Mof CaCO3 alkalinity were studied. The experimental results

HCO 3:10-3 M, Injection volume:5μl

are shown in Table 2. Most cations and anions in thepresence of 0.005M to 0.34M did not interfere with the- 103 -determination of alkalinity.

spectrophotometric titratation, and was 10 to 30 minutes for3・ 5 Calibration curve and precision

conventional methd (titration method). We achieved highFigure 6 shows typical traces obtained by repeatedthroughput for the analysis for alkalinity compaired with theinjectionsconventional method. The relative standard deviation for tenofstandard

alkalinity

solutions.

Alinearrelationship was observed between the peak height anddeterminations was 4.5% for 40 mg/l of CaC03 alkalinity.

alkalinity concentration in the range from 0.5 to 120mg/1 of

3・ 6 Comparison between

CaC03. The detection limit was calculated from flow trace

methodproposedand titration

The validity of the proposed method has been examined by

Table 2 Tolerable amounts of divers ions on the determinationof alkalinity

Added asTolerable amounts (M)analyzing synthetic samples and real samples which wereNaK+
Ca2+
Mg2+
NH4+

NaCl
KCl
CaCl2
MgSO4

0.34
0.090
0.00500.050

obtained from Fukuoka prefecture. The results of theNH4Cl

0.0090-NaCl
NaBr
NaI
Na2SO4
NaNO3
NaNO2

0.34
0.10
0.080
0.067
0.094
0.087

Ions+

Cl
BrISO42NO3NO2-

proposed method were compared with those of the titration
method.
The results are listed in Table 3. Based on fivemeasurements for each sample using the respective method,
the standard deviation was within 5%.
The values determined by the proposed method agreed wellwith those obtained by the titration method.

100Table 3 Determination of alkalinity in synthetic samples andnatural waters

80Samples
Synthetic samples 1

60
5min
40

Proposedmethod(mg/l)

Titration
method(mg/l)

28.9

29.5

Synthetic samples 2

22.3

22.5

River water 1

57.8

56.0

River water 2

40.3

39.5

Tap water

22.8

24.0

204 CONCLUSIONS
The determination of alkalinity in water samples wasachieved by means of the flow injection method employing aFig.6 Typical continuous signal traces for alkalinity

fluorescence detector. This method was based on theSample size:5μl

acid-base reaction between alkalinity and fluorescein (whichConcentration:20-100mg/ml as CaCO3

was an acid). Fivemicro-liters of the sample solution were(signal to noise ratio of 3) .

injected, and an increase in the fluorescence intensity of theThe sampling rate was around 80 samples per hour. Turner

fluorescein at 517 nm was detected. The dominant naturalet.al.11) reported that the analytical throughput was 30

water ions such as Na+, K+, Ca2+, Mg2+, Cl-, and SO42- did not

samples per hour using flow injection method with- 104 -interfere with the determination of alkalinity. The results of6) T. Hironaka, M. Oshima and S. Motomizu: Determination

the analysis of various water samples obtained using theof total carbonate-carbon in river water by ion

proposed FIA system corresponded closely to those bychromatography with photometrie detection, BUNSEKI

obtained by obtained using the standard titration method.

KAGAKU, 36, 503, 1987.

The proposed FIA system can provide a rapid and simple

7) F. Canete, A. Rios, M.D.L. de Castro and M. Valcarcel:analysis, with a high throughput of 80 samples per hour,Determination of analytical parameters in drinking waterrequiring no complicated operation.

byflow injection

determination

ofanalysis PartⅠ

SimultaneouspH,andtotal

alkalinity

ionic

concentration, Analyst, 112, 263, 1987.

REFERENCES

8) R.B.Willis ahd G.L. Mullins: Automated analysis forl) T.E. Larson and L. Henley:Determination of low alkalinity

water alkalinity, Anal. Chem., 112, 263, 1983.

or acidity in water, Anal. Chem., 27, 851, 1955.
2) J.F.J Thomas and J.J.J. Lynch: Determination of carbonate

9) E. Hillbom, J.Liden and S. Pettersson: Probe for in situ

alkalinity in natural waters, J. AM. Water Works Assoc.,

measurement of alkalinity and pH in natural waters :Anal.

52, 259,1960.

Chem., 55, 1180, 1983.
10)L.K.Shpigun, I.Ya Kolotyrkina, Y.A.Zolotov:Experience3) American Public Health Association; American Water
Works Association; Water Pollution Control Federation

withflow-injection

analysisinmarine“Standard Methods for the Examination of Water andresearch:Anal. Chim. Acta, 261,307, 1992.

chemical11)D.R.Turner, S.Knox and M.Whitfield :Flow injection

Waste water”, 15th ed.; American Public Healthtitration of alkalinity in natural waters:Anal.Proc., 24,360,

Association: Washington, DC, pp 253, 1980.

1987.

4) G.A.Rechnltz: Report 238490/7 GA U･ S. Natiional
Thechnical Information Service, 1974
5) H.Small, T.S.Stevens and W.C.Bauman: Novel ion
exchange chromatographic method using conductimetricdetection, Anal. Chem., 47, 1801, 1975.

アルカリ度のフローインジェクション分析
松枝隆彦，大石興弘

フローインジェクション法による天然水中のアルカリ度の簡易迅速な分析法を検討した。こ本法はフルオレスセインの蛍光強度のpH依存性を利用したもので、その強度はアルカリ度濃度と比例する。ﾌﾛｰ系はリザーバー、ポンプ、ラインサンプラー、コイル及び蛍光検出器より構成され、５μlの試料をﾌﾛｰ系に注入し、フルオレスセインの蛍光強度の変化を測定する。蛍光検出器の励起及び蛍光波長はそれぞれ、490nm及び517nmである。検出限界値は CaCO3 換算で0.5 mg/1、変動係数は4.5％であった。分析速度は１時間当たり80試料で操作は簡便である。天然水中に存在する Na+, K+,Ca2+, Mg2+, Cl-, 及び SO42-等のイオンはアルカリ度の測定に影響しない。本法の結果は滴定法の結果とよく一致した。

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