Martin G. Ondrus University of Wisconsin-Stout Menomonie, WI 54751
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The Determination of NOx and Particulates in Cigaret Smoke A student laboratory experiment
When first conceived, this experiment was intended t o provide students with a n opportunity t o determine analyticallv the - - -~ concentrations of several common imourities in a contaminated air sample. The cigaret was chosen simply hecause it can he used convenientlv for t h e eeneration of small quantities of highly "polluted" a$ in the la%oratory. Recently, however. the experiment has evolved into one with a consumer orientation in which the principal goal is t o compare two or more ciearet brands with respect to t h e nature of the smoke they produce. More than 2200 compounds have been identified in tobacco and tobacco smoke ( 1 ) . Nitrogen oxides, carbon monoxide, hydrogen cyanide, and ammonia are a few of the many gases in tobacco smoke which contribute t o its biological activity. T h e alkaloid nicotine is one of many compounds which make up the solids and oily liquids often referred to as "tar." Cigaret analysts prefer t o call this material "total particulate matter." In this rxperiment the particulate matter per puff is d e t e r m i n d 3s the werage uf the total particulare matter iadated from the first three puffs of a rigaret. Swndard 33 ml puffs (21 d ' 2 - s n duration takeu at I -min intervals are used throughout. from the smoke with I'articul;ires are removed ,I inmml~ranefilter connected to a 60 rnl syringe. Total particulate m;ttter is determined on a n analvtiml balmre 1rmn the incre:tre in weight of the tilter. T h r a m b i n ~ : dconrentration of nitric oxide and nitrogen dioxide rtog~.tl~er referrrd toas NO,) isdetermined in a single ~ u f rof filtered smoke. l i t t l e NO) is oresrnt in t'regh smoke i.0,hut i r is firmed rapidly irum NO ;I.; the undiluted smoke ares ~m p l ~ t c - (21. . . The oxidation of NO to 2 1 0 2 is e s s r n t i i ~ l rl o in less than 20 min. Analysis of NO; depends upon the formation of NO2 which reacts with water according t o eqn. (1). ~
F I L T E R HOLDER CIGARET
I
~
2 NO?
+ HzO
-
2 H+
+ N02- + No1-
(1) Nitrite ion (nitrous acid) reacts with a n azo-dye forming reagent containing sulfanilic acid and N(1-naphthylJ-ethylenediamine t o form a stable pink color within 15 min. T h e absorbance is determined spectrophotometrically a t 550 nm. Sodium nitrite solutions are used t o prepare a calibration curve. Althoueh t h e stoichiometric ratio of NO?- to NO7 is expected to be"l:2 from eqn. 1, several investigators ( 4 , s )have established t h a t 1mole of NOz- produces the same color intensity a s 1.39 mole of NOz. At present the experiment is being used near the end of the semester in a one-semester introductory chemistry course for nonmajors. It is applicable also t o courses in environmental or consumer chemistrv. When oerformed bv students workine in pairs, it is completed easily within a 3-hr laboratory period providing t h a t a n adequate number of balances and spectrophotometers is available. ~
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Equipment and Reagents Analytical Balance. (Capable of weighing to the nearest 0.001 9.1 Speetrophotometer. (Such as the Bausch and Lomh Spectronie 20) Graduated Pipet. (One 5 ml pipet for each pair of students). Syringes. (Five large disposable syringes with caps for each pair
60 n~ SYRINGE
CIGARET
Device for sampling cigaret smoke
of students). Plastic syringes such as Monoject with calibrations to 60 ml are recommended. Membrane Filters and Filter Holders. (Four 25 mm filters and one syringe type filter holder for eaeh pair of students). Although membrane filters and holders can be obtained from a variety of suppliers, our ex~eriencewith Sartorius filter holders has been favorable. Thev are equipped with standard Luer male and female fittings and support screens on both sides of the filter for filtration in either direction.They are available through the Beckman Science Essentials catalog in packages of 12. Cellulose nitrate or cellulose acetate filters with a pore size of 0.8 fim work well for aerosol analysis and are available in packages of 100. Ciparet Holder. (One per pair of students). The cigaret holder (see Figure) is prepared from three 1-in. pieces of rubber tubing of %= in., 'la in.. and 'la in. inside diameter. A ciearet should fit snuelv into the largest diameter tubine. while the smallest diameter tuhine should connection between the large and small diameter tubing. Stock 5.0 fi glml NOz- Solution. (Approximately 20 ml for eaeh pair of students). Prepare a solution containing 1000 fig NOS- per milliliter by diluting 1.50g NaN02to 1.00 I. Dilute 20-fold toproduce a solution containing 5.0 fig nitrite ion per milliliter. NO. Indicator Mixture. (3.50 ml for each oair ofstudentsl. Dissolve 5 g of nnhgdrous rulianil:~arid i n nlmust ;i lit*? (of s%ntcrrwl3in1ne 1111 mlofglaciai ~ r ~ tacid. i c ,\&II I O L d g d i d i d Vtl napl>rhvl~-~thylenediamine dihydrochloride and dilute to 1 liter. Keep tightly stoppered to avoid coloration due to NO2 in the air. The solution should be prepared just prior to its use since storage at room temperature far more than a few days causes noticeable deterioration. Refrigeration in a well-stoppered bottle prolongs the shelf life ( 6 ) . Student Experimental Procedure Standards. Using a graduated 5 ml pipet, add 1.00 ml of 5.0 pglml NOn- solution to a 25 ml graduated cylinder. Dilute to the 25 ml mark with NO, indicator. Mix and pour 10-20 ml into a labeled test tube and stopper it securely. Discard the remaining solution and rinse the graduated cylinder with distilled water. Repeat the above procedure with 2.00 ml, 3.00 ml, and 4.00 ml of stock nitrite solution. The concentrations of NOz- represented by the four standards are 0.2 ueIml.0.4 uelml. 0.6 uelml. and 0.8ueIml. respectively. All four stanhard d&ns'sh&id bekept in iioppered test tubes far 15 min or longer to ensure complete color development. Sampling. Obtain four membrane filters using only forceps to handle them. Fingerprints on the surface will greatly impair their filtering capacity. They should be handled gently to avoid poking holes in them with the forceps. For easy identification, a felt tip pen may he used to make one or more dots on the edge of eaeh filter. Place the first filter in the filter holder and carefully connect the two filter holder halves tightening them snugly. Attach the membrane filter apparatus with cigaret holder to an empty ti0 ml syringe (see Pi,uurel. Rinse four other 60 ml syringes with a few milliliters of indicator solution and then fill them with exactly 25 ml of the NO, indicator.
Volume 56, Number 8. August 1979 / 551
Table 1. Typlcal Student Results for Standard and Low Tar Klng Size Filter .. Clgarets rand
Puffs (Nurnbwlcig)
Partic~iate~' (mglpuff)
8 9 8 7 8 10 7 7 8 7 9 9 8 7
1.5 1.5 1.7 1.5 1.5 1.9 2.1 1.3 1.5 1.1 0.6 1.2 0.9 1.2
KooiB Kooia Kooie Kooi' Winston@ Winstone Winston* Winstonm Winstonm Winstonm Reale Realm RealD Reala
* V ~ I Y Brepresent B the average of
NO,. (PP~)
950 790 670 500 770 890 500 890 710 870 370 520 390 400
duplicate determinations.
Puffs (Numberlcig)
Parlicuiates' (rnglpuff)
8 8 7 6 8
1.51-0.1 1.6 f 0.1 1.1 f 0.2 0.8 f 0.1 0.8 i 0.1
Winstona Filter Kings KwP Filter Kings Vantagem Truee
Real"
(2) ,
(1.39) (1000 mlA)
'
(2)
E!
where Vi is the volume of indicator used (50 ml), V, is the volume of smoke in a puff (35 ml) and 1.39is thestoichiometricratioof NO* to
Nn-- .
Calculate the concentration of NO, in parts per million (plh) according to eqn. (3), ppm NOx = pl N o d l =
(3)
, where R is the gas constant (0.082 l.atm/"Kmole), T is the absolute temperature (-300DK), P is the pressure (-1 atm), and 46 is the
molecular weight of NOz. Note: In eqns. (2) and (3) nitrogen oxides are treated as NO2 because NO is assumed to have been converted to NOn during the 30 min development period. Syringes calibrated to a maximum of 50 ml may be used for NO, determinations if they are filled initially with 15 ml of indicator reaeent rather than 25 ml. With the smaller indicator volume, a 3 5 ml
NO,# IPP~)
574i 90 704 i 162 706i 133 396 93 438 i 82
*
m e uncertainties are averape deviations tom the mean of four determinationo.
Make sure that all air bubbles have heen expelled along with any excess solution. Cap the syringesand numher them fallowing thesame scheme that wasused for the membrane filters. Carry out duplicate determinations, using the following procedure, on each of two different brands. (Compare a "full flavor" cigaretsuch as KooP or Winston' to a "low tar" cigaret such as True" or Real"). Light a cigaret making sure that the entire tip is smoldering. Immediately place i t in the cigaret holder and use the empty 60 ml syringe to draw a 35 ml puff of 2-sec duration. Between puffs, the filter apparatus should he disconnected from the syringe t o expel the filtered smoke into the air. (Any visible cloudiness in the filtered smoke indicates that the membrane filter is either perforated or seated incorrectly). Wait 1min and draw asecond 35 ml puff. After thesecond puff, the cigaret and membrane filter holder should he transferred to the first indicator syringe. When 1min has elapsed since the second puff, draw a 35 ml, 2-sec puff through the filter into the indicator syringe. This will necessitate pulling the plunger to the 60 rnl mark. Diiwnnrct the filter huldrr i n m the syringe. cap Ihesyrlngr, and shake virurourl~.Alhm thr filrrrrd sm~lketo remmn in thp syringe for :I0 rnln wuh mcnsionnl s h ~ k i n r'l'hr . rirnret should he dri~ardvd and the membrane filter removed from its holder. When color development a complete expel all gas from each syringe while retaining the exposed indicator. Draw an additional 25 ml of unexposed indicator into the syringe. This dilution to 50 ml is usually necessary to reduce the color intensity to a readable level. During the period of color development, the membrane filters should be weighed and the two brands compared with respect to the total number of standard puffs per cigaret. The numher of puffs per cigaret may he measured without membrane filtration. Be sure t o allow a l-min interval between puffs. Data a n d Calculations Reweigh all four membrane filters and determine the weight of particulates (in milligrams) in three puffs by subtracting the lnitial weight from the new weight. Calculate the number of milligrams of particulates per puff and the average for each brand. The number of milligrams of particulates per cigaret may be estimated for each brand from the average number of milligrams per puff and the number of puffs per cigaret. With the spectrophotometer set to a wavelength of 550 nm, measure 552 1 Journal of Chemical Education
fig NO,/I = (fig NOz-Iml)
Results a n d Discussion
Table 2. Comparlson of Selected Cigaret Brands Brand
the absorbance of the four standards and the four indicator solutions which have heen exposed to tobacco smoke. Use unexposed NO, indicator as a blank. Prepare a standard curve and determine the nitrite ion concentration in each exposed indicator sample. Use eqn. (2) to calculate the number of micrograms of NO, (as N o d per liter of smoke,
to a volume of 50 ml. Typical student results for several brands are listed in Table 1. These data were gathered by nonscienee majors near the end of our one-semester introductory chemistry course. The variation in NO, concentration between student groups is due largely to inconsistency in the duration of the puff. The more rapidly the smoke is drawn, the hieher will be the combustion temoerature-This increased tempersmoke samples. The data in Table 2 were collected by the author t o allow a comparison between several well-known cigaret brands. The NO, concentrations compare favorably with literature values of 442,871, and 780 oom measured in the fourth puff of three unspecified brands of kingsize eigarets (3).The partic&te values seem&sonahle in that the "low tar" brands Vantage," True,a and Real' appear to be significantly lower than the other hrands. Our students are generally required to estimate the total particulates per cigaret from the weight of particulates per puff and the numher of puffs per cigaret. The results of these calculations are generally somewhat lower than the weight of tar per cigaret as reported by the Federal Trade Commission. This is to be expected since the student data is based upon the initial three puffs which are lower in particulates than the latter puffs. We have been most successful when using king size filter cigarets for this experiment. Higher particulate values would be expected from unfiltered king size brands such as Pall Mall? but the increased level of particulates in unfiltered smoke often causes the membrane filters to become clogged after two puffs. Filter eigarets cause a great restriction in gas flow through the membrane filter after three or four puffs. Numerous variations of this experiment are conceivable. One interesting approach involves comparing NO, and particulates in the initialand in the final puffsof the same cigaret. Dramatically higher concentrations are observed in the last few puffs of the cigaret. A great deal of student discussion can he generated by tabulating experimental data a t the end of the laboratory period or preferably the following day in lecture. Reasons for variation from one student group to another as well as differences between brands may be explored. Although the primary goal of this experiment is to give the student an introduction to gas phase and aerosol analysis, it also provides an opportunity to better appreciate the chemical nature of cigaret smoke and why it is hazardous to health. Literature Cited (1) Schmeltz,I.. and Hoffmann. D.. Chem. Re"., 77,306 (1977). (2) Vibins.C.,and Lophsrdt,L O . . C h m i n d . (hndon!,974 (19751. (3) Norman,V..snd K~iLh.C.H..Noture.205,915 11985). (4) Sa1tzrnan.B. E.,Anai. Chem., 26.1949(1954). ( 5 ) Shaw. J.T..Afmos. Enuimn., 1.81 (1967). (6) "1976Annual Bmk of ASTM Standards." Part 26. Method D1607-76.P. 487
