Determination Of Total Halogen Content In Halogen-free Fluxes By .

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As originally published in the SMTA Proceedings.DETERMINATION OF TOTAL HALOGEN CONTENT IN HALOGEN-FREEFLUXES BY INDUCTIVELY COUPLED PLASMAAND SOME LIMITATIONS OF ION CHROMATOGRAPHYChristopher J. Pontius, George Kraeger, Ron Lasky, Ph.D., P.E.Indium CorporationClinton, NY, UScpontius@indium.com; gkrager@indium.com; rlasky@indium.comABSTRACTBrominated flame retardants (BFRs) are coming underheavy scrutiny due to increasing evidence of the risks theypose to the environment and human health. Therefore, it isimportant for industrial quality laboratories to follow robustmethods to assure commercial products meet the safetyrequirements established by the governing bodies of theworld. Currently, the most common method to determinehalogen content is oxygen combustion, followed by ionchromatography. The oxygen combustion test is widelyestablished in environmental as well as in industriallaboratories. One current accepted test method, EN14582,may under-report bromine and chlorine content by as muchas 65%. The use of inductively coupled plasma (ICP)methods of detection appears to resolve this discrepancy.Flux marketed as “zero intentionally-added halogens” wascombusted in a bomb calorimeter vessel under 30atm ofhigh-purity oxygen in the presence of 25ml of water. Theresultant solution was analyzed using both ionchromatography (IC) and ICP. The flux was found tocontain 10ppm of each element using both techniques.Samples were then spiked using a common flux additivecontaining chlorine and bromine, combusted in the samemanner, and analyzed. At a low concentration (15ppm Br,6ppm Cl), the average %recovery of Br was 60.7% by ICand 100.8% by ICP; the %recovery of Cl was 109.5% by ICand 84.8% by ICP. At a moderate concentration (150ppmBr, 65ppm Cl), the %recovery of Br was 25.5% by IC and86.9% by ICP; the %recovery of Cl was 81.8% by IC and104.2% by ICP. The effect of pH and buffering capacity ofthe absorbing solution was explored by ICP in an attempt tooptimize the sequestration of Cl and Br in the solution asstable oxyanions; however, the results of hypotheticallyoptimal solutions were no more accurate than those usinganalytical water as the absorbing solution. Additionally,thirty samples of flux containing 275ppm intentionallyadded organic bromine were combusted and analyzed usingthe techniques described. The average %recovery ofbromine by IC was 64.3% and 105.1% by ICP.Key words: Halogen, halogen content, measuring halogenINTRODUCTIONEN 14582(a) [1] is one of the most widely-employed testmethods for determining the halogen content of organicmaterials, worldwide. It calls for the utilization of an oxygenbomb combustion vessel to destroy organic matrices andconvert bound halogens to their freely-soluble halide form,which are then detected and quantified by ionchromatography (IC). IC is a very versatile technique in thatit can provide results for fluoride (F-), chloride (Cl-),bromide (Br-), nitrate (NO3-), phosphate (PO4-3), sulfate(SO4-2), and iodide (I-) in a single 30–45 minute analysisover a four to five order of magnitude concentration range.There are several caveats to EN14582, however. Selectionof the absorption solution is critical to method performanceand depends on the expected result; analytical-grade wateris used for very low concentrations of anions whilecarbonate or caustic solutions are used to neutralize highconcentrations. Each reagent you add to the absorptionsolution has the potential to increase the blank value foreach anion. EN14582 states that pure analytical-grade watermay be used as an absorption solution if the expectedhalogen and sulfate content is less than 10g/kg (10,000ppmor 1%). This recommendation does not hold up whenapplied to flux due to its high load of nitrogen, phosphorus,and sulfur-containing chemicals, which will also contributeto the overall acidification of the absorption solution. Thecombustion products from a 1g halogen-free flux samplehave been found to drop the pH of analytical-grade waterabsorption solution to below pH 1. This is undesirablebecause in an environment of high temperature, low-pH,and high partial-pressure of oxygen, halides can formoxyanions which will not be detected using common IC.Unfortunately, using absorption solutions with carbonate,bicarbonate, or hydroxides has the potential to introducelevels of halides greater than that which is in the sample.Silva, et al. suggested combining the results of IC with theresults of a sodium thiosulfate titration of hypochlorate(OCl-) to generate a total chlorine content (TCC) result [2].In the case of flux analysis, it is important to quantify allhalogens, and not just chlorine. To address the possibilitythat combusted flux samples have a high probability ofproducing oxyanions proportionate to the concentration ofhalides, and thus producing under reported values, we haveexplored the possibility of conducting the analysis ofchlorine, bromine, and iodine by inductively coupledplasma atomic emission spectroscopy (ICP-AES). Thedetermination of chlorine by this method is only possibleusing instruments with oxygen-free sealed optics, andfluorine must still be quantified by IC.Proceedings of SMTA International, Sep. 27 - Oct. 1, 2015, Rosemont, ILPage 349

EQUIPMENT AND REAGENTSCombustionA Parr 1108CL oxygen combustion vessel was used for allcombustions. This model resists corrosion by chlorine andbromine in excess of 1% of sample weight. It was operatedin accordance with the manufacturer’s recommendedoperating procedures. Silva, et al. theorized that the mostaccurate chlorine results would be generated using anabsorption solution which would maintain a pH of 10, thepKa of OCl-. Three molar strengths of KOH absorbersolution were evaluated for their ability to maintain a pHabove 10 and stabilize chlorine in the solution. The KOHwas verified to be free of significant chloride and bromide( 10ppm) prior to use by ICP.Anion-ICAnalysis was performed using a Metrohm 883 Basic ICsystem with a MSM suppressor module and O3/1.5mmol/L NaHCO3 at a flow rate of 0.7ml/min.This eluent has been selected because it maintains theelution order of common anions while reducing the elutiontime, facilitating quantitation of iodide. Separation utilized aMetrosep A Supp 5 250cm/4.0mm column and a MetrosepA Supp 4/5 Guard column. The calibration curve from0.01ppm to 10ppm was created using fresh dilutions from acustom NIST-traceable standard solution from InorganicVentures containing 1000mg/L each of F-, Cl-, NO2-, Br-,NO3-2, PO4-3, SO4-2, and I-. 20µL of standards and sampleswere injected using a Metrohm 863 Compact Autosampler.the beginning of the chromatogram. KOH absorptionsolutions were analyzed by ICP alone.All unspiked samples of flux with no intentionally-addedhalogens were verified to contain 10ppm or less ofbromine and chlorine by both IC and ICP, regardless ofabsorption solution. Samples spiked with 0.01%bromochloroacetophenone had a theoretical content of14ppm bromine and 6ppm chlorine. Samples spiked with0.1% bromochloroacetophenone had a theoretical content of147ppm bromine and 65ppm chlorine.Only samples using analytical-grade water as the absorptionsolution were tested using both analytical methods. Thesesamples produced inconsistent results when analyzed by IC.Using ICP, the results were more consistent and moreaccurate. At these Br/Cl levels, increasing molarity KOHabsorption solutions produced decreasingly favorableresults. All results are summarized in Table 1 (see end ofpaper for enlarged table).Table 1. Summary of experimental results and calculateddataICPAnalysis was performed using a Spectro Ciros system.Calibration was performed using 1ppm and 100ppm freshdilutions of the same standard solution used for anion-ICanalysis.SAMPLE PREPARATION1g portions of no intentionally-added halogens flux werecombusted under 30-35atm of ultra-high purity oxygen. Theproducts were absorbed in 25ml 18.2MOhm analyticalgrade water; this is the maximum volume of absorbingsolution that could be added to the combustion vesselwithout compromising the sample. The effect of increasingCl/Br concentration was investigated by spiking acetophenone in tetraethylene glycol dimethylether to maintain the flux matrix. Additional data werecompiled from routine quality control data from a halogenfree flux with a formulated bromine content of 275ppm.ICP quantitation of chlorine and bromine was practicallyimplemented and the results of ongoing quality monitoringof a flux formulated with 275ppm bromine are summarizedin Table 2 (see end of paper for enlarged table).RESULTSSilva, et al. investigated the content of various refusederived fuels and reported TCC levels of 6-24g/kg, 600024000ppm [2]. The content of halogen-free fluxes is muchlower, making the sensitivity of the test much moreimportant. For this reason, the KOH absorption solutionscould not be analyzed by anion-IC because a dilution of 1000 was required to reduce the potassium interference atProceedings of SMTA International, Sep. 27 - Oct. 1, 2015, Rosemont, ILPage 350

Table 2. Summary of thirty quality control samplesanalyzed by both IC and ICPCONCLUSIONSIt appears from these results that ICP detection of bromineand chlorine may be favorable to IC detection atconcentrations less than 300ppm and potentially at allconcentrations. Experimental results demonstrate areduction in error of about 75% at the concentrations tested,from 35–40% to 5–10%.It is possible that KOH absorption solutions could beanalyzed by Anion-IC following treatment with cationexchange filters; this may be evaluated during future work.The use of sodium carbonate/bicarbonate solutions forabsorption was not explored but may be useable on newerIC systems which remove carbonate from the eluent postseparation pre-detection. In past experiences, highconcentrations of carbonate in sample solutions interferedwith bromide determination. This artifact may not be asmuch of an issue when quantifying bromine at higherconcentrations.REFERENCES[1] European Committee for Standardization, 2007, “EN14582, Characterization of waste – Halogen and sulfurcontent – Oxygen combustion in closed systems anddetermination methods”[2] Silva, R. B. et al, 2014, “Which chlorine ions arecurrently being quantified as total chloride on solidalternative fuels?” Fuel Processing Technology 128, pp.6167.RELATED ARTICLESJensen, T., 2011, “A Review of Test Methods andClassifications for Halogen-Free Soldering Materials”Indium Corp. Tech Paper as presented at APEX EXPO2011.Jensen, T. and Lasky, R., 2010, “Challenges TowardImplementing a Halogen-Free PCB Assembly Process”Indium Corp. Tech Paper as presented at APEX EXPO2010.Proceedings of SMTA International, Sep. 27 - Oct. 1, 2015, Rosemont, ILPage 351

Table 1. Summary of experimental results and calculated dataProceedings of SMTA International, Sep. 27 - Oct. 1, 2015, Rosemont, ILPage 352

Table 2. Summary of thirty quality control samples analyzed by both IC and ICPProceedings of SMTA International, Sep. 27 - Oct. 1, 2015, Rosemont, ILPage 353

each anion. EN14582 states that pure analytical-grade water may be used as an absorption solution if the expected halogen and sulfate content is less than 10g/kg (10,000ppm or 1%). This recommendation does not hold up when applied to flux due to its high load of nitrogen, phosphorus,

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