Determination of Water Content of Water-soluble Paints by Gas Chromatography

Journal of Donghua University (Eng. Ed.) Vol. 20 No.1 (2003) 77Determination of Water Content of Water-soluble Paints by GasChromatographyGU Run-nan (顾润南), QIN Wei-min (钦维民), XIAO Ge (肖舸)06 ACollege of Chenistry and Chemicul Engineering, Donghua University, Shanghai, 200051This paper describes the determination of watercontent ofwater- solublepaintsbygasExperimentalchromatography. The water in paints is extracted bydimethyl formamide ( DMF ) as a solvent.1 ApparatusIsopropanol is used as an internal standard. The(1 ) Gas chromatograph- Shimaza GC - 14A gasmixture is separated by low-speed centrifugation.chromatograph with a thernoconductivity detector is used.Then a 1-uL sample of theupernatant from the(2) Column- -The gas chromatographic column is 1.1 mprepared solution is injected into the gasof 3 mm outside diameter tubing of glass, packed with 60 ~ 80chromatograph. The water content is determined bymesh 401 porous polymer micro-ball.internal standard calibration curve. The rate of(3) Recorder- -A recording potentiometer with a fllrecovery of added standard of this method is morescale deflection of 1 to 10 mV, full-scale response time of 2 sthan 98%。Relative mean deviation is less than 3%.and sufficient sensitivity and stability may be used to meet theThe linearity of calibration curve is good andrequirements.relativity coefficient is higher than 0.998.(4) Liquid charging devices- -Micro-syringes of 1 μLKeywords : twater corutent, paints, gas chromatography.and syringe of 1 ,5 mL capacity may be used.(5) Septum sample vial- 5 mL(6) Electron balance- - +0. 000 1 g (Shimaza)Introduction(7) Graduated pipet- -1 mL, 2 mL(8) CentrifugeWith the improvement of people's living standard,2 Reagents and materialspurchase and decoration of houses have gradually come into(1) Disilled waterfashion. However, when entering a house which has just been(2) Dimetylormamide (A. R.)decorated， you will smell some odour caused by volatile(3) Iso-propanol (A. R. )organic compounds ( VOC) in paints. These VoC are not onlyAnalytical purity grade chemicals should be used in allstimulant 10 nose or eyes but also harmful to human body.tests.Some are even more carcinogens. With the popularity of green(4) Carrier gas- Hydrogen of 99.99% or higher purityconsuming concept, green building materials of environmental3 Determination methodmark have become the main stream of intemational markets'".(1) Preparation and deternination of a series of internalIn order to control the VoC content of paints, a set ofstandardsdetermination methods should be established. Because there areIn this method， iso-propanol is used as an intemalvarious kinds of VOC in a paint and there exist different formsstandard and dimethylformamide (DMF) as a solvent.of VOC in dflent paints, it is dffcult to analyze every VOCFirst, 0.2 mL iso-propanol and 2. 0 mL DMF are addedin paints. However, a water-soluble paint consists of threeinto each of five septum :1 sample vials. Then no water is addedparts: solid, water and VoC. If both solid and water contentinto the first vial, which is a blank. Finally with 1 mL syringeare known, VOC content in the paint can be calculated. Thand dfferent weighing method, 0.1, 0.2, 0.3 or0.4 g ofdeternination of solid content is eaily performed, thus thewater weighed to 0.1 mg is added respectively into each of theproblem is concentrated on how to determine the water contentother four vials. Each solution is shaked evenly.of a wate-soluble paint. Since traditional Karl Fischer methodA 1 μL aliquot of each above solution is injected into thefor water content is troublesome. And sometimes when thecolumn and the chromatogram is recorded. The retention ordermethod is used to determine the water content of paints, it isand approximate retention time are ( 1 ) water, aboutdifficult to obtain accurate results2). Based on the reference0.09 min, (2) iso-propanol, about 0. 388 min and (3) DMF,[3] and repeated experiments, a set of feasible, simple andabout 2. 85 min. (Fig. 1)convenient gas chromatographic methods to determine watercontent of water-soluble paints is established.中国煤化工Received Sep. 10 ,2001MYHCNMHG78Journal of Donghua University (Eng. Ed.) Vol. 20 No.1 (2003)added into a septum vial. 0. 6 g of water-soluble paint weighedto0.1 mg is added into the vial. Then the vial is sealed.0.09 min2) A centrifuge is used to shake the vial and facilitateiso-propanol0.388 minstting of solids.3) A 1 uL sample of the supernatant from the preparedsolutions is injected into the chromatographic column. The, DMFchromatogram is recorded. The chromatograpbic conditions2.85 min .used is described in Table 1.(4) Calculation of water content in paints:Fig. 1 Typical chromatogramBased on the raio of peak areas of water to iso-propanolTable 1 Condions of gas chromatographAnpo/A; on the chromatogram of the paint, the weight of waterin the paint (WH2o) may be obtained from the above standardDetectotThermal conductivity dector (TCD)Carier gasHydrogen (H2)curve or its linear equation. Then the percentage of waterFlow rate50 mL/ minconcentration in the paint can be calculated by means of theDetector curreat 100 mAfollowing equation:Temperature:H20% = Wipo/W, x 100Sample inlet200七Detector200CWhere WHyo = weight of water in the paintColumn140CSpecimen size1山w。= weight of paint.The intermal standard calibration curve is plotted (Fig. 2).Results and DiscussionHere the weight of added water in standards (Wuno) is theabscissa and the ratio of the area of water peak (Ao) to that1 Linearity of intermal standard calibrationof iso-propanol peak (A.) in the chromatogram of eachcurvestandard is the ordinate.According to chromatographic theories, if all experimentalconditions are constant, weight of a constituent is directly3.5proportional to the area of is corresponding peak. In this test,the constuent to be analyzed is water, so there exists the2.6relation: Wno = AH2o xfino where fhxo is the corection factor.Since a constant volume of the internal standard, iso-propanol,2(V,) is added into the sample, the following equation is1.5obtained:Wno =AmoxXfno = Anpo XJa2oxw,/W. =0. 5Ano xfngo x Vp,/ASfwhere P: = density of iso-propanol0.20. 30.40.5W, = weight of iso-propanolWHy0/gA, = area of iso-propanol peakf = correction factor of iso-propanolFig.2 Intemal standard calibration curveIn given conditions, fu2o, Pn,f are all constants and V;isSince the internal standard， iso-propanol， and thean accurate value, 0.2 m, so Wno∞Anpo/A, that is, thesolvent, DMF, are all analytical purity grade, not absolutelyanhydrous, the calibration curve plotted must include the pointweight of water is linear with the ratio of peak areas of water toof blank, or, the point of Wno = 0.0000g Therefore, theiso-propanol. If all reagents used are anhydrous, then An2o/A,calibration curve is a straight line without passing through the= a x Wgno, otherwise the blank value must be taken intoorigin of the coordinates, whose equation is:account. Thus the linear equation of the calibration curve is asAupo/A. = aWho +bfollowing:where, a, b are all constants.Ano/A, =axWn20 +b(3) Analysis of paints1) 0. 20 mL of iso-propanol and 2. 00 mL of DMF are中国煤化工YHCNMHGJournal of Donghua University(Eng. Ed.) Vol. 20 No.1 (2003) 79Table 2 Data 1 of intemal standard calibration curveFrom these data it is found that the reproducibility andprecision of this method is satisfactory, with a relative meanlo.2345deviation less than 3%.Wn2o/g 0.0000 0.1087 0.2098 0.3159 0. 40903 Test of added standard recoveryAno4780 38812 65 65790 300128 625In order to determine the feasibility of this method, the39203 45510 40666 38792 43 149test of recovery of added standard was made. After the paintAnpo/Aj 0.1219 0.8528 1.6145 2.3278_ 2. 9809was analyzed, water content of the paint was obtained, anFrom the data of Tablc 2, the regression linear equationaccurately known amount of standard sample, i.e. water, wasadded into the paint. Then this method was used to measureis:Ampo/A, = 7.0157W12o +0.1156the amount of the standard water added. The value ofRelativity cofficient:y = 0. 999measurement was compared with that of standard water actuallyTable 3 Data 2 of internal standard calibration curveadded. The rate of recovery of added standard could be4obtained.Whz2o/g 0.000 0.1216 0.2394 0.3441 0.4983Rate of added standard recovery = 0W"n2o/OWn2o xAn2O5 92142 48167971 103926 119 392100%31328 32326 31 671 34 30127 082where0W" n is the weight of standard water measured byAu20/A_ 0.1890 1.3141 2.1462 3.0298 4.4085this method.AWngo is the weight of standard water actually addedThe reression linear equation: Ampo/A, = 8. 341 6Wn2o +after the paint has been analyzed.0.2099 γ = 0.999Table 6 Test of added standard recoveryfound that the linearity of intemal standard calibration curve isSampleNBP -8 paintBory paintgood, y≥0.998, which is in agreement with the theory.Equation of intemal. y=7.8951x+ y = 9.0479%x +2 Test of reproducibility and precisionstandard calibration curve0. 034 430.09498In the past three years, hundreds of paints were analyzedwith this method. The results obtained were analyzed0.999 40.9997statistically to test the reproducibility and precision of thisAno/A:(y)1.756 31. 8295method. The results corresponding to the above two sets ofWn2o/g (x) .0.218 10.191 sdata are shown as follows:Table4 Data 1 of paint determination0Wr2o/g0.11100.121 7WhitePulongAfter adding standardgluepaintAn2o/A;2. 62052. 921 4w,/g0. 34580. 4269Afer adding standardAn2o/A,(asy) 1.39001.3921 1.3910|1.5331 1.5319 1.5343.Wn2o/g0.32720.3124Wz2o/g (asx) 0.18170.18200. 18180.202 1 0. 201 9 0. 2022Linear equationy=7.0157x +0.1560W"npo/g0. 10910. 1209H20(%)52.5452.63 52.57 47.34 47.29 47.36Rate of added standardMean of H2098. 2999.3452. 5847.33recovery (%)(%)Relative mean0.640.56After repeated tests of added standard recovery, it isdeviation( %)found that all rates of added standard recovery for this methodTable 5 Data 2 of paint determinationare over 98% .FloorTOA4 Points for attention about this methodIn order to eliminate errors caused by the fluctuation ofW,/g0. 507 70. 6350experimental conditions so as to make results more accurateAno/A.() |2.554 I 2.5382 2.5454 2.4599 2.44292.4511and reliable, the series of intermal standard solutions and theWa2o/g (x) 0.281 0 0.279 I 0.2800 0.2697 0.267 70.2687raint sample solution should be prepared and analyzedy=8. 3416x +0. 2099simultaneously.55.35 54.97 55.15 42.47 42.16 42.31Mcan of H20Conclusion55. 1642.31Rclative meanthod to determine the2.36.2.44中国煤化工wateras chromatography.THCNMHG80Journal of Donghua University (Eng. Ed.) Vol. 20 No.1 (2003)We tested the linearity of intemnal standard calibration curve,good, with a relativity cofficient higher than 0. 998.reproducibility and precision, rate of added standard recoveryfor this method. Based on hundreds of tests, the stisticalReferencesresults show:(1) This method has good reproducibility and precision,[1] Pfaender F K, Jonas R B, Stevens A A, et al, Enuiron Seiwith a relaive mean deviation less than 3%o;Tecknol, 1978. 12(4) ,438(2) This method is fast, convenient and reliable, with a[2] Housion T E, Poore M w, JAir Waste Managet Assoe, 1996, 46rate of added standard recovery more than 98% ;[3] Annual Book of ASTM Standards D3792 -91(3) The linearity of calibration curve for this method is中国煤化工MYHCNMHG