Influence of air humidity on sampling efficiency of some solid adsorbents used for sampling organics from work-room air

Chemosphere, Vo1.13, No.3, pp 437-444,1984 Printed in Great Britain

0045-6535/84 $3.OO + .OO O1984 Pergamon Press Ltd.

INFLUENCE OF AIR HUMIDITY ON SAMPLINGEFFICIENCY OF SOMESOLID ADSORBENTS USED FOR SAMPLINGORGANICSFROMWORK-ROOMAIR

Kurt Andersson, Jan-Olof Levin,

Roger Lindahl and Carl-Axel Nilsson

National Board of Occupational Safety and Health Research Department in UmeA Box 6104 S-900 O6 UMEA SWEDEN

ABSTRACT The influence of air humidity on the sampling efficiency of Amberlite XAD porous polymers and activated charcoal was studied by determining the recovery of various organics at 20% and 85% relative humidity. The sampling efficiency of XAD-7 was found to decrease with increasing relative humidity, while the sampling efficiency of XAD-2 and activated eharcoal was relatively unaffected for the compounds studied. Activated charcoal had a greater capacity than Amberlite XAD for several types of compounds, however. INTRODUCTION The use of solid adsorbents is one of the most important methods for monitoring harmful substances in work-place atmospheres,l The adsorbent is placed in a metal or glass tube containing a bed of adsorbent, through which air is drawn at a regulated flow rate, using a personal sampling pump. Adsorbed compounds are either heat or solvent desorbed. The f i r s t standardized miniature adsorbent tube to find widespread use was the NIOSH charcoal tube. 2 Several types of organic compounds can not be sampled on activated charcoal owing to decomposition or irreversible adsorption. For these compounds adsorbents of the porous polymer type, for example Amberlite XAD, Tenax, Porapak and the Chromosorb lO0 series, are useful alternatives. 3 For several years, we have been evaluating the Amberlite XAD polymers for the sampling of organic compounds in work-place atmospheres.4"I0 The Amberlite XAD-2 resin is a porous styrene-divinyl benzene polymer which is best suited for sampling aromatics. 4'5'8'g Amberlite XAD-7 is of a polyacrylic ester type, and has proved suitable for several aliphatic compounds.6'7'9'I0 The majority of the compounds which have been studied are of the kind that react or decompose on activated charcoal or show poor recovery from that adsorbent. In this work we have studied the influence of air humidity on the sampling efficiency of Amberlite XAD adsorbents for sampling certain organic compounds. In those cases where activated charcoal is an alternative, i t has been included for comparison. * To whom reprint requests and correspondence should be addressed.

437

438

EXPERIMENTAL Materials Solvents used were diethyl ether (May & Baker, p . a . ) , dichloromethane (Merck, p.a.), carbon disulfide (Merck, p.a.) and methanol (Merck, p.a.). The standard compounds used were of p.a. purity. Amberlite XAD (Rohm & Haas, techn.) was purified by repeated washing with d i s t i l l e d water to remove inorganic salts. Fines were removed by decanting. The polymer was further washed with methanol five times, dried and fractionated (20/50 mesh). Finally, the adsorbent was extracted twice in a Soxhlet apparatus for 24 hours with diethyl ether and dried at 700 overnight. The XAD was f i l l e d in glass tubes 50 x 4 mm ( i . d . ) in two sections, 80 and 40 mg, with silanized glass wool between sections and at both ends. Commercial XAD tubes, made by SKC Inc. (XAD-2 l o t 128, XAD-7 l o t 164), 50 x 4 mm ( i . d . ) , with two sections (80 + 40 mg), and 20/40 mesh, were also used. No significant differences in recoveries of the compounds studied between commercial tubes and tubes prepared by us could be noticed. Activated charcoal was of the standard commercial type (coconut-base, 20/40 mesh, SKC Inc., lot 120) in glass tubes 50 x 4 mm ( i . d . ) , with two sections (lO0 + 50 mg). For a l l adsorbents the length of the trapping section was 15 mm. Recovery experiments Air with a known relative humidity was produced by saturation in gas dispersion bottles with water and dilution with dry a i r according to Fig. I . Pressurized a i r was f i r s t f i l t e r e d in a dust/oil f i l t e r and then regulated with two pressure regulators Pl and P2. The second (P2) enabled good precision in small pressure variations at low pressures (about 0.2 bar). The gas stream was s p l i t among three glass capillary tubings Cl (80x0.50 mm i . d . ) , C2 (50x0.61 mm i . d . ) and C3 (50x0.61 mm i . d . ) , giving three flows, the ratio between which was almost independent of pressure. The three-way valves Vl and V2 enabled the portion of a i r passing through the gas dispersion bottles D to be varied. Two flow regulators with rotameters (Fl and F2) were used for making s~all flow adjustments. Finally the saturated a i r and dry a i r were mixed in the chamber M to provide a i r with the desired relative humidity. The volume of the mixing chamber was approximately 200 mL. The glass capillary tubings CI-C3 were chosen such that the valves Vl and V2 could be set to provide relative humidities of 20, 50 and 85% by means of small adjustments of the flow regulators Fl and F2. With greater adjustments of Fl and F2 any relative humidity between lO and 85% was attainable. The apparatus was operated at room temperature.

P1

P2

C1

F1

C2 C3

e-

v V2 I

D

d •;

F2

t

:--"

H~ mar

__ - -

be

Figure I . Apparatus used to produce humidified a i r . See text for explanation of symbols.

439

To provide constant flow rates for seven parallel adsorbent tubes, the humidified a i r was s p l i t among eight glass capillary tubings. For a flow of 200 mL/min glass capillaries with a diameter of 0.30 mm and a length of 20 mmwere used. One of the capillaries was connected to a relative humidi t y meter (HUMICAP 14, Vaisala OY, Helsinki, Finland). A glass tube, 80 mm x 4 mm ( i . d . ) , provided with an injection port was connected to each of the other capillaries. The compound to be investigated was dissolved in diethyl ether and lO uL of this solution was injected through the injection port into the glass tube. I f necessary, the injection tubes were heated in an aluminium block to allow vaporization of compounds with low vapour pressure. The adsorbent tubes were directly connected to the injection tubes, and the flows were regulated with the pressure regulator P2 and measured with a rotameter. After 5-20 L of a i r had been sampled, the compound was desorbed by shaking the adsorbent beds with 3.0 mL of solvent for 30 min. Analysis The solutions were submitted to gas-chromatographic analysis and recovery was determined using external standard quantitation. The presence of 5% or more in the control section was considered a breakthrough. The analyses were performed with the use of a Pye Unicam Model 204 gas chromatograph with flame ionization or electron capture detector. The column was a 1.5 m x 4 mm ( i . d . ) glass column f i l l e d with stationary phase on Chromosorb WHP lO0-120 mesh. Stationary phases and operating conditions are stated in Table I. Table I. Gas-chromatographic conditions for the analysis of compounds studied in this work. Detector, FID; carrier gas, nitrogen; and flow, 40 mL/min. Compound

Stationary phase

Phenol

I0% Reoplex 400

Temperature (°C) Col. Inj. Det. 75

125

200

2,3,4,6-Cl4-Phenola

I% OV 17

155

250

300

Epichlorohydrin

0.2% Carbowax 1500 on Carbopack C

80

180

180

Ethylene glycol

20% Carbowax 20 M

175

200

200

2-Methoxyethanol

20% Carbowax 20 M

90

150

175

Nitrobenzene

I0% Reoplex 400

160

175

200

2-Nitropropane

I0% Reoplex 400

90

125

200

Isopropyl nitrate

0.2% Carbowax 1500 on Carbopack C

135

150

250

Styrene

0.1% SP lO00 on Carbopack C

225

250

250

Naphthalene Amyl acetate

I0% Reoplex 400 20% Carbowax 20 M

195

200

200

lO0

125

250

Butyl acetate

I0% Carbowax 20 M

lO0

125

200

a. Analysed as acetate with electron capture detection 5

440

RESULTS AND DISCUSSION Influence of a i r humidity on recovery of organics from Amberlite XAD and activated charcoal

I.

Acetates

Acetates generally have r e l a t i v e l y high TLVsI I and an adsorbent for these compounds must therefore have a large capacity. As Table I I shows, standard tubes (80 mg) of XAD-2 and XAD-7 do not have s u f f i c i e n t l y high capacity for sampling butyl acetate and amyl acetate at levels two to three times the TLV. With the use of 150 mg XAD-7, recovery is almost quantitative, provided that no more than 6 L of a i r is sampled. Activated charcoal, however, has a greater capacity and no breakthrough occurs even when the sampling volume is 20-25 L. The amount of ester retained on XAD or charcoal is not s i g n i f i c a n t l y affected by relative humidity. Table I I . Recovery of butyl acetate (8.8 mg) and amyl acetate (8.8 mg) from Amberlite XAD-2, XAD-7 and activated charcoal at relative humidity 20% (RH 20) and 85% (RH 85) with the use of carbon disulfide (charcoal) and diethyl ether (XAD) for desorption. Experiments were performed in t r i p l i c a t e . RSD = Relative standard deviation.

Compound

Adsorbent

Air volume (L)

Recovery(%) and RSD (%) RH 20 RH 85

Butyl acetate

XAD-2

6a

23b

2

25b

5

Butyl acetate

XAD-7

6

48b

13

35b

9

Butyl acetate Butyl acetate

XAD-7 c XAD-7c

6 24

lO0 74b

3 lO

95 44b

2 30

Butyl acetate

charcoal

6

lO0

l

Butyl acetate Amyl acetate

charcoal XAD-2

24 5d

98 41b

l l

97 38b

2 2

Amyl acetate

XAD-7

5

71b

5

68b

14

Amyl acetate

charcoal

5

96

l

96

2

Amyl acetate

charcoal

20

97

l

97

l

I02

5

a. Corresponds to 1470 mg/m3 (TLVI I = 710 mg/m3) b. Breakthrough to control section c. Tube with two sections 150 + 150 mg d. Corresponds to 1760 mg/m3 (TLVI I = 530 mg/m3) 2.

Pheno~

We have previously shown that the recovery of phenol and chlorophenols from activated charcoal with the use of solvent desorption is very poor.4'5 On the other hand, Amberlite XAD-2 provided excellent recoveries of these compounds at levels of lO-lO00 ug phenol and 0.25-25 ug chlorophenols. 4'5 These experiments were performed at a relative humidity (RH) of approximately 40%. In this work we have studied the recovery at 20 and 85% RH. The results are shown in Table I I I . As can be seen from the table, recoveries are good at both relative humidities. When sampling 24 L there is a slight breakthrough for phenol to the back-up section.

441

Table I I I . Recovery of phenol and 2,3,4,6-tetrachlorophenol from Amberlite XAD-2 at relative humidity 20% (RH 20) and 85% (RH 85) using diethyl ether desorption. Experiments were performed in t r i p l i cate. RSD = Relative standard deviation.

Compound

Amount (ug)

Phenol Phenol

Air v o l u m e (L)

500 500

Cl4-Phenol

12.5

Cl4-Phenol

12.5

Recovery(%)and RSD(%) RH 20 RH 85

6a 24

94 76c

3 3

94 82c

5b

90

8

93

2 lO

95

6

93

2

20

4

a. Corresponds to 83 mg/m3 (TLVII = 19 mg/m3) b. Corresponds to 2.5 mg/m3 (TLVII = 0.5 mg/m3) c. Breakthrough to control section

5.

Ethyleneglycol and mono~the~s of ~thylene glycol

We have shown that the recovery of ethylene glycol and its monoethers from activated charcoal is poor with most solvents, except 5% methanol in dichloromethane. Recoveries were generally excellent from XAD-2 for ethylene glycol and XAD-7 for the monoethers with the use of diethyl ether desorption and 150 mg adsorbent tubes.7 Table IV shows that a tube with 80 mg XAD-7 is insufficient to retain 2.0 mg 2-methoxyethanol when 5.0 L air is drawn through. The recovery is not much affected by relative humidity. As the table shows, activated charcoal has greater capacity at both relative humidities. For ethylene glycol, however, recovery from charcoal decreases at 85% RH. Table IV. Recovery of ethylene glycol (6.25 mg) and 2-methoxyethanol (2 mg) from Amberlite XAD-2, XAD-7 and activated charcoal at relative humidity 20% (RH 20) and 85% (RH 85) with the use of 5% methanol in dichloromethane for desorption. Experiments were performed in t r i p l i c a t e . RSD = Relative standard deviation.

Compound

Adsorbent

Ethylene glycol Ethylene glycol 2-Methoxyethanol

XAD-2 charcoal XAD-7

2-Methoxyethanol 2-Methoxyethanol

charcoal charcoal

Air volume (L) 5a 5 5b 5 20

a. Corresponds to 1250 mg/m3 (TLV 11 = 125 mg/m3) b. Corresponds to 400 mg/m3 (TLV 11 = 80 mg/m3) c. Breakthrough to control section

Recovery(%) and RSD (%) RH 20 RH 85 90 94 58c

1 5 5

94 77 59c

5 4 4

91 94

3 2

95 93

1 2

442

4.

Nitro compounds and nZt.,u~te~

Several nitro compounds provide poor recoveries from activated charcoal. 9 The best adsorbent for aromatic nitro compounds was found to be XAD-2, and for aliphatic nitro compounds XAD-7.9 As Table V shows, the recovery of nitrobenzene is excellent at both relative humidities, and there is no breakthrough even at a sampling volume of 20 L at a level corresponding to approximately twice the TLV. For 2-nitropropane, there is a slight breakthrough to the control section at a relative humidi t y of 20% when sampling 5 L at twice the TLV. The breakthrough increases at 85% RH. For sampling 5 L at lO times the TLV (I.75 mg) 150 mg of XAD-7 is needed. For isopropyl nitrate there is a breakthrough at 85% RH when sampling 5 L at five times the TLV even with the use of 150 mg XAD-7. Since this compound can be sampled on activated charcoal with no breakthrough at high relative humidity and large sampling volume, charcoal is recommended for sampling isopropyl nitrate. Table V. Recovery of nitrobenzene, 2-nitropropane and isopropyl nitrate from Amberlite XAD-2, XAD-7 and activated charcoal at relative humidity 20% (RH 20) and 85% RH 85) with diethyl ether desorption. Experiments were performed in t r i p l i c a t e . RSD = Relative standard deviation.

Compound

Amount (mg)

Adsorbent

Air volume (L)

Recovery(%) and RSD (%) RH 20 RH 85

Nitrobenzene

0.25

XAD-2

5a

99

2

Nitrobenzene 2-Nitropropane

0.25 0.35

XAD-2 XAD-7

20 5b

96 88c

6 4

I03 98 63c

l l 6

2-Nitropropane

1.75

XAD-7

5

59c

8

37c

lO

2-Nitropropane

1.75

XAD-7d

5

91

2

92

5

Isopropyl nitrate

2.5

XAD-7

5e

40c

lO

17c

18

Isopropyl nitrate

2.5

XAD-7d

5

96

2

51c

37

Isopropyl nitrate

2.5

charcoal

5

lO0

l

lO0

l

Isopropyl nitrate

2.5

charcoal

20

lOl

l

99

l

a. Corresponds to 50 mg/m3 (TLVI I = 5 mg/m3) b. Corresponds to 70 mg/m3 (TLVI I = 35 mg/m3) c. Breakthrough to control section d. Tube with two sections 150 ÷ 150 mg e. Corresponds to 500 mg/m3 (TLVI I = I05 mg/m3)

5.

Chlorohydrins

Activated charcoal and Amberlite XAD-7 were previously evaluated for the a i r sampling of epichlorohydrin and ethylene chlorohydrin. 6 Amberlite XAD-7 was found to be an excellent adsorbent for these compounds. Besides, epichlorohydrin could be sampled on activated charcoal. The influence of high relative humidity was not studied. Table I I I shows the recovery of epichlorohydrin from Amberlite XAD-7 and activated charcoal at different relative humidities. XAD-7 gives good recovery at 20% RH, but recovery is decreased to about 50% at 85% RH. Therefore, the use of two XAD-7 tubes is recommended when sampling epichlorohydrin at high levels and high relative humidity. As can be seen fro~ Table Vl, Recovery from activated charcoal is not influenced by humidity at the level investigated.

443

Table VI. Recovery of epichlorohydrin (200 ug) from Amberlite XAD-7 and activated charcoal at relative humidity 20% (RH 20) and 85% (RH 85) using dichloromethane desorption. Experiments were performed in t r i p l i c a t e . RSD = Relative standard deviation.

Adsorbent

Air volume (L)

XAD-7 Charcoal Charcoal

5a 5 20

Recovery (%) and RSD (%) RH 20 RH 85 93

2

5l b

0

92 99

4 l

97 96

3 2

a. Corresponds to 40 mg/m3 (TLVII = lO mg/m3) b. Breakthrough to control section J

6.

Avto~

hydrocarbons

Normally, aliphatic and aromatic hydrocarbons can be sampled on activated charcoal. 12 Polycyclic aromatic hydrocarbons (PAH), however, show poor recoveries from charcoal owing to irreversible adsorption, and for the sampling of gas phase PAH Amberlite XAD-2 is recomended. 8 Table Vll shows the recovery of styrene and naphthalene from XAD-2 and activated charcoal. Charcoal has a better capacity for styrene than XAD-2, but XAD-2 gives excellent recovery of naphthalene. As can be seen from Table VII, there is no dependence of recovery on relative humidity. This is true for both compounds and both adsorbents. Table VII. Recovery of styrene (2.75 mg) and naphthalene (I.25 mg) from Amberlite XAD-2 activated charcoal at relative humidity 20% (RH 20) and 85% (RH 85) with the use of carbon disulfide (charcoal) and diethyl ether (XAD) for desorption. Experiments were performed in t r i p l i c a t e . RSD = Relative standard deviation.

Compound

Adsorbent

Styrene

XAD-2

Styrene Styrene Naphthalene Naphthalene Naphthalene Naphthalene

Air volume (L)

Recovery(%) and RSD (%) RH 20 RH 85

5a

60b

4

63b

charcoal charcoal XAD-2

5 20 5c

89 90 96

3 2 4

90 94 91

XAD-2 charcoal charcoal

20 5 20

lOl 75 74

l l 4

93 74 79

a. Corresponds to S50 mg/m3 (TLV11 = 215 mg/m3) b. Breakthrough to control section c. Corresponds to 250 mg/m3 (TLV11 = 50 mg/m3)

444

CONCLUSIONS This work shows that a i r humidity has no great influence on the sampling efficiency of XAD and activated charcoal for the compounds studied. Few studies have been made of the effect of a i r humidity on the sampling efficiency of porous polymers. Pellizzari ~>t aZ. reported that the breakthrough volumes and collection efficiencies for several organics were not affected by relative humidities of 41-92% with the use of Tenax GC, an adsorbent of the same chemical type as XAD-2.15 Sydor and Pietrzyk studied the capacity of XAD polymers for several organic compounds with the coelution of water. 3 For XAD-2 there was an overall decrease in capacity, and for XAD-7 an increase In contrast to this our work shows that there is a slight decrease in the sampling efficiency of XAD-7 at 85% RH for several compounds. The unpolar XAD-2 shows no dependence on relative humidity, however. Despite the low polarity of charcoal, some studies indicate that the sampling efficiency is affected by high relative humidity, and that considerable amounts of moisture can be adsorbed.13'14 When the relative humidity was increased from seven to ninety-four percent, a reduction of greater than 50% in the breakthrough capacity for toluene was observed.13 In our recovery study, no dependence on humidity was noted for activated charcoal, except for the most polar compound, ethyl. ene glycol, which showed a decrease in recovery at 85% RH. The present work also shows that most organics are more strongly retained on activated charcoal than on XAD, which means that smaller sampling volumes and/or longer adsorption tubes have to be used when sampling on XAD. REFERENCES I.

T. Coker, in Detection and Measurement of Hazardous Gases, (C.F. Cullis and J.G. Firth, eds) Heinemann, London 1981, p. l l 3 .

2.

L.D. White, D.G. Taylor, P.A. Mauer and R.E. Kupel, A~.. Hy9. Assoc. J., 31, 225 (1970).

3.

E.D. Pellizzari, J.E. Bunch and B.H. Carpenter, Environ. Sci. Tech., 9, 552 (1975).

4.

J.-O. Levin, C.-A. Nilsson and K. Andersson Chemosphere, 6, 595 (1977).

5.

K. Andersson, J.-O. Levin and C.-A. Hilsson, Chemosphere, lO___z,137 (1981).

6.

K. Andersson, J.-O. Levin, R. Lindahl and C.-A. Nilsson, Chemosphere, lO, 143 (1981).

7.

K. Andersson, J.-O. Levin, R. Lindahl and C.-A. Nilsson, Chemosphere, I I , I l l 5 (1982).

8.

K. Andersson, J.-O. Levin and C.-A. Nilsson, Chemosphere, 12__ z197 (1983).

9.

K. Andersson, J.-O. Levin and C.-A. Nilsson, Chemosphere, 12__z377 (1983).

lO. K. Andersson, J.-O. Levin and C.-A. Nilsson, Chemosphere, 12___t821 (1983). I I . American Conference of Governmental Industrial Hygienists, Threshold Limit Values for Chemical Substances and Physical Agents in the Work-Room Wnvironment with Intended Changes for 1982, ACGIH, Cincinnati, Ohio 1982. 12. National Institute for Occupational Safety and Health, NIOSH Manual of Analytical Methods, 2nd ed., vol. 2, DHEW, NIOSH, Cincinnati, Ohio 1977. 13. A.T. Saalwaechter, C.S. McCammon Jr, C.P. Roper and K.S. Carlberg, Am. Ind. Hy9. Assoc. J., 38, 476 (1977). 14. R.D. Burnett, Am. Ind. Hy9. Assoc. J., 37 (1976). 15. E.D. Pellizzari, J.E. Bunch, R.E. Berkley and J. McRae, Anal. L e t t . , 9, 45 (1976). 16. R. Sydor and D.J. Pietrzyk, Anal. Chem., 50, 1842 (1978). (Received in The Netherlands 12 December 1983)