original paper determination of chloride in food grade

Original Paper

Determination of Chloride in Food Grade Salt

Yasushi NIINO,* Noriko SHIMIZU,* Hitomi NISIMURA** and Noboru OGATA*

Mercurometry (ISO 2481),potentiometry (ISO 6227),and argentometry (JTS) for determination ofchloride in common salt were studied as mutual comparison regarding the operation,error,time requiredand cost.Mercurometry was effected by pH and quantity of diphenylcarbazone.Excessive addition ofnitric acid caused a decrease in repeatability because of an increase in blank value and unstable colorat the end-point.Too little addition of nitric acid gave too little determination value.So addition of0.5 to 1.0ml of 2 N-nitric acid and preparation about pH 2 were recommended.The color of the end-point was changed by the quantity of diphenylcarbazon,but determination value was not affected.Aserious disadvantage in mercurometry was a disagreement of color with the color-matching solution,andthe instability of end-point color gave frequently some anxiety to ,the operator.

Repeatability in potentiometry in the ruled six combinations of electrodes was not different from others,but a combination of silver-ion selective electrode and calomel electrode gave relatively good accurate re-sults.Repeatability of titration was 1:potentiometry,2:argentometry,3:mercurometry in the other ofexcellence.But each standard deviation in the total operation of determination was nearly equal becausethe dilution error was greater than the titration error.The comparison of accuracy of each method wasobtained from the deviation from the standard value of the International Standard Seawater.The argen-tometry was the most accurate,the mercurometry gave lower value,and the potentiometry gave highervalue.

Time required for making a sample was about 25 min in mercurometry,about 30min in potentiometry,and about 20min in argentometry after pipetting the sample solution.The reagent cost,apparatus costand personnel expenses were estimated,and the total cost of argentometry was more reasonable thanmercurometry in spite of expensive reagent cost because the weight of personnel expenses was greaterthan reagents and apparatus cost.

1.INTRODUCTION

Analytical method for determination of chlo-

ride in food grade salt has been discussed inCodex Comittee on Food Additives under Codex

Alimentarius Commission since 1975.ISO 2481,mercurometric method for chloride determinationof sodium chloride for industrial use,was pro-

posed to CCFA in 1982,for food grade salt.Onthe other hand,argentometry (Mohr's method)

and potentiometric method based on ISO 6227are generally used for a standard analytical

procedure for common salt in Japan and someother countries.The authors have believed thatmercuric reagent should preferably be avoided

from the view point of mercuric pollution,al-thotigh a procedure of the waste water treatmentis established for prevention of the mercuric

pollution in Japan specially in food industries.The use of mercuric reagent is not acceptable in

the national sentiments.Moreover,we regardMohr's method the most simple,rapid and ac-

curate method.Therefore,we found the neces-sity of comparison of mercurometry,potentiome-try and argentometry on the accuracy,repeat-

ability,easiness of operation,time required,costof analysis and the others to revise ISO 2481 to

add argentometry as alternative method in chloridedetermination in food grade salt.

2.OUTLINES OF ANALYTICALPROCEDURES

2.1 Mercurometry (ISO 2481)Test sample solution: The sample salt is taken

out to weigh 100 g,disolved,filtrated by glassfilter and diluted in a 1,000 ml volumetric flask.

*Central Research Institute,The Japan Tobacco Inc.,Umegaoka,Midori-ku,Yokohama,Japan

**Odawara Experiment Station,The Japan Tobacco Inc.,Sakawa,Odawara,Japan

―136―

Y. Niino et al.: Determination of Chloride in Food Grade Salt 137

The test solution is prepared by taking 50 ml of

sample solution and dilution in a 500 ml volu-metric flask.

Titration: 25ml of the test solution is placed

in a conical flask,diluted to approximately 200ml,then added 3 drops of the bromophenol bluesolution and the nitric acid solution (2N) drop

by drop until the color changes from blue to

yellow.Further,3 drops of this acid and thesame volume of diphenylcarbazon solution

(0.5%) as the same volume as in the standardend-point matching solution are added.The

titration is carried out with mercury nitratesolution (0.1N) until the color matches the

mauve of the standard end-point matching solu-tion. The consumption of mercury nitrate solu-tion was about 40ml in common salt.

The standard end-point matching solution is

prepared by the same operation as in the abovetitration using 200ml of pure water.

2.2. Potentiometry (ISO 6227)Test sample solution:Chloride in the test

sample solution is contained above 12.5mg andthe volume of solution is adjusted to 50 ml.

Titration:Titration is carried out with silver

nitrate solution (0.1N),and the end-point isdetermined from the point of inflection on the

differential curve of the potential measuredby electrodes.The measuring electrode is asilver-electrode,chloride ion-electrode or silver

ion-electrode,and the reference electrode isa calomel electrode or mercury sulphate

electrode.2.3 Argentometry (Mohr's method by JTS

standard)

Test sample solution:The sample salt is takenand weighed to be 20g,dissolved and diluted in

a 500ml volumetric flask.The test solution is

prepared by taking 50ml of the solution anddilution in a 500ml volumetric flask.

Titration:20ml of the test solution is placedin a conical flask,diluted to approximately 40ml,and added 1ml of potassium chromate

solution (5%) as indicator.The titration iscarried out with the silver nitrate solution

(0.1N) until the color of reddish orange does notvanish any more even though the solution isstirred vigorously.

2.4 The standard solution in this experimentOn common salt,the same test solution was

used in the same series of the test which was

prepared by conformity with 2.3 argentometry asmentioned above.The International StandardSeawater was applied for the tests of accuracy.The test solution was prepared by weighing 200g

of the standard seawater (19.373g/kg) and dilu-tion to 2,000ml.The titrations were carried out

using 25ml of the test solution.The concentration of the mercury (II) nitrate

and silver nitrate solution were prepared ap-

proximately 0.1N.Consequently,the samplingerror should be a little,and the titration values

were about 17ml in common salt and about14ml in the International Standard Seawater,respectively.

3. PROCEDURE OF MERCUROMETRY

3.1 Effect of pHThe effect of pH was already reported by J.V.

Dubsky,1) I.Robert,2) and F.E.Klerke.3) The

pH recommended did not agreed with the onementioned in the above report,but determinationvalues were decreased in acidic solution.In this

Fig.-1 Effect of nitric acid in mercurometry.

(1) Titration values,(2) Difference of titrationvalue and blank.

138 Bull. Soc. Sea Water Sci. Jpn. Vol.39 No.3 (1985)

paper,the relation between the titration valueand the volume of added nitric acid was ex-amined by using 20ml of sodium chloride solu-

tion (0.1N),and the results were shown inFig.-1.The titration and blank value were in-creased with increase of added nitric acid simi-

larly as reported in the previous papers.Accuracy

was relatively good in 1 to 2ml of nitric acidwhose pH was about 2,but the increase of blankvalue was not preferable for repeatability.And

the color was unstable with increase of nitricacid in as Fig.-2.From these results,the

authors would like to recommend that thevolume of nitric acid should not be 3 drops but0.5 to 1ml and about pH 2.

As a supplementary experiment,a test samplesolution containing 25% of sodium glutamatewas titrated by mercurometry for a notice of the

effect of buffer action.The results were asfollows,and the error was not recognized.

non-added 60.54Cl%

added 60.56Cl%3.2 Effect of diphenylcarbazon

Changes of absorbance of the solution at theend-point were examined at 0.5 and 1 ml ofdiphenylcarbazon solution,and the results were

shown in Fig.-3.The absorbances were in-creased in the test solutions and decreased in the

blank solutions with lapse of time.The velocityof change of color was more remarkable in the

Fig.-2 Effect of nitric acid to color stabilityin mercurometry.

(1) 0.3ml,(2) 1.0ml.

case of addition of 1 ml.The color of the test

solution at the end-point was nearly reddish and

gradually changed to mauve,and the color of

blank solution was mauve and relatively stable.

Consequently,the strict agreement of color be-

tween test solution and color matching solution

was impossible.Therefore,the disagreement

and instability of color frequently gave some

anxiety to the operator.From these phe-

nomena,a comparison of determination value

Fig.-3 Effect of diphenylcarbazon to colorstability in mercurometry.

Test solution:(1) 1.0 ml,(2) 0.5 ml.Blank:

(3) 1.0 ml.(4) 0.3 ml.

Fig.-4 Effect of diphenylcarbazon to analyti-

cal results in mercurometry.

○ Member A,△ Member B,● ▲ Average.

Repetition: 8 times.


and repeatability were made by using the Inter-

national Standard Seawater by 2 members.Theresults were shown in Fig.-4.As a result,there

was no significant difference in each determina-tion by added volume of diphenylcarbazon in

spite of the above problems.

4. REPEATABILITY AND ACCURACY

4.1 Choice of electrode

Three kinds of measuring electrodes and twokinds of reference electrodes are ruled in ISO6227.The number of combination is six,the

values obtained were compared on accuracy andrepeatability.The results were shown in Fig.-

5.There was no significant differences on ac-

Fig.-5 Comparison of electrode combination.

Argent: Argentometry, AG: Ag electrode, AGS:

Ag selective ion electrode, CLS: Cl selective ion

electrode, CA: Calomel electrode,HG:Hg sul-

phate electrode, Repetition: 8 times,←→:±1σ

range.

curacy and repeatability according to the statisticestimation.

4.2 Comparison of argentometry and mer-curometry

The test solution of common salt and standardseawater were titrated by argentometry and mer-

curometry. At first,the tests were carried out intwo laboratories and by two operators, and thetitrations were carried out two times a day and

for four days in total.As these tests were madeby using the same solution, the dilution error

could be eliminated. The results were plotted inFig.-6 as the each datum, average,and the

standard value of standard seawater. Argentome-try was more excellent than mercurometry on

repeatability estimated by the standard deviation.At second, the test was carried out in two

laboratories, by six operators and by two times

of titration. As the dilution of sample was in-dependently done from the same sample, thistest included the dilution error. The results

were shown in Fig.-7 as the range of measuredvalues. Repeatabilities and reproducibilities ob-

tained from the data in Fig.-7.Mercurometry Argentometry

Repeatability 0.08% 0.06%

Reproducibility 0.13 0.15

Fig.-6 Comparison of error in argentometry

and mercurometry eliminated the dilu-

tion error.

---: Standard value of standard seawater,

Repitation: 8 times,•©•¨•}1ƒÐ range.


Fig.-7 Comparison of error in argentometry and mercurometry

included the dilution error.---: Standard value of standard seawater, Repetition: 2 times.

4.3 Miscellaneous problemsTime required for making a sample from the

preparation of test solution to the end of analysiswas as follows:

Mercurometry 25min

Potentiometry 30minArgentometry 20min

Mercurometry by ISO 2481 includes the followingextra operations compared with argentometry:1) Neutralization by nitric acid, 2) Comparison

of color, 3) Large titration value, 4) Use,of bigconical flask, 5) Treatment of waste water.In-crease of time required in potentiometry by ISO

6227 was mainly caused from the long stabiliza-tion time of potentiometer.

5. DISCUSSION

5.1 Comparison of repeatabilityThe standard deviations from all of the above

experiments on determination of solar salt were

shown in Table—1. Repeatability was 1: Po-

tentiometry, 2: Argentometry, 3: Mercurometry

in the order of excellence in the case of the data

excluded dilution error, but it was nearly equal

between mercurometry and argentometry in the

case of the data included dilution error. The

variation coefficients in each operation of dilu-

tion were estimated from the previous paper, 4)

and the standard deviations were shown in

Table-2 obtained from assuming the use of a

hand-operated burret at ISO 2481 (mercurome-

try) and an automatic one at JTS (argentometry).

The enlargement of the variation coefficient (ƒÐ/X)

might be caused from use of hand-operated

burret in ISO 2481 method and from decrease of

titration volume in JTS method.As a result,

each of the standard deviations was nearly among

three methods because dilution error was greater

than titration error.


Table-1 Standard deviations on determination of chloride in solar salt.

Table-2 Estimation of standard deviation in operation of dilution.

Table-3 The deviation from the standard value.

Ag: Silver electrode, AgS: Silver-ion selective electrode, ClS: Chloride-ion selective electrode, Ca: Calomel

electrode,Hg:Mercury sulphate electrode,"t" was obtained from t=X/ƒÐ•ãn,and t values showed a prob-

ability on the rightness of the hypothesis which the data from each method will be differed from the

standard value.

5.2 Accuracy

Accuracy of each method was compared with

the deviation of determination values from the

standard value of standard seawater.All data

were compiled in Table-3. The average and

confidence limits,which were calculated from

±3σ/√n,were shown in Fig.-8.

These results showed that argentometry was the

most accurate, mercurometry gave a little lower

value and potentiometry gave a little higher

value. The combination of silver-ion selective

electrode and calomel electrode gave relatively

accurate values in each combination. But we

should not come to an immediate conclusion

because the number of data was short and the

dilution error was relatively large as stated

above.

5.3 Cost of analysis

Argentometry and potentiometry were fre-

quently criticized about the high cost of analysisbecause of expensiveness of silver nitrate and

potentiometer.The cost of reagent was mostlydecided from silver nitrate.A comparison be-

tween mercurometry (ISO 2481) and argentometry (JTS) was shown in Table-4.

The cost of apparatus for a sample were esti-

mated as

mercurometry \ 71.3

potentiometry 113.0argentometry 80.0

which were obtained by assuming the durabilityas follows: glass vessels can be used 300 times,

dispenser, stirrer and burret can be used 3,000times respectively, electric apparatus can be used


Fig.-8 Deviation of determination value from standard seawater.

○: Average, ← →: Confidence limit, ARG: Argentometry, MER: Mer-

curometry, AG: Ag electrode, AGS: Ag selective ion electrode, CLS: Cl

selective ion electrode, CA: Calomel electrode, HG: Hg Sulphate electrode.

Table-4 Comparison of reagent cost.

Table-5 Characteristics of each method.

* The costs regarding reagent and apparatus.

30,000 times.

But personnel expenses are usually much

greater than the expenses of reagents and appa-

ratus in these kinds of hand-operation analysis.

Consequently,the cost of analysis should be

estimated from time required, and we estimated

as an example that a sample of the personnel

expenses was ••1,125 in mercurimetry,••900 in

argentometry, and ••1,350 in potentiometry.

As a result, the total cost of argentometry was

more reasonable than mercurometry in spite of

expensive reagent cost because the weight of

personnel expenses was greater than reagent andapparatus costs.

6.CONCLUSION

Mercurometry (ISO 2481),potentiometry (ISO

6227),and argentometry (JTS) for determinationof chloride in common salt were studied as

mutual comparison regarding the operation,error, time required and cost. Mercurometrywas effected by pH and quantity of diphenyl-

carbazon, whose effects were smaller than the


error originated from preparation of the test

solution.But the disagreement of color with

the color-matching solution and the instability of

end-point color gave frequently some anxiety to

the operator.The peculiarities of these methods

may be characterized as Table-5. But the

accuracies and repeatabilities in the total opera-

tion of determination were nearly equal because

the dilution error was greater than the titration

error.The total cost of argentometry was more

reasonable than mercurometry in spite of use of

expensive reagent because the personnel expenses

were much larger than the expenses of reagent

and apparatus.

Acknowledgment The examples of analysis wereobtained in cooperation with the members of CentralResearch Institute and Odawara Experiment Station,Japan Tobacco Inc.This manuscript has benefitted

from discussion with and comments by H.Yamanakaand T.Hashimoto,Japan Tobacco Inc.Theauthors thank these members.

REFERENCES

1) J. V. Dubsky and J. Trtilek, J. Mikrochem., 12,315 (1933)

2) I. Robert, Ind. Eng. Chem. Anal. Ed., 22, 553

(1936)3) F. E. Klerke, Anal. Chem., 22, 553 (1950)

4) N. Ogata, Kaisui Gakkaishi (Bull. Soc. Sea WaterSci. Jpn.), 24, 259 (1971)

和文要旨

食塩中の塩化物の定量

新野靖,清水典子,西村ひとみ,尾方昇

硝酸水銀滴定法(ISO2481),電位差滴定法(ISO

6227),および硝酸銀滴定法(日本専売公社法)によ

る食塩中の塩化物イオンの定量について,操作,精度,

所要時間,コストなどの面から比較検討した.硝酸水

銀滴定法は検液のpHとジフェニルカルバゾンの添加

量によって影響された.硝酸添加量は過剰になるとブ

ランク値を増加させ,また色調の不安定を生ずるし,

不足すると定量値が低くなるから,2N硝酸添加量

0.5～1.0mlとし検液を約pH2にすると適当であっ

た.ジフェニルカルバゾンの添加量によって終点の色

調は変化するが,定量の精度に影響しなかった.なお

硝酸水銀滴定法の欠点は終点色調と終点判定用基準液

の色調が一致せず,また終点の色調が不安定で分析者

にしばしば不安感を与える点にある.

電位差滴定法は規定されている6種の電極の組合せ

では相互に繰返し精度の差は認められなかったが,正

確さについては銀イオン選択電極とカロメル電極の組

合せで比較的よい結果をえた.滴定の繰返し精度は,

1:電位差滴定法,2:硝酸銀滴定法,3:硝酸水銀滴

定法の順に良好な結果をえた.しかし定量の全操作を

通じての標準偏差はいずれもほぼ同一になった.これ

は希釈誤差が滴定誤差より大きいためと考えられる.

各方法の正確さは国際標準海水の基準値からの片寄り

によって比較した.その結果硝酸銀滴定法が最も正確

であり,硝酸水銀滴定法はやや低い値を示し,電位差

滴定法はやや高い値を示した.

概略の分析所要時間は検液採取後で,硝酸水銀滴定

法25分,電位差滴定法30分,硝酸銀滴定法20分となっ

た.試薬コスト,装置コスト,人件費を試算したが人

件費が試薬コストおよび装置コストより高いために試

薬が高価な硝酸銀滴定法のほうが試薬の安い硝酸水銀

滴定法よりむしろ全コストとしては安くなった.

(Received Feb. 9, 1985)

original paper determination of chloride in food grade

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