CA1212605A - Gaseous contaminant dosimeter with modified absorbant medium - Google Patents

Abstract

TITLE
Gaseous Contaminant Dosimeter With Modified Absorbant Medium ABSTRACT
A personal dosimeter for the collection of formaldehyde is improved by modifying the sodium bisulfite absorbant medium with sodium bicarbonate.

Description

~2~

TITLE
Gaseous Contaminant Dosi~eter WIth Modi~ied Absorbant Medium BACKGROUND OF T~E INVENTION
5Field ~f The Invention This in~ention is related to a pexs~n~ldosime-I ter ~r registering gaseous contamlnants ~n the atmos-¦ phere. More particularly, it is related to a dosimeter for detecting formaldehyde wherein a sodium bisul~ite absorbant medlum is modtfied w~th sodium b~carbonate.
i escri~tion Of The Prior Art In response to the increasing concern about the health of workers who are exposed to harmf~l pollut-ants in the air, it has become necessary to monitor the 15 concentration of the air-borne contaminants. One de-velopment ~or this purpose involved a rather large air pump which would force air to be sampled through a fil~er, trapping par~iculate contaminants. This obvi-ously is unavailing for the monitoring of gaseous contaminants andr even for particles, is not accurate for detarmining the concentration o~ the pa~tisles ~n the sampled atmosphere.
Personal sampling devices which are worn by individual workers and which passively collect the con-taminants have also been used. For example, a devicewhich utilized the molecular diffusion of the gas to be monitored to collect the sample has been described in the ~merican Industrial Hygiene Association Journal, ~olume 34, pages 78-81 (1973). This device and others like it, called impinging tubes, are often cumbersome to use since their designs and delicate constructions necessitate that they always be oriented properly to sample accurately the atmosphere and to prevent dislo-cation of the sampling mechanism within the tube.

~2~L~6~5 The need arose ~ox ~he devel~pm,e~t o~ per-ssnal dosimeters that si,mply but accurately collected gaseous contamlnants in proportion to theix averaye ~, atmospheric concentration. Examples of dosimeters deslyned for color~etric analysis are disclosed in Kring U.S. 4,208,371 issued June 17, 1980; Kring et al.
U.S. 4,235 ! 097 issued November 25, 1980; and Kring U.S. 4,269,804 lssued May 26, 1981. ~he color intens-~ty o~ the exposed collecting medium in those dosime-ters is proportional to the dose-level o~ gas sampled.
The color stabillty of suitable collecting mediums, ho~ever, ls ~affected by several variables including storage life.
A need became apparent ~or the a~ailability o~ a more ~table absorbant medium, particularly for do-simeters used ln the detection of formaldehyde.
'SI~ Y OF ~HE INVEN~ION
According to the present invention, there is provided'a personal dosimeter for collecting a gaseous contaminant in proportion to its average ambient con-centration during the collection time where the dosime-ter consists essentially of a closed receptacle;
within the receptacle, an absorbant collect-~S ~n~ medium o~ sodium bisulfite and sodium bicarbonate ~or the gaseous conta~inant;
a diffusion device, forming part of the boundary of the receptacle, the device containing a plurality of through-and-through channels adapted for the gaseous contaminant to diffuse therethrough from the atmosphere to the interior of the receptacle, the channels each having a length-to-diametex ratio o~ at least 3 and the said channels providing the only com-munication between the atmosphere and the interior of the receptacle; and a pDXOUS, hydrophQbic, inert ~il~ c~Vexing the interlor open~ngs o~ the channeIs.
The dosimeter of the invention may optionally contain a blister separately sealed and containing a 5 blank o~ the same sodium bisulfite and sodium bicarbon-ate medium and also may optionally contain at least one compartment separateIy sealed and adapted to contain a testing reagent.
DETAILED DESCRIPTION OF THE INVEN~ION
The dosimeters of this invention collect a gaseous ~oxmaldehyde contaminant in proportion to its average concentration in the atmosphere during the collection period and provide for the expedient deter-mination of this concentration. This is achieved by 1~ passively sampling the gaseous contaminant in ambient air in proportion to its concentration therein by allowing the contaminantto diffuse into an interior portion of the dosimeter where it is maintained, by an absorbant collection medium situated therein r until it 20 is analyzed.
The collecting medium holds the gaseous con-taminant or i.ts ions in a form that is more readily analyzable than is the gaseous form. After collection, the collect~g medium ~nd, if used, the blank medium are r~d 25 from the dosimeter and treated with appropriate re-agents to produce color, the intensity of which is dependent upon the amount of gaseous contaminant col-lected and analysis of the blank medium. The time-average ambient concentration can then be determined, 30 as later explained, with a previously-calibrated color-imeter or spectrophotometer. Alternatively, the con-taminant can be separated from the collecting medium and its quantity determined, for example, by gas ~2:~2~5 chromatography wherein the results of the gas chroma-tography analysis have been previously callbrated against known time-average ambient concentrations of the contaminant. The preferred method of determination is colorimetric.
Generally, the collecting medium is a matexial that absorbs, adsorbs, reacts or othexwise combines with the gaseous contaminant being measured. Regard-less of the manner in which the medium interacts, as above, with the contaminant, the ~uantity or strength of the collecting medium in the dosimeter should be sufficient to interact ve~y nearly completely with the total quantity of ~aseous contaminant which is anticipated to be collected. The collecting medium will often b~
15 speci~ic to the particular gaseous colltaminant being monitored. Examples, meant to be representative but not limiting, include distilled water or a solution of sodium bisulfite to absorb formald~ehyde.
Methods for colori~etric ~nal~sis, for example, 20 for sulfur dioxide, nitrogen dioxide, ammonia, or for~
maldehyde, in air, are described in National Institute for Occupatior.al Safety and Health method numbers 160 (publicatlon 121, 1975), 108 ~publication 136, 1974), 205 (publication 121, lg75) and 125 (publication 136, 25 197~), respecti~eIy. The techniques therein described are readily adaptable with respect to ahsorbing solu-tions and color-forming reagents for use in connection with collection by the dosimeter of the present inven-~ion.
It has now been found that the addition of sodium bicarbonate to the sodium bisulfite absorbant collecting medium reduces decomposition of the bisul-fite, thereby improving stability of the collecting

2~

medium solution. It has also been found that the addl-tion of the sodium ~icarbonate to the sodium bisulfite medium reduces interference from phenol. Phenol is a serious negative interference in chromotropic acid-sulfuric acid analytical procedures for formaldehyde insolution.
- The colIecting medium solution of this inven-tion generally conststs essentially of 0.001 to 3.0%
sodlum bisulfite by weight based on weight of a~ueous solution modified by 0.001 to 2.0~ sodium bicarbonate by weight based on weight of aqueous solution. Prefer-ably .01 to 2.5% sodtum blsulfite by weight based on weight o~ aqueous solution is modified with .01 to 1.0%
sodium bicarbonate by weight based on welght of aqueous solution. Most preferably 0.5 ~o ~.0% sodium bisulfite is modified by .02 to .05% sodium bicarbonate. A 1%
sodtum bisulfite by weight based on weight of aqueous solution is modified by 0.03% sodium bicarbonate by weight based on the wetght of aqueous solution may be considered a best mode. Concentrations higher than

3.0% of sodium bisulfite and 2.0% sodium bicarbonate can be used but do not appPar to provide further hene-fits.
The sodium bicarbonate modifier can be added ~5 to the sodium bisulfite collecting medium by any means known in the art ~or combining small premeasured quanti-ties of solutions either before or ater the sodium bisulfite solution is placed within a dosimeter pouch or blister.
The following Examples illustrate the inven-tion.
EXAMPLE I
.
A typical dosimeter badge of the invention is assembled from clean th~rmoformed ionomer resin film to which a molded diffuser of ionomer resin is heat sealed along with a strip of polymersor copolymers of tetra-fluoroethylene and hexafluoropropylene. This ~2~2~05 subassembly is then tr~ns~erred to a li~uid ~illing st~t~on where 2.4- ~ 0.1 milliltters of absorbiny solu-tion is added to the absorbing and blank solution cavities. The ~inal step is heat sealing a clean flat sheet o~ ionomer resin o~er the solution ca~ities.
The absorbing solution for the formaldehyde badges is formulated as follows:
Dissolve 1.O gram of sodium bisulfite (NaHS03) in 100 ml. of (formaldehyde free) distilled-deionized water. Add 0.033 grams of sodium bicarbonate (NaHC03) to this solutionO
EXAMPLE II
A mixed solution of sodium bisulfite andsodium bicarbonate modifier performs as well in sampling for-maldehyde in air as an unmodified bisulfite solution a~ shown by badga tests in exposure chambers containing known but different amounts formaldehyde (CH2O). The calibration factor was the same within exror limits with both solutions.
Badges containing either regular or modified absorbing solution were exposed to known concentrations of formaldehyde in aîr for various time periods. ~fter exposure badges were analyzed by withdrawing 2.0 milli-liters (ml.) of absorbing solution and adding 0.3 ml. of 1~ chromotropic acid solution and 3.0 ml. of concen-trated sulfuric acid, mixing the contents thoroughly, and heating at 90C for 15 minutes in a constant tempera-ture hot water bath. After the solutions have cooled to room tempexature, the color intensity is read in a standard spectrophotometer using 40 mm light path length rectangular cuvettes~ The exposed color acti-vated solution is compared with a similar amount of color activated (unexposed) badge solution. The absorbance difference is divided by the known formalde-hyde exposure dose (ppm.hours) to arrive at the cali-bration factor.

~2~ 05 Calibration Factor ..(Ab.sorbanc.e/.p.pm.hr. CH2O.
Exposure Chamber CH~0Unmodified Modified 1 18.70.0405 0.0419 2 ' 17.90.0484 0.0513 3 18.70.0518 0.0529

4 18.50.0478 0.0~58 17.70.0463 0.0469 EXAMPLE ;I I I
In addition to the fa.ct that the bicarbonate modified bisulfite solution performs as well in absorb-ing formaldehyde as the unmodified solution, it has several other advantages. The first of the advantages of the unmodified solution is that it i~ noticeably more stable undar refrigerated storage conditions as shown by the data below.
% Loss in 1~ Bisulfite Exposure Storage Vvia Titration ChamberTime (Days) Test Refrig. Unmodified Modified 4 7~ 33 EXAMPLE IV
Second, modified solutions are somewhat more stable at room temperature as shown by the following data.
% Loss in 1~ Bisulf.ite Storage Via Titration Time (Days) Test Room Temp. Unmodified Modified 2 64 - 2.8 ~35 4 88 58 58 ~2~26~5 The unmodified or regular formaldehyde badge absorblng solution 34% of the bisul~ite in solution had decomposed in 40 days at room temperature whereas 2.8%
was lost from the modified solution after 64 days.
The solution seemed to level off at 58~ loss up to 129 ; days storage whereas the regular solution had lost 71%
of the bisulftte. This is h~w we obtained the stability data.
In Example III and Example IV, solutions of both l~ sodium bisulfite and 1% sodium bisulfite con-taining 0.03% sodium bicarbonate were stored in cleanglass containers under room temperature and refrigerated conditions. After various storage times a l.O ml. of each solution is withdrawn from the container and added to 25 ml. of 0.01 normal iodine solution. The unreacted iodine is titrated with 0.01 normal standardized sodium thlosulfate solution using starch solution indicator.
The amount of iodine loss is a direct measure of the bisulfite content of the stored absorbing solutions.
That is, a standard oxidatlon-reduction titration method.
EXAMP~ V
Thirdly, absorbance readings for blank solutions are lower when modified with sodium bicarbonate than unmodified solutions as shown by the data below. All values are duplicate reading averages. The differences in absorbanca readings are statistically significant.
Absorbance vs. Distilled Water (40mm Path) Color Activated By Chromo~ropic Acid-_ Sulfurlc Acid Procedure Test Unmodified Modified l 0.034 0.022 2 0.044 0.033 3 0.008 0.006 4 0.045 0.02~
0.038 0.033 6 0.059 0.045 ~g ~212~5~5 The data tabulated in this example were ob-tained from the color act~va~ed blank badyes which were used to readout color activated exposed badges as described - in Example II. Blank badge solutions after color activa-

5 tion are read out in a 40 mm path cuvette agatnst distilled water in a second 40 mm cuvette~ This data is routinely collected after every badge exposure test.
EXAMPLE VI
Finally, the modified bisulfite absorbing solution is a~fected less by other airborne contami-nants present with formaldehyde. The standard NIOSH
impinger test P~CAM 125 which specifies water as the absorbing solution lists the following effects of the airborne contaminants. I'Ethanol and higher molecu-lar weight alcohols and olefinic compounds in mixtureswith formaldehyde are negative interferences." These result in lower color levels for the same amount of formaldehyde. "Phenols result in a 10-20% negative interference (color reduction) when present in an 8:1 excess over formaldehyde. Aromatic hydxocarbons also constitute a negative interference."
When 1~ sodium bisulfite is used as the absorbing solution in a passive dosimeter only phenol which has an affinity or the solution is a negative interference as shown in the table below, test 1-4.
Percent Change in Color Compound D~se After 20 ppm.hrs. Formaldehyde Test Tested ~ h-rs. Sam?le ~ose-Unmodified Abs.Soln.
1 Ethanol 2000 0 2 n-Bu~anol 800 -2 3 Toluene1200 ~2 4 Phenol 40 -16 -Modified Abs. Soln.
-5 Phenol 40 -4 s Changes of 0-4% are not ~tatistically sig-nificant. The fact that sodium bicarbonate added to sodium bisulfite reduced the interference ~rom phenol from 16 to 4% is a signlficant effect not expected or anticipated from current literature re~erences.
- ~or example, in the'abo~e test~ eigh-t badges were ~trst exposed to approximately 20 ppm^hours of formaldehyde. Four of the exposed badges were put in a second chamber and exposed to 500 ppm of ethanol ;n air for four hours (or 2000 ppm-hours). The same type test ~as repeated for eac~'of the four contaminants using badges wlth regular ahsorbtng solution (1% sodium bi-sulfite). Finally, eight badges containing the modified absorbing solution were exposed to 20 ppm-hours of for-maldehyd~ and four of the exposed ~adges were exposed to5 ppm o~ phenol ~or eight hours. In each of the five tests the final color of the four control badges was compared ~ith the second four exposed to the interfering contaminant.
In use, a dosimeter of this invention is ex-posed to the air containing the gaseous contaminant fora period of time for which the average contaminant con-centration is sought. When the collecting medium is an absorbing solution, for example, a measured amount ~ the solution is then withdrawn from the dosimeter by, for example, a hypodermic syringe.
When the analysis is to be made photometric-ally, the withd'rawn absorbing solution is mixed with appropriate color foxming reagents which change the color o~ the absorbing solution~ The intensity of color so formed is dependent upon the amount of gaseous con-taminant collected. Although it is often desirable to have a self-contained dosimeter~ as shQwn in U.S. Patent 4,208,371, in which the reagents are contained in the ~æ~z~05 dosimeter and no withdrawal of material is necessary, this is sometimes impractical~ An example o~ ~his is where the reagents are highly acidic, as in the color-production for formaldehyde where the reagents are chromotropic acid concentrated sul~uric acid. In such cases, it is diff~cult to package the reagents in astable and safe form, and the simple dosimeter of the present ~nvention is well suited for these applications.
The dosimeter of this invention can be cali-brated to give a direct relationship between cvlorimet-r;c or spectrophotometric readings and average ambient concentration of the gaseous contaminant. This can be accomplished by following a calibration procedure similar to that described in U.S. Patent 4,208,371.
- 15 In such a procedure, several dosimeters are ~xposed over a given period of time to various known concentra-tions of contaminant for which the calibration factor is sought. ~he dosimeters contain the same kinds and amounts o~ collecting medium. Spectrophotometr~c read-ings, for example, are determined for at least twodosimeters at each of several known concentrations, and a straight line is plotted, the slope of which is ob-tained by using a least-squares analysis, through the data points is the calibration factor in UllitS of absorbance per ppm-hour dose level.
A dosimeter useful in this invention may optionall~ include a blister separately sealed and con-taining a blank of the absorbant collecting medium.
The blank absorbant medium contained in the added blis-ter is the same absorbing materi~l as present in thediffuser containing absorbing blister. Both media are present in measured amounts. The blank does not increase in absorbance after the dosimeter is exposed to a gaseous contaminant. When the collecting medium ~Z~2~
1~
is anal~zed, the blank ~bsorbant medium from the added, separately sealed blis~er is used as a standaxd which has been exposed to the same environmental conditions, particularly shelf-life, as the collecting absorbant medium.
A dosimeter useful in this invention may also optionally contain at least one compartment separately sealed and adapted to contain a testing reagent, the seals of each compar~ment bein~ individually breakable such that the reagents can be separately released into the reaction chamber as shown in U.S. Pa~ent 4,269,804 ~ssued May 26, 1981 to Kring.
The doslmeters are examples o preferred embodtments of the present invention but the invention ig not limited t~ereto. The diffusion device, for example, can be in the shape of a plug sealed into the ~ace of two sheets. Similarly, the receptacle of the dosimeter need not be pouch-like as hereinbefore refer-enced, but for example, could be in the form of a rigid cuvette.

Claims (10)

WHAT IS CLAIMED IS:

1. A personal dosimeter for collecting a gaseous contaminant in proportion to its average ambient concentration during the collection time, the dosimeter consisting essentially of a closed receptacle;
within the receptacle, an absorbant collecting medium for the gaseous contaminant of 0.001 to 3.0%
sodium bisulfite by weight based on weight of aqueous solution and 0.001 to 2.0% sodium bicarbonate by weight based on weight of aqueous solution;
a diffusion device, forming part of the boundary of said receptacle, the device containing a plurality of through-and-through channels adapted for the gaseous contaminant to diffuse therethrough from the atmosphere to the interior of the receptacle, said channels each having a length-to-diameter ratio of at least 3 and said channels providing the only communication between the atmosphere and the interior of the receptacle; and a porous, hydrophobic, inert film covering the interior openings of said channels.

2. The dosimeter of Claim 1 in which the col-lecting medium is .01 to 2.5% sodium bisulfite and .01 to 1.0% sodium bicarbonate.

3. The dosimeter of Claim 1 in which the collecting medium is 0.5 to 2.0% sodium bisulfite and .02 to .05% sodium bicarbonate.

4. The dosimeter of Claim 2 in which the gaseous contaminant is formaldahyde.

5. The dosimeter of Claim 3 in which the gaseous contaminant is formaldehyde.

6. A personal dosimeter for collecting a gaseous contaminant in proportion to its average ambient concentration during the collection time, the dosimeter consisting essentially of a closed receptacle;
within the receptacle, an absorbant collecting medium for the gaseous contaminant of 0.001 to 3% sodium bisulfite by weight based on weight of aqueous solution and 0.001 to 2.0% sodium bicarbonate by weight based on weight of aqueous solution;
a blister separately sealed and containing a blank absorbant medium;
a diffusion device, forming a part of the boundary of said receptacle, the device containing a plurality of through-and-through channels adapted for the gaseous contaminant to diffuse therethrough from the atmosphere to the interior of the receptacle, said channels each having a length-to-diameter ratio of at least 3 and said channels providing the only communication between the atmosphere and the interior of the receptacle; and a porous, hydrophobic inert film covering the interior openings of said channels.

7. The dosimeter of Claim 6 in which the col-lecting medium is .01 to 2.5% sodium bisulfite and .01 to 1.0% sodium bicarbonate.

8. The dosimeter of Claim 6 in which the col-lecting medium is 0.5 to 2.0% sodium bisulfite and .02 to .05% sodium bicarbonate.

9. The dosimeter of Claim 7 in which the gaseous contaminant is formaldehyde.

10. The dosimeter of Claim 8 in which the gaseous contaminant is formaldehyde.