## 5910 UV-ABSORBING ORGANIC CONSTITUENTS*

5910 A. Introduction

1. Applications



### Because some organic compounds commonly found in waterand wastewater (e.g., lignin, tannin, humic substances, and various aromatic compounds) strongly absorb ultraviolet (UV) radiation, UV absorption is a useful surrogate measure of such constituents in fresh waters, 1–3 

### salt waters, 4–6 

### and wastewa

ters. 7,8 

### Strong correlations may exist between UV absorption and organic carbon content, color, and precursors of trihalomethanes (THMs) and other disinfection byproducts. 9,10 

### UV absorption has been used to monitor industrial wastewater effluents 11 

### and to evaluate the effectiveness of coagulation, 10 

### carbon adsorp

tion, 12–14 

### and other water treatment processes that remove or

ganics. 10,15 

### Specific absorption (the ratio of UV absorption to organic carbon concentration) has been used to characterize natural organic matter. 10,16–18 

### Some regulatory programs include specific UV absorbance (SUVA)—a ratio of UV absorption todissolved organic carbon concentration—to help control disinfection byproducts.

Although UV absorption can be used to detect certain individual organic contaminants after separation [e.g., by high-performance liquid chromatography (HPLC)], as described in Part 6000, the method described here is not suitable for detecting trace concentrations of individual chemicals. Rather, it provides

an indication of the aggregate concentration of UV-absorbing organic constituents.

2. References

1. D OBBS , R.A., R.H. WISE & R.B. D EAN . 1972. The use of ultra-violet

absorbance for monitoring the total organic carbon of water and
wastewater. Water Res . 6:1173. 2. WILSON , A.L. 1959. Determination of fulvic acids in water. J. Appl. Chem . 9:501. 3. C OOPER , W.J. & J.C. Y OUNG . 1984. Chemical non-specific organic analysis. In R.A. Minear & L. Keith, eds. Water Analysis, Vol. 3. Academic Press, New York, N.Y. 4. O GURA , N. & T. H ANYA . 1968. Ultra-violet absorbance of the seawater, in relation to organic and inorganic matters. Int. J. Oceanol. Limnol . 1:91. 5. O GURA , N. & T. H ANYA . 1968. Ultra-violet absorbance as an index of pollution of seawater. J. Water Pollut. Control Fed. 40:464. 6.. F OSTER , P. & A.W. M ORRIS . 1971. The use of ultra-violet absorption measurements for the estimation of organic pollution in inshore sea
waters. Water Res. 5:19. 7. B UNCH , R.L., E.F. B ARTH & M.B. ETTINGER . 1961. Organic materials in secondary effluents. J. Water Pollut. Control Fed. 33:122. 8. M RKVA , M. 1971. Use of ultra-violet spectrophotometry in the determination of organic impurities in sewage. Wasserwirtsch. Wassertech . 21:280. 9. S INGER , P.C., J.J. B ARRY , III, G.M. PALEN & A.E. S CRIVNER . 1981. Trihalomethane formation in North Carolina drinking waters. J. Amer. Water Works Assoc. 73:392. 10. EDZWALD , J.K., W.C. B ECKER & K.L. WATTIER . 1985. Surrogate parameters for monitoring organic matter and THM precursors. J. Amer. Water Works Assoc. 77(4):122. 11. B RAMER , H.C., M.J. WALSH & S.C. C ARUSO . 1966. Instrument for monitoring trace organic compounds in water. Water Sewage Works 113:275. 12. B ISHOP , D.F., L.S. M ARSHALL , T.P. O’FARRELL , R.B. D EAN , B. O’C ONNOR , R.A. D OBBS , S.H. GRIGGS & R.V. V ILLIERS . 1967. Studies on activated carbon treatment. J. Water Pollut. Control Fed. 39:188. 13. S ONTHEIMER , H.N., E. H EILKER , M.R. J EKEL , H. N OLTE & F.H. V OLIMER . 1978. The Mu  ̈lheim process. J. Amer. Water Works Assoc. 70(7):393. 14. S UMMERS , R.S., L. C UMMINGS , J. D EM ARCO , D.J. H ARTMAN , D. M ETZ , E.W. H OWE , B. M ACLEOD & M. S IMPSON . 1992. Standardized Protocol for the Evaluation of GAC, No. 90615. AWWA Research Foundation & American Water Works Assoc., Denver, Colo. 15. KRASNER , S., P. WESTERHOFF , B. C HEN , B.RITTMANN , S. NAM & G. AMY . 2009. Impact of wastewater treatment processes on organic carbon, organic nitrogen and DBP precursors in effluent organic
matter. Environ. Sci. Technol. 43(8):2911. 16. T HURMAN , E.M. 1985. Organic Geochemistry of Natural Waters.Martinus Nijhoff/Dr. W. Junk Publishers, Dordrecht, Netherlands. 17. O WEN , D.M., G.L. AMY & Z.K. C HOWDHURY . 1993. Characterization of Natural Organic Matter and Its Relationship to Treatability, No. 90631. AWWA Research Foundation & American Water Works Assoc., Denver, Colo. 18. WEISHAAR , J.L., G.R. A IKEN , B.A. B ERGAMASCHI , M.S. FRAM , R. FUJII & K. M OPPER . 2003. Evaluation of specific ultraviolet absorbance as an indicator of the chemical composition and reactivity of dissolved organic carbon. Environ. Sci. Technol. 37(8):4702. * Approved by Standard Methods Committee, 2011. Joint Task Group: Suzanne M. Teague (chair), Ali Haghani, Edward W.D. Huffman, Jr., Louis A. Kaplan, Ilke E. McAliley, Mark A. Schlautman.

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## 5910 B. Ultraviolet Absorption Method

1. General Discussion



### a. Principle: UV-absorbing organics in a sample absorb UVlight in proportion to their concentration. Filter samples to control particle-related variations in UV absorption. The sample’s pH should be adjusted before filtration; however, certain organicconstituents (e.g., humic substances) may be lost to filters, suspended particles, or vessel walls at lower pH values. 1 

### When filtering samples for SUVA determination, do not adjust pH before filtration.

UV absorption historically has been measured at 253.7 nm (often rounded to 254 nm), but the choice of wavelength is arbitrary. Experienced analysts may choose a wavelength that minimizes interferences while maximizing absorption by the compound(s) of interest. If using a wavelength other than 253.7 nm, state that wavelength when reporting results.

b. Interferences: The primary interferences in UV-absorption measurements are from colloidal particles and UV-absorbing inorganics—notably iron, nitrate, nitrite, and bromide. Certain oxidants and reducing agents (e.g., ozone, chlorate, chlorite, chloramines, and thiosulfate) also absorb ultraviolet light at 253.7 nm. Many natural waters and treated drinking waters have been shown to be free of these interferences.

Evaluate and correct for UV absorption contributed by specific interfering substances. If cumulative corrections exceed 10% of the total absorption, select another wavelength and/or method. Also, UV absorption by organic matter may vary when pH is below 4 or above 10, so avoid these ranges. 2



### A UV absorption scan from 200 to 400 nm can be used to determine the presence of interferences. Typical absorptionscans of natural organic matter are featureless curves of increasing absorption with decreasing wavelength. Sharp peaks or irregularities in the scan may indicate inorganic interferences. Because many organic compounds in water and wastewater (e.g., carboxylic acids and carbohydrates) do not absorb significantlyin UV wavelengths, correlate UV absorption to dissolved organic carbon (DOC) or soluble chemical oxygen demand (COD). However, use such correlations with care because they may vary from water to water, seasonally or during storms on the same water, and between raw and treated waters. In addition, chemical oxidation of the organic material (e.g., ozonation, chlorination) may reduce UV absorption without removing organics and thusmay change correlations. Because UV absorption and correlations with UV absorption are site-specific, they may not be comparable from one water source to another.

c. Minimum detectable concentration: The minimum detectable concentration cannot be determined rigorously because this is a nonspecific measurement. Also, the minimum detectableconcentration of a particular constituent depends on the relationship between UV absorption, the desired characteristic (e.g., trihalomethane formation potential or DOC), and any interfering substances. For precise measurement, select cell path length to provide a minimum absorbance of approximately 0.005 cm  1 

### and a maximum absorbance of approximately 0.950 cm  1 

### . Di

lute high-strength samples to fall within the determined range.

d. Sampling and storage: Collect samples in amber glassbottles that have been washed, thoroughly rinsed with organicfree water, and baked at 400°C for at least 1 hour. Seal with tetrafluoroethylene (TFE)-lined caps. If individual TFE septa are used, wash and rinse thoroughly with organic-free water, wrap in foil and bake at 100°C for 1 hour or soak the septa in 10% sodium persulfate for 1 hour at 60°C and rinse thoroughly with organic-free water. 3 

### Pre-cleaned containers from commercial vendors may also be available. Store samples at 6°C; samples requiring shipping should be transported on ice. Adjust pH (if needed) and analyze within 48 hours.

Samples may be filtered in the field. If samples require pH adjustment, make the adjustment before filtration. Do not adjust pH of samples for SUVA determination. 1



### 2. Apparatus



### a. Spectrophotometer, for use between 200 and 400 nm, withmatched quartz cells providing a light path of 1 cm. For lowabsorbance samples, use a path length of 5 or 10 cm. A scanning spectrophotometer is useful.

b. Filter : Use a glass fiber filter* without organic binder, or use TFE, polycarbonate, or silver filters. Polyethersulfone (PES)or hydrophilic polypropylene (HPP) filters are also recommended. 4 

### Other filters that neither sorb UV-absorbing organicsof interest nor leach interfering substances (e.g., nitrate or organics) into the water may be used, especially if colloidal matter must be removed. The specific filter used should be reported with the data. Practical filter diameters are 2.2 to 4.7 cm, although this may vary. Pre-rinse filter with a sample of organic-free water to remove soluble impurities. As an option, glass fiber filters may be combusted at high temperatures (450 to 500°C for at least 2 hours) before rinsing. If alternate separation techniques, filters, or filter preparations are used, demonstrate that equivalent results are produced.

Filter pore size will influence test results, especially in raw waters. When filtering samples for SUVA determination, check the applicable regulatory constraints to see if a filter with an absolute pore size of 0.45  m is required, because glass fiber filters generally do not meet this requirement. For highly turbid samples, pre-filters (including glass fiber) may be used to remove interferences and minimize clogging of 0.45-  m filters. 5 

### c. Filter assembly, g lass, TFE, stainless steel or other material that neither sorbs UV-absorbing organics nor leaches interfering substances, capable of holding the selected filters. Polypropylene syringes with syringe-type filter holders or peristaltic pumps with in-line filter holders may be used as an alternative to vacuum filtration. 3



### 3. Reagents



### a. Organic-free water: Reagent water containing less than 0.010 cm  1 

### of UV-absorbing compounds. For optimum perfor

mance, reagent water of less than 0.0045 cm  1 

### is recommended.

* Whatman grade 934AH; Gelman type A/E; Millipore type AP40; ED Scientific Specialties grade 161; or other products that give demonstrably equivalent results. UV-ABSORBING ORGANIC CONSTITUENTS (5910)/Ultraviolet Absorption Method

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### b. Hydrochloric acid (optional), HCl, 0.1 N

. c. Sodium hydroxide (optional), NaOH, 0.1 N

. d. Phosphate buffer (optional) : Dissolve 4.08 g dried anhydrous KH 2

### PO 4 

### and 2.84 g dried anhydrous Na 2 

### HPO 4 

### in 800 mL organic-free water. Verify that pH is 7.0 and dilute to 1 L with organic-free water. Store in a brown glass bottle at 4°C. Preparefresh weekly (or more frequently if microbial growth is observed).

e. Organic carbon stock solution: Dissolve 2.1254 g anhydrous primary-standard grade potassium biphthalate, C 8 

### H 5 

### KO 4

### [also known as potassium hydrogen phthalate (KHP)], in organic-free water and dilute to 1000 mL (1.00 mL  1.00 mg carbon). Commercially prepared standards are also available.

4. Procedure



### a. Sample volume: Select sample volume based on cell path length, volume needed for filter rinsing, and/or dilution required to produce a UV absorbance between 0.005 and 0.950 cm  1 

### . For most applications, a 50- to 125-mL sample is adequate.

b. Sample preparation: Wash filter and filter assembly by passing a sufficient volume of organic-free water through the filter (to waste) to yield a filter blank of 0.010 cm  1 

### . Forspecific applications and correlations, sample pH may be adjusted with HCl or NaOH. In poorly buffered samples, an appropriate non-UV absorbing buffer system (e.g., a phosphate buffer) may be used. Take care to avoid precipitate formation during pH adjustment. UV absorbance of fulvic acid solutions apparently remains constant between pH 4 and 10. 2 

### Samplesanalyzed for SUVA determination should be run without adjusting the pH of the original sample. Report sample pH value used with recorded absorbance. Once sample pH has been adjusted and/or measured, rinse filter with sample and discard filtrate. If using 4.7-cm PES or HPP filters, they can be adequately rinsed with 25 mL sample to bind sites that may adsorb UV-absorbing constituents. 4 

### This volume is also adequate for glass fiber filters. Smaller filters may require proportionately less. If other filter materials are used, confirm whether these volumes are adequate or if more is needed. Analyze the subsequent filtrate as a sample. Prepare an organic-free water filter blank and the sample in an identical manner.

c. Spectrophotometric measurement: Let spectrophotometerequilibrate according to manufacturer’s instructions. Set wavelength to 253.7 nm (or 254 nm) and adjust spectrophotometer to read zero absorbance with organic-free water. Measure UV absorbance of at least two filtered portions of sample at room temperature.

5. Calculation



### Report mean UV absorption in units of cm  1 

### using the fol

lowing notation. To report units in m  1 

### , multiply the equation by 100.

UV λpH 

#  A
b 

# D 

### where:

UV  pH  mean UV absorption, cm -1 (subscript denotes wavelength used, nm, and superscript denotes pH used if other than 7.0), b  cell path length, cm, A   mean absorbance measured, and D  dilution factor resulting from pH adjustment and/or dilution with organic-free water.

D final sample volume initial sample volume



### Correct results for absorption contributed by known interfering substances. If UV absorption contributed by interfering substances exceeds 10% of total UV absorption, do not use UV absorption at 253.7 nm as an indicator of organics.

6. Quality Control



### The quality control (QC) practices considered to be an integralpart of each method are summarized in Table 5020:I. Additionally, follow all QC described in the method itself.

a. Replicate measurements: Use at least two portions of filtered sample.

b. Duplicate analyses: Analyze every tenth sample in duplicate (i.e., duplicating the entire procedure) to assess methodprecision. Calculate relative percent difference (RPD) for duplicate analyses (D 1 

### and D 2 

### , where each duplicate is the average of replicate readings) using the formula below:

% RPD  D 1  D 2   D 1  D 2  /2  100



### For UV values  0.045 cm  1 

### , the RPD limit is  10%. For UV values 0.045cm  1 

### , the RPD limit is  20%.

c. Baseline absorbance: Check system baseline UV absorbance after every 10 samples by measuring the absorbance of an organic-free water blank. A non-zero absorbance reading for the blank may indicate the need for cell cleaning, problems with the reference cell if a dual-beam instrument is being used, or a variation in spectrophotometer response caused by heating or power fluctuations over time.

d. Filter blanks: With each batch of filtered samples, analyze a portion of organic-free water that has been passed through a rinsed filter. The volume of organic-free water should be equal to the volume of a sample. Filter blanks should read 0.010 cm  1 

### ;if not, larger rinsing volumes may be required. Also, the appropriateness of the filter and/or the filtering apparatus may need to be evaluated.

e. Filtrate turbidity check (optional): If a UV value or calculated SUVA value seems unusually high for a specific samplesource, check filtrate turbidity. Turbidities greater than 0.5 nephelometric turbidity units (NTU) indicate that the sample may require pretreatment steps, such as centrifugation. 5



### f. Spectrophotometer check: Difficulties in comparing UV absorption data from different spectrophotometers have beenreported. KHP standards were prepared in pH 7, phosphatebuffered (3 d) reagent water without acidification and analyzed in UV-ABSORBING ORGANIC CONSTITUENTS (5910)/Ultraviolet Absorption Method

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### five laboratories. Results suggest acceptable precision (Table5910:I). These data also are useful for checking spectrophotometer results with KHP standards commonly used for total organic carbon (TOC) and/or COD analysis. A correlation equation for this 40-sample data set is:

UV 254  0.0144 KHP  0.0018



### with correlation coefficient ( r 2 

### )  0.987, UV 254 

### expressed in

cm  1 

### , and KHP expressed as mg/L as C.

This equation can help verify spectrophotometer performance. For example, if a set of UV 254 

### analyses is performed and results are in the 0.010 range, prepare a KHP standard of 0.5 mg/L as C. The projected UV 254 

### of this KHP standard would be 0.009 cm  1



### . If measured UV 254 

### is outside the 13% relative standard deviation (RSD) of 0.009 cm  1 

### (using the RSD in Table 5910:I as a guide), the spectrophotometer may be suspect and require maintenance. The correlation between UV 254 

### and KHP standards ispresented solely as a useful means of verifying spectrophotometer performance. Prepare at least one KHP standard in the range of interest and measure it with each analytical run. Commercially prepared standards may also be available for this purpose.

7. Precision and Bias



### Table 5910:I shows interlaboratory precision data for 40 KHP samples. The RSD ranged from 9.38 to 12.8%.

Single-operator precision data are presented in Table 5910:II for fulvic acid solutions. 6 

### The RSD ranged from 0.9 to 6%. Because UV absorption is an aggregate measure of organiccarbon, true standards are unavailable and bias cannot be determined.

The precision of analyses by this method was determined under the Information Collection Rule (ICR). 7 

### Precision was determined as RPD for duplicate analyses and was calculatedonly when both analyses in the duplicate pair showed concentrations at, or greater than, the Information Collection Rule minimum reporting level (MRL  0.009 cm  1 

### ). Results were as follows: 8

Data Quality

Variable Percentile N 10 25 50 (median) 75 90
Precision (RPD) 33306* 0.0 0.0 0.0 2.2 4.9

* 2744 excluded - both samples less than MRL. N OTE : Median sample result was 0.040 cm -1

.



### 8. References

1. KAPLAN , L.A. 1992. Comparison of high-temperature and persulfate

oxidation methods for the determination of dissolved organic carbon in freshwaters. Limnol. Oceanogr. 37:1119. 2. EDZWALD , J.K., W.C. B ECKER & K.L. WATTIER . 1985. Surrogate parameters for monitoring organic matter and THM precursors. J. Amer. Water Works Assoc. 77(4):122. T ABLE 5910:I. P RECISION OF UV ANALYSES AND C ORRELATION TO KHP S AMPLES

UV 254 Result for Given KHP Sample Concentration*

cm -1
Analysis 0.54 0.93 1.79 4.87 9.61 25.0 50.0 100.0
Laboratory 1 0.008 0.015 0.034 0.079 0.158 0.323 0.638 1.282 Laboratory 2 0.009 0.016 0.026 0.070 0.134 0.401 0.803 1.612 Laboratory 3 0.010 0.017 0.027 0.081 0.161 0.353 0.695 1.343 Laboratory 4 0.007 0.020 0.033 0.070 0.132 0.319 0.750 1.590 Laboratory 5 0.009 0.018 0.030 0.087 0.140 0.394 0.643 1.447 Mean 0.0086 0.0172 0.0300 0.0774 0.1450 0.3580 0.7058 1.4548 Standard deviation 0.0011 0.0019 0.0035 0.0074 .0136 0.0384 .0708 0.1461 Relative standard deviation, %† 12.8 11.1 11.7 9.56 9.38 10.7 10.0 10.0
* KHP sample concentration mg/L as C, measured as in Section 5310C. † The percent relative standard deviation is given by:

% RSD 

#  standard deviation ( S) mean (X ) 

#  100

T ABLE 5910:II. S INGLE -O PERATOR P RECISION FOR UV A BSORPTION M EASUREMENTS OF FULVIC A CID S OLUTIONS

Result

cm -1

DOC Concentration mg/L Replicate No. 2.5 4.9 10.0

1 0.110 0.240 0.480 2 0.120 0.230 0.480 3 0.110 0.240 0.470 4 0.100 0.230 0.480 5 0.110 0.240 0.480 6 0.100 0.240 0.470 7 0.110 0.240 0.480 8 0.110 0.230 0.480 9 0.120 0.240 0.480 10 0.110 0.240 0.480 Mean 0.110 0.237 0.478 Standard deviation 0.0067 0.00483 0.00422 % Relative standard

deviation 6.06 2.05 0.882 UV-ABSORBING ORGANIC CONSTITUENTS (5910)/Ultraviolet Absorption Method

43. KAPLAN , L.A. 1994. A field and laboratory procedure to collect,process, and preserve freshwater samples for dissolved organic carbon analysis. Limnol. Oceanogr. 39(6):1470. 4. KARANFIL , T., I. ERDOGAN & M. S CHLAUTMAN . 2003. Selecting filter membranes for measuring DOC and UV 254 . J. Amer. Water Works Assoc. 95(3):86. 5. KARANFIL , T., I. E RDOGAN & M. S CHLAUTMAN . 2005. The impact of filtrate turbidity on UV 254 determination. J. Amer. Water Works Assoc. 97(5):125. 6. M ALLEY , J.P., J R . 1988. A Fundamental Study of Dissolved Air Flotation for Treatment of Low Turbidity Waters Containing Natural Organic Matter. Ph.D. thesis (unpublished), Univ. Massachusetts, Amherst.Line Height Adjustment 7. U.S. Environmental PROTECTION AGENCY . 1996. Monitoring Requirements for Public Drinking Water Supplies: Cryptosporidium, Giardia, Viruses, Disinfection Byproducts, Water Treatment Plant Data and Other Information Requirements. Final Rule. Fed. Reg. 61(94):24354. 8. FAIR , P.S., R.K. S ORRELL , M. KARAPONDO , B.J. B OHL , C.P. FREBIS & M.A. FEIGE . 2002. Quality of ICR monitoring data. In M.J. McGuire, J. McLain & A. Oblensky, eds. Information Collection Rule DataAnalysis. American Water Works Assoc. Research Foundation, Denver, Colo. UV-ABSORBING ORGANIC CONSTITUENTS (5910)/Ultraviolet Absorption Method

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