NIOSH Manual of Analytical Methods (NMAM) 5th Edition

Title: o-Cresol in Urine

Analyte: o-Cresol

Author/developer: Maria Carolina Siso and James B. Perkins 

Date: February 2015

NOTE: Method developed under contract CDC-200-2001-08000

Disclaimer: Mention of any company or product does not constitute endorsement by the National 

Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. In addition, 

citations to websites external to NIOSH do not constitute NIOSH endorsement of the sponsoring 

organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of 

these websites. All web addresses referenced in this document were accessible as of the publication 

date.

BACKUP DATA REPORT

NIOSH Method No. 8321
Backup data report for NIOSH Manual of Analytical Methods 5th edition

o-CRESOL in URINE: Backup Data Report

INTRODUCTION AND BACKGROUND

The National Institute for Occupational Safety and Health (NIOSH) requested the 

development of a method for the determination of o-cresol in urine. The presence of o-cresol in 

urine can be the product from two sources of exposure. One of them is direct exposure to ocresol, and the second, no less important, is exposure to toluene. 

o-Cresol

In 90% of the uses, cresols are organic intermediates in the manufacturing of phenolic 

and epoxy resins and plasticizers, herbicides, rubber and plastic antioxidants, dyes, deodorizing 

and odor-enhancing compounds, and pharmaceuticals. Additional industrial uses of o-cresol or 

mixtures of cresols include antiseptics and disinfectants, cleaning compounds, degreasers, paint 

strippers and paints, adhesive and connected products, additives to phenol-formaldehyde resins, 

wood preservatives, photography, ore flotation agent, and cutting oils [1]. 

Symptoms of exposure to o-cresol may include skin eruptions, as well as liver and kidney 

damage [2]. o-Cresol may cause burns to the eyes, headache, dizziness, nausea, vomiting, 

stomach pain, exhaustion, and possibly coma [3]. It may also cause painless blanching or 

erythema, profuse sweating, intense thirst, diarrhea, cyanosis from methemoglobinemia, 

hemolysis, convulsions, pulmonary edema, death from respiratory failure, jaundice, oliguria, and 

anuria [4]. When o-cresol comes into contact with the skin, it may cause prickling, intensive 

burning, loss of feeling, wrinkling, white discoloration, softening, and later, gangrene. Other 

symptoms include extensive damage to the eyes, blindness, weakness of muscles, dimness of 

vision, ringing of ears, rapid breathing, mental confusion and loss of consciousness [5]. o-Cresol
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may cause skin burns, central nervous system depression and gastroenteric disturbances [6, 7]. It 

may also cause skin and eye irritation [8]. 

The United States Environmental Protection Agency has classified o-cresol as a possible 

human carcinogen [9]. o-Cresol is not included for classification of cancer risk by the 

International Agency for Research on Cancer [10]. 

Toluene

o-Cresol is a metabolite of toluene, accounting for a small percentage of the absorbed 

toluene dose. When absorbed, toluene is primarily oxidized to benzoic acid, which is then 

conjugated with glycine to produce hippuric acid. A small quantity of the toluene absorbed (less 

than 1%) is oxidized at the aromatic ring and excreted in urine as cresols [11]. 

Toluene is one of the most extensively used industrial solvents. Because a high number 

of workers are exposed annually and because of its effects on the central nervous system, a 

reliable and unambiguous method for toluene exposure assessment is needed. Hippuric acid is 

the most frequently used biomarker in the biological monitoring of occupational exposure to 

toluene. This product of solvent biotransformation may be also found in the urine of individuals 

who have not been exposed to this solvent. Hippuric acid is a normal component of urine and its 

concentration is typically increased with increased consumption of phenolic compounds (e.g., 

tea, wine, fruit juices). These phenols are converted to benzoic acid, which is then converted to 

hippuric acid and excreted in the urine. A smaller fraction of the absorbed toluene is oxidized to 

aromatic compounds, including ortho-cresol, which is not found significantly in the urine of 

nonexposed individuals. The concentration of hippuric acid in the urine of individuals exposed to 

a low toluene concentration does not differ from that of individuals not exposed to the solvent 

[12]. This has led to the conclusion that hippuric acid should not be utilized in the biological 
Backup data report for NIOSH Manual of Analytical Methods 5th edition

monitoring of occupational exposure to low levels of toluene in the air. Toluene can be measured 

in blood [13], but collecting blood is more invasive to the individual. 

Toluene is a clear, colorless liquid with a distinctive smell. It is added to gasoline along 

with benzene and xylene. Toluene occurs naturally in crude oil and in the tolu tree. It is produced 

in the process of making gasoline and other fuels from crude oil, in making coke from coal, and 

as a by-product in the manufacture of styrene. Toluene is used in making paints, paint thinners, 

fingernail polish, lacquers, adhesives, and rubber. It is also used in printing and leather tanning 

processes. It is disposed of at hazardous waste sites as used solvent or at landfills where it is 

present in discarded paints, paint thinners, and fingernail polish [14]. The odor of toluene can be 

detected in air at a concentration of 8 parts of toluene per million parts of air (ppm). Toluene can 

be tasted in water at a concentration of 0.04–1 ppm. People who work with gasoline, kerosene, 

heating oil, paints, and lacquers are at the greatest risk of exposure. Because toluene is a 

common solvent and is found in many consumer products, people can be exposed to toluene at 

home and outdoors while using gasoline, nail polish, cosmetics, rubber cement, paints, 

paintbrush cleaners, stain removers, fabric dyes, inks, and adhesives. Smokers are exposed to 

small amounts of toluene from cigarette smoke. Low-to-moderate, day-after-day exposure in the 

workplace can cause tiredness, confusion, weakness, drunken-type actions, memory loss, nausea, 

and loss of appetite. These symptoms usually disappear when exposure is stopped. Researchers 

do not know if long-term exposure to low levels of toluene will cause any permanent effects on 

the brain or body after many years [14]. Further research on the biological effects of toluene 

exposure is needed to determine exposure levels that lead to irreversible neurobehavioral 

changes [11]. 
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Analysis 

Numerous methods for the determination of cresols have appeared in the literature, based 

on different analytical techniques, e.g., high-performance liquid chromatography with ultraviolet 

detection (HPLC-UV) [15], gas chromatography with flame ionization detection (GC-FID) [16], 

and GC with mass spectrometric (MS) detection [17]. The methodology presented in this report 

is based on the preparation of urine extracts and the subsequent analysis by GC-MS. The use of 

the highly selective MS has a great advantage over other detectors as it eliminates many of the 

interferences of other organic compounds that may be present in the samples. 

The isomers of cresol are excreted in urine as their glucuronides and sulfates. To analyze 

for cresols directly, they must be first separated from the biological conjugate and matrix. This is 

usually accomplished by heating a urine sample with a concentrated mineral acid (e.g., 

hydrochloric acid, sulfuric acid) for 30 minutes to 1 hour. The transfer of cresol from the 

aqueous hydrolysate to an organic solvent is accomplished by simple extraction with a volatile 

organic solvent such as methylene chloride or ethyl ether [18]. 

In the present method, the sample preparation technique is an adaptation of the procedure 

used in NIOSH method 8305 [19]. The acid used was concentrated hydrochloric acid and the 

organic extraction solvent was methyl tert-butyl ether (MTBE). Nitrobenzene was used as an 

internal standard to normalize the peak areas of o-cresol detected in the samples [19]. The 

extracts were quantified by operating the mass spectrometer in the selected-ion monitoring (SIM) 

mode, which provides higher sensitivity than the full scan mode.

REAGENTS AND MATERIALS

Presented in Table 1 is the list of reagents and solvents used for this method and its 

evaluation. Urine used for the study was provided by volunteer donation and stored at 4 oC. 
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TABLE 1. LIST OF CHEMICALS

Chemical Vendor CAS # Purity Lot #

o-Cresol Chem Service 95-48-7 99.5% 225-31A

Hydrochloric acid Fisher 7647-01-0 35-38% 4101080-07549

Methanol Burdick & Jackson 67-56-1 GC2 BW298 / BT477

Methyl-tert-butyl ether Omnisolv 1634-04-4 99.96% 42086

Nitrobenzene Chem Service 98-95-3 99.5% 219-78A

Sodium sulfate anhydrous Mallinckrodt 7757-82-6 AR 8024X12612

Water DataChem Laboratories 7732-18-5 ASTM Type II N/A

Preparation of Primary Stock and Internal Standard Solutions

The nitrobenzene (internal standard) solution and o-cresol primary stock solutions were 

prepared as noted in Table 2. The solutions were stored at -10 oC. 

TABLE 2. PRIMARY STOCK AND INTERNAL STANDARD SOLUTION 

PREPARATION

ID Description Conc Preparation

IS Internal Standard 508 0.1276 g nitrobenzene (99.5% pure) in

250 mL methanol 

PSS Primary Stock Standard 10,680 0.1073 g o-cresol (99.5% pure) in 10 mL 

methanol 

ISS1 Intermediate Stock Standard 1 1,068 0.5 mL PSS diluted to 5 mL with methanol

ISS2 Intermediate Stock Standard 2 106.8 0.05 mL PSS diluted to 5 mL with 

methanol 

SAMPLE PREPARATION AND INSTRUMENT CONDITIONS

Sample Preparation

The same preparation method was used consistently for all the samples and standards 

throughout the study. Aliquots of 5 mL of human urine were dispensed into 15 mL graduated 

polypropylene centrifuge tubes. The working standards were spiked with specific amounts of ocresol. All samples and standards were acidified with 1 mL of concentrated hydrochloric acid. 
Backup data report for NIOSH Manual of Analytical Methods 5th edition

The tubes were capped, shaken vigorously for about one minute, and immersed in a water bath at 95

oC for 1.5 hours. After this, they were removed from the bath and allowed to cool to room temperature. 

Aliquots of 0.250 mL nitrobenzene internal standard solution (see Table 2) were added to each 

tube, then water (ASTM Type II) was added to the 10 mL calibration mark, and finally 2 mL of MTBE 

were added. The tubes were capped again and shaken vigorously for about 2 minutes. 

After the phases separated, the top organic phase was transferred to 2-mL GC amber vials 

containing around 0.2 g of sodium sulfate (to absorb any water present). The vials were capped and 

stored at 4 oC until ready for analysis. 

Instrument Conditions

• Instrument: Hewlett Packard (HP) Model 5890 gas chromatograph equipped with an 

HP Model 5972 mass spectrometer and an HP Model 7673 autosampler

• Column: fused silica capillary column (DB-5ms, 30 m x 0.32 mm I.D., 0.5 μm film)

• Carrier gas: helium 

• Gas flow: 1.30 mL/min

• Pressure: constant 

• Oven Program: 50 °C for two minutes; 10 °C/min, up to 150 °C; 20 °C/min, up to 310 

°C; hold for 5 minutes

• Injector temperature: 265 oC 

• MS detector temperature: 285 oC 

• Injection volume: 2 μL

• Injection mode: splitless

• MS Detector: set to monitor ions m/z 108, 107, 77, and 123 in SIM mode with a dwell 

time of 30 msec. Ions m/z 108 and 123 were the quantifying ions for o-cresol and 

nitrobenzene, respectively. Ions m/z 107 and 77 were used for qualitative purposes to confirm ocresol and nitrobenzene, respectively.

Calibration 

Nine working standards ranging from 0.043 μg/mL to 64.1 μg/mL were prepared by 

spiking into 5 mL of urine the amounts shown in Table 3. 
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TABLE 3. PREPARATION OF WORKING STANDARDS

Standard # Stock Solution

Volume Taken 

(mL)

Final Dilution 

Volume (mL)

o-Cresol in Urine 

(μg/mL)

W$1 ISS2 0.002 5.0 0.043

W$2 ISS2 0.005 5.0 0.107

W$3 ISS2 0.010 5.0 0.214

W$4 ISS2 0.050 5.0 1.07

W$5 ISS2 0.100 5.0 2.14

W$6 PSS 0.005 5.0 10.7

W$7 PSS 0.010 5.0 21.4

W$8 PSS 0.020 5.0 42.7

W$9 PSS 0.030 5.0 64.1

Blank - 0 5.0 0

QC ISS2 0.005-0.025 5.0 0.1- 0.5

The calibration curve was made by plotting response ratios (Y axis) vs. concentration ratios (X 

axis) of o-cresol to nitrobenzene, using a quadratic model fitting. 

Chromatographic Analysis 

Figure 1 displays a representative chromatogram when the previously described conditions are 

employed. This chromatogram is from a 40 μg/mL standard prepared in the urine pool used for the 

calibration standards utilized in the User Check evaluation (Appendix 2.) The unlabeled peak in the center 

appears in nearly every individual urine or urine pool. Full-scan mass spectra determined this peak to be pcresol, possibly co-eluting with m-cresol. The mass spectra of these compounds are very similar to ocresol. While adequate separation is obtained under method conditions, it would be possible to misidentify 

this peak and caution should be used. The breakdown of proteins in the body, specifically tyrosine and 

phenylalanine, lead to a “normal” endogenous appearance of p-cresol in the urine [16]. 
Backup data report for NIOSH Manual of Analytical Methods 5th edition

FIGURE 1. Chromatogram of a 40 μg/mL standard prepared in urine

The conditions applied extend the run time considerably beyond the elution of the last peak. This is 

necessary to bake out any higher-molecular-weight compounds that may be present in the sample extract. 

LIMITS OF DETECTION AND QUANTITATION STUDY

For the limit of detection (LOD) and limit of quantitation (LOQ) study, urine standards 

ranging from 0.0107 μg/mL to 64.1 μg/mL were analyzed. The four lower concentrations were 

prepared in triplicate, as shown in Table 4. 
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TABLE 4. LOD/LOQ STANDARDS

STD # o-Cresol (μg/mL urine)

$1 0.0107

$2 0.0107

$3 0.0107

$4 0.0214

$5 0.0214

$6 0.0214

$7 0.0427

$8 0.0427

$9 0.0427

$10 0.107

$11 0.107

$12 0.107

$13 0.214

$14 1.07

$15 2.14

$16 10.7

$17 21.4

$18 64.1

The LOD and LOQ calculated by fitting the data from the analysis of these standards to a 

quadratic curve and applying Burkart’s Method [21] are shown in Table 5. 

TABLE 5. LOD/LOQ STUDY RESULTS

R2 LOD LOQ

0.9998 0.009 μg/mL urine 0.03 μg/mL urine

Since the LOD estimated by this method is lower than the lowest standard used in the 

study, the value of the lowest standard becomes the new LOD. The final LOD and LOQ for the 

method are shown in Table 6. 

TABLE 6. METHOD LOD/LOQ

LOD LOQ

0.01 μg/mL urine 0.03 μg/mL urine
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LONG-TERM STABILITY STUDY

This study was directed to evaluate the behavior of o-cresol in urine samples over a 

period of time and under two different typically-used storage temperatures. A set of thirty-nine 

tubes containing 5 mL of urine from the same source were spiked with o-cresol at a 

concentration of approximately 30 x LOQ. Twelve of these tubes were left at room temperature. 

The other twenty-seven tubes were stored in the refrigerator at 4 oC. All the specimens were 

protected from light.

The recoveries of o-cresol obtained for the stability study are presented in Table 7. 

TABLE 7. RESULTS FOR LONG-TERM STABILITY STUDY

Initial Concentration = 0.854 μg/mL 

Replicates Recoveries (μg/mL)

Day Temperature R1 R2 R3 R4 R5 R6

Average 

Recovery %

STD. 

DEV.

1 4 oC 0.846 0.915 0.951 0.947 0.921 1.16 112 12.4 

7 4 oC 0.847 0.857 0.806 0.817 0.827 0.822 97.1 2.2 

10 4 oC 0.808 0.954 0.872 - - - 103 6.1 

14 4 oC 0.842 0.739 0.779 - - - 92.1 6.1 

21 4 oC 0.753 0.828 0.883 - - - 96.2 7.6 

30 4 oC 1.01 0.845 0.837 0.749 0.920 0.945 104 10.7 

1 ~22 oC 0.881 0.855 1.15 0.829 0.809 0.722 102 16.9 

7 ~22 oC 0.767 0.712 0.767 0.814 0.831 0.704 89.7 6.0 

The average recoveries for the samples stored at 4 oC ranged from 92.1 to 112 %, 

illustrating that refrigeration at 4 oC is effective for analyte preservation. On the other hand, the 

samples stored at room temperature began to show analyte loss after 7 days, as seen by 

comparing the average value obtained for the set left at room temperature (89.7%) with the 

average value obtained for the set stored at 4 oC after 7 days (97.1%). It is recommended to keep 
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the samples refrigerated to minimize the amount of bacterial growth and possible analyte 

degradation. 

PRECISION, BIAS, AND ACCURACY STUDY

The study was performed to evaluate the precision, bias, and accuracy of the method 

against the acceptance criteria. The precision reflects the ability of the method to replicate 

measurement results. It is assumed to be constant or homogeneous over all concentrations tested 

for the method evaluation. The accuracy criterion requires that a method give a result that is 

within ±25% of the true concentration with a probability of 0.95 for an individual observation 

(i.e., that the accuracy of an acceptable method is no greater than 25%). Bias, as the 

uncorrectable relative discrepancy between the mean of the distribution of measurements from a 

method and the true concentration being measured, must not be greater than 10% [22]. 

The five concentration levels considered for the study ranged from 1 x LOQ to 100 x 

LOQ. Each level was evaluated with six replicates. Three blank samples were included in the 

study, with non-detectable amounts of o-cresol present in the results. The samples were prepared 

according to the method. The recoveries obtained and the average for each level are presented in 

Table 8.

TABLE 8. o-CRESOL RECOVERIES

Level ~1 x LOQ ~3 x LOQ ~10 x LOQ ~30 x LOQ ~100 x LOQ

o-Cresol μg/mL urine 0.0214 0.0854 0.214 0.854 2.14

Recovery o-Cresol (%) 122

136 

126 

108 

108 

112 

96.0

93.7 

90.2 

89.0 

86.7 

80.8 

78.0

85.5 

90.7 

88.3 

88.3 

89.7 

91.6

98.1 

102 

91.2 

94.3 

97.7 

95.7

95.9 

77.2 

78.9 

85.9 

106 

Average Recovery (%) 118 89.4 86.8 95.8 89.9

Precision CV 0.0956 0.0601 0.0532 0.0446 0.124 
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Bartlett’s test for homogeneity of the individual coefficients of variation for all test levels 

gave a Chi squared value of 6.98, which was acceptable for a 95% distribution, allowing the data 

to be pooled from all 5 levels. There were no Grubb’s outliers at any level; however, the F′ test 

for homogeneity of bias failed for a 95% distribution. After omitting the lowest level, 1 x LOQ, 

both tests, Bartlett’s and F′, passed for a 95% distribution.

The accuracy was obtained using a nomogram relating accuracy to precision and bias. 

The ordinate axis of the graph is method precision while the abscissa is method bias. Accuracy is 

marked by the curved lines on the graph [22]. The results of the study are shown in Table 9. 

TABLE 9. PRECISION, BIAS, AND ACCURACY

Compound Range Studied 

(μg/mL urine)

Precision 

Overall SrT

Average 

Bias

Bias Range Accuracy (%)

o-Cresol in Urine 0.0214 to 2.14 0.0771 -0.0952 -0.132 to -0.0416 21

The detailed data used in calculating the precision, bias, and accuracy are included in 

Appendix 1. 

SUMMARY

The data generated during the development of this method met NIOSH criteria for 

precision, bias, and accuracy in all studies performed [22] and proved to be adequate for the 

purpose it was developed. The method also meets guidelines for bioanalytical method 

development and evaluation [23]. 

REFERENCES

1. IPCS [2005]. o-Cresol (Screening Information Data Set – SIDs). International 

Programme on Chemical Safety.www.inchem.org/documents/sids/sids/95487.pdf. 

2. Sax NI [1985]. Dangerous properties of industrial materials report. Bi-monthly updates. 

May/June 1985. Vol. 5, #3. New York: Van Nostrand Reinhold Company, Inc., pp. 30- 

34. 

3. Bretherick L [1986]. Hazards in the chemical laboratory. 4th Ed. London: The Royal 

Society of Chemistry, pp. 257-258. 
Backup data report for NIOSH Manual of Analytical Methods 5th edition

4. Dreisbach RH [1983]. Handbook of poisoning: prevention, diagnosis and treatment. 11th 

Ed. Los Altos, CA: Lange Medical Publications, pp. 402-405. 

5. Sittig M [1985]. Handbook of toxic and hazardous chemicals and carcinogens. 2nd Ed. 

Park Ridge, NJ: Noyes Publications, pp. 263-264. 

6. U.S. Coast Guard, Department of Transportation [1985]. CHRIS hazardous chemical 

data. U.S. Coast Guard. Washington, D.C. Vol. 1. 

7. Clayton GD, Clayton FE [1981]. Patty's industrial hygiene and toxicology, Vol. 2. Third 

Revised Edition. New York: John Wiley and Sons, pp. 2597-2601. 

8. Sax NI, Lewis RJ Sr [1989]. Dangerous properties of industrial materials. 7th Ed. Vol. II. 

New York: Van Nostrand Reinhold, p. 970, #CNX000. 

9. US EPA [2011]. 2-Methylphenol (CASRN 95-48-7). United States Environmental 

Protection Agency. www.epa.gov/iris/subst/0300.htm. 

10. IARC [2010]. International Agency for Research on Cancer. 

http://monographs.iarc.fr/ENG/Classification/ClassificationsAlphaOrder.pdf. 

11. DeRosa E, Bartolucci GB, Sigon M, Callegaro R, Perbellini L, Brugnone F [1987]. 

Hippuric acid and ortho-cresol as biological indicators of occupational exposure to 

toluene. Am J Ind Med 11(5):529-537. 

12. Amorim LC, Alvarez-Leite EM [1997]. Determination of o-cresol by gas 

chromatography and comparison with hippuric acid levels in urine samples of individuals 

exposed to toluene. J Toxicol Environ Health 50(4):401-7. 

13. NIOSH [2014]. Toluene in blood: Method 8007. In Ashley K, O’Connor PF, eds. NIOSH

th

Manual of Analytical Methods, 5 ed. Cincinnati, OH: U.S. Department of Health and 

Human Services, Centers for Disease Control and Prevention, National Institute for 

Occupational Safety and Health, DHHS (NIOSH), Publication No. 2014-151. 

www.cdc.gov/niosh/nmam.

14. Agency for Toxic Substances and Disease Registry (ATSDR) [2000]. Toxicological 

profile for toluene. Atlanta, GA: U.S. Department of Health and Human Services, Public 

Health Service.

15. Yoshikawa M, Tagushi Y, Arashidani K, Kodama Y [1986]. Determination of cresols in 

urine by high-performance liquid chromatography. J Chromatogr 362(3):425-429. 

16. Needham LL, Head SL, Cline RE [1984]. Determination of phenols and cresols inurine 

by gas chromatography. Anal Lett17(B14):1555-1565. 

17. Angerer J, Wulf H [1985]. Occupational chronic exposure to organic solvents. XI. 

Alkylbenzene exposure of varnish workers: Effects on hematopoietic system. IntArch 

Occup Environ Health. 56:307-321. 
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18. Agency for Toxic Substances and Disease Registry (ATSDR) [1992]. Toxicological 

profile for cresols. Atlanta, GA: U.S.Department of Health and Human Services, Public 

Health Service.

19. NIOSH [1994]. Phenol and p-cresol in urine: Method 8305. In Eller PM, CassinelliME,

th

eds. NIOSH Manual of Analytical Methods, 4 ed. Cincinnati, OH: U.S. Department of 

Health and Human Services, Centers for Disease Control and Prevention, National 

Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 94-113. 

20. Annual Book of ASTM Standards, Volume 11.01, 1986. Standard D 1193. Standard 

specification for reagent water.

21. Burkart JA [1986]. General procedures for limit of detection calculations in the industrial 

hygiene chemistry laboratory. Appl Ind Hyg 1(3):153-155. 

22. NIOSH [1995]. Guidelines for air sampling and analytical method development and 

evaluation. BY KennedyER, Fischbach TJ, Song R, Eller PM, Shulman SA. Cincinnati, 

OH: Department of Health and Human Services, Centers for Disease Control and 

Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) 

Publication No. 95-117. 

23. FDA [2001]. Guidance for industry: Bioanalytical method validation. US Food and Drug 

Administration. http://www.fda.gov/downloads/Drugs/Guidances/ucm070107.pdf.

Written By: María Carolina Siso and James B. Perkins, DataChem Laboratories, Inc, Salt Lake 

City, Utah under NIOSH CDC Contract 200-2001-08000. 

Edited By: John M. Reynolds, Roxanne W. Olson, ALS Environmental, formerly DataChem 

Laboratories, Inc., Salt Lake City, Utah. Final editing and User Check data added by Dale A. 

Shoemaker, Ph.D., NIOSH/DART/CEMB. 
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APPENDIX 1

RECOVERY DATA FOR o-CRESOL IN URINE

Part 1 (n=6) 

Level ~1 x LOQ ~1 x LOQ ~3 x LOQ ~3 x LOQ ~10 x LOQ ~10 x LOQ ~30 x LOQ ~30 x LOQ ~100 x LOQ ~100 x LOQ

o-Cresol Applied 0.0214

μg/mL

0.0214

μg/mL

0.0854

μg/mL

0.0854

μg/mL

0.214

μg/mL

0.214

μg/mL

0.854

μg/mL

0.854

μg/mL

2.14

μg/mL

2.14

μg/mL

o-Cresol Recovered μg/mL % μg/mL % μg/mL % μg/mL % μg/mL %

Sample 1 0.026 121.5 0.082 96.0 0.167 78.0 0.782 91.6 2.048 95.7

Sample 2 0.029 135.5 0.080 93.7 0.183 85.5 0.838 98.1 2.053 95.9

Sample 3 0.027 126.2 0.077 90.2 0.194 90.7 0.873 102.2 1.653 77.2

Sample 4 0.023 107.5 0.076 89.0 0.189 88.3 0.779 91.2 1.689 78.9

Sample 5 0.023 107.5 0.074 86.7 0.189 88.3 0.805 94.3 1.839 85.9

Sample 6 0.024 112.1 0.069 80.8 0.192 89.7 0.834 97.7 2.264 105.8

Average 0.025 118.4 0.076 89.4 0.186 86.8 0.819 95.8 1.924 89.9

Std Dev 0.0024 11.32 0.0046 5.37 0.0099 4.61 0.0365 4.28 0.2381 11.13

CV2 0.09561 0.09561 0.06013 0.06013 0.05317 0.05317 0.04461 0.04461 0.12374 0.12374

RECOVERY DATA FOR o-CRESOL IN URINE

Part 2

Statistical Element Value

CV2 pooled

(all 5 levels included) 0.08110

CV2 pooled

(omitting lowest concentration level) 0.07705

o-cresol recovered weighted average

(all 5 levels included) 96.06 %

o-cresol recovered weighted average

(omitting lowest concentration level) 90.48 %

chi squared

(all 5 levels included) χ

2 = 6.9846

chi squared

(lowest level omitted) χ

2 = 6.5082

Bartlett’s criteria for 5 concentration levels (5% of 

significance level) 9.49 ≥ χ

2< 

, χ

2 = 6.9846 ⇔ “PASS”

Bartlett’s criteria for 4 concentration levels (5% of 

significance level) 7.81 ≥ χ

2< 

, χ

2 = 6.5082 ⇔ “PASS”

F′ criteria (at 0.05) for 5 concentration levels F′ = 2.7587

F′ criteria (at 0.05) for 4 concentration levels F′ = 3.0984

F′ method for 5 concentration levels FM′ = 12.0796 > F′⇔ “DO NOT PASS”

F′ method for 4 concentration levels FM′ = 1.2075 < F′ ⇔ “PASS”
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BIAS CALCULATION FOR o-CRESOL IN URINE

B = �

oo − cresol recovered

oo − cresol applied � − 1

Test Concentration Levels 1 x LOQ 3 x LOQ 10 x LOQ 30 x LOQ 100 x LOQ 

1 0.21495 -0.03981 -0.21963 -0.08431 -0.04299

2 0.35514 -0.06323 -0.14486 -0.01874 -0.04065

3 0.26168 -0.09836 -0.09346 0.02225 -0.22757

4 0.07477 -0.11007 -0.11682 -0.08782 -0.21075

5 0.07477 -0.13349 -0.11682 -0.05738 -0.14065

6 0.12150 -0.19204 -0.10280 -0.02342 0.05794

Average Bias 0.183801 -0.106167 -0.132399 -0.041569 -0.100779

Standard Deviation 0.11318 0.05375 0.04613 0.04275 0.11127 

N 6 6 6 6 6

Weighted Average for Bias = -0.09523 

Average Standard Deviation = 0.06348 
Backup data report for NIOSH Manual of Analytical Methods 5th edition

Appendix 2

Review of User Check for NIOSH Method 8321 (o-Cresol in urine)

User check samples were prepared by a NIOSH researcher (Dr. Clayton B’Hymer, BHAB) to be 

analyzed by ALS Environmental using draft NIOSH Method 8321. A total of 25 urine samples 

were prepared. The urine was obtained from volunteers at NIOSH and then combined and mixed 

in the BHAB labs into a single pool of urine from which all samples were prepared. The final 

volume of each sample was 20 mL. Five samples were left blank. Five samples were prepared 

containing the analyte at each of the following levels: 0.253 μg/mL, 0.506 μg/mL, 5.06 μg/mL, 

and 30.35 μg/mL. The samples were shipped frozen to ALS Environmental on July 8, 2014 and 

arrived there the next day. The samples were analyzed on July 25, 2014. No significant 

deviations from the analytical procedure in NIOSH Method 8321 were noted. 

For this analysis, the Reporting Limit (RL, which is equivalent to the limit of quantitation, LOQ) 

was determined by ALS to be 0.070 μg/mL. As mentioned above, the spike levels ranged from 

0.253 to 30.35 μg/mL, which is 4 to 430 times the RL and fall within the range of the calibration 

curve. The calibration curve covers concentrations from 0.040 to 60.0 μg/mL. 

o-Cresol was detected in the blank urines, which is to be expected, so blank correction is

required for this set of samples. The average concentration found in the blank samples was 0.047

μg/mL with a relative standard deviation (RSD) of 2.3%. While this value is below the reporting

limit set by ALS, it is above the lowest point of the calibration curve and was measured with

high precision, so it is appropriate to add the blank value to the known spiked amount to give a

“true” target value. A summary table for each level is shown below and a table of data for all

samples can be found at the end of this report.

Table 2.1 Recovery results

True target 

conc (μg/mL)

Average Recovery (%) Standard 

Deviation

% RSD

0.300 96.7 0.76 0.79

0.553 98.4 0.61 0.62

5.11 100.3 0.63 0.63

30.40 92.8 1.30 1.40

Overall 97.1 2.95 3.03

The recovery accuracy at every level is within +/- 8% of the true value, which is well within the 

+/- 15% accuracy required for bioanalytical methods by the US Food and Drug Administration 

[1]. The relative standard deviation (RSD, which is a measure of precision) for all levels ranged 

from 0.6 to 1.4 per cent, which is also well within acceptable limits. The contract lab reported no 

difficulties understanding the draft method nor in setting it up or analyzing the samples. The 

User Check laboratory followed the procedure and the method has been shown to have adequate 

precision and accuracy. It is recommended that the method, NIOSH Method 8321 (o-Cresol in 

urine) be approved and accepted for inclusion in the NIOSH Manual of Analytical Methods. 

RSD=relative standard deviation
Backup data report for NIOSH Manual of Analytical Methods 5th edition

Table 2.2 Recovery data table 

Spike 

ID

Target 

conc 

(μg/mL)

Found 

conc* 

(μg/mL)

Target

+ blank

(μg/mL)

Found 

conc 

(μg/mL)

Recovery 

(%)

4 0 0.048 0 0.048

7 0 0.046 0 0.046

14 0 0.048 0 0.048

16 0 0.048 0 0.048

25 0 0.046 0 0.046

1 0.253 0.287 0.300 0.287 95.7

9 0.253 0.289 0.300 0.289 96.3

12 0.253 0.291 0.300 0.291 97.0

19 0.253 0.293 0.300 0.293 97.7

21 0.253 0.291 0.300 0.291 97.0

3 0.506 0.549 0.553 0.549 99.3

8 0.506 0.543 0.553 0.543 98.2

15 0.506 0.544 0.553 0.544 98.4

17 0.506 0.546 0.553 0.546 98.7

24 0.506 0.540 0.553 0.540 97.6

5 5.06 5.12 5.11 5.12 100.3

10 5.06 5.11 5.11 5.11 100.1

11 5.06 5.18 5.11 5.18 101.4

20 5.06 5.10 5.11 5.10 99.9

22 5.06 5.11 5.11 5.11 100.1

2 30.35 28.6 30.40 28.6 94.1

6 30.35 27.7 30.40 27.7 91.1

13 30.35 28.4 30.40 28.4 93.4

18 30.35 27.9 30.40 27.9 91.8

23 30.35 28.5 30.40 28.5 93.8

*Ave blank=0.047

Ave = Average; SD = standard deviation; RSD = relative standard deviation.

SD and RSD are calculated using the recovery values.

Dale Shoemaker, PhD 

Research Chemist

August 27, 2014 

[1] FDA [2001]. Guidance for industry: Bioanalytical method validation.

http://www.fda.gov/downloads/Drugs/Guidances/ucm070107.pdf