s

NBS SPECIAL PUBLICATION 260-48

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Standard Reference Materials:

DESCRIPTION AND USE

OF PRECISION THERMOMETERS

FOR THE CLINICAL LABORATORY,

SRM 933 AND SRM 934

100

. U.5T

no.2<oO-48
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QClOO

), Standard Reference Materials:

' Description and Use of Precision Thermometers

for the Clinical Laboratory, SRM 933 and SRM 934

B. W. Mangum and J. A. Wise

Heat Division

Institute for Basic Standards

U 5 . National Bureau of Standards

Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secrefary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued May 1974
Library of Congress Cataloging in Publication Data

Mangum, Billy Wilson, 1931-

Description and use of precision thermometers for

the clinical laboratory, SEM 933 and SEM 934.

(Standard Reference Materials) (National Bureau of

Standards Special Publication 260-48)

Supt. of Docs. No.: C 13.10: 260-48.

1. Thermometers and thermometry, Medical.

2. Medical laboratories --Equipment and supply.

I. Wise, Jacquelyn A. , joint author. II. Title.

III. Series: United States. National Bureau of

Standards. Standard Reference Materials. IV. United

States. National Bureau of Standards. Special Publication, 260-48.

QC100.U57 No. 260-48 [RB36.2] 389'. 08s

[616. 07' 56' 028] 74-7455

National Bureau of Standards Special Publication 260-48

Nat. Bur. Stand. (U.S.), Spec. Publ. 260-48, 23 pages (May 1974) CODEN: XNBSAV

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1974

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. C13.10:260-48). Price 60 cents.
PREFACE

Standard Reference Materials (SRM's) as defined by the

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Materials: Description and Use of Precision

Thermometers for the Clinical Laboratory,

SRM 933 and SRM 934. Authors Mangum

and Wise - NBS.

*Send order with remittance to: Superintendent of Documents, U.S. Government Printing Office,

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vi
CONTENTS

PAGE

I. INTRODUCTION 1

II. DESCRIPTION OF SRM 933 AND SRM 934 THERMOMETERS 2

III. CALIBRATION OF THE THERMOMETERS 3

IV. PROCEDURES FOR PROPER USAGE OF LIQUID-IN-GLASS

THERMOMETERS 3

A. Check for Separated Mercury Columns and for Gas

Bubbles 4

B. Ice Point Determination 5

C. Emergent Stem Correction 7

V. SUMMARY AND CONCLUSIONS 9

VI. REFERENCES 9

LIST OF FIGURES

Figure No . PAGE

1. The three thermometers of SRM 933. The subdivisions are 0.05 °C and the graduations have longer lines at intervals

of 0.10 °C and 0.50 °C 11

2. A drawing showing the principle features of a solid-stem

liquid-in-glass thermometer 12

3. The thermometer of SRM 934. The divisions are 0.05 °C

and the graduations have longer lines at intervals of

0.10 °C and 0.50 °C 13

vii

STANDARD REFERENCE MATERIALS: DESCRIPTION AND USE

OF PRECISION THERMOMETERS FOR THE CLINICAL LABORATORY,

SRM 933 and SRM 934

by

B. W. Mangum and J. A. Wise

Heat Division

Institute for Basic Standards

National Bureau of Standards

Department of Commerce

Washington, D. C. 20234

Because of the high sensitivity to temperature

of many facets of the clinical laboratory, e.g.

in enzyme reactions and in pH and blood gas

analysis, there is a need for accurate temperature measurement and its control. In order to

help satisfy these needs and to aid in getting

a usable and accurate temperature scale into the

clinical laboratory, the National Bureau of Standards has developed SRM 933 and SRM 934. These

are precision thermometers, which are calibrated

at 0 °C, 25 °C, 30 °C, and 37 °C and their description, their calibration, and the procedures

for their proper usage are discussed.

Key words: Clinical laboratory; enzymology; health

care; liquid-in-glass thermometers; standard ref- erence material; SRM 933; SRM 934; thermometers.

I. INTRODUCTION

The accurate measurement and control of temperature is of critical

importance in many aspects of the clinical laboratory and in the hospital

in general. The temperatures at which enzyme rate analyses are conducted,

for example, are very important because of their high sensitivity to this

parameter [1-4]. Furthermore, in order to obtain reproducible results

within a given clinical laboratory and in order to make a meaningful intercomparison among laboratories, the temperature not only must be care1
fully controlled but must be known absolutely. In recognition of this

situation, the Expert Panel on Enzymes, which was created by the International Federation of Clinical Chemistry Committee on Standards, has

recommended [5], among other suggestions in their Proposal for I.F.C.C.

Reference Methods for Enzymes, that the set point in degrees Celsius of

the reaction temperature is to be assigned as a part of the method, that

the temperature accuracy must be assured to + 0.05 °C by calibration

against the International Practical Temperature Scale of 1968 [6], that

the temperature variation of the reaction mixture should be held within

the open interval -0.05 °C and +0.05 °C of the set point, and that the

choice of reaction temperature for an IFCC reference method should be

either 25.00, 30.00 or 37.00 °C. Of course, enzyme reactions are not

unique in being sensitive to the temperature; pH and blood gas analysis

are two others in a long list that could be mentioned [1]

Because of these needs and in order to assist in getting a usable

temperature scale into the clinical laboratories (and hospitals generally)

,

NBS is providing precision laboratory thermometers, SRM 933 and SRM 934,

designed specifically for use in the clinical laboratory. These SRM's,

were produced in cooperation with the Medical Thermometry Program of the

Temperature Section in the Heat Division. Many specifications requested

by clinical laboratory personnel concerned with accurate temperature

measurements have been incorporated in the design.

II. DESCRIPTION OF SRM 933 AND SRM 934 THERMOMETERS

The three thermometers comprising SRM 933 are shown in figure 1 and

the linear dimensions of the thermometers are as indicated. These are solid-stem mercury-in-glass type instruments. In order to clarify potential problems in terminology, the principal features of a solid-stem

liquid-in-glass thermometer are shown in figure 2. The stems have a plain front, enameled back, and are of lead glass thermometer tubing 7 mm

in diameter. The bulbs are also 7 mm in diameter. Nitrogen gas fills

the space above the mercury. Special markings consist of a serial number, the namufacturer's name or trade mark, and a 95 mm immersion line.

2
Each thermometer has an auxiliary scale from -0.20 °C to +0.20 °C with

0.05 °C subdivisions. The main scale of the thermometer on the left of

figure 1 is 24.00 °C to 26.00 °C with 0.05 subdivisions, that for the

thermometer in the middle is 29.00 °C to 31.00 °C with 0.05 °C subdivisions, and that for thermometer on the right of figure 1 is 36.00 °C to

38.00 °C with 0.05 °C subdivisions. The graduations have longer lines

at intervals of 0.10 °C and 0.50 °C. In addition, there are numbers

every 1 °C. These three thermometers are packaged in one box.

SRM 934 is comprised of the one thermometer shown in figure 3 and

its linear dimensions are as indicated. Except for the main scale,

which is 24.00 °C to 38.00 °C with 0.05 °C subdivisions, and its overall

length, the specifications of this thermometer are the same as those for

SRM 933.

III. CALIBRATION OF THE THERMOMETERS

Each thermometer was tested at the ice point (0 °C) by placing it

in an ice bath and at the temperatures above 0 °C by placing it in a stirred-liquid comparison bath [7]. Calibrations were performed at

0 °C, 25 °C, 30 °C, and 37 °C and the temperatures were determined by a standard precision platinum resistance thermometer [8] which was also in

the comparison bath. The temperature of the calibration laboratory was

23 °C. The thermometer was read with the aid of a 10 power telescope,

which was placed perpendicularly to the thermometer in order to reduce

parallax errors. Before each reading, the mercury thermometer was gently

tapped to eliminate any error due to a sticking mercury column. The

maximum error associated with any calibration point is no greater than

0.03 °C.

IV. PROCEDURES FOR PROPER USAGE OF LIQUID-IN -GLASS THERMOMETERS

The items discussed in this section are included to focus attention

on some of the more common problems encountered in the use of liquid-inglass thermometers and thus to help assure that the thermometer will be

3
used properly and, thereby, will yield the desired performance. All

examples in this paper are given as an aid in the understanding of the

subject being discussed, and have not been specifically adapted to the

individual thermometers of SRM 933 and SRM 934.

A. CHECK FOR SEPARATED MERCURY COLUMNS AND FOR GAS BUBBLES

Many times, because of rough handling during shipment, separation

will occur in the mercury column or gas bubbles will appear in the bulb.

When the thermometer is received it should be throughly examined for

such occurrences. The process of joining separated mercury columns consists of one

or a series of manipulations

:

a) The bulb of the thermometer may be cooled in a solution of common salt, ice, and water (or other cooling agent) to bring the

mercury slowly down into the bulb. Only the bulb should be cooled and never the stem or mercury column. Moderate tapping of the bulb on a rubber stopper or similar soft spongy object, or the application of

centrifugal force by swinging the thermometer in a short arc, usually

serves to unite the mercury in the bulb. If the salt solution does not

provide sufficient cooling, carbon dioxide snow (dry ice) may be used.

Since the temperature of dry ice is about -78 °C and mercury freezes at

about -39 °C, the mercury will solidify. On warming, care must be taken

to warm the top of the bulb first so that pressures in the bulb due to

the expanding mercury may be relieved.

b) The mercury can sometimes be reunited by warming the bulb until

the column reaches the separated portion in either the contraction chamber or the expansion chamber. If this procedure is used, the bulb should never be heated in an open flame. Great care is necessary to avoid

filling the expansion chamber completely with mercury which might produce

pressures great enough to burst the bulb. The expansion chamber should never be more than two thirds full. Joining the mercury is more readily

accomplished if the quantity in either cavity has first been shattered

into droplets by tapping the thermometer laterally against the hand.

4
Gas bubbles, which are sometimes found along the surface of the

mercury in the thermometer bulb, may be collected by "washing" the bulb

with a large gas bubble. As outlined in section (a) above, bring all of

the mercury into the bulb. Hold the thermometer in a horizontal position

and gently tap it against the hand to form a large gas bubble. Force the

bubble to travel around the walls of the bulb by rotating the thermometer

and tapping it against the palm of the hand. When the entire surface has

been "washed", rotate the bubble to the top of the bulb and reunite the

mercury as described above.

All of these manipulations require patience (and experience is

helpful) but they will yield the desired results if care is used. A

convenient method of ascertaining that all the mercury has been joined is

a check of the ice point. It should agree with the ice-point reading on

the Report of Calibration by within approximately one scale division or better.

B. ICE POINT DETERMINATION

The ice point, known as a reference point, is found on the auxiliary

scale. It is a temperature that can be easily duplicated in any laboratory and is used to check the thermometer periodically for changes in

bulb volume.

To make an ice bath, a Dewar flask may be used as a container, since

the insulating properties of the vessel retard the melting of ice. Ice

shaved from clear cakes or from that made with distilled water is mixed

with distilled water to form a tightly packed slush. Enough water is

used to afford good contact with the thermometers but not so much as to

float the ice. At periodic intervals excess water is siphoned from the

bath. Care should be taken to prevent contamination of the ice and water.

Any change in the ice point will be reflected in the other calibration

points by the same amount and in the same direction. An example is given

below:

5
Original Corrections

Temperature

From NBS Report

Correction

-0.013 °C +0.013 °C

25.000 °C +0.010 °C

30.000 °C +0.008 °C

37.000 °C +0.015 °C

A later ice-point reading, taken after the thermometer has been at a temperature of about 23 °C for not less than three days, may be -0.020 °C.

This means that the ice-point correction will be +0.020 °C and a new set

of corrections should be made by adding +0.007 to all of the original

corrections. The new table would look as follows:

Temperature

-0.020 °C

25.000 °C

30.000 °C

37.000 °C

Correction

+0.020 °C

+0.017 °C

+0.015 °C

+0.022 °C

Because of bulb expansion, a temporary ice point depression will be

introduced when the thermometer is heated above room temperature (23 °C).

Because of this depression, the thermometer should never be used at a given temperature shortly after it has been heated beyond that temperature. An error of 0.01 °C or less for each 10 °C difference between the

two temperatures may be introduced. If the thermometer has been heated

beyond the temperature at which it is to be used and if the corrections

are to be used as given on the Report of Calibration, it must be kept

at room temperature (approximately 23 °C) for not less than three days

to assure recovery of the bulb.

A small reading telescope with a magnification of 10 diameters aids

in reading the thermometer indication and reduces parallax errors. Gently tapping the thermometer just before reading may prevent the

sticking of a falling meniscus. On the other hand, too vigorous a tap

will occasionally cause the mercury to rebound to an erroneously high

reading. 6
C. EMERGENT STEM CORRECTION

The scale corrections for these thermometers are reported for the

condition of immersion to the depth of the immersion mark (95 mm) , and

for the temperature of the emergent stem as reported on the Report of

Calibration. The emergent stem is defined as the length of mercury

column and stem exposed to the ambient temperature. The temperature of

the laboratory was 23 °C when the measurements were made. If the thermometer is used under stem-temperature conditions other than that specified, the formula given below will provide the appropriate correction,

which should be added to the thermometer reading along with the correction from the Report of Calibration to produce the true temperature.

stem correction = 0.00016 n (t - t , )

,

sp obs

where

0.00016 = differential expansion coefficient of mercury in glass

for Celsius thermometers,

t = specified mean temperature of the emergent stem (for which

reported scale corrections apply)

t obs

= observec' mean temperature of the emergent stem,

and n = number of scale degrees equivalent to the length of emergent

stem.

In using the formula it should be noted that n applies to the whole

length of emergent stem, i.e., from the immersion mark to the top of the

mercury column. The ungraduated length between the immersion mark and

the first graduation on the scale must, therefore, be evaluated in terms

of scale degrees and included in the value of n. To measure the emergent stem temperature, a small auxiliary thermometer, generally 15 cm long with a range from 0 °C to 100 °C and

graduated in 1 °C intervals, is suspended above the bath adjacent to the

main thermometer, with the bulb approximately at the center of the liquid

column.

For SRM 933, it will be noted that there would have to be a temperature difference of at least 2 °C to produce approximately a millidegree

7
change in the thermometer reading. In this example n % 2.6

stem correction = 0.00016 x 2.6 x + 2 = + 0.0008 °C

For SRM 934, a 2 °C difference would produce the following results,

assuming n approximately equals 4.4, 9.4 and 16.4 for 25 °C, 30 °C, and

37 °C,

Temperature Correction

25 °C 0.00016 x 4.4 x + 2 = +0.0014 °C

30 °C 0.00016 x 9.4 x + 2 = +0.0030 °C

37 °C 0.00016 x 16.4 x + 2 = +0.0052 °C

To help clarify any difficulty that may remain, an example of how

to apply the corrections is given below:

Thermometer = SRM 934,

The reading of the thermometer (immersed 95 mm in the bath) = 30.013 °C,

Measured emergent stem temperature = 29 °C,

Number of degrees from immersion mark to point of reading (30 °C) = 9.4,

Correction on the Report of Calibration at 30 °C = -0.019 (stem

temp. = 26 °C).

An ice point check produced the same result as shown on the Report

of Calibration.

First find the stem temperature correction:

stem correction = 0.00016 xnx(t - t ,) sp obs

= 0.00016 x 9.4 x (26 - 29)

= -0.005°

True temperature = thermometer reading + stem correction + reported

correction

= 30.013 + (-0.005) + (-0.019)

= 29.989 °C

8
V. SUMMARY AND CONCLUSIONS

In order to obtain the accuracy of temperature measurements of

which the thermometers of SRM 933 and SRM 934 are capable, the following

items should be closely observed when using them:

1) check for a separated mercury column and gas bubbles in the bulb,

2) check the ice point periodically for changes in the bulb volume,

3) always use the thermometer at the proper immersion (95 mm)

,

4) correct for emergent stem temperatures different from those

listed in the Report of Calibration,

5) gently tap the thermometer before reading,

and 6) read with a telescope, if possible to avoid parallax errors. With the introduction and use of these SRM thermometers in the

typical clinical laboratory, there will be a marked improvement in the

laboratory's measurement capability. The thermometers will provide a means by which the laboratory personnel can make a start toward eliminating

any uncertainty in their testing which is due to inaccurate temperature

measurement and, in many cases, its control. This will assist efforts

at improving measurement reproducibility within a given laboratory and

intercomparisons among laboratories.

VI . REFERENCES

1. Bowers, G.N. , Jr. and McComb, R.B., A Continuous Spectrophotometric

Method for Measuring the Activity of Serum Alkaline Phosphatase,

Clin. Chem. 12, 70 (1966).

2. Bowers, G.N., Jr., Measurement of Isocitric Dehydrogenase Activity in

Body Fluids, Clin. Chem. _5, 509 (1959).

3. Amador, E., Dorfman, L.E., and Wacker, W.E.C., Serum Lactic Dehydrogenase Activity: An Analytical Assessment of Current Assays, Clin.

Chem. 9, 931 (1963).

4. Worthington Enzyme Manual, Section III, Clinical Reagents, Worthington

Biochemical Corporation, Freehold, New Jersey, 1972, pp. 179-216.

5. Bowers, G.N., Jr., Bergmeyer, H.U., Moss, D.W., Draft Proposal (No.

8) for I.F.C.C. Reference Methods for Enzymes, Clin. Chem. 19_, 268

(1973).
6. The International Practical Temperature Scale of 1968, Metrologia

_5, 35 (1969).

7. Swindells, J.F., Calibration of Liquid-in-Glass Thermometers, Nat.

Bur. Stand. Monograph 90 , Superintendent of Documents, U.S.

Government Printing Office, Washington, D.C. 20402.

8. Riddle, J.L., Furukawa, G.T., and Plumb, H.H., Platinum Resistance

Thermometry, Nat. Bur. Stand. Monograph 126 , Superintendent of

Documents, U.S. Government Printing Office, Washington, D.C. 20402.

10
9

r

0

+ 1 CD

CO

E

E

+ 1 CO

rO

CO

CO

0

T

10 mm MINIMUM

1

A

25 mm MINIMUM

15 10 mm

18 + mm —

T

30 ± 5 mm

Figure 1. The three thermometers of SRM 933. The subdivisions are

0.05 °C and the graduations have longer lines at intervals of 0.10 °C

and 0.50 °C.

11
12
T

IX) + 1 CD

CD

CO

+ 1 in oo

co

0

10mm MINIMUM

r

25 mm MINIMUM

L

15± 10 mm

L

"T

18t 5 mm

i

30+5 mm

1

Figure 3. The thermometer of SRM 9 34. The divisions are 0.05 °C and

the graduations have longer lines at intervals of 0.10 °C and 0.50 °C.

13

NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS SP 260-482. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

STANDARD REFERENCE MATERIALS: DESCRIPTION AND USE OF

PRECISION THERMOMETERS FOR THE CLINICAL LABORATORY, SRM 933

AND SRM 934

0. Publication Date Mav 1974

6. Performing Organization Code

7. AUTHOR(S)

B. W. Mangum and J„ A„ Wise

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Pro|ect/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as No. 9.

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Library of Congress Catalog Card Number: 74-7455

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Because of the high sensitivity to temperature of many facets of the clinical

laboratory, e.g. in enzyme reactions and in pH and blood gas analysis, there is a

need for accurate temperature measurements and its control. In order to help satisfy

these needs and to aid in getting a usable and accurate temperature scale into the

clinical laboratory, the National Bureau of Standards has developed SRM 933 and SRM

934 0 These are precision thermometers, which are calibrated at 0 °C, 25 °C, 30 °C,

and 37 °C and their description, their calibration, and the procedures for their

proper usage are discussed.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Clinical laboratory; enzymology; health care; liquid-in-glass thermometers; standard

reference material; SRM 933; SRM 934; thermometers.

18. AVAILABILITY [j£ Unlimited

I | For Official D istribution. Do Not Release to NTIS

I

I Order From Sup. of Doc, U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. CI 3. 10: 2o0—48

I 1 Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

19. SECURITY CLASS

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21. NO. OF PAGES

23

22. Price

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